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Code of Practice Use of Geotextile Filters on Waterways

(MAG)

Federal Waterway Engeneering and Research Institute

(Bundesanstalt für Wasserbau - BAW)

Edition 1993

Code of Practice Use of Geotextile Filters on Waterways

(MAG)

Publisher (self publishing house ) : Kußmaulstraße 17, 76187 Karlsruhe, Telefon (0721) 9726-0, Telefax (0721) 9726-454

Reprint, translation or other reproductions even extracts permitted only by editor approval (C) BAW 1993

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Symbols used ........................................................................................................................................................................................... 4 1 Preliminary remarks............................................................................................................................................................... 5 2 Terms ....................................................................................................................................................................................... 5 2.1 Geotextile........................................................................................................................................................................................... 5 2.2 Nonwoven.......................................................................................................................................................................................... 5 2.3 Woven................................................................................................................................................................................................ 5 2.4 Composite material ............................................................................................................................................................................ 5 2.5 Filter layer.......................................................................................................................................................................................... 5 2.6 Separation layer ................................................................................................................................................................................. 5 2.7 Drainage layer.................................................................................................................................................................................... 5 2.8 Erosion............................................................................................................................................................................................... 5 2.9 Suffosion............................................................................................................................................................................................ 5 2.10 Colmatation...................................................................................................................................................................................... 5 2.11 Dynamic hydraulic loading.............................................................................................................................................................. 5 2.12 Static hydraulic loading ................................................................................................................................................................... 5 3 Principles for the use of a geotextile as a filter layer or separation layer........................................................................... 5 3.1 General............................................................................................................................................................................................... 5 3.2 Necessity for a geotextile................................................................................................................................................................... 5 3.2.1 Filter layer....................................................................................................................................................................................... 5 3.2.2 Separation layer .............................................................................................................................................................................. 6 3.3 Basis for design.................................................................................................................................................................................. 6 3.3.1 Subsoil ............................................................................................................................................................................................ 6 3.3.1.1 Items of subsoil report................................................................................................................................................................... 6 3.3.1.2 Non-cohesive soils ....................................................................................................................................................................... 6 3.3.1.3 Cohesive soils .............................................................................................................................................................................. 6 3.3.1.4 Inhomogeneous subgrade............................................................................................................................................................. 6 3.3.1.5 Suffosive soils.............................................................................................................................................................................. 6 3.3.2 Hydraulic loading ........................................................................................................................................................................... 7 3.3.3 Mechanical loads ............................................................................................................................................................................ 7 3.3.3.1 General......................................................................................................................................................................................... 7 3.3.3.2 Construction works ...................................................................................................................................................................... 7 3.3.3.3 Waterway operations ................................................................................................................................................................... 7 3.3.4 Quality of water in the filter zone ................................................................................................................................................... 7 3.3.4.1 pH-value....................................................................................................................................................................................... 7 3.3.4.2 Chemical and biological factors................................................................................................................................................... 7 3.3.5 UV-resistance.................................................................................................................................................................................. 7 3.3.6 Penetrability by roots ...................................................................................................................................................................... 7 4 Types of filter and armour-layer construction .................................................................................................................... 8 4.1 General............................................................................................................................................................................................... 8 4.2 Geotextile directly on the subgrade (standard application)................................................................................................................ 8 4.3 Geotextile on a granular levelling sublayer ....................................................................................................................................... 8 4.4 Geotextile combined with an unbound granular filter........................................................................................................................ 8 4.5 Granular interlayer between geotextile and top layer ........................................................................................................................ 8 4.6 Geotextile with a structural addition .................................................................................................................................................. 8 4.6.1 General............................................................................................................................................................................................ 8 4.6.2 Geotextile with an additional layer ................................................................................................................................................. 8 4.6.3 Geotextile with attached fascine-grid (sink mattress) ..................................................................................................................... 9 4.6.4 Geotextile with mineral filler .......................................................................................................................................................... 9 4.7 Edges of a slope protection ................................................................................................................................................................ 9 4.8 Connections with structures ............................................................................................................................................................... 9 4.9 Overlaps and seams............................................................................................................................................................................ 9 4.10 Armour layers .................................................................................................................................................................................. 9 5 Requirements........................................................................................................................................................................... 10 5.1 General............................................................................................................................................................................................... 10 5.2 Filtration stability............................................................................................................................................................................... 10 5.2.1 General............................................................................................................................................................................................ 10 5.2.2 Soil-type design procedure of the BAW ......................................................................................................................................... 10 5.2.2.1 Basis............................................................................................................................................................................................. 10 5.2.2.2 Application principle for permeable top layers............................................................................................................................ 10 5.2.2.3 Application principle for impermeable top layers........................................................................................................................ 11 5.2.3 Filter rules ....................................................................................................................................................................................... 11 5.2.3.1 General......................................................................................................................................................................................... 11 5.2.3.2 Design of a filter layer ................................................................................................................................................................. 11 5.2.3.3 Design of a separation layer......................................................................................................................................................... 12 5.3 Material properties .............................................................................................................................................................................. 12

Contents Page

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5.3.1 General............................................................................................................................................................................................ 12 5.3.2 Permeability .................................................................................................................................................................................... 12 5.3.3 Opening size ................................................................................................................................................................................... 12 5.3.4 Layer thickness ............................................................................................................................................................................... 12 5.3.4.1 Related to the filtration function .................................................................................................................................................. 12 5.3.4.2 Related to the separation function................................................................................................................................................ 13 5.3.5 Tensile strength and strain .............................................................................................................................................................. 13 5.3.6 Resistance to dynamic perforation loads......................................................................................................................................... 13 5.3.7 Resistance to abrasion loads ........................................................................................................................................................... 13 5.3.8 Resistance to static puncture loads.................................................................................................................................................. 14 5.3.9 Resistance to high temperatures...................................................................................................................................................... 14 5.3.10 Friction coefficient........................................................................................................................................................................ 14 5.3.11 Mass per unit area ......................................................................................................................................................................... 14 6 Tests.......................................................................................................................................................................................... 14 6.1 General............................................................................................................................................................................................... 14 6.2 Basic test............................................................................................................................................................................................ 14 6.3 Suitability test .................................................................................................................................................................................... 14 6.4 Quality control during manufacture ................................................................................................................................................... 14 6.5 Control tests by the Principal ............................................................................................................................................................. 14 7 Instructions for inviting tenders and for construction works.............................................................................................. 15 7.1 Tender documents.............................................................................................................................................................................. 15 7.2 Construction works ............................................................................................................................................................................ 15 7.2.1 Preparation of the filter subgrade.................................................................................................................................................... 15 7.2.2 Installation in the dry ...................................................................................................................................................................... 15 7.2.3 Installation under water.................................................................................................................................................................. 15 7.3 Inventory documents.......................................................................................................................................................................... 15 8 References................................................................................................................................................................................ 16 9 Index of keywords ................................................................................................................................................................... 17 10 Index of annexes ...................................................................................................................................................................... 18

Symbols used cu = apparent cohesion of soil Cu = uniformity coefficient ( defined as d60 / d10 ) di = particle diameter of soil corresponding to i % by weight of finer particles Di = particle diameter of granular filter corresponding to i % by weight of finer particles Dw = filtration opening size of a geotextile or its individual layers ( in future intended O90 ) DX = type of top layer construction h = hydraulic head ∆h = change in hydraulic head i = hydraulic gradient ( h / T ) IP = plasticity index k = coefficient of permeability kn = coefficient of normal permeability of a geotextile Mt = total mass of soil passing Ml = mass of soil passing during the last test phase q = flow rate T = layer thickness ∆t = time difference v = flow velocity Vh = velocity of change in hydraulic head Vs = ship velocity wL = liquid limit wP = plastic limit β = angle of slope to horizontal µ = mass per unit area ϕ ' = effective angle of internal friction σ = normal stress

Contents Page

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1 Preliminary remarks

This Code of Practice applies to geotextiles used as a filter layer or separation layer in bank and bottom revetment systems of waterways and the associated structures such as e.g. dams or lateral trenches. A prerequisite for the use of geotextiles is the fulfilment of certain application-related technical requirements in accordance with the Technical Supply Conditions for Geotextile Filters (TLG) /1/.

2 Terms 2.1 Geotextile

A geotextile is a manufactured sheet-like permeable textile con-struction material. It may be fabricated as a nonwoven, woven or composite material.

2.2 Nonwoven

A nonwoven is a single-layer geotextile fabricated by bonding of fibre fleeces. Fibre fleeces consist of staple fibres (3-15 cm) or filaments (endless fibres) randomly orientated /15/. Bonding can be mechanical (by needle-punching), by adhesion or by cohesion (melting).

2.3 Woven

A woven is a single-layer geotextile consisting of interlacing thread systems. Threads in longitudinal direction are called warp threads, in cross direction weft threads /15/.

2.4 Composite material

A composite material is a multilayer geotextile of which the indivi-dual layers differ clearly in their structure.

2.5 Filter layer

A filter layer must restrain subsoil under all the possible hydraulic conditions (mechanical filtration stability), while allowing the passage of soil pore water without detrimental rising of seepage line (hydraulic filtration stability).

2.6 Separation layer

A separation layer must prevent intermixing or interpenetration of adjacent dissimilar granular layers or must prevent erosion while its permeability - opposed to a filter layer - is of subordinate importance. At the same time it can be used to promote colmatation, if desired.

2.7 Drainage layer

A drainage layer must collect and transport water in its plane.

2.8 Erosion

Erosion is the removal and thus the particle loss of nearly all soil fractions by currents of pore water or surface water.

2.9 Suffosion

Suffosion is the displacement or washing-out of fine-soil fractions by pore water flow without change of the soil skeleton in the structure.

2.10 Colmatation

Colmatation is the reduction in permeability of a soil or a filter layer by solid-matter incorporation (clogging, blocking) or by accumu-lation

2.11 Dynamic hydraulic loading

Hydraulic loads are dynamic in the sense of this code if the change in hydraulic head ∆h within time ∆t occurs with a velocity

Vh = ∆h/∆t > ksoil

(e.g. quick drawdown of water level, waves, turbulent currents). They cause relatively high hydraulic gradients in the interface zone between soil and filter layer and, as a result of this, turbulent flow through the filter /26/.

2.12 Static hydraulic loading

Hydraulic loads are static in the sense of this code if the change in hydraulic head ∆h within time ∆t occurs with a velocity

Vh = ∆h/∆t ≤ ksoil

(e.g. slow fluctuations of water level, small wave-heights and flow velocities). They cause relatively small hydraulic gradients in the interface zone between soil and filter layer and, as a result of this, laminar flow through the filter /26/.

3 Principles for the use of a geotextile as a filter layer or separation layer

3.1 General

The necessary single steps from designing to tendering a geotextile filter are shown in Annex 10. They apply likewise to a sepa-ration layer.

3.2 Necessity for a geotextile 3.2.1 Filter layer

A filter is necessary between two layers of differing granular materials if a significant fraction of the finer-grained layer cannot be restrained by the coarser layer under the expected pore water flow. The necessity for a geotextile filter can be checked according to Annex 1. A geotextile filter layer must be dimensioned with regard to

grain sizes and permeability of the adjacent subsoil, con-sidering the type of pore water flow (turbulent, laminar, see 2.11, 2.12),

mechanical stresses caused during construction works and by waterway operations,

chemical properties of water in the filter zone, possible short-term ultra-violet light (UV) weathering during

construction works and if need be, penetrability by roots in the zone of fluctuating water

levels and above this, depending on the revetment system chosen.

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3.2.2 Separation layer

A separation layer can be needed if a) intermixing of widely differing granulations is to be prevented with regard to long-term settlements (e.g. sand or topsoil on

coarse gravel or stones, rip-rap groyns on mud, coarse bed course on fine subsoil),

b) interpenetration of two layers of widely differing grain sizes shall be prevented with regard to long-term function of one of the two layers (e.g. rip-rap on clay lining, clay lining on very coarse subsoil), c) erosion of subsoil beneath a hard lining (e.g. asphaltic) shall be

prevented in the case of cracks and at the same time self-sealing of the lining system due to colmatation is to be promoted,

d) a changing compact rock (e.g. sandstone, claystone) is erodible by weathering, hydraulic impacts or mechanical influences (e.g. moving of armourstone).

A geotextile separation layer must be designed concerning

safe restraining of subsoil, mechanical stresses caused during construction works and by

later operations, chemical properties of water, possible short-term UV-weathering during construction works

and penetrability by roots (if desired).

In cases of dynamic impacts caused e.g. by turbulent currents, waves or vibratory compaction, the need for a separation layer can be assessed according to Annex 1.

