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CONTENTS

NO. PAGE

1 INTRODUCTION 2

2 EMBEDDED WALL 2

3 DRIVEN SHEET PILES WALLS 34 PROPPED WALLS 6

5 CONTIGUOUS BORED-PILES WALLS 86 SECANT BORED-PILES WALLS 10

7 DIAPHRAGM WALLS 12

8 REFERENCES 17

INTRODUCTION

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In many construction operations it is often necessary to alter the ground-surface profile in such

way as to produce vertical or near-vertical faces. Sometimes these new faces may be capable

of self-support, but in other instances a lateral retaining structure will be required to provide a

support. In stability and analyses, both the nature of the wall structure and that of supported

material are important, as too is the way the wall may move or yield after construction. If a wall

structure caused to move towards the soil being supported, the horizontal pressure in the soil

will increase; these are referred to a passive pressures. If the wall moves away from the

supported soil, the horizontal soil pressures decrease and are referred to then as active

pressures. If the wall structure is rigid and does not yield, the horizontal soil pressures are said

to be at rest pressures. The various types of earth-retaining structure fall into three broad

groups. There are gravity walls, embedded walls, and reinforce4d and anchored earth.

EMBEDDED WALL

This section deals with retaining walls that are usually installed in undisturbed ground, after

which excavation takes place on side. These consist of vertical or placed sheets or piles that

may be anchored , tied or propped, or may act as simple cantilever; their own weight does not

feature in stability analyses. Structurally, such walls can be formed from driven sheet-piles,

secant piles, contiguous piles or as a diaphragm wall. They may act as simple cantilevers or

provided with single or multiple anchors or prop . Embedded walls differ from gravity wall in

several ways :

1. There are flexural and are designed structurally as simple or propped cantilevers

2. Their weight is ignored in stability analyses

3. They depend for support upon passive resistance mobilized in the soil

4. Excavation usually follows installation, rather than backfilling

Types of Embedded walls

DRIVEN SHEET-PILE WALLS

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BRACED OR PROPPED WALLS

CONTIGUOUS BORED PILE WALLS

SECANT BORED-PILE WALLS

DIAPHRAGM WALLS

Driven Sheet Pile Wall

Driven sheet pile walls have provided for more than 90 years a reliable method in special

foundation and water construction. Nowadays, the most differing types of sheet piles are driven,

vibrated or pressed into the ground.

Bauer prefers to install sheet piles with high frequency top vibrators with adjustable static

moments. The resulting low vibrations allow for works being carried out inner-city, also in the

vicinity of buildings. If necessary the installation of the sheet piles is supported by jets of water

at high pressure or predrilling.

In case of particularly hard ground or firm soil the soil can be replaced with cased drillings. For

the installation of sheet piles with a length of more than 30 m the most differing equipment is at

our disposal.

Sheet Piling consists of a series of panels with interlocking connections, driven into the ground

with impact or vibratory hammers to form an impermeable barrier, and retain soils and water.

Sheets can be made of a variety of materials such as steel, vinyl, plastic, wood, reinforced

concrete and fiberglass. The ability of a sheet pile section to perform is dependent on its

geometry and the soils it is driven into. Permanent and temporary sheet piling application

examples include shoring walls of trenches and other excavations, cofferdam construction,

barriers for groundwater treatment systems, containment wells, coastal protection, bulkheads

and seawalls, groundwater diversion and control, riffle structures, retaining walls, flood

protection, tunnel cut and cover, beach erosion protection and slope stabilization. Smaller sheet

pile walls are typically designed to cantilever where large walls are usually anchored. Sheet

piling has been a proven technology within the construction industry for many years.

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Example of driven sheet piles wall

Driving Sheet Pile Walls

There are several ways of driving sheet pile walls into position; threading into pre-cut trenches,

pressed, impact-driven and vibratory driven.

Threading sheet pile walls into pre-cut trenches is a suitable technique for use on most soils.

After a trench has been excavated or holes drilled in the ground, they are filled with a

suspension and sheet piles can be driven in up to their full depth.

Pressing sheet pile walls is a process that can be used if there are noise and vibration

limitations due to the construction taking place in residential areas or near to existing buildings.

