soil consolidation 1

8/17/2019 Soil Consolidation 1

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Soil ConsolidationPart 1

KAEA 3233 - SOIL MECHANICS II

Department of Civil Engineering

Faculty of Engineering

University of Malaya


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Unsuitable ground


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1.0 What Is Consolidation


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What Is Consolidation

unlike


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Ground Settlement


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Consolidation Theory


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Effect of on ’

START Soil Particle

• may be taken up by soil particles if they are allowed tomove and rearrange. However, was not taken up by soilparticle as movement of solid particles are restraint by water

in the pores (water is incompressible); hence pore water isthe one that picking up the

Pore water

is taken up by pore water

ue = us +

where ue = excess pore water pressure

us = static pore water pressure (before P

is applied)(atmospheric pressure)

1.1 Consolidation Theory


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AT TIME t

Soil Particles

• Rearranging while pore water dissipating (flowing out)

• is being transferred gradually to soil particle.

Pore Water

• Pore water draining out due to existence of pressuredifference (ue and us). This process is known asdissipation of pore water pressure and will continue untilpore water pressure ue reduces to uss (steady state porewater pressure)

• The soil at this state is said in drained condition. Beforedissipation of pore water, the soil is said to be inundrained condition. The time required for pore water todissipate depends on permeability of the soil.



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COMPLETE Soil Particles

• New particle arrangement established.

• All is taken up by soil particles

Pore water

• All been completely transferred to soil particle ’ 0 + ’

• Dissipation of pore water pressure is completedwhere ue has reached uss

• Soil is said to be in drained condition



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Consolidation Analogy - 1-Dimensional

water pore watervalve flow control (soil permeability)Load P pressure/external loadspring soil solid particle

Spring andpiston system

State of the System Spring Pore Water

Equilibrium ’ 0 u0

Applied Load P () ;closed valve

’ 0 u0 +

Applied Load P () ;opened valve( = a + b)

’ 0 + a u0 + b

Complete ’ 0 + ’ u0

For clay soil only



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Consolidationprocess –

stages of , ’and u

Consolidation Analogy - 1-Dimensional



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So….. Consolidation

Definition:

Gradual reduction in volume of fully saturated soil of low permeabilitydue to drainage of some of the pore water, the process continuing untilthe excess pore water pressure set up by an increase in total stresshas completely dissipated.

End results:Consolidation settlement which can be measured by recording levels atreference points on the ground surface

Consolidation progress measurement:

Through measuring changes in pore water pressure using piezometer.


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BS 1377-Part5: 1990

At the end of the test , draw curves of• Consolidation settlement against time• Void ratio against stress

1-D Consolidation Test – Oedometer Test

Video: Consolidation Test

Video: Soil sample preparation

http://localhost/var/www/apps/conversion/tmp/scratch_4/Consolidation%20test.avihttp://localhost/var/www/apps/conversion/tmp/scratch_4/Soil%20sample%20preparation.avihttp://localhost/var/www/apps/conversion/tmp/scratch_4/Soil%20sample%20preparation.avihttp://localhost/var/www/apps/conversion/tmp/scratch_4/Consolidation%20test.avi


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1-D Consolidation Test – Load Incremental Data


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Void Ratio-Pressure Plots

where:Ws = dry weight of specimen; A = area of specimen; Gs = specific gravity of soilsolids; w = unit weight of water


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During compression, changes in soil structure continuously take place andthe clay does not revert to the original structure during expansion.

Compressibility Characteristics


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Video: NC and OChttps://spoonfeedme.com.au/course/148/super/soil101/geology-soil-and-

geotechnical-engineering/video/12007

https://spoonfeedme.com.au/course/148/super/soil101/geology-soil-and-geotechnical-engineering/video/12007https://spoonfeedme.com.au/course/148/super/soil101/geology-soil-and-geotechnical-engineering/video/12007


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Preconsolidated Pressure

1= 1


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Effects of Sample Disturbance

Normally consolidated Overconsolidated


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The slope of virgin compression line for in-situ soil is slightlygreater than the slope of virgin compression line obtained fromthe lab test due to the fact that the soil has been disturbed during

sample preparation.

However, the void ratio at the beginning of the lab test (e0) is thesame for both in-situ and lab samples .

Lab virgin line may be expected to intersect the in-situ virgin lineat ~0.42 e0

Effects of Sample Disturbance


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Draw horizontal linerepresenting e0 and 0.42e0

Draw vertical line ’ c until itcrosses the horizontal line e0 (label this intersection point

as E)

Extend downwards thestraight line of the lab curveuntil it crosses the horizontalline 0.42e0 (label thisintersection point as F)

Connect EF which representthe straight part of the in-situcurve (in-situ virginconsolidation line)

Construction of In-situ consolidation line

In-situ virgin consolidation line


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Label ’ 0 as current effectivestress

Draw vertical line ’ 0 until it

crosses horizontal line e0(label this intersection pointas G)

Draw a parallel line with theaverage slope of the lab curve

part (GH) from G

In-situ overconsolidated line

Construction of In-situ consolidation line


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The result of a laboratory consolidation test on clay specimenare given in the table.

Pressure (kN/m2) 25 50 100 200 400 800

Total height ofspecimen at the end

of consolidation (mm)

17.65 17.40 17.03 16.56 16.15 15.88

Initial height of specimen = 19 mm, Gs = 2.68, mass of dry specimen= 95.2 g and area of specimen = 31.68 cm2

• Plot e - log ’ curve • Determine the preconsolidation pressure• Determine the compression index C c

Example 1

soil consolidation 1

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