3.3 Basis for design 3.3.1 Subsoil 3.3.1.1 Items of subsoil report

The subsoil report must include the following details and be representative of the construction section in which the geotextile filter or separation layer is to be installed: a) grain-size distribution: this is needed

to check whether a filter (see 3.2.1) or separation layer (see 3.2.2) is necessary;

to check the stability to suffosion (see 3.3.1.5); for geotextile design (see 5.2); for assessment of subsoil with regard to non-cohesive or cohesive nature (see 3.3.1.2, 3.3.1.3); to assess k-value of subsoil (Annex 4).

b) effective angle of internal friction (ϕ'): this is needed

to assess local stability of slopes exposed to seepage flow (see 3.3.1.2);

to assess geotextile's friction coefficient (see 5.3.10). c) coefficient of permeability (k-value): this is needed

to assess the type of hydraulic loading (see 2.11, 2.12); to assess needed permeability of the geotextile (see 5.3.2).

Determination by laboratory tests is only necessary in cases where its exact knowledge is required for safety reasons.

Otherwise assessment according to Annex 4 is sufficient. d) apparent cohesion of subsoil (cu) and plasticity index (Ip): These are needed for the determination of filtration properties

of a geotextile filter (see 5.2.2.2, 5.2.3).

e) sequence and inclination of strata: The advice given in subclause 3.3.1.4 concerning stratified soils lying in the slope area must be heeded.

f) quality of water in the filter zone: The chemical quality of water must be known with regard to

detrimental influences on a geotextile (see 3.3.4).

3.3.1.2 Non-cohesive soils

Sloped non-cohesive soils or soils of low cohesion are susceptible to sliding or to formation of erosion channels under the impact of pore water or surface water currents, if the angle of slope is

β ≥ ϕ'/2.

Under the impact of shipping (waves, quick drawdown of water level) slope instability will occur earlier. This must be considered when choosing the type of filter construction (see 4). For filter design, soils with grain fractions d20 ≥ 0,006 mm must be regarded as non-cohesive (see 5.2), if no more accurate investigations with respect to the apparent cohesion and plasticity index are available.

3.3.1.3 Cohesive soils

Cohesive soils have a very low mobility of particles and a very low permeability. This may be taken into account when designing a filter (see 5.2). Possible concentrated water veins must be considered when choosing the type of filter construction (see 4).

3.3.1.4 Inhomogeneous subgrade

A subgrade is inhomogeneous in the sense of this code if there exist alternating layers of non-cohesive fine-grained or mixed-grained

soils and coarse-grained soils according to DIN 18 196 /16/, inhomogeneous soils (lenses), remains of former structures, which are to remain in the subsoil

(e.g. parts of a former armour layer). This must be taken into account when choosing the type of filter construction (see 4), if inhomogeneous subgrade is situated below the highest water level. In the case of e.g. continuous influx of groundwater, transport of fine-soil particles beneath the geotextile to a deeper situated and more permeable layer must be prevented.

3.3.1.5 Suffosive soils

Stability of subsoil to suffosion must be proved for non-cohesive soils with gap gradation or for non-cohesive, non-uniform soils (Cu ≥ 8). In the case of doubt laboratory tests are recommended. Since the effective local gradient is generally not known or may even be enhanced by later measures, geometric stability to suffo-sion must be checked especially for silty subsoils (Annex 2)/12/13/. In the case of silty suffosive subsoils the seepage line can be raised by colmatation of the geotextile caused by leached fine particles (possible consequences: decrease in stability of slope or of slope revetment, waterlogging due to a rise in groundwater level). If the occurence of suffosion is possible, a suitable type of filter construction must be chosen (see 4) or the geotextile must be designed according to subclause 5.2.1.

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3.3.2 Hydraulic loading

When ascertaining the filtration requirements of a geotextile (see 5.2), the following types of hydraulic loads have to be distin-guished:

a) dynamic hydraulic loading b) static hydraulic loading.

Whether dynamic or static hydraulic loading is relevant in the particular application can be determined using the criteria of subclauses 2.11 and 2.12. The hydraulic influence of shipping or comparable hydraulic impacts always cause dynamic hydraulic filter loading which may lead to pumping movements of a geotextile in cases where the cover layer surcharge does not act on the entire geotextile surface (see 4.10).

3.3.3 Mechanical loads 3.3.3.1 General

During installation or construction works, or even during waterway operation, a geotextile can be subjected to considerable mechanical loads. For that reason, it must be adequately dimensioned as regards strength properties, or appropriate precautionary measures must be taken.

3.3.3.2 Construction works

During construction works a geotextile can be subjected to the following mechanical stresses: a) installation of the geotextile

tensile stresses: are unimportant if the geotextile is installed by rolling it out. When placed under water using a pontoon tensile forces depend on the flow pressure of currents acting on the geotextile area /21/ (see 5.3.5).

b) placement of aggregate on the geotextile

tensile stresses: will occur due to spanning of the geotextile across irregularities in the subgrade under the weight of the material placed (see 7.2.2).

dynamic perforation stresses: are caused only when very coarse aggregate (armourstone) is dropped. When placing under water by dropping from the water surface, drop energy of stones will be only max. 15% of that registrated in the dry from a drop height of 2 m (see 5.3.6) /25/20/.

puncture stresses: will occur during compaction works if any angular material is in contact with the geotextile (see 5.3.8).

c) driving on the layer overlying the geotextile:

puncture stresses: the magnitude of these loads depends on thickness, grain size, grain shape of overlying layer, on weight of construction equipment and on strength of subsoil (see 5.3.8).

3.3.3.3 Waterway operations

The following mechanical loads on a geotextile can be caused during waterway operations (currents, waves, quick drawdown of water level):

tensile stresses: can occur in connection with subgrade defor-mations or uplift pressure in case of quick water level fluctu-ations, if big cavities with corresponding water volume exist beneath a geotextile and the cover-layer surcharge does not act on the entire geotextile surface (see 4.10).

abrasion loads: can be caused by chafing movements of rock material or movements of a geotextile on sharp-edged structural elements (see 5.3.7).

3.3.4 Quality of water in the filter zone 3.3.4.1 pH-value

The long-term durability of geotextiles manufactured of the following fibre raw materials /1/ - Polyacrylic (PAC) - Polyamide (PA) - Polyethylene (PE) - Polypropylene (PP)

} 3 < pH < 12

- Polyester (PES) 3 < pH < 10 is not problematical as regards acidic or basic soils and water if the pH-value is in the above-mentioned range (Annex 5).

3.3.4.2 Chemical and biological factors

By precipitation or flocculation from the water of e.g. a) sintering products or b) ochreous products the permeability of a geotextile can be considerably reduced . Sintering can occur due to groundwater containing dissolved lime in the case of drop of water pressure (change in flow conditions) or increase of

water temperature together with oxygen contact.

Groundwater with a fairly high degree of hardness, i.e. a German degree of hardness ≥ 12° DH, is liable to cause sintering if CO2 is present at the same time /10/. Chemical ochre formation must be taken into account if the groundwater contains dissolved divalent iron or manganese. If water pressure falls or temperature increases a trivalent insoluble chemical combination will arise through oxidation (hydroxide), in the presence of dissolved O2 in the water. This will than flocculate /10/11/29/. Ochre formation can also occur on a biological basis due to meta- bolic activity of iron and manganese microbes /11/. Sintering and ochre formation are generally only important in the zone of fluctuating water levels. Thus danger of sintering or ochre formation must be checked only if the zone of fluctuating water levels occupies more than 50% of the percolated filter area (e.g. tidal zone, undammed rivers). If a possible sintering or ochre formation has to be considered, the use of a highly permeable granular filter according to MAK /6/ is recommended.

3.3.5 UV-resistance

The long-term resistance to ultra-violet light (UV) weathering of geotextiles manufactured of the usual fibre raw materials (see 3.3.4.1) is highly variable (Annex 5). Resistance of UV-sensitive raw materials can be considerably improved by stabilizers. How-ever permanent UV- weathering must be prevented by the layer(s) overlying the geotextile.

3.3.6 Penetrability by roots

Experiences to date show that geotextiles used in waterways are in principle penetrable by grasses, bushes and trees. Penetrability will be improved with increasing - pore size (opening size) and - mobility of fibres (nonwovens) or yarns (wovens).

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4 Types of filter and armour-layer construction 4.1 General

When using a permeable armour layer the following types of filter construction have to be taken into consideration depending on subsoil, slope inclination, hydraulic loadings and installation conditions of the geotextile: a) geotextile directly on the subgrade (standard application), b) geotextile on a granular levelling sublayer, c) geotextile combined with an unbound granular filter, d) granular interlayer between geotextile and armour layer. The type of filter and armour-layer construction must guarantee, especially on slopes, a stable interface between geotextile and subsoil for all possible hydraulic loadings (see 3.3.2), to prevent the removal of subsoil. Erosion channels beneath the geotextile can be the initial point of destruction of a bank protection. For this reason it is necessary that the geotextile is in complete contact with the subgrade. Beyond this, cavities beneath the geotextile with a correspondingly large water volume impair local mechanical stability of a bank revetment in the case of quick water-level decrease due to uplift pressure. For the edges of a filter area and their connections to structures a special type of construction must generally be chosen. Under an impermeable cover layer a geotextile fulfils only a separation function (see 3.2.2 and 5.2.2.3).

4.2 Geotextile directly on the subgrade (standard application)

Placing a geotextile directly on the subgrade (if necessary with a structural addition, see 4.6) is the standard construction method (Annex 3, sheet 1). This is used in the following cases: a) subsoil is homogeneous and existing vegetation and remains of former structures will be completely removed (see 3.3.1.4); b) because of subsoil properties an even subgrade can be constructed and will remain stable during construction (see 3.3.1.2); c) when subsoil is susceptible to erosion: the cover layer effects a full-area contact of the geotextile with the subgrade (see 4.10); d) when subsoil is susceptible to suffosion: no structural addition may be used which could lead to colmatation of the geotextile (see 4.6.2); e) there is no concentrated groundwater flow (e.g. cleavage water), exceeding the hydraulic capacity of the geotextile filter layer (see 4.6.2). .

4.3 Geotextile on a granular levelling sublayer

On slopes a granular levelling sublayer beneath the geotextile (Annex 3, sheet 1) is recommended in the following cases: a) because of subsoil properties an even subgrade cannot be constructed or it will not remain stable during construction (see 3.3.1.2); b) inhomogeneous subgrade (see 3.3.1.4); c) suffosive subsoil (see 3.3.1.5); d) existing vegetation will, as an exception, not be removed. The granular levelling sublayer effects a homogeneous and smooth formation for the geotextile. Grading curves of levelling sublayer and subsoil must be compatible to avoid settlements which may occur if the levelling sublayer is too coarse or to avoid rising of the seepage line if it is too fine (MAK /6/).

Recommended grain-sizes of the levelling sublayer, valid for subsoils with d15 < 0,7 mm, are given in Annex 4. The quantity of material must be chosen so that existing cavities or irregularities will be fully filled up and a calculated cover thickness of at least 5 cm is guaranteed (when placing under water 10 cm). On slopes steeper than 1:3 crushed granular material should be used when installation takes place under water. The geotextile must be designed with respect to the properties of the levelling sublayer (see 5.2 and 5.3).

4.4 Geotextile combined with an unbound granular filter

Under certain boundary conditions a geotextile can be applied too as an upper filter layer on an unbound granular filter according to MAK /6/ (Annex 3, sheet 1), e.g.: a) when widely differing soil-types are present in the subgrade re- quiring, as a result of filter design, different geotextile structures; b) when using excavation material suitable for filter purposes; c) for decompression in the case of heavy local ingress of groundwater (e.g. cleavage water); d) in drainage applications. Requirements on the geotextile can generally be reduced (see 5.3.4.1).

4.5 Granular interlayer between geotextile and top layer

Experience from tidal zone have proved that it is advantageous in the case of erosive subsoils to place on slopes between the geo-textile filter and a permeable top layer, consisting of large armour-stone of class II or larger, a smaller grained interlayer (Annex 3, sheet 1 ) of which the grain size must be tuned to the top layer as regards mechanical filtration stability (MAK /6/). This type of con-struction effects a full-area contact of the geotextile with the sub-grade, even during heavy hydrodynamic impacts (see 4.10).

4.6 Geotextile with a structural addition 4.6.1 General

In the case of difficult circumstances as regards installation under water the following structural additions to a geotextile are to be taken into consideration depending on the boundary conditions of the application : a) additional layer on the underside of the geotextile; b) fascine-grid attached to the geotextile; c) factory-made incorporation of mineral material between two geotextile layers.