The sheet piles are driven into the ground by hydraulic pressure. The pressing plant can be

supported by a crane, guided by a leader or be supported by heads already in position.

Impact driven sheet pile walls can be positioned in the ground using either slow or rapid-action

systems. Drop hammers and diesel hammers are slow-action, with between 24 and 32 blows

per minutes and are used in cohesive soils. These hammers allow the pore water pressure to

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disperse between blows. Rapid-action hammers give between 100 and 400 blows per minute at

a lighter driving weight than slow-action hammers.

Vibratory sheet pile driving is derived from harmonic excitation of the sheet pile, causing the

restructuring of the soil along with decreasing the friction between the soil and sheet pile.

Harmonic excitation is produced by eccentric weights in the vibrator.

Sheet pile walls are constructed by :

1. Laying out a sequence of sheet pile sections, and ensuring that sheet piles will interlock.

2. Driving (or vibrating) the individual sheet piles to the desired depth.

3. Driving the second sheet pile with the interlocks between the first sheet pile and second

"locked"

4. Repeating steps 2 & 3 until the wall perimeter is completed

5. Use connector elements when more complex shapes are used.

Advantages of Sheet Pile Walls

1. Provides high resistance to driving stresses.

2. Light weight

3. Can be reused on several projects.

4. Long service life above or below water with modest protection.

5. Easy to adapt the pile length by either welding or bolting

6. Joints are less apt to deform during driving.

Disadvantages of Sheet Pile Walls

1. Sections can rarely be used as part of the permanent structure.2. Installation of sheet piles is difficult in soils with boulders or cobbles. In such cases, the

desired wall depths may not be reached.

3. Excavation shapes are dictated by the sheet pile section and interlocking elements.

4. Sheet pile driving may cause neighborhood distrurbace

5. Settlements in adjacent properties may take place due to installation vibrations

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Propped Walls

A propped shear wall is a unique steel and concrete bracing system for retrofit seismic

strengthening of existing buildings that combine friction damping with the best aspects of steel

braces and concrete shear walls. This system creates a highperformance lateral bracing system

that is less expensive and less architecturally intrusive than either steel braced frames or

concrete shear walls acting alone. The system consists of a tall slender concrete shear wall

propped near the top with multi-story diagonal steel braces. During large earthquakes, the

slotted bolted friction connections of the steel props, along with flexural yielding at the base of

the shear wall, provide seismic energy dissipating mechanisms.

Tipping Mar has used this strategy in the seismic retrofit of twenty structures in the

earthquake-prone San Francisco, CA, bay area. In this article, the most recent propped shear

wall projects will demonstrate how this lateral strengthening system works.

In structural engineering, a shear wall is a wall composed of braced panels (also known

as shear panels) to counter the effects of lateral loadacting on a

structure. Wind andearthquakeloads are the most common loads braced wall lines are

designed to counteract. Under severalbuilding codes, including the International Building

Code(where it is called a braced wall line) and Uniform Building Code, all exterior wall lines in

wood or steel frame construction must be braced. Depending on the size of the building some

interior walls must be braced as well.

A common method of constructing a braced wall line in wood frames is to create braced

panels in the wall line using structural plywood sheathing with specific nailing at the edges and

supporting framing of the panel. A more traditional method is to use let-in diagonal wood bracing

throughout the wall line, and a newer alternative is let-in metal T-bracing (Simpson TWB) butthese methods may not be viable for buildings with many door and window openings and may

not meet seismic or high wind zone codes.

Such walls can be either "load bearing" or "non-load bearing". Shear walls are a type

ofstructural system that provides lateral resistance to a building or structure. They resist "in-

plane" loads that are applied along its height. The applied load is generally transferred to the

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wall by a diaphragmor collector ordrag member. They are built in wood, concrete, and CMU

(masonry).

Plywood is the conventional material used in the construction of Shear Walls, but with

advances in technology and modern building methods, there are other prefabricated options,

such as Hardipanel and Simpson Strong Wall, which have made it possible to inject shear

assemblies into narrow walls that fall at either side of an opening in a shear wall. Sheet steel

and steel-backed shear panels (i.e. Sure-Board) in the place of structural plywood in shear walls

has proved to be far stronger in seismic resistance.

