Compressility of soil
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Preconsolidation stress Pressure, logp
Example
A soil layer shown as the following figure has a height of 10m which has fully consolidated. gsat=18kN/m3 (1)What is the preconsolidation pressure; and (2)What is the OCR of soil at point A when remove 2m high soil.
mv=1/ES=a/(1+e1)
Stress history of soil 应力历史 Depositing
Keep present condition for a long time Erosion
Normally-consolidated soil (正常固结土)
Over-consolidated soil (超固结土)
Ring
Consolidometer (odemeter)( 固 结仪，压缩仪)
Soil specimen
Deformation, pressure, and time
One-dimensional laboratory consolidation test
Time, log scale Sd Immediate settlement Settlement, S Sc Primary consolidation settlement
Soil mechanics becomes a branch of science
Soil consolidation
Valve closed Valve closed
Du=0
Du=P/A
t=0 Spring-cylinder model
Soil consolidation
Valve open
determination in lab tests (压缩参数及确定方
法)
Settlement calculation methods (沉降计算方法)
Fundamentals of soil compression
Fundamentals of soil compression
Time, t Sd Immediate settlement Settlement, S Sc Primary consolidation settlement Ss Secondary consolidation settlement
Note: P is the current effective stress
Stress history of soil 应力历史 Depositing
Keep present condition for a long time Erosion
Normally-consolidated soil (正常固结土)
E0 (1 2 )bp1 / s1
p1= 比例极限荷载 b= 承压板的边长或直径 s1= p1所对应的沉降量 ，取p-s曲线上的直线 段末端值。没有直线段时，取s1= (0.01- 0.015)b所 对应的荷载为p1
深层平板载荷试验 旁压试验 土的弹性模量
自学
课本：P133-137
Void ratio-pressure plots e=Vv/Vs=Hv/Hs
Void Soil specimen Solid
Hs=w/(AGsgw)
De=DVv/Vs=DHv/Hs
One-dimensional laboratory consolidation test
Void ratio-pressure plots (e-p curve) Compression coefficient 压缩系数 a=(e1-e2)/(P1-P2)
Over-consolidated soil (超固结土)
Under-consolidated soil (欠固结土)
OCR=1
OCR>1
OCR<1
e-logp curve with loading, unloading and reloading
Loading
Void ratio, e
Unloading Reloading
P1 P2 Pressure, logp
Cs=1/5~1/10 Cc
Correlations for compression index
Skempton (1944)
Cc=0.009(LL-10)
Rendon-Herrero (1944)
Nagaraj and Murty(1985)
Cc=0.2343Gs(LL(%)/100)
DP/P=1 Void ratio, e DP/P<1 DP/P>1
Smaller load increment ratio can obtain more accurate compression curve to the virgin one.