4.6.2 Geotextile with an additional layer

An additional layer on the underside of a geotextile (Annex 3, sheet 2) - reduces forming of folds during installation and thus improves the contact with the subgrade already before installation of the top layer (important on erosive subsoils, see 3.3.1.2); - enhances the resistance to dynamic perforation (see 5.3.6) or to puncture loads (see 5.3.8); - can enhance friction coefficient (see 5.3.10) and thus improve positional stability of the geotextile on steep slopes.

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The opening size of the additional layer must be tuned to the grading of the subsoil. Additional layers can be subdivided into those with a relatively small-pore structure , i.e.opening sizes, which must be accom- modated to grain-sizes of subsoil if they are to stabilize the inter-face between geotextile and subgrade (stabilization layer) and those with a relatively large-pore structure (anchorage layer). After a short time of hydraulic impact the latter effect the anchorage of the geotextile in the subgrade. An additional layer must be clearly visible with the naked eye in order to ensure the correct installation position. For the structure of an additional layer the parameters given in Table 1 are recommended. Table 1: recommendations for the structure of an additional layer

soil type of subsoil

(subgrade)

type of additional

layer

opening size Dw (O90)

(mm)

thickness T

(mm)

soil type small-pore 0.3 - 2.0 5 - 15

2-4 large-pore 8.0 - 20 15 - 25

An additional layer must not be applied

beneath a lining, because it will operate like a drainage layer in the case of leakage (see 5.2.2.3);

on slopes if the subsoil is extremely susceptible to erosion (see 3.3.1.2) and contains stones. Stones can lead to undesired "tenting" of the additional layer and thus form large voids or promote formation of erosion channels beneath the geotextile;

on slopes directly on suffosive subsoil (see 3.3.1.5), because the additional layer can become nearly impervious as a result of col-matation due to incorporation of fine-soil particles;

in the case of heavy ingress of groundwater or cleavage water, because an overpressure acting on a large area can arise behind the geotextile as a result of filter layer permeability being much lower compared with the permeability of the additional layer.

4.6.3 Geotextile with attached fascine-grid (sink mattress)

A full-area and nearly unwrinkled installation of geotextiles is possi-ble when a fascine-grid is attached to the upper side of the geotextile (Annex 3, sheet 2). When installing under water (sink mattress) the structure must be sunk by placing the cover material on it or by using a beam.The fascine-grid also improves the stability of aggre-gate overlying the geotextile. This type of filter construction may be taken into account especially for bottom protection works which are executed in great water depths, or for slope protections without toe support (e.g. very long slopes under water).

4.6.4 Geotextile with mineral filler

The mass per unit area of a geotextile can be considerably increased by factory-made incorporation of aggregate (e.g. sand, fine gravel) between two geotextile layers. When installed under water, this enhances the positional stability of the geotextile during the stage of construction without surcharge (no change of position by floating and no rise of folds).

4.7 Edges of a slope protection

When installed on a slope, the upper edge of a geotextile must be protected against subsurface erosion caused by surface water or wave run-up overtopping even during the construction period (Annex 3, sheet 3). This applies especially to geotextiles with an additional layer (see 4.6.2). The lateral edges at the beginning and the end of the filter area must also be protected against subsurface erosion in the case of wave impact or of turbulent currents (e.g. by embedding in the subsoil). Toe forms appropriate as a lower fastening of a slope revetment are shown in Annex 3, sheet 4 /7/.

4.8 Connections with structures

The connection of a geotextile filter with a structure has to be per-formed in such a way that the subsoil to be protected is not un-covered at any point even if the connection deforms (rise of joints). The connection must maintain a long-term filter stability. Connections with a smooth building surface being executed in the dry can be performed e.g. with an overlapping separate geotextile fitting piece tightly attached to the building. The fitting must be formed in such a way that it will not be exposed to detrimental strains in the case of movement of the building (Annex 3, sheet 5). Connections with a smooth or non-planar building surface (e.g. sheet-pile wall) can be performed in the dry as well as under water with an overlapping granular filter or with a concrete seal (Annex 3, sheet 5).

4.9 Overlaps and seams

The overlap of two geotextile units must be (ZTV-W /2/): in the dry ≥ 0,50 m, under water ≥ 1,0 m .

Overlap strips shall run on slopes in the direction of inclination. If it is not possible to avoid horizontal overlaps on a slope, the lower sheet must always pass over the upper one (Annex 3, sheet 5). Additional layers must not overlap. Seams must be manufactured with a distance to the geotextile selvedge of at least 3 cm. Prayer seams are to be placed with the edges to the top, to prevent rising of the geotextile (Annex 3, sheet 5).

4.10 Armour layers

The armour layer (top layer) must be designed or structured in such a way that the geotextile obtains a long-term protection from damage due to shipping traffic and UV-weathering (see 3.3.5). On slopes at the same time a full-area contact of the geotextile with the subgrade must be effected under the expected hydraulic impacts (see 4.1). The smaller the particle size of the overlying aggregate, the more homogeneous is the contact of the geotextile with the subgrade (see 4.5). Types of armour-layer constructions appropriate for slope or bottom protection (standard top layers /7/) are shown in Annex 3, sheet 6.

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An adequate protection of the geotextile from UV-weathering and damage e.g. by anchor cast, anchor furrowing or collision by ships has been proved through field experiments and empirical observa-tion, when layer thickness is as follows:

unsorted coarse fill material: T ≥ 0,70 m, loose armourstone size class II or III: T ≥ 0,60 m, armourstone size class II, partially grouted: T ≥ 0,40 m, armourstone size class II, fully grouted: T ≥ 0,30 m, asphaltic concrete: T ≥ 0,15 m.

The TLW /3/ apply to size classification of armourstone. The corresponding ranges of particle-size distribution are given in Annex 5.

5 Requirements 5.1 General

A geotextile and its seams must be designed with respect to both to filtration stability and to strength properties. The requirements can be established on the basis of - performance tests, - design rules or - confident empirical knowledge. When a geotextile is used as a filter layer in a slope or bottom pro-tection in waterways according to Annex 3, sheet 6, the adoption of the standard requirements according to the classification procedure of the BAW is recommended, which has been set up mainly on per-formance tests connected with empirical values. Using this, all re-quirements on the geotextile are established when assigning the subsoil to a soil type or soil-type range (soil-type design procedure) and choosing the type of top-layer construction (Table 2 and 3). As regards different geotextile applications, top-layer constructions or hydraulic boundary conditions, the individual values to be required must be separately determined or evaluated for the type of application concerned.

5.2 Filtration stability 5.2.1 General

Requirements on filtration stability of a geotextile can be esta-blished in the case of permeable top layers according to the following filter criteria: a) dynamic hydraulic loadings

soil-type procedure of the BAW (see 5.2.2), filter rules ( see 5.2.3);

b) static hydraulic loadings filter rules (see 5.2.3).

For applications, in which dynamic hydraulic loadings are relevant (see 3.3.2), the mechanical filtration stability takes preference. When a grading band exists containing soils in the boundary zone between non-cohesive and cohesive, mechanical filtration stability must be always designed with regard to the finest non-cohesive grading curve of the band. It is sufficient if the permeability of the geotextile will not be lower than the most permeable granulation of the band even considering possible entrapment of soil particles. On the other hand, when static hydraulic loadings exist, hydraulic filtration stability takes preference.The geotextile must be designed to be as permeable as possible with regard to the most permeable granulation of the grading band, so that the finest non-cohesive granulation will just be restrained.

When using a geotextile on a suffosive subsoil, the following possibilities are given, but paying attention to subclause 4.6.2.:

dimensioning of the geotextile pore sizes so large that the mobile grain fractions are allowed to pass, or

dimensioning of the geotextile pore sizes so small that the mobile grain fractions will be restrained. Stability and service- ability of the structure must not be endangered by the possible resulting rise of seepage line.

When using a geotextile beneath an impermeable top layer (lining) special criteria apply (see 5.2.2.3)

5.2.2 Soil-type design procedure of the BAW 5.2.2.1 Basis

The soil-type design procedure has been developed by the BAW to evaluate the suitability of a geotextile as a filter layer in slope or bottom protection on shipping canals. It has been established with respect to dynamic hydraulic filter loads as these occur in water-ways /24/. Thus it shall be applied to dynamic hydraulic filter loadings only.

For utilization of the soil-type design procedure the range of non-cohesive and low cohesive soils from medium silt to medium gravel has been classified into four soil types (Annex 6) based on the grain-size limits of DIN 18 196 /16/.

In the course of the basic test being prescribed to each new geo-textile product /1/2/, the external dynamic hydraulic filter loadings acting in waterways are simulated in a performance test as follows:

a) quick drawdown and rerise cycles of water level by the flow- through method /5/. b) turbulent flow parallel to the filter surface of return currents, waves, screw-race by the reversing turbulent flow method /5/.

The soil mass passing through the gotextile and the permeability of the geotextile considering entrapped soil particles are determined. The test is performed with a granulation close to the fine-grained border of the individual soil-type ranges (Annex 6), which often are present in the German Waterways. The test can also be done with the in-situ soil in the course of a suitability test (see 6.3) in the case of need.

For permeable soils (soil types 1-3) the flow-through method yields the more unfavourable values of soil loss, whereas for low perme-able soils (soil type 4) the reversing turbulent flow method does.

5.2.2.2 Application principle for permeable top layers

The grading-curve of the subsoil forming the subgrade is needed (see 3.2.1). If the subsoil is cohesive cu and Ip should also be known. If cu and Ip are unknown or if cu < 10 kN/m2 and Ip < 0,15 the geotextile must always be designed - to be on the safe side - for soil type 4. If the subsoil has been classified to be of non-cohesive nature in the sense of subclause 3.3.1.2, it must be assigned with its finest- grained, non-cohesive grading curve to the validity range of one of the soil types 1 - 4 (Annex 6, sheet 1 and 2). The soil type which encloses the grain fractions d5 - d60 of the subsoil in its validity range is decisive for filtration specification.

The filtration properties of a geotextile are sufficient for all granu-lations of a certain validity range if the limit values given in Table 2 concerning layer thickness (see 5.3.4.1), mass of soil passing and kn (at h = 0,25 m) are met in the basic test with the assigned soil type (see 5.2.2.1). The limit value for soil mass passing in the last test phase (Ml) is an indication of adequate stabilization of soil loss during the test period.

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Table 2 : standard requirements on filtration properties of a geotextile according to TLG /1/

beneath a permeable top layer

1 2 3 4 5 6

Nr. soil type of subsoil filter layer thickness permissible soil loss kn-value of the soil- (subgrade) (T)

(mm)

total mass (Mt ) of soil passing (g/184 cm2) 1)

mass (Ml) of soil passing in the last test phase (g/184 cm2) 1)

filled geotextile 5)

(m/s)

1 soil type 1 T ≥ 4,5 2) kn ≥ 8 ⋅10−4

2 soil type 2 T ≥ 4,5 2) Mt ≤ 300 3) Ml ≤ 30 kn ≥ 6 ⋅10−4

3 soil type 3 T ≥ 4,5 kn ≥ 1 ⋅10−4

4 soil type 4 T ≥ 6,0 kn ≥ 1 ⋅10−7

5 cohesive soils with

cu ≥ 10 kN/m2 and Ip ≥ 0,15 4)

no requirement

requirements related to soil types 1-4 (free selection) apply

requirement related to soil type 4 applies

6 cohesive soils with

cu < 10 kN/m2 or Ip< 0,15 4)

no requirement

requirements related to soil type 4 apply

beneath an impermeable top layer (lining)

7 independent of soil type of subsoil

T < 5,0 requirements related to soil type 4 apply kn < 1 ⋅10−5

1) grams, related to the exposed test area /5/ 2) valid only for gradings which may lead to reduction of permeability due to clogging or blocking (see 5.3.2) 3) 300 g / 184 cm2 = 16,3 kg/m2 4) where cu and Ip are unknown, requirements of soil type 4 apply 5) h = 0,25 m

If the subsoil includes a band of grading curves exceeding the limits of the validity range of one soil type, the geotextile filter must be designed for all those soil types of which the validity range is cut by the grading band grain fractions d5 - d60 , i.e. all related require-ments apply (see example Annex 7).

Note The admissible soil loss of the flow-through method (see 5.2.2.1) has been established to date for safety reasons at 25 (2,5) g due to the small number of test cycles compared with the reversing turbulent flow method (TLG 1987). Since studies with multiple loading times did not significantly enhance the mass of soil loss, limit values have been equalized with those of soil type 4 (TLG 1993).

