soil a material

8/13/2019 Soil a Material

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Chapter I: Soil as a construction

material

CauGie-Ninh Binh Road


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2

Soil Improvement andstabilization

If soil near the ground surface is strong and has sufficient bearing capacity, thshallow foundation is adopted.

If the top soil is weak loose, soft or saturated, then the loads of the super-structures has to be transferred to deep foundation-Pile foundation.

Third method comes under the heading foundation soil improvement. In the case of earth dams, there is no other alternative than compacting the

remolded soil in layers to the required density and moisture content. The soil fthe dam will be excavated at the adjoining areas and transported to the site.

Soil improvement is frequently termed soil stabilization, which in its brosense is alteration of any property of a soil to improve its engineeringperformance. Soil improvement can be achieved through the following modes

1. Increases shear strength

2. Reduces permeability, and

3. Reduces compressibility


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Contents

Compaction Dynamic compaction Sand Drains Vertical Drains Prefabricated Vertical Drains

Sand compaction pile Soil deep mixing method


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Compaction


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Soil Compaction in the Field:

1- Rammers

2- Vibratory Plates

3- Smooth Rollers

4- Rubber-Tire

5- Sheep foot Roller

6- Dynamic Compaction


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Definition :

Soil compaction is defined as the method of mechanically increasing the denof soil by reducing volume of air.

Solids

Water

Air

Solids

Water

Air

Compressedsoil

Load

SoilMatrix

gsoil (1) =WT1V

T1

gsoil (2) =WT1

VT2

gsoil (2) > gsoil (1)


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Factor Affecting Soil Compaction :1- Soil Type2- Water Content (w c)3- Compaction Effort Required (Energy)

Why Soil Compaction :1- Increase Soil Strength2- Reduce Soil Settlement3- Reduce Soil Permeability

4- Reduce Frost Damage5- Reduce Erosion Damage

Types of Compaction : (Static or Dynamic)1- Vibration2- Impact3- Kneading4- Pressure

Water is added tolubricate the contact

surfaces of soil particlesand improve the

compressibility of the soilmatrix


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Soil Compaction in the Lab:

1- Standard Proctor Test2- Modified Proctor Test

Standard Proctor Test Modified Proctor Test

2 5 c m

4 5 c m

2,5 kg 4,5 kg


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Hammer weight = 2,5 kgFalling height = 25 cmAmount of layers = 3

No. of blows/layer = 25Compaction effort = 595 kJ/m 3 Soil type = pass sieve no. 4 (4,76 mm)

Hammer weight = 4Falling height = 4Amount of layers

No. of blows/layer Compaction effort Soil type = pass sie

1- Standard Proctor Test 2- Modified Pr


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1- Standard Proctor Test

wc1 wc2 wc3 wc4 wc5

gd1 gd2 gd3 gd4 gd5

OptimumWater

Content

Dry Density

gd max

Zero Air Void CuSr =100%

C

C

1

2

3

4

5

(OWC)

10 cm diameter compaction mold.(V = 1/30 of a cubic foot)

2.5 kg hammer

25 blowsper layer

H = 12 in

Wet toOptimum

Dry toOptimum

Increasing Water Content

eG w s

dry 1

g g

gdry =gwet

Wc100

%1+

g ZAV =Gs gw

Wc Gs1+Sr


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1- Standard Proctor TestASTM D-698 or AASHTO T-99

2- Modified Proctor TestASTM D-1557 or AASHTO T-180

Energy = 595 kJ/m3

Energy = 2693 kJ/m 3

Number of blows per layer x Number of layers x Weight of hammer x Height of drop hammer

Volume of moldEnergy =

MC

Dry Density

gd max

CompactionCurve for StandardProctor

(OMC)

d max

(OMC)

Zero Air Void CuSr < 100%

Zero Air Void CurveSr =100%

Zero Air Void CurveSr = 60%

CompactionCurve forModifiedProctor


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Water Content

Dry Density

Effect of Energy on Soil Compaction

HigherEnergy

Increasing compaction energy Lower OWC and higher dry density

In the field

increasing compaction energy =increasing number of passes orreducing lift depth

In the labincreasing compaction energy =

increasing number of blows


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Field Soil Compaction

Because of the differences between lab and field compaction methods, the maximum drydensity in the field may reach 90% to 95%.

Dry Density

gd max

(OMC)

ZAV

95% gd max


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Checking Soil Density in the Field:

1- Sand Cone (ASTM D1556-90)

2- Balloon Dens meterThe same as the sand cone, except a rubberballoon is used to determine the volume of the hole

3- Nuclear Density (ASTM D2292-91 )

Nuclear Density meters are a quick and fairly accurate way of determining density and moisture content. The meter uses aradioactive isotope source (Cesium 137) at the soil surface (backscatter) or from a probe placed into the soil (directtransmission). The isotope source gives off photons (usually Gamma rays) which radiate back to the mater's detectors on the bottomof the unit. Dense soil absorbs more radiation than loose soil and the readings reflect overall density. Water content (ASTM D3017)can also be read, all within a few minutes.