Pressure, logp
Effect of load increment ratio
Normally consolidated clay e0
Void ratio, e Virgin consolidation curve; Slope=Cc consolidation curve for remolded soil; Slope<Cc
0.42e0 pc
Pressure, logp
土的变形模量
Plate loading test
目的：1. 测试地基承载力； 2. 测试地基土变形模量； 3. 研究黄土的湿陷特性。 材料：千斤顶式载荷架（图5-14， 教科书p.131） 观测：1.时间间隔 (p.131) 2.终止加载判别标准 (p.131)
结果应用：确定土的变形模量E0
s (1 2 )bp0 / E0
则:
1 2 D z D z E E 1
2 2 1 1 2 2 E Es , 1 1 1 D z E D z
E < Es
35
Settlement calculation methods
Effect of disturbance on void ratio-pressure relationship
Overconsolidated clay e0
Virgin consolidation curve; Slope=Cc Void ratio, e
0.42e0 p0 pc
Pressure, logp
Cc=0.141Gs1.2[(1+e0)/Gs]2.38
Compressibility and coefficient of volume compressibility
Compressibility (压缩模量)
Es=Dp/[(e1-e2)/(1+e1)]=(1+e1)/a
Coefficient of volume compressibility (体积压缩系数)
Under-consolidated soil (欠固结土)
Overconsolidation ratio OCR=Pc/P
OCR- Overconsolidation ratio;
Pc- Preconsolidation pressure; and P-present effective vertical pressure
3m
7m
5m A
Steps of determine the presoncolidation pressure
Casagranda (1936)
a
Void ratio, e
f
b
a a
d c
pc
Pressure, logp
Effect of disturbance on void ratio-pressure relationship
e2
Void ratio, e
e1
Generally, P1=0.1MPa, P2=0.2MPa
a1-2<0.1MPa-1
P1 P2 Pressure, P
Low
0.1<=a1-2<0.5MPa-1 Medium a1-2>=0.5MPa-1 High
One-dimensional laboratory consolidation test
Compressibility of Soil (土的压缩)
Dr. Fei Wang IGE, Southeast University
Contents
Fundamentals of soil compression (土压缩的基
本原理)
Compression parameters and their
变形模量E与压缩模量Es关系
变形模量 E 与压缩模量 Es 之间的关系（相同的初始状态） 由虎克定律: 侧限条件下:
D z
D z D x D y E E
D x D y 0; D x D y D z 1
2 2 D z 1 E 1
Valve open
Du<P/A
Du=0
t= ∞ 0<t< ∞ Spring-cylinder model (continued)
Compression parameters and their
determination in lab tests
One-dimensional laboratory consolidation test
1.Relocations of soil particles
2.Expulsion of water or air from the void spaces
Soil consolidation
Effective stress principle One-dimensional soil consolidation theory
Effect of other factors on void ratio-pressure relationship
t=7days Void ratio, e t=1days t=14days
Pressure, logp
Effect of load duration
Virgin compression
Void ratio-pressure plots (e-logp curve)
e1 Void ratio, e e2
Compression Index 压缩指数 Cc=(e1-e2)/(logP1-logP2)
Cc<0.2 low, 0.2<Cc<0.4 medium, Cc>0.4 High
Swell Index 回弹指数
Ss
Secondary consolidation settlement
Time-deformation plot during consolidation for a given load increment
One-dimensional laboratory consolidation test
Example
A soil layer shown as the following figure has a height of 10m which has fully consolidated. gsat=18kN/m3 (1)What is the preconsolidation pressure; and (2)What is the OCR of soil at point A when remove 2m high soil.
mv=1/ES=a/(1+e1)
Stress history of soil 应力历史 Depositing
Keep present condition for a long time Erosion
Normally-consolidated soil (正常固结土)
Over-consolidated soil (超固结土)
Ring
Consolidometer (odemeter)( 固 结仪，压缩仪)
Soil specimen
Deformation, pressure, and time
One-dimensional laboratory consolidation test
Time, log scale Sd Immediate settlement Settlement, S Sc Primary consolidation settlement
Soil mechanics becomes a branch of science
Soil consolidation
Valve closed Valve closed
Du=0
Du=P/A
t=0 Spring-cylinder model
Soil consolidation
Valve open
determination in lab tests (压缩参数及确定方
法)
Settlement calculation methods (沉降计算方法)
Fundamentals of soil compression
Fundamentals of soil compression
Time, t Sd Immediate settlement Settlement, S Sc Primary consolidation settlement Ss Secondary consolidation settlement
Note: P is the current effective stress
Stress history of soil 应力历史 Depositing
Keep present condition for a long time Erosion
Normally-consolidated soil (正常固结土)
E0 (1 2 )bp1 / s1
p1= 比例极限荷载 b= 承压板的边长或直径 s1= p1所对应的沉降量 ，取p-s曲线上的直线 段末端值。没有直线段时，取s1= (0.01- 0.015)b所 对应的荷载为p1
深层平板载荷试验 旁压试验 土的弹性模量
自学
课本：P133-137
Void ratio-pressure plots e=Vv/Vs=Hv/Hs
Void Soil specimen Solid
Hs=w/(AGsgw)
De=DVv/Vs=DHv/Hs
One-dimensional laboratory consolidation test
Void ratio-pressure plots (e-p curve) Compression coefficient 压缩系数 a=(e1-e2)/(P1-P2)
Over-consolidated soil (超固结土)
Under-consolidated soil (欠固结土)
OCR=1
OCR>1
OCR<1
e-logp curve with loading, unloading and reloading
Loading
Void ratio, e
Unloading Reloading
P1 P2 Pressure, logp
Cs=1/5~1/10 Cc
Correlations for compression index
Skempton (1944)
Cc=0.009(LL-10)
Rendon-Herrero (1944)
Nagaraj and Murty(1985)
Cc=0.2343Gs(LL(%)/100)
DP/P=1 Void ratio, e DP/P<1 DP/P>1
Smaller load increment ratio can obtain more accurate compression curve to the virgin one.