The kn -value of the soil-filled geotextile must in principle be at least twice of the subsoil's (considerable silty soils at least tenfold). Reduced filtration requirements apply to cohesive subsoils (e.g. sealing clay) dependent on apparent cohesion and plasticity index. In cases where cu ≥ 10 kN/m2 and IP ≥ 0,15 (Table 2, line 5), based on results of filtration tests /19/, any geotextile which meets the requirements on admissible loss of soil mass of one of the soil types 1-4 is appropriate as a filter. In cases where cu < 10 kN/m2 or IP < 0,15 any geotextile which complies with admissible loss of soil mass valid for soil type 4 is appropriate as a filter.

5.2.2.3 Application principle for impermeable top layers

When a geotextile is provided as a separation layer beneath an impermeable top layer (hard lining), it shall be able to promote at the same time self-sealing of the lining in the case of cracks /7/. For this purpose it is sufficient to dimension the mechanical filtration stability, independent of soil type of subsoil, for the silt fraction (soil type 4, Table 2, line 7). In this case permeability and layer thickness should be as small as possible. In the case of leakage nonwovens are acting due to permeability in their plane like a drainage layer (seepage loss, see too 4.6.2).

5.2.3 Filter rules 5.2.3.1 General

For geotextiles provided as a filter layer beneath permeable armour layers the filter rules of AK 14/ AA 6.14 apply. They are based on the determination of the largest opening size of a geotextile (see 5.3.3) which is just still admissible for the grading of the subsoil to be protected considering the type of hydraulic loading. They have been derived from distinct existing filter rules being valid only for a certain range of gradings, with the objective of a generally valid dimensioning rule. Thus they represent a compromise for some soils, and as such, deviations from the given filter rules can be necessary, depending on boundary conditions of a construction task.

5.2.3.2 Design of a filter layer

When designing a geotextile filter layer according to the filter rules /8/14/, it must be distinguished between the grain-size ranges

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A, B, C and at the same time between static and dynamic hydraulic loadings of the filter area. The design rules and an example of application are given in Annex 8 Concerning soils in the grain-size range A, a geotextile used as a filter beneath a structure sensitive to settlement must be designed for dynamic hydraulic loads according to the soil-type design procedure (see 5.2.2).

5.2.3.3 Design of a separation layer

A separation layer has to be designed merely to provide safe soil restraint (see 2.6 and 3.2.2). For this purpose it is sufficient to establish an upper limit of admissible opening size (see 5.3.3) related to the boundary conditions of construction works.

5.3 Material properties 5.3.1 General

The general material requirements of the TLG /1/ and ZTV-W /2/ apply. Geotextiles must be so flexible or extensible that they will ensure under the weight of the cover layer a full-area contact with a sub-grade showing normal irregularities, without forfeiting filtration stability. Needle-punched nonwovens are much more flexible and extensible than products bonded by adhesion or melting or than wovens. A structural addition reduces the flexibility of a geotextile. A geotextile and its seams must be dimensioned or designed in such a way that the expected mechanical loads will not affect the filtration properties or even cause damages. Normally, only loads caused during construction works are relevant to the material properties to be specified (see 3.3.3.2). The most important physical and chemical properties of the usual fibre raw materials (see 3.3.4.1) can be gathered from Annex 5. Based on current experience these fibre raw materials are ecologi-cally compatible.

5.3.2 Permeability

The permeability of a geotextile is influenced by porosity (non-wovens about 80-95%), pore size, pore-size distribution and layer thickness. Permeability is given as - flow velocity v (m/s), - flow rate q (l/m2/s) or - coefficient of normal permeability kn (m/s). v (q) increases with increasing hydraulic head h (fig.). kn decreases with increasing hydraulic gradient i and is constant in the laminar range (i ≤ 2) only. Thus it makes sense, when comparing permea-bilities, to compare index values at a certain h (h = 0,25m or h = 0,05 m /5/), considering that v (q, kn) increases too with increa-sing water temperature and is given for geotextiles at 20° C (k of soils at 10° C according to DIN 18 130 /17/).

Permeability of a brand-new (unused) geotextile can be reduced in the service state by the following effects: a) soil-particle entrapment (clogging, blocking): clogging (nonwovens) may occur when Dw > 0,5 x d2 , blocking (woven) when U < 3. Reduction of v (q, kn) can generally be judged by performance tests only (see 5.2.2.1), but can be considered too, based on practical experience on thick non-wovens (T > 2 mm), when using a safety factor as follows: - silty soils : kn ≥ 50 x ksoil - low silty soils : k ≥ 10 x ksoil . } at h ≥ 0,05 m b) accumulation of fines: is mainly relevant on suffosive subsoils (see 3.3.1.5). c) sintering, ochre formation (see 3.3.4.2). d) uniform surcharge: under a pressure of σ ≤ 2 kPa the reduction in v (q, kn) is negligible even for thick nonwovens (T > 2 mm) with minimum strength according to subclause 5.3.5 (unpublished investigations of the BAW). e) reduction of percolated filter area by large armour-layer elements (see 5.3.4.1).

5.3.3 Opening size

The range of pore sizes of a geotextile or of its single layers is described as a substitute with the parameter Dw (effective opening size, soon probably indicated as O90 ). Dw is determined by sieving, the geotextile being used as a sieve. Dw (O90) = X means that 90 % of the pores are equal to or smaller than the grain diameter X. Dw (O90) is used in geotextile design according to filter rules as a characteristic parameter for soil restraint (see 5.2.3.2). Its magni-tude is not unchangable. It can be reduced due to surcharge or even be enlarged due to geotextile deformations or due to fibre shifting caused by dynamic impacts, dependent on type or on strength of a geotextile. That must be assessed in the case of a high safety level, if necessary, in a suitability test (see 6.3); concerning nonwovens with strengths according to subclause 5.3.5 and wovens with fixed crossing points this is generally not relevant. Dw says nothing about the hydraulic filtration stability of a geo-textile which is influenced too by porosity, pore-size distribution and layer thickness (see 5.3.2 and 5.3.4.1). Dw of an additional layer: see subclause 4.6.2.

5.3.4 Layer thickness 5.3.4.1 Related to the filtration function

The filtration stability of a geotextile can be influenced by layer thickness. With increasing layer thickness - consequences of possible variations of mass per unit area on variations of opening size are reduced (safety to erosion). - sensitivity of a geotextile to large variations of grading curves of subsoil is reduced (safety to erosion). - hydrodynamic impacts (waves, turbulent currents) acting through the geotextile on the subsoil are damped, i.e. geotextile pore sizes can be larger without impairing soil restraint (safety to colmatation). - ability to drain off soil water even from those filter areas which are covered e.g. with very large elements of an armour layer, will be improved (mechanical stability). In the normal case the minimum values given in Table 2 apply to layer thickness. Layer thickness is dispensable as a filter requirement a) in the case of a low safety level; b) when the subsoil is exactly known and of homogeneous nature (very small grading band);

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c) on coarse subsoils if no significant reduction of permeability due to clogging or blocking can occur (see 5.3.2); d) in the case of subordinate importance of geotextile permeability in the plane (relatively small particle sizes of the overlying layer).

5.3.4.2 Related to the separation function

When a geotextile fulfils a separation function (see 3.2.2) there is no need to require a minimum layer thickness. Layer thickness depends only on the required strength properties.

5.3.5 Tensile strength and strain

The required minimum values of tensile strength at failure of a geotextile are given in Table 3, valid when used under armour layers inclined 1:2 or less. According to current practical experience they are sufficient to cover the normal tensile stresses which are unavoidable (see 3.3.3) and consider even tensile forces arising from the flow pressure of currents (v ≤ 1,50 m/s) when installed under water /20/21/23/. As regards geotextiles being exposed to wear, sufficient residual tensile strengths must additionally be proved after execution of abrasion test (see 5.3.7). On slopes steeper than 1:2 or in the case of current loadings being substantially higher when the geotextile is placed, the necessary tensile strengths at failure must be proved separately. Strains of nonwovens due to uniaxial tensile sresses at failure may be up to 150 %. Those of wovens are generally much below 20 %. As regards geotextiles connected to a fascine-grid (sink mattress) the tensile srengths at failure to be required depend on size of the sink and the placing method (see 4.6.3).

5.3.6 Resistance to dynamic perforation loads

When placing a cover layer consisting of armourstone the geo-textile is subjected to dynamic perforation loads influenced by - shape and weight of stones, - drop height of stones, - strength of subsoil and - placing in the dry or under water.

The geotextile's ability to resist to these loads without damage must be proved. The values for drop energy given in Table 3 correspond to perforation loads caused by an armourstone of size class II of 30 kg (60 kg, size class III) dropped in the dry from a height of 2 m /3/5/. Table 3 applies too to placing under water (see 3.3.3.2) on account of the many imponderables when dumping armourstone. Drop energy can be established similarly for requirements on resistance to dynamic perforation loads of lighter or heavier stones. Practical experience has shown that geotextiles with a mass per unit area of µ ≥ 500 g/m2 and maximum strength according to Table 3 are sufficiently resistant to perforation by stones of size class II when placed on sand or finer-grained subsoils (soil types 2 - 4). In the case of coarser subsoil or heavier stones a sufficient resistance to dynamic perforation loads must be proved, if need be in a suita-bility test (see 6.3).

5.3.7 Resistance to abrasion loads

Abrasion loads can lead long-term to damages of a geotextile (see 3.3.3.3). According to practical experience these loads occur in the zone of fluctuating water levels with an important magnitude only in connection with unbound protective layers with large voids (armour-stone of size class II or larger) or with permeable concrete block-systems caused by chafing movements of single stones under frequent heavy wave impacts. A geotextile is considered resistant to abrasion loads if 75 % of the required layer thickness (otherwise original layer thickness) and of the required maximum tensile strengths are still left after execution of abrasion test /5/ (Table 3). If abrasion impacts due to bed load transport must be taken into account in bottom protection (e.g. protective measures against scour in the tail water of barrages), in the case of armour layers with large voids the geotextile must be solidly protected against abrasion loads by an overlying smaller-grained interlayer (e.g. crushed rock) which is compatible with the overlying cover layer. Synthetic materials are not sufficiently long-term resistant to abrasion loads of this kind.

Table 3: Standard requirements on strength properties of a geotextile according to TLG /1/

Nr. material properties Type of top-layer construction according to Annex 3, sheet 6

D 1 armourstone

D 2 / D 3 armourstone

D4, coverings

class II class III class II + grout µ <

3kN/m² µ ≥

3kN/m²

1 tensile strength at failure according to DIN 53 857 longitudinal and transverse

kN/m ≥ 12,0 ≥ 12,0 ≥ 12,0 ≥ 9,0 1) ≥ 12,0

2 resistance to dynamic perforation (drop energy) Nm ≥ 600 ≥1200 ≥ 600 -

3 resistance to abrasion

residual thickness (T) of the filter layer after abrasion test

mm soil type 1-3:T≥3,5 soil type 4 :T≥4,5

- -2)

tensile strength at failure after abrasion test (residual tensile strength)

kN/m ≥ 9,0 - -2)

1) when installed under water ≥ 12,0 kN/m 2) precast stones like D1

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5.3.8 Resistance to static puncture loads

In cases where static puncture impacts on a geotextile cannot be avoided (see 3.3.3.2) a suitability test (see 6.3) of resistance to static puncture loads is recommended on a test area under condi-tions of construction site if damage to the geotextile cannot be excluded from practical experience. Geotextiles which are resistant to dynamic perforation loads accor-ding to Table 3 are resistant to static puncture loads too if a protec-tive layer with a thickness according to subclause 4.10 is used, since dynamic perforation loads cause a greater dynamic impact on the geotextile surface. When using geotextiles in a service way or in roads of a construc-tion site the "Recommendations for the Use of Geotextiles in Earth-works " /9/, should be referred to.

5.3.9 Resistance to high temperatures

When an armour layer is constructed directly on a geotextile using hot bituminous matters, proof of resistance to high temperatures (adequate residual tensile strength, see 5.3.5) is not necessary for the usual fibre raw materials (with exception of PE, see Annex 5). For these, the BAW has proved by a great number of tests that geotex-tiles which are placed under material heated up to 200°C /5/ are sufficiently heat resistant.