EXAMPLE OF PROPPED WALLS

Contiguous bored-pile walls

Closely spaced bored piles can be used to form a retaining wall, perhaps for the construction of

a deep basement or a cut and cover tunnel. The piles may be constructed so that they virtually

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touch each other (contiguous). The gaps between the piles can be grouted to form a watertight

retaining wall.

Piles are installed at centres generally 150 mm greater than their diameter therefore leaving

gaps in the structural wall where soil is exposed during excavation. This option is suitable where

the retained soil is usually firm to stiff (not generally granular) and where the ground water table

is below the level of the maximum excavation. This is the most economic option and normally

the fastest method to construct.

Alternatively every other pile may be constructed, with their centres less than two diameters

apart. In-fill piles are then bored, cutting into the adjacent piles to form a continuous structure.

To aid construction, the first sets of piles may be cast with a lower grade of concrete. These

may not be load-bearing and act as seals between the main load bearing piles.

As the piles interlock, this form of construction leads to a more efficient form of structure. During

excavation of the soil, the piles will generally require propping before the permanent floor androof structure are completed.

Because of the form of construction, the exposed piles will be fairly rough in appearance. Thus,

in most cases, an inner wall, which may or may not be structural, will be built or some

decorative surface applied; for example sprayed concrete or cladding. A method of drainage will

generally be required between the piles and any inner wall.

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Failure of contiguous bored-pile walls

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Steps to avoid failures of contiguous bored-pile walls

The critical design considerations, namely the need for struts, must be properly shown on the

construction drawings. At no time should these considerations be altered without prior

consent by the design professional engineer (PE). If major modifications are to be made, the

PE must carry out a re-analysis to check for structural adequacy of the alteration before

implementation.

The design of earth retaining walls should allow for hydrostatic pressure built up behind it and

unplanned over-excavation. Precautions should be made to taken to prevent unnecessary

built-up of hydrostatic pressure.

Instruments to monitor ground movement should be installed to provide an early warning

system and enable corrective action to be taken early.

Secant Bored-pile Walls

Secant pile walls are formed by constructing intersecting reinforced concrete piles. The piles are

reinforced with either steel rebar or with steel beams and are constructed by either drilling under

mud or augering. Primary piles are installed first with secondary piles constructed in between

primary piles once the latter gain sufficient strength. Pile overlap is typically in the order of 3

inches (8 cm).

Figure 1 Secant Pile Wall is a retaining wall made of piles

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Advantage of secant pile walls :

1. Increased construction alignment flexibility.

2. Increased wall stiffness compared to sheet piles.

3. Can be installed in difficult ground (cobbles/boulders).

4. Less noisy construction.

Disadvantage of secant pile walls:

1. Verticality tolerances may be hard to achieve for deep piles.

2. Total waterproofing is very difficult to obtain in joints.

3. Increased cost compared to sheet pile walls.

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Diaphragm walls

Diaphragm walls refer to the in-situ construction of vertical walls by means of deep trench

excavations. Stability of the excavation is maintained by the use of a drilling fluid, usually a

bentonite suspension.

The walls are constructed in discrete panel lengths ranging typically between 2.5m and 7.0m

using purpose built grabs or, in appropriate circumstances, milling machines (hydromills).

Excavation is typically carried out using either rope-suspended mechanical or hydraulically

operated grabs. Standard grabs range in weight from 8-20 tonnes. The grabs are mounted on

80-120 tonne hydraulic base crane units providing stability and suitable line pull.

Specific applications and ground conditions demand the use of hydromills hydraulically

operated reverse circulation trench cutters where the excavation technique is by 'cutting' as

opposed to 'digging'. This technique is appropriate for deeper diaphragm walls and walls located

in granular materials and soft rock.

Where panels are constructed in a line, abutting one another to form a retaining wall, the term

diaphragm walling applies. Purpose made stop ends are used to form the joints between

adjacent panels and a water bar can be incorporated across these joints. Where additional

bending moment capacity or wall stiffness is required more complicated arrangements can be

constructed. The examples are the 'L' shaped or 'T' shaped panels.