A small hole (6" x 6" deep) is dug in the compacted material to be tested. The soil is removedand weighed, then dried and weighed again to determine its moisture content. A soil'smoisture is figured as a percentage. The specific volume of the hole is determined by filling itwith calibrated dry sand from a jar and cone device. The dry weight of the soil removed isdivided by the volume of sand needed to fill the hole. This gives us the density of thecompacted soil in lbs per cubic foot. This density is compared to the maximum Proctordensity obtained earlier, which gives us the relative density of the soil that was justcompacted.


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Nuclear Density Sand Cone


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Compaction Specifications

Compaction performance parameters are given on a construction project in one two ways:

1- Method Specificationdetailed instructions specify machine type, lift depths, number of passe

machine speed and moisture content. A "recipe" is given as part of the jobspecifications to accomplish the compaction needed.

2- End-result Specification Only final compaction requirements are specified ( 95% modified

standard Proctor ). This method, gives the contractor much more flexibility indetermining the best, most economical method of meeting the required specs.


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Dynamic compaction

Uses a special crane to lif

to heights of 40 to 100 fee(1feet=0,3m) then drop thweights onto the ground

Cost effective method of loose sands and silty soils30 feet deep


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Vertical Drains


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Settlementrequirement Remaining consolidation settlement or residual settlement at centerline of thesubgrade after construction completion will follow the Table II-1 of VietnStandard 22 TCN 262-2000 :

i) Embankment location on soft soil ground for Highway of category 80a) Near abutment: less or equal 10cm.b) At culverts or under public highway: less or equal 20cm.

c) At normal embankment: less or equal 30cm.

ii) In the construction of embankment and pre-loading At centerline, settlement velocity of the embankment bottom shall not exceed

10mm/ day.


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Stability requirement Factor of safety for embankment stabilityForecasted slope stability following calculation results for eachembankment stage (embanking and pre-loading) and for designedembankment (regarding maximum vehicle loading) is equal or overminimum stability as follows:

During construction, F s = 1.2 For long term stability, F s = 1.4


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SPT

Small SPT


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Geotechnical

properties

SPT


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Using Geo-slope to calculate slopestability


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SasproProgram


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Vertical drain:


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Vertical drain: Sand drains Vertical drains are artificially-created drainage paths which are

inserted into the soft clay subsoil. Thus, the pore water

squeezed out during consolidation of the clay due to thehydraulic gradients created by the preloading, can flowfaster in the horizontal direction towards the vertical drains.

It is taken advantage of the fact, that most clay deposits exhibita higher horizontal permeability compared to the vertical.

Subsequently, these pore water can flow freely along thevertical drains vertically towards the permeable layers.

Therefore, the vertical drain installation reduces the length ofthe drainage path and, consequently, accelerates theconsolidation process and allows the clay to gain rapid strengthincrease to carry the new load by its own


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Vertical drain: Sand drains

At Hanoi-Laocai road

f b d l


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Prefabricated Vertical Drains

http://www.youtube.com/watch?v=gFH-DdnwsrI
http://www.youtube.com/watch?v=gFH-DdnwsrIhttp://www.youtube.com/watch?v=gFH-DdnwsrIhttp://www.youtube.com/watch?v=gFH-DdnwsrIhttp://www.youtube.com/watch?v=gFH-DdnwsrI


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P f b i d V i l D i


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Prefabricated Vertical Drains


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In case of vertical drains being installed, consolidation degree will


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Ur UvU 1*11

H

t CvTv2*

g , gaccording to the Carillo formula as follow:

Where

U: Overall consolidation degree

Uv: Vertical consolidation degree

Ur: Radial (horizontal) consolidation degree

Uv value was looked up base on the value of vertical time factor Tv thafollow:

Where

Cv: Vertical consolidation coefficient, cm 2/day

t: time, day

H: Length of drainage path, cm (=H/2 in case of 2 side drainage)

The above formula of Tv is also the formula applied to calculate the co

case of natural ground conditions.


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SAND COMPACTION PILES


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SAND COMPACTION PILES AND STONE COLUMNS

Sand Compaction Piles Sand compaction piles consists of driving a hollow steel pipe with the bottom

closed with a collapsible plate down to the required depth; filling it with sand, andwithdrawing the pipe while air pressure is directed against the sand inside it.

The in-situ soil is densified while the pipe is being withdrawn, and the sandbackfill prevents the soil surrounding the compaction pipe from collapsing as thepipe is withdrawn.

Stone Columns

The method described for installing sand compaction piles or the vibroflotdescribed earlier can be used to construct stone columns. The size of the stonesused for this purpose range from about 6 to 40 mm. Stone columns haveparticular application in soft inorganic, cohesive soils and are generally insertedon a volume displacement basis.

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SOIL STABILIZATION BY INJECTION


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SOIL STABILIZATION BY INJECTIONOF SUITABLE GROUTS

Grouting is a process whereby fluid like materials, either in suspension, orsolution form, are injected into the subsurface soil or rock. The purpose of

injecting a grout may be any one or more of the following: 1. To decrease permeability. 2. To increase shear strength. 3. To decrease compressibility.

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