5.3.10 Friction coefficient

In slope protection a minimum value of the friction coefficient of a geotextile related to the subsoil generally must not be required. Because of irregularities of interface between geotextile and the subsoil resulting from armour-layer installation (e.g. top layer according to Annex 3, sheet 6) the friction coefficient of the geotextile can be assumed equal to the effective angle of internal friction of the subsoil /22/, if interlocking between the geotextile and the subsoil is possible due to relation of geotextile opening size and grain sizes of the subsoil (see 5.3.3). Otherwise it has to be reduced by the factor 0.8. On slopes steeper than 1:2 the friction coefficient of the geotextile or of the geotextile type must be known. If need be, it is to be determined in the course of a suitability test (see 6.3). The friction behaviour of a geotextile on cohesive soils with softened surface can be significantly improved by an additional layer with the largest possible pore sizes (see 4.6.2), because the cohesion of subsoil takes effect when the additional-layer fibres penetrate into the subsoil.

5.3.11 Mass per unit area

The mass per unit area of a geotextile results from the specified material and filtration properties. This is used as a characteristic relative value in quality controls and therefore must be determined in each test (see 6). Based on practical experience this may be used as a standard value for achieving specific material properties.

6 Tests 6.1 General

Tests for quality assurance can be subdivided into - the basic test, - suitability test(s), - quality control during manufacture and - control tests by the Principal.

They must be performed for geotextiles according to the TLG /1/ (Annex 9) and ZTV-W /2/ by an approved testing authority following the RPG /5/.

6.2 Basic test

The basic test is a test by the Contractor to demonstrate the funda-mental suitability of untried construction materials, construction-material mixtures and construction-material systems for the inten-ded purpose.

6.3 Suitability test

The suitability test is a test by the Contractor to demonstrate the suitability of the construction materials, construction-material mixtures and the construction-material system for the intended pur-pose taking into consideration the installation method in accordance with the specifications of the building contract. This must be per-formed in good time before construction commences. A suitability test is necessary a) to prove the fulfilment of those requirements which are justified by specific conditions relating to the construction works and thus are not covered by the certificate of the basic test; b) in the case of a high required safety level and a subsoil which is critical with respect to the geotextile filtration properties (performance tests by using the subsoil granulation as a test soil); c) in the case of an untried installation method, or if no experience exists in geotextile installation under water; d) if the foreseen base materials deviate as regards source or type from those of the basic test, i.e. if a significant change of their properties can be assumed.

6.4 Quality control during manufacture

Quality control must be guaranteed by factory production control tests of the manufacturer and of an approved body (TLG /1/). Factory production control tests are tests by the Contractor to check whether the quality of construction materials, construction-material mixtures and the construction-material system comply with the contractual specifications.

6.5 Control tests by the Principal

Control tests are tests by the Principal to check if the quality pro-perties of the construction materials, construction-material mixtures and the construction-material system fulfil the contractual require-ments. Samples for control tests must be taken on the directive of the Principal by the Contractor and be sent to the testing laboratory by the Principal. The following must be stated for the samples : - contractual requirements, - product name, - roll number, - name of the construction project, - range for which the sample is representative, - geotextile upper side for placing purposes, - date of sampling, - name of the authorized person. If seams are manufactured on the construction site a trial seam should be tested before commencement of placing (ZTV-W /2/). The samples taken from one delivery must be sent to the testing laboratory by the Principal in good time so that the test results are available before commencement of placing (TLG /1/).

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7 Instructions for inviting tenders and for construction works

7.1 Tender documents

The inviting of tenders for supply of geotextiles must always be based on the Technical Supply Conditions for Geotextile Filters (TLG /1/). When setting up the tender documents for geotextiles used in a standard top layer by means of the catalogue of standard-specifi-cation texts (STLK) /4/ all relevant particular requirements accor-ding to the TLG are unambiguously established by assigning the subsoil to be protected, following the soil-type design procedure of the BAW (see 5.2.2) and by indicating the type of top-layer con-struction if the symbols of the standard top layer and of the soil type or soil-type range are indicated in the bill of quantities. In the case of deviating or additional requirements all decisive requirements must be included in the construction-works description (Annex 10). If special connections are to be performed (see 4.7 and 4.8) they must be detailed in the tender documents and drawn if need be. If a construction contract is concluded the technical contract condi-tions ZTV-W (LB 210) must be established as part of the contract. Admissible tolerances as regards preparation of the subgrade must be indicated in the tender documents. When the geotextile is to be placed under water, it must be pro-vided in the tender documents that the supplier indicates the in-stallation method as regards - preparation of the filter subgrade, - description of the placement equipment or of the installation method - extent of intended diver operations (see 7.2.3).

7.2 Construction works 7.2.1 Preparation of the filter subgrade

The filter subgrade must be evenly levelled. Cavities, which may often occur when constructing the subgrade on a cohesive subsoil, and also erosion channels, must be filled up with soil of filter qua-lity (see 4.3). Any vegetation, exposed stones or foreign bodies must be removed. Otherwise a larger quantity of geotextiles may be required, and this may amount to 30% of the filter area /20/, resul-ting from the larger surface of an irregular subgrade compared with a regular one. This may have consequences for the execution of overlaps or connections with structures as insufficient fabric may be available to ensure complete coverage. On slopes the local mecha-nical stability of the armour layer can be reduced due to large ca-vities beneath the geotextile (see 4.1).

7.2.2 Installation in the dry

Installation of geotextiles in the dry is generally not problematical (see 3.3.3.2). Nevertheless it must be ensured that measures to secure the geotextile against displacements caused by wind, waves (tidal zone) etc. do not lead to perforation of the later percolated filter area /2/ and that they do not result in uncontrollable tensile strengths when placing the protective layer. The geotextile must be allowed to slide on the subgrade. Driving on geotextiles without a sufficient protective layer must be avoided (see 3.3.3.2).

7.2.3 Installation under water

Placing a geotextile unit under water in the the planned position is

only possible with technical assistance or by using a structural addition (see 4.6), since geotextiles do not sink to the subgrade without surcharge because of their low unit weight (Annex 5) and entrapped air bubbles. The following demands are to be made on the installation method (does not apply to sink mattresses, see 4.6.3): a) The geotextile should be in contact with the subgrade if at all possible when cover layer aggregate is placed on it, or it should be held only in a small distance above it (< 0,50 m), while pre- stressing it moderately. Sinking a floating geoextile unit in the planned position and without folds is not possible simply by placing aggregate on it. In addition coarse aggregate (stones) may get beneath the geotextile (risk of perforation ; reduction of mechanical stability of the top layer on slopes, see 4.1; increased risk of abrasion damages). The satisfactory position of the geotextile must be checked by a diver in each case before placing the protective layer if this is not guaranteed by the installation method or by the structural addition used (see 4.6). b) The area of overlaps must be checked by a diver immediately before installing the adjacent geotextile unit to ensure full-area coverage and freedom from stones if this is not guaranteed by the structural addition used and by the placing method. A geotextile protruding from an impermeable top layer (lining) may lead to uncontrollable water losses in a sealing section depending on the geotextile transmissivity /20/ (see too 5.2.2.3). c) Fixings of a geotextile which may cause damage of the filter area (e.g. pinning) are inadmissible. d) All edges over which the geotextile is turned must be rounded off to minimize chafing loads due to movements of the installation equipment or of the geotextile itself. In the section of the construction site the authorized maximum speed of navigation should be limited to Vs = 6 km/h, to exclude as far as possible slippage or erosion of the filter subgrade, damage of the geotextile unit caused by the flow pressure and displacement of overlaps caused by return currents or waves. If necessary the navi-gational span must be reduced by traffic signs to a width much less than already effected by the floating equipment of the construction site. When placing a granular levelling sublayer the recommendations given in subclause 4.3 must be heeded.

7.3 Inventory documents

With respect to the later maintenance works or repairs inventory documents must be established from the actual revetment structure giving all the essential details such as: - nature of subsoil according to DIN 4022 /28/ and to DIN 18 196 /16/ - product name of the geotextile and test report of the basic test and/or of suitability test(s), - type of geotextile joints (seams or overlaps), indication of roll width, - revetment structure, - type of toe support, - indication of geographical location of construction section, - abnormalities during construction execution (e.g. defects re- gistered by control tests or reservations resulting from the final inspection) and - diver reports.

16

8 References

/1/ Technical Supply Conditions for Geotextile Filters (TLG); obtainable at Drucksachenstelle bei der WSD Mitte, Am Waterlooplatz 9, 30169 Hannover /2/ Supplementary Technical Contract Conditions - Hydraulic Engineering (ZTV-W) for Embankment and Bottom Revet- ments, service area 210; obtainable at Drucksachenstelle bei der WSD Mitte, Am Waterlooplatz 9, 30169 Hannover /3/ Technical Supply Conditions for Armourstone (TLW), obtainable at Drucksachenstelle bei der WSD Mitte, Am Water- looplatz 9, 30169 Hannover /4/ Catalogue of Standard Specification Texts - Hydraulic Engi- neering (STLK) for Embankment and Bottom Revetments, service area 210; obtainable at Drucksachenstelle bei der WSD Mitte, Am Waterlooplatz 9, 30169 Hannover /5/ Guidelines for Testing Geotextile Filters in Navigable Water- ways (RPG), BAW Karlsruhe /6/ Code of Practice Use of Granular Filters on Waterways (MAK), BAW Karlsruhe /7/ Code of Practice Use of Standard Construction Types for Embankment and Bottom Revetments on Waterways (MAR), BAW Karlsruhe /8/ Guideline Nr. 306: "Use of geotextiles in hydraulic engineering"; editor: Deutscher Verband für Wasserwirtschaft und Kulturbau e V. (DVWK), edition 1991 /9/ "Directions for Use of Geotextiles in Earthworks", Forschungs- gesellschaft für Sraßen- und Verkehrswesen / Köln /10/ "Das Geotextilhandbuch", Schweizerischer Verband der Geo- textilfachleute (SVG), secretariat c/o EMPA, Postfach, 9001 St. Gallen / Switzerland /11/ Nold "Brunnenfilterbuch", J. F. Nold & Co., 63811 Stock- stadt /12/ Kezdi, A.: "Handbuch der Bodenmechanik", VEB Verlag für Bauwesen Berlin /13/ Busch / Luckner : "Geohydraulik für Studium und Praxis", Ferdinand Enke Verlag, Stuttgart /14/ DVWK-Schriften Nr. 76; "Use and testing of plastics in earthworks and water engineering"; recommendations of Working Group 14 of the Deutsche Gesellschaft für Erd- und Grundbau e.V., Hamburg, Berlin; Parey 1986 /15/ DIN 60 000; Textiles; basic terms and definitions /16/ DIN 18 196; Earthworks and foundations; soil classification system for civil engineering purposes /17/ DIN 18 130, part 1; Soil, testing procedures and testing equipment; determination of the coefficient of water permeability; laboratory tests /18/ DIN 53 857, part 1 and 2;Testing of textiles; simple tensile test on strips of textile fabrics /19/ Abromeit, H.-U.: "Reqirements on filtration properties of a geotextile used on clay linings", BAW-Brief Nr. 3/91

/20/ Abromeit, H.-U.: "Installation of geotextile filters under water by technical means"; Mitteilungen des Franzius-Instituts für Wasserbau und Küsteningenieurwesen der Universität Han- nover, Nr. 62/1986 /21/ Abromeit, H.-U.: "Tensile stresses on a geotextile due to the influences of shipping when installation is performed from the water surface", BAW-Brief Nr. 5/1989 /22/ Grett, H.-D.: "Friction behaviour of geotextiles being in contact with cohesive or non-cohesive soils"; Mitteilungen des Franzius-Instituts für Wasserbau und Küsteningenieurwesen der Universität Hannover, Nr. 59/1984 /23/ Knieß, H.G./ List, H.-J.: "Long-term durability of geotextile filters"; unpublished research report of the BAW, Karlsruhe 1982 /24/ Knieß, H.G.: "Criteria and attempt for technical and economi- cal design of inland-waterway revetments", Mitteilungsblatt der Bundesanstalt für Wasserbau, Karlsruhe, Nr. 53, August 1983 /25/ Knieß, H.G.: "Dumping of stones under water", Mitteilungs- blatt der Bundesanstalt für Wasserbau, Karlsruhe, Nr. 50, 1981 /26/ Schnitter , G./ Zeller, J.: "Seapage flow in earth dams due to fluctuation of a dammed up water level"; Schweizerische Bau- zeitung, 75. Jahrgang, Nr. 52/1957 /27/ "Denkendorfer Fasertafel 1986", Institut für Textil- und Ver- fahrenstechnik, Körschtalstraße 26, 73770 Denkendorf /28/ DIN 4022, part 1; Subsoil and groundwater; designation and description of soil and rock /29/ Kuntze, H.: "Verockerungen; Diagnose und Therapie"; Schrif- tenreihe des Kuratoriums für Wasser- und Kulturwesen, Nr. 32 (1978)