Standard widths of diaphragm walling equipment are 600, 800, 1000, 1200 and 1500mm

although greater can be provided. Depths are typically constructed up to 50m using grabs and

up to 80m using standard hydromills. One significant advantage of using diaphragm walling is

the facility to incorporate floor slab connections and recessed formwork into the walls.

Verticality tolerances are typically up to 1:200 and onboard monitoring is now available to

provide real-time monitoring of excavation accuracy Management of the bentonite or alternative

drilling fluid requires controlled use of specialist desanding, desilting and centrifuge equipment.

Unit capacities range from 100 to 500m/hour.

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Diaphragm walls are particularly suited in the construction of deep basements when used in

conjunction with "top down" construction techniques. The "top down" method of construction is

designed to enable above ground construction work to be carried out simultaneously with the

excavation of the basement resulting in significant saving of time on a project.

Application

Diaphragm walls can be used in most ground conditions to construct underground stations in

city centres, multi-level underground car parks, road junctions and underpasses, and open cut

and cut & cover rail tunnels as well as deep shafts for tunnel ventilation, intervention shafts

and water treatment plants.

Diaphragm walls are often located in confined innercity areas where space is at a premium.

Diaphragm walls are typically constructed in reinforced concrete to provide the required

structural capacity, but they may also be designed as unreinforced plastic cut offs (or slurry

walls) to stop water flow through porous strata.

Diaphragm walls are typically 20m to 50m deep, but may extend to considerably greater depth.

Advantages

i. Box outs can be incorporated in diaphragm walls to facilitate easy connections for slabs,

stairs and other parts.

ii. Waterbar can be incorporated.

iii. Less joints required than a piled wall.

iv. Top-down basement construction gives significant advantages in programme.

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Diaphragm walls excavation

Grab used for excavation

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Diaphragm wall reinforcement and concreteing

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Reinforcement

The finished wall after excavation

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REFERENCES

1. Roy Whitlow; Basic Soil Mechanics, Fourth Edition, 2004; Pearson Education South Asia

Private Limited

2. AS Hornby; Oxford Advanced Learners Dictionary, International Students Edition, Seventh

Edition, 2005; Oxford University Press

3. http://www.skanska.co.uk/upload/Sevices/Piling/Datasheets/Diaphragm%20Walls.pdf

4. http://www.dublinporttunnel.ie/about/building/pdf/cut_and_cover_sections.pdf

5. http://www.gnpgeo.com.my/download/spec/others/DWS.pdf

6. http://www.lta.gov.sg/projects/images/DW%20Final.pdf

7. http://www.bachy-soletanche.com/SBF/sitev4_uk.nsf/technique/diaphragm-wall

8. http://dictionary.cambridge.org/

9. http://www.deepexcavation.com/en/sheet-pile-walls

10. http://www.skanska.co.uk/upload/Sevices/Piling/Datasheets/Bored%20Pile%20Retaining

%20Walls%20Datahseet.pdf

11. http://www.modernsteel.com/Uploads/Issues/January_2001/0101_04_shear%20walls.pdf

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http://www.deepexcavation.com/en/sheet-pile-wallshttp://www.skanska.co.uk/upload/Sevices/Piling/Datasheets/Bored%20Pile%20Retaining%20Walls%20Datahseet.pdfhttp://www.skanska.co.uk/upload/Sevices/Piling/Datasheets/Bored%20Pile%20Retaining%20Walls%20Datahseet.pdfhttp://www.modernsteel.com/Uploads/Issues/January_2001/0101_04_shear%20walls.pdfhttp://www.deepexcavation.com/en/sheet-pile-wallshttp://www.skanska.co.uk/upload/Sevices/Piling/Datasheets/Bored%20Pile%20Retaining%20Walls%20Datahseet.pdfhttp://www.skanska.co.uk/upload/Sevices/Piling/Datasheets/Bored%20Pile%20Retaining%20Walls%20Datahseet.pdfhttp://www.modernsteel.com/Uploads/Issues/January_2001/0101_04_shear%20walls.pdf

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