17

9 Index of keywords A abrasion loads, see 3.3.3.3, 5.3.7

abrasion resistance, see 5.3.5, 5.3.7 additional layer, see 4.6.2, 4.9, 5.3.3, 5.3.10 angle of internal friction, see 3.3.1.1, 3.3.1.2 armour layers, see 4.10 armourstone, see 4.10 authorized maximum speed of navigation, see 7.2.3

B basic test, see 5.2.2.1, 5.2.2.2, 6.2 bill of quantities, see 7.1 biological ochre formation, see 3.3.4.2 blocking, see 2.10, 5.2.2.2, 5.3.2 bottom protection - connections with structures, see 4.8 - standard type of construction, see 4.10

C catalogue of standard-specification texts, see 7.1 chemical ochre formation, see 3.3.4.2 classification procedure of the BAW, see 5.1, 7.1 cleavage water, see 4.2, 4.3, 4.6.2 clogging, see 2.10, 5.2.2.2, 5.3.2 cohesive soil, see 3.3.1.3, 5.2.2.2 colmatation, see 2.10, 3.3.1.4, 3.3.1.5, 4.6.2, 5.3.2, 5.3.4.1 connections with structures, see 4.8, 7.1, 7.2.1 construction works, see 7.2 - description, see 7.1 - in the dry, see 7.2.2 - under water, see 7.2.3 construction-site roads, see 5.3.8 construction types, see 4 ff. control tests, see 6.5

D drainage layer, see 2.7, 5.2.2.3 durability, see 3.3.4.1, 3.3.5 dynamic hydraulic loading, see 2.11, 3.3.2, 5.2.1, 5.2.2.1, 5.2.3.2, 5.3.4.1

E erosion, see 2.8, 3.3.1.2, 4.1, 4.5, 4.6.2, 5.3.4.1 F fascine-grid, see 4.6.3

fibre raw materials, see 3.3.4.1, 5.3.1 filter, see 2.5 - hydraulic loadings, see 3.3.2 - mechanical impacts, see 3.3.3 - necessity, see 3.2 - rules, see 5.2.1, 5.2.3 - subgrade, see 4.2, 4.3, 7.1, 7.2 - types of construction, see 4.1 ff. filtration stability, see 5.2, 5.3.2, 5.3.3, 5.3.4.1 flexibility, see 5.3.1 flow pressure of currents, see 3.3.3.2, 5.3.5, 7.2.3 flow-through method, see 5.2.2.1 friction coefficient, see 4.6.2, 5.3.10

G grading band, see 5.2.1, 5.2.2.2, 5.3.4.1 grain-size distribution, see 3.3.1.1, 5.2.2.2 granular filter, see 3.3.4.2, 4.4, 4.8 granular interlayer, see 4.5 granular levelling layer, see 4.3

H hydraulic filter loadings - dynamic, see 2.11, 3.3.2, 5.2.1, 5.2.2.1, 5.2.3.2, 5.3.4.1 - static, see 2.12, 3.3.2, 5.2.1, 5.2.3.2 hydraulic filtration stability, see 2.5, 5.2.1, 5.2.2, 5.2.3, 5.3.2, 5.3.3, 5.3.4.1 hydraulic gradient, see 2.11, 2.12, 5.3.2

I inhomogeneous subgrade, see 3.3.1.4, 4.3 installation - in the dry, see 7.2.2 - loads, see 3.3.3.2 - under water, see 7.2.3 interlayer, granular, see 4.5 inventory documents, see 7.3

K k-value - geotextile, see 5.2.2, 5.2.3, 5.3.2 - soil, see 3.3.1.1, 5.3.2

L levelling sublayer, granular, see 4.3 lining, see 4.6.2, 5.2.2.3, 7.2.3 loads, mechanical, see 3.3.3 long-term durability, see 3.3.4.1, 3.3.5

M manufacturer production controls, see 6.4 mass per unit area, see 5.3.6, 5.3.11 material properties, see 5.3 - additional layer, see 4.6.2 - resistance to abrasion loads, see 5.3.7 - resistance to perforation loads, see 4.6.2, 5.3.6 - resistance to static puncture loads, 5.3.8 - tensile strengths, see 5.3.5, 5.3.7 - thickness, 5.3.4

mechanical filter loads, see 3.3.3 - execution of construction works, see 3.3.3.2 - waterway operations, see 3.3.3.3 mechanical filtration stability, see 2.5, 5.2.1, 5.2.2, 5.2.3, 5.3.3 mechanical stability, see 3.3.1.2, 4.1, 4.2, 4.5, 4.6.2, 5.3.4.1, 7.2.1, 7.2.3

N non-cohesive soil, see 3.3.1.2, 5.2.2.2, 5.2.3 nonwoven, see 2.2, 5.2.2.3, 5.3.1, 5.3.2

O ochre formation, see 3.3.4.2, 5.3.2 opening size, see 4.6.2, 5.2.3, 5.3.2, 5.3.3 overlaps, see 4.9, 7.2.1, 7.2.3

P penetrability by roots, see 3.3.6 perforation loads, see 3.3.3.2 performance test, see 5.2.2.1, 5.3.2, 6.3 pH-value, see 3.3.4.1 plasticity index Ip, see 3.3.1.1, 3.3.1.2, 5.2.2.2, 5.2.3.2 production control by an approved body, see 6.4 puncture loads, see 3.3.3.2

Q quality control, see 6.4 R requirements

- filtration stability, see 5.2 - material properties, see 5.3 residual tensile strength, see 5.3.5, 5.3.7, 5.3.9 resistance - abrasion, see 5.3.5, 5.3.7 - dynamic perforation, see 5.3.6 - high temperatures, see 5.3.9 - long term, see 3.3.4.1 - static puncture, see 5.3.8 - UV weathering, see 3.3.5, 4.10, 5.3.1 reversing turbulent flow method, see 5.2.2.1

S sealing clay, see 5.2.2.2 seams, see 4.9, 5.1, 5.3.1 seepage loss, see 5.2.2.3, 7.2.3 ? separation layer, see 2.6, 3.2.2, 5.2.3.3, 5.3.4.2 sink mattress, see 4.6.3, 5.3.5, 7.2.3 sintering, see 3.3.4.2, 5.3.2 site traffic, see 3.3.3.2 slope protection, see 4.10 - edges, see 4.7 - toe forms, see 4.6.3, 4.7 soil, see subsoil soil types, see 5.1, 5.2.2.1 soil-type design procedure, see 5.2.2 standard top layers, see 4.10 static hydraulic loadings, see 2.12, 3.3.2, 5.2.1, 5.2.3.2 strain, see 5.3.1, 5.3.5 structural addition, see 4.6 ff subgrade, see 4.2, 4.3, 4.6.2, 7.2.1, 7.2.2, 7.2.3 subsoil, see 3.3.1 - description, see 3.3.1.1 - cohesive, see 3.3.1.3, 5.2.2.2 - susceptible to erosion, see 3.3.1.2 - inhomogeneous, see 3.3.1.4 - non-cohesive, see 3.3.1.2, 5.2.2.2 - susceptible to suffosion, see 3.3.1.5 suffosion, see 2.9, 3.3.1.5, 4.3, 4.6.2, 5.2.1, 5.3.2 suitability test, see 5.2.2.1, 5.3.3, 5.3.8, 5.3.10, 6.3 surface water, see 4.7

T tender documents, see 7.1 tensile strength, see material properties tensile stresses, see 3.3.3.2, 3.3.3.3 tests, see 6 ff - basic test, see 6.2 - control tests by the Principal, see 6.5 - production control by an approved body, see 6.4 - production control by the manufacturer, see 6.4 - suitability tests, see 6.3 thickness - additional layer, see 4.6.2 - armour layer, see 4.10 - geotextile, see 5.2.2.2, 5.2.2.3, 5.3.3, 5.3.4, 5.3.7 - levelling sublayer, see 4.3 toe forms, see 4.6.3, 4.7 top layers, see 4.10

U uplift pressure, see 3.3.3.3, 4.1 UV-weathering, see 3.3.5, 4.10

V vegetation, see 3.3.6, 4.2, 4.3, 7.2.1 W water in the filter zone, see 3.3.4

water permeability, 3.3.4.2, 5.3.2 waterway operations, see 3.3.3.3 woven, see 2.3, 5.3.1, 5.3.2

Z zone of fluctuating water levels, see 3.3.4.2 ZTV-W, service area 210, see 5.3.1, 6.5, 7.1

18

10 Index of Annexes Page

Annex 1 Check of the necessity for a filter layer (separation layer) ................................................................................................ 19

Annex 2

sheet 1-2: Check of suffosion stability of a soil using its grading curve (geometric suffosion stability) .......................................... 20

Annex 3

sheet 1: Types of filter construction................................................................................................................................................... 22

sheet 2 : Geotextile with a structural addition ................................................................................................................................... 23

sheet 3: Examples of the upper edge construction of a slope protection (see 4.7) .......................................................................... 24

sheet 4: Toe forms of a slope protection (example of an armourstone layer partially grouted) ................................................... 25

sheet 5: Connections with a structure (see 4.8) ................................................................................................................................. 26

sheet 6: Standard top layers for a slope and bottom protection according to the MAR /7/ (see 4.10).......................................... 27

Annex 4 Grain-size range recommended for a granular levelling sublayer (see 4.3) and assessment of

soil permeability; diagram of BEYER, relation of HAZEN .............................................................................................. 28

Annex 5 Grading bands of the armourstone size classes 0 - V according to the Technical Supply

Conditions for Armourstone (TLW) /3/ and fibre raw materials used for geotextiles and their

properties /27/ ........................................................................................................................................................................ 29

Annex 6

sheet 1: Validity range of the soil types 1 and 2 (see 5.2.2) .............................................................................................................. 30

sheet 2: Validity range of the soil types 3 and 4 (see 5.2.2) .............................................................................................................. 31

Annex 7

sheet 1-4: Examples of a filter application in a permeable slope protection of a ship-canal using the

soil-type design procedure of the BAW ............................................................................................................................... 32

Annex 8

sheet 1-3: Filter rules of the AK 14 / AA 6.14....................................................................................................................................... 36

Annex 9 Table on standard tests according to the Technical Supply Conditions for

Geotextile Filters (TLG)........................................................................................................................................................ 39

Annex 10 Process of design and tender-document specification......................................................................................................... 40

19

Annex 1 Check of the necessity for a filter layer (separation layer) A filter is necessary between the soil to be protected and the intended cover layer if the admissible ratio value A50 according to the diagram of CISTIN / ZIEMS is exceeded (see fig.).

fig.: diagram of CISTIN / ZIEMS A50 = ratio of the mean grain diameter D50 of the cover layer and d50 of the subsoil to be protected CUI = uniformity coefficient of the subsoil CUII= uniformity coefficient of the cover-layer material Note The validity of the CISTIN / ZIEMS diagram /13/ has been proved for soils in the range of 0.1 < d < 30 mm and for filter granulations in the range of 4 <D < 100 mm. Since being determined on the basis of geometric size ratios this may be used too for the assessment of the necessity for a filter as regards coarser granulations. It can be used likewise to assess the necessity for a separation layer in the case of dynamic impacts (see 3.2.2). Examples of application a) A cover layer consisting of armourstone size class II on subsoil consisting of coarse very gravelly sand subsoil: d60 = 2.0 mm d50 = 1.5 mm d10 = 0.4 mm CUI = 5 cover layer: D50 = 170 mm (Annex 5) CUII = 1.7 from the diagram of CISTIN / ZIEMS : admissible A50 = 11 existing A50 = D50 / d50 = 170 / 1.5 = 113 > admissible A50 A filter is necessary. b) A cover layer consisting of armourstone size class II on subsoil consisting of gravel subsoil: d60 = 20 mm d50 = 16 mm d10 = 4 mm CUI = 5 cover layer: D50 = 170 mm (Annex 5) CUII = 1.7 from the diagram of CISTIN / ZIEMS : admissible A50 = 11 existing A50 = D50 / d50 = 170 / 16 = 10.6 < admissible A50 A filter is not necessary.

20

Annex 2, sheet 1 Check of suffosion stability of a soil using its grading curve (geometric suffosion stability) Principle 1. Cut the grading curve of the soil (see fig.1) at an arbitrary grain diameter. The finer grain diameters are regarded as the base fraction (db),

the coarser grain diameters as the filter fraction (df). Read at the cut diameter (dc) the weight percentage (wsc).

2. Determine a separate grading curve of the base fraction and of the filter fraction (see fig. 1) according to equations 1 and 2. For this, at

least 5 evenly graded grain diameters should be used in each case.

a) determination of the base-fraction grading curve: for a chosen grain diameter db(i) applies wb(i) = ws / wsc × 100 % (equation 1) b) determination of the filter-fraction grading curve: for a chosen grain diameter df(i) applies

wf(i) = wb - wsc

100% - wsc × 100% (equation 2)

with wb(i) = percentage by weight of the base-fraction grading curve at the chosen grain diameter db(i) wf(i) = percentage by weight of the filter-fraction grading curve at the chosen grain diameter df(i) ws = percentage by weight of the soil at the chosen grain diameter db(i) or df(i) of its grading curve wsc = percentage by weight of the soil at the chosen cut diameter dc of its grading curve. 3. Check the mechanical filtration stability of the grading curves of the filter and of the base fraction according to CISTIN / ZIEMS (Annex

1). If the admissible ratio A50 is kept, the filtration stability between the two chosen grain fractions is given. 4. Repeat the steps 1. to 3. using further cut diameters (see fig. 2). A soil is stable to suffosion if the mechanical (geometric) filtration

stability between the grading curves of the filter and of the base fraction exists for any cut diameter.

fig.1 : soil grading curve and grading curves of the base and of the filter fraction for one chosen cut diameter dc

21

Annex 2, sheet 2

Example of calculation 1. Cut the soil grading curve (see fig. 1) at the chosen grain diameter dc = 1 mm into the base and the filter fraction.

At the cut diameter dc read wsc = 48 %. 2. In order to determine the grading curve of the base and of the filter fraction the following , nearly evenly graded grain diameters are to be

used: db(i) = 0.1; 0.15; 0.2; 0.35; 0.6 mm df(i) = 2.0; 4.0; 6.0; 10; 16; 20 mm. For e.g. db3 = 0.2 mm, ws = 19 % (see fig. 1) from equation 1 : wb3 = 19 % / 48 % x 100 % = 39 %. For e.g. df3 = 6 mm, ws = 59 % (see fig. 1) from equation 2 :

wf3 = 59% - 48%100% - 48% × 100% = 21 %

Accordingly calculate the percentage by weight of the base and of the filter-fraction grading curves using the remaining established grain diameters. The two grading curves are constructed by straight-line connection of the points determined in this way.

3. In order to check the filtration stability between the base and the filter fraction the following characteristic grain diameters of their grading

curves are needed: base fraction filter fraction d60 = 0.3 mm D60 = 22 mm d50 = 0.25 mm D50 = 19 mm d10 = 0.09 mm D10 = 2.75 mm CUI = d60 / d10 = 3.3 CUII = D60 / D10 = 8. From Annex 1 with CUI = 3.3 and CUII = 8: admissible A50 = 22 existing A50 = D50 / d50 = 19 / 0.25 = 76 > admissible A50 .

There is no mechanical filtration stability between the grading curves of the base and of the filter fraction, i.e. the soil is not stable to suffosion as regards the investigated cut diameter.

fig. 2: investigated cut diameters

22

Annex 3, sheet 1 Types of filter construction Geotextile directly on the subgrade (standard application, see 4.2)

permeable granular armour layer

geotextile

subsoil Geotextile on a granular levelling sublayer (see 4.3)

permeable granular armour layer geotextile

granular levelling sublayer

subsoil

Geotextile combined with an unbound granular filter (see 4.4)

permeable granular armour layer geotextile

unbound granular filter

subsoil

Granular interlayer between geotextile and top layer (see 4.5)

top layer consisting of large armourstone

granular interlayer (filter stable to the top layer)

geotextile

subsoil

23

Annex 3, sheet 2 Geotextile with a structural addition Geotextile with an additional layer (see 4.6.2) a) with relatively small pores cm

b) with relatively large pores cm

c) fascine-grid (sink mattress), see 4.6.3

24

Annex 3, sheet 3 Examples of the upper edge construction of a slope protection (see 4.7) Upper edge of the filter a) in the case of low surface-water discharge

b) in the case of high surface-water discharge

c) in the case of a long slope

25

Annex 3, sheet 4 Toe forms of a slope protection (example of an armourstone layer partially grouted) a) toe carpet: on soils only slightly susceptible to erosion (d50 > 2 mm and Cu > 3)

b) embedded toe: design for a scour depth of d ≥ 1.5 m in the case of non-cohesive fine-grained soil d ≥ 0.75 m in the case of gravelly soil

c) toe sheet-pile wall: design for a scour depth of d ≥ 1.5 m in the case of non-cohesive fine-grained soil d ≥ 0.75 m in the case of gravelly soil

26

Annex 3, sheet 5 Connections with a structure (see 4.8) a) smooth surface

b) non-planar surface (e.g. sheet-pile wall) variant 1

variant 2

overlap on slopes, seams (see 4.9)

27

Annex 3, sheet 6 Standard top layers for a slope and bottom protection according to the MAR /7/ (see 4.10)

D 1

armourstone size class II or III according to the TLW /3/ geotextile filter subsoil or lining susceptible to erosion or non-resistant to dynamic perforation loads

D 2

armourstone size class II according to the TLW /3/ partially grouted with impermeable mortar

geotextile filter

subsoil or lining susceptible to erosion or non-resistant to dynamic perforation loads

D 3a

armourstone size class II according to the TLW /3/ fully grouted with permeable mortar geotextile filter subsoil or lining susceptible to erosion or non-resistant to dynamic perforation loads

D 3b

armourstone size class II according to the TLW /3/ fully grouted with impermeable mortar

geotextile separation layer subsoil

D 4a

impermeable covering, e.g.asphaltic concrete geotextile separation layer subsoil

D 4b

permeable covering, e.g. concrete blocks, gabions (applicable only in the zone of fluctuating water levels)

geotextile filter

subsoil or lining susceptible to erosion or non-resistant to dynamic perforation loads

28

Annex 4 Grain-size range recommended for a granular levelling sublayer (see 4.3)

assessment of soil permeability 1. Diagram of BEYER

2. Relation according to HAZEN valid for non-cohesive soils a) uniform soils (Cu ≤ 5):

ksoil = (1.0 to 1.5) × d102 ; (d10 given in cm , k given in m / s)

b) non-uniform soils (Cu > 5):

ksoil = (1.0 to 1.5)

CU × d10

2 ; (d10 given in cm, k given in m / s).

29

Annex 5 Grading bands of the armourstone size classes 0 - V according to the Technical Supply Conditions for Armourstone (TLW) /3/

Fibre raw materials used for geotextiles and their properties /27/

type of fibre raw material

density (g/cm3)

biological resistance

resistance to acid water

(pH ≥ 3)

resistance to basic water

(pH ≤ 12)

resistance to ultra-violet radiation 1)

softening point (°C) /

melting point (°C)

Polyacrylic (PAC) 1.14 - 1.18 + + + + + + +

+ + (50 - 60) 200 / -

Polyamide (PA) 1.14 + + + +

+ (5 - 15) 2)

PA 6 180 - 200 / 215 - 220

PA 6.6 220 - 235 / 255 - 260

Polyester (PES) 1.36 - 1.38 + + + + +

+ (5 - 15) 2)

230 - 240 / 250 - 260

high density Polyethylene (PE) 0.95 - 0.96 + + + + + +

+ + + (no values available)

105 - 120 / 125 - 135

Polypropylene (PP) 0.90 - 0.92 + + + + + +

+ (0 - 10) 3)

150 - 160 / 160 - 175

+ + + exellent stability, + + good stability, + sufficient stability 1) residual strength in % of initial strength (tested on yarns) after direct weathering for 12 months, location Florida 2) improved as regards stabilized types 3) essential improvement possible with stabilizers

30

Annex 6, sheet 1 Validity range of the soil types 1 and 2 (see 5.2.2)

test soil ST 1: k = 4 × 10-4 m / s (mean value)

test soil ST 2: k = 3 × 10-4 m / s (mean value)

31

Annex 6, sheet 2 Validity range of the soil types 3 and 4 (see 5.2.2)

test soil ST 3: k = 6 x 10-5 m / s (mean value)

test soil ST 4: k = 1 x 10-9 m / s (mean value)

32

Annex 7, sheet 1

Examples of a filter application in a permeable slope protection of a ship-canal using the soil-type design procedure of the BAW 1. Example of soils lying in the range of the soil types 1 to 4 1.1 Local boundary conditions Given:

- a subsoil including the grading band SU to SE according to fig. 1 (no critical alternating layers, see 3.3.1.4) with the following soil mechanical values: • SU: ϕ' = 30° cu, Ip unknown • SE : ϕ' = 35° - execution of the construction works mainly under water; - wave and current impacts caused by shipping even during construction works; - top layer consisting of armourstone (D1), size class III; - slope inclination 1:3 (β = 18,4°).

fig.1: grading band of the subsoil 1.2 Assessment of the subsoil

For the assessment of subsoil properties the - grading curves (grading band) and - effective angle of internal friction of the present soils SU to SE are available.

These soils are classified to be of non-cohesive nature (d20 ≥ 0.006 mm), but to be susceptible to erosion during the con-struction stage (β ≥ ϕ' / 2). They are not suffosive (Cu < 8). Special effects of the water in the sense of subclause 3.3.4 are not relevant.

1.3 Assessment of the hydraulic loadings

According to subclause 3.3.2 dynamic hyraulic loadings must be considered in filter design. 1.4 Choice of the type of filter construction

In connection with the design top layer D1 (size class III) a filter is necessary according to Annex 1. Because the subsoil is susceptible to erosion the geotextile shall be provided with an additional layer (see 4.6.2).

33

Annex 7, sheet 2 1.5 Design of the geotextile filter 1.5.1 Assignment of the subsoil to the soil types 1 to 4 As regards the grain fractions d5 to d60 the grading band SU to SE (fig.1) must be compared with the validity range of the soil types 1 to 4

and assigned to them (Annex 6). The result is • SU = soil type 4 (fig. 2a) • SE = soil type 2 (fig. 2b). SU is relevant to the mechanical filtration stability of the geotextile, SE to the hydraulic one (see 5.2.1).

fig. 2a: position of SU fig. 2b: position of SE 1.5.2 Material properties

Because of the provided type of top-layer construction, geotextile requirements are needed concerning - tensile strengths - resistance to dynamic perforation and - resistance to abrasion. For the design slope inclination the material requirements according to Table 3, top layer D1 (III), can be utilized.

1.6 Specifications in the tender documents

To tender a geotextile with an additional layer meeting the filtration requirements related to the soil types 2 to 4 and the material properties required for a top-layer construction D1 (size class III). Wording of the geotextile specification text in the tender documents: "geotextile with additional layer for a standard top layer D1, soil types 2 to 4, according to the TLG, Annex 2" (see 7.1). Herewith the following specified limit values are relevant to a geotextile filter related to the subsoils present SU to SE (see Tables 2 and 3):

admissible mass of soil passing (related to the finest-grained non-cohesive soil type) - soil type 4 : ≤ 300 (30) g;

k-value of the soil-filled geotextile (related to the most permeable soil type) - soil type 2 : kn > 6 ⋅10-4 m/s;

thickness of the filter layer : T ≥ 6 mm (soil type 4 is relevant, see too 5.3.4.1); tensile strength at failure : ≥ 1200 N/10 cm = 12 kN/m; resistance to dynamic perforation loads related to armourstone size class III on soil types 2 - 4: > 1200 Nm; resistance to abrasion loads

- residual thickness of the filter layer after abrasion test: T ≥ 4.5 mm (soil type 4 is relevant) - residual tensile strength after abrasion test: ≥ 900 N/10 cm = 9 kN/m;

additional layer on soil types 2 - 4 small-pore structure : Dw = 0.3 - 2.0 mm; T = 5 - 15 mm large-pore structure : Dw = 8 - 20 mm; T = 15 - 25 mm.

1.7 Choice of the geotextile

Any geotextile is appropriate for the revetment construction forseen which can be shown to meet the requirements of the above subclause 1.6 (see too 6.2)

34

Annex 7, sheet 3 2. Example of soils lying only partly in the validity range of the soil types 1 to 4 2.1 Local boundary conditions Given:

- a subsoil in alternating layers including the grading band TM to SU according to fig.3 with the following soil mechanical values: • TM : cu = 15 kN/m2 Ip = 0.18 • SU : ϕ' = 37 °; - wave and current impacts caused by shipping; - top layer consisting of armourstone, size class II partially grouted (D2);

- slope inclination 1:3 (β = 18.4°); - remains of former revetment structures are present; - execution of the construction works in the dry; - seepage efflux from the slope during construction;

fig. 3: grading band of the subsoil 2.2 Assessment of the suboil

For the assessment of subsoil properties the - grading curves (grading band) and - characteristic soil mechanical parameters of the present soils TM to SU are available.

TM is of cohesive, SU of non-cohesive nature. Both soil groups are not susceptible to erosion (see 3.3.1.2, 3.3.1.3). Non-cohesive granulations lying between TM and SU can be instable during construction and erodible if β ≥ ϕ' / 2. The subsoil is not inhomogeneous in the sense of subclause 3.3.1.4 if the former revetment remains are to be removed. Having checked the stability to suffosion (Annex 2) the soils are assessed to be of non-suffosive nature. Special effects of the water in the sense of subclause 3.3.4 are not relevant.

2.3 Assessment of the hydraulic loadings According to subclause 3.3.2 dynamic hydraulic loadings must be considered in filter design. 2.4 Choice of the type of filter construction In connection with the design top layer D2 (size class II) a filter is necessary according to Annex 1. The following types of construction

can be considered alternatively: a) geotextile without additional layer directly on the subgrade if the former revetment remains are to be removed; b) geotextile on a granular levelling sublayer if the former revetment remains are not to be removed or if the slope is not stable during construction (see above 2.2).

2.5 Design of the geotextile filter 2.5.1 Assignment of the subsoil to the soil types 1 to 4 2.5.1.1 Geotextile without additional layer directly on the subgrade

As regards the grain fractions d5 to d60 the grading band TM to SU (see fig. 3) must be compared with the validity range of the soil types 1 to 4 (Annex 6) and assigned to them as far as possible. The result is • SU = soil type 3 (fig 4a);

• TM includes the range in which the filtration requirements may be reduced if cu and Ip are known. If grading curves exist between SU and TM (here supposed) these lie in the range of soil type 4, which in each case is relevant to the mechanical filtration stability design. For the hydraulic filtration stability design SU is relevant.

35

Annex 7, sheet 4

fig. 4a: position of SU fig. 4b : position of TM 2.5.1.2 Geotextile on a granular levelling sublayer The granulation of the granular levelling sublayer must comply with the cinditions in subclause 4.3. Gradings of the levelling sublayer

lying in the recommended range (see Annex 4) must be assigned to the soil type 1. 2.5.2 Material properties

Because of the provided type of top-layer construction, geotextile requirements are needed concerning - tensile strengths and - resistance to dynamic perforation . For the design slope inclination the material requirements according to Table 3, top layer D2, are sufficient in the case of expected usual installation stresses.

2.6 Specifications in the tender documents 2.6.1 Geotextile without additional layer directly on the subgrade

To tender a geotextile without additional layer meeting the filtration requirements related to the soil types 3 and 4 and the material properties required for the top-layer construction D2. Wording of the geotextile specification text in the tender documents: "geotextile without additional layer for a standard top layer D2, soil types 3 to 4, according to the TLG, Annex 2" (see 7.1). Herewith the following specified limit values are relevantt to a geotextile filter related to the present soil groups TM to SU (see Tables 2 and 3):

admissible mass of soil passing (related to the finest-grained non-cohesive soil type) - soil type 4 : ≤ 300 (30) g; k-value of the soil-filled geotextile (related to the most permeable soil type) - soil type 3 : kn > 1.2 ⋅ 10-4 m/s; thickness of the filter layer : T ≥ 6 mm (soil type 4 is relevant); tensile strength at failure : ≥ 1 200 Nm/ 10 cm = 12 kN/m; resistance to dynamic perforation loads related to armourstone size class II on soil type 3-4: > 600 Nm. 2.6.2 Geotexttile on a granular levelling sublayer

To tender a geotextile without an additional layer meeting the filtration requirements related to soil type 1 (if the levelling-sublayer grading curve lies in the range of the grading band according to Annex 4) and the material properties required for a top-layer construction D2. Wording of the geotextile specification text in the tender documents:"geotextile without additional layer for a standard top layer D2, soil type 1, according to the TLG, Annex 2". Herewith the following specified limit values are relevant to a geotextile filter applied on a granular levelling sublayer (see Tables 2 and 3):

admissible mass of soil passing - soil type 1 : ≤ 300 (30) g; k-value of the soil-filled geotextile -soil type 1 : kn > 8 ⋅ 10-4 m/s; thickness of the filter layer : T ≥ 4.5 mm; required only if reduction of permeability due to clogging or blocking is possible, i.e. Dw >

0.5⋅ d2 (see 5.3.2); tensile strength at failure: > 600 Nm. 2.7 Choice of the geotextile

Any geotextile is appropriate for the revetment construction forseen which can be shown to meet (see 6.2) the requirements of the above subclause 2.6.1 or 2.6.2 (depending on the type of filter construction chosen).

36

Annex 8, sheet 1 Filter rules of the AK 14 / AA 6.14 Table 1: Filter rules of the AK 14 / AA 6.14 /8/ for design of the mechanical filtration stability of a geotextile

37

Annex 8, sheet 2 When designing the mechanical filtration stability of a geotextile on the basis of the largest admissible opening size Dw (O90 ) according to the filter rules of the AK 14 the following grain-size ranges are to be distinguished.

- grain-size range A: d40 ≤ 0.06 mm - grain-size range B: d15 ≥ 0.06 mm - grain-size range C: d15 < 0.06 mm and d40 > 0.06 mm

The relevant filter rules are given in Table 1. The largest admissible opening size resulting from them should be used to ensure the permeability as high as possible. With respect to safety to colmatation the lower limit value of the admissible opening size should be: Dw (O90) ≥ 0.8 ⋅ max. O90 /8/.

The grading curve of the subsoil must not cut the specially featured ranges given in the individual grain-size distribution diagrams. Concerning the hatched area of the grain-size range A a relatively open filter design is admissible due to the effective cohesion /8/ (see too 3.3.1.3).

The hydraulic filtration stability is guaranteed for mechanically bonded nonwovens in contact with silt or sand if the kn-value of the brand-new product measured under a normal stress of 2 kPa meets the following condition /8/:

kn ≥ 50 ⋅ ksoil. Examples of application In the following examples of application only the principal method for the design of the geotextile filtration properties according to the filter rules is shown. Further requirements must be established following subclause 5.3 (see example Annex 7).

The grading bands of Annex 7, fig. 1 and 3, are used as examples of application.

Example 1 (see Annex 7, fig. 1): grading band SU - SE

Table 2: characteristic grain diameters of the limiting grading curves SUand SE

According to subclause 5.2.1 , in the case of hydrodynamic loadings, the mechanical filtration stability is to be designed for SU and the hydraulic filtration stability for SE.

mechanical filtration stability to SU (Table 2)

- Check of the criteria relevant to a soil with a high grain mobility: 1.Cu = 7.1 < 15 (criterion is met) the further criteria must not be checked. The result is: SU is a subsoil with a high grain mobility.

- Determination of the limit values of the admissible opening sizes Dw (O90):

hydrostatic loadings hydrodynamic loadings Dw < d90 = 0.2 mm Dw < d90 = 0.2 mm < 0.3 mm

upper limit value: Dw < 0.2 mm (valid for hydrostatic and hydrodynamic loadings) lower limit value: Dw ≥ 0.8 ⋅ max. Dw = 0.8 ⋅ 0.2 = 0.16 mm.

hydraulic filtration stability to SE (Table 2)

- Assessment of the k-value of the subsoil according to Annex 4 (diagram of BEYER): kSE = 1 ⋅ 10-4 m/s

- Permeability of the brand-new geotextile (kn): kn ≥ 50⋅ kSE ≥ 5 ⋅ 10-3 m/s.

geotextile requirements in the tender documents

1. filtration stability: 0.16 ≤ DW < 0.2 mm; kn ≥ 5 ⋅ 10-3 m/s 2. layer thickness and other requirements see example 1 in Annex 7.

soil group d10 (mm)

d15 (mm)

d40 (mm)

d50 (mm)

d60 (mm)

CU (-)

d90 (mm)

grain-size range

SU 0.014 0.018 0.055 0.075 0.10 7.1 0.2 A (d40 ≤ 0.06 mm)

SE 0.10 0.11 0.15 0.17 0.20 2.0 0.4 B (d15 > 0.06 mm)

38

Annex 8, sheet 3 Example 2 (Annex 7, fig. 3): grading band TM-SU Table 3: characteristic grain diameters of the limiting grading curves TM and SU

When dynamic hydraulic loads are relevant, according to sublause 5.2.1 the mechanical filtration stability is to be designed for the finest-grained non-cohesive grading curve, the hydraulic filtration stability for the coarsest-grained (most permeable) grading curve of the grading band (here SU). As regards the finest non-cohesive grading curve the grain fractions given in Table 3a apply (here supposed, but in practice to be determined by laboratory tests). Table 3a: characteristic grain diameters of SU (supposed finest-grained non-cohesive grading curve)

mechanical filtration stability to SU (Table 3a) - Check of the criteria relevant to a subsoil with a high grain mobility

1. Cu = 25 > 15 (criterion is not met) 2. 0.02 < d < 0.1 mm = 20 - 30% (graphically assessed) 3. Ip = 0.08 < 0.15 (criterion is met).

The result is:SU is a subsoil with high grain mobility.

- Determination of the limit values of the admissible opening sizes Dw (O90):

hydrostatic loadings hydrodynamic loadings Dw < d90 = 1.0 mm Dw< 1.5 × d10 √ Cu = 0.045 mm ( relevant upper limit value) Dw ≥ 0.8 mm (lower limit) Dw < d50 = 0.12 mm Dw ≥ 0.045 ⋅ 0.8 = 0.036 mm (lower limit value)

hydraulic filtration stability to SU (Table 3) - Assessment of the k-value of the subsoil according to Annex 4 (HAZEN): kSU = 3.6 ⋅ 10-5 m/s - 5.4 ⋅ 10-5 m/s - Permeability of the brand-new geotextile (kn): kn ≥ 50 ⋅ kSU ≥ 2.7 ⋅ 10-3 m/s. geotextile requirements in the tender documents

1. filtration sttability: hydrostatic loads hydrodynamic loads 0.8 ≤ Dw < 1.0 mm 0.036 ≤ Dw < 0.045 mm kn ≥ 2.7 ⋅ 10-3 m/s kn ≥ 2.7 ⋅ 10-3 m/s 2. layer thickness and other requirements see example 1 in Annex 7. Note (1) In the case of a suffosive subsoil attention should be paid to subclause 3.3.1.5. (2) As regards geotextile permeability the tender documents must state at which water head h or gradient i the minimum value kn shall apply (see too subclause 5.3.2).

soil group d10 (mm)

d15 (mm)

d40 (mm)

d50 (mm)

d60 (mm)

CU (-)

d90 (mm)

Ip (-)

grain-size range

TM - - 0.007 0.02 0.05 - 0.4 0.18 hatched area

SU 0.06 0.09 0.30 0.40 0.50 8.3 2.0 - B (d15 > 0.06 mm)

finest-grained non-cohesive soil

group

d10 (mm)

d15 (mm)

d40 (mm)

d50 (mm)

d60 (mm)

CU (-)

d90 (mm)

grain-size range

SU 0.006 0.012 0.08 0.12 0.15 25 1.0 C (d15 < 0.06 mm d40 > 0.06 mm)

39

Annex 9

Table on standard tests according to the Technical Supply Conditions for Geotextile Filters (TLG)

tests to be carried out basic test (proof of funda-mental

suitability)

suitability test (prior to construction)

quality control tests (during production)

control tests carried out by the Principal

(1) (2) (3) (4) (5)

basic raw materials general material properties according to paragraph (4) - (7)

x

x

(x) -

- -

- -

mass per unit area • filter layer • additional layer

thickness • filter layer • additional layer

tensile strength at failure • longitudinal direction • transverse direction • seams

water permeability 1)

• v/h- or kn /i-curve • index value for v or kn at h = 0.05 or 0.25 m

opening size • filter layer • additional layer

x x

x x

x x x

x x

x x

x x

x x

x x

(x)

-

(x)

(x) -

x x

x x

x x x

- x

x x

x x

x x

x x x

- x

(x) x

filtration stability according to the BAW test method

resistance to dynamic perforation loads

resistance to abrasion loads

resistance to temperatures of up to 200 °C 2)

x

x

x

x

(x)

(x)

(x)

(x)

-

-

-

-

-

-

-

-

(x) depending on conditions of the construction works 1) v = flow velocity h = hydraulic head kn = coefficient of normal permeability i = hydraulic gradient 2) only relevant to fibre raw materials known not to be resistant to high temperatures

code of practice use of geotextile filters on waterways (mag) · fibre fleeces. fibre fleeces...

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