Pressure, logp
Effect of load increment ratio
Normally consolidated clay e0
Void ratio, e Virgin consolidation curve; Slope=Cc consolidation curve for remolded soil; Slope<Cc
0.42e0 pc
Pressure, logp
土的变形模量
Plate loading test
目的：1. 测试地基承载力； 2. 测试地基土变形模量； 3. 研究黄土的湿陷特性。 材料：千斤顶式载荷架（图5-14， 教科书p.131） 观测：1.时间间隔 (p.131) 2.终止加载判别标准 (p.131)
结果应用：确定土的变形模量E0
s (1 2 )bp0 / E0
则:
1 2 D z D z E E 1
2 2 1 1 2 2 E Es , 1 1 1 D z E D z
E < Es
35
Settlement calculation methods
Effect of disturbance on void ratio-pressure relationship
Overconsolidated clay e0
Virgin consolidation curve; Slope=Cc Void ratio, e
0.42e0 p0 pc
Pressure, logp
Cc=0.141Gs1.2[(1+e0)/Gs]2.38
Compressibility and coefficient of volume compressibility
Compressibility (压缩模量)
Es=Dp/[(e1-e2)/(1+e1)]=(1+e1)/a
Coefficient of volume compressibility (体积压缩系数)
Under-consolidated soil (欠固结土)
Overconsolidation ratio OCR=Pc/P
OCR- Overconsolidation ratio;
Pc- Preconsolidation pressure; and P-present effective vertical pressure
3m
7m
5m A
Steps of determine the presoncolidation pressure
Casagranda (1936)
a
Void ratio, e
f
b
a a
d c
pc
Pressure, logp
Effect of disturbance on void ratio-pressure relationship
e2
Void ratio, e
e1
Generally, P1=0.1MPa, P2=0.2MPa
a1-2<0.1MPa-1
P1 P2 Pressure, P
Low
0.1<=a1-2<0.5MPa-1 Medium a1-2>=0.5MPa-1 High
One-dimensional laboratory consolidation test
Compressibility of Soil (土的压缩)
Dr. Fei Wang IGE, Southeast University
Contents
Fundamentals of soil compression (土压缩的基
本原理)
Compression parameters and their
变形模量E与压缩模量Es关系
变形模量 E 与压缩模量 Es 之间的关系（相同的初始状态） 由虎克定律: 侧限条件下:
D z
D z D x D y E E
D x D y 0; D x D y D z 1
2 2 D z 1 E 1
Valve open
Du<P/A
Du=0
t= ∞ 0<t< ∞ Spring-cylinder model (continued)
Compression parameters and their
determination in lab tests
One-dimensional laboratory consolidation test
1.Relocations of soil particles
2.Expulsion of water or air from the void spaces
Soil consolidation
Effective stress principle One-dimensional soil consolidation theory
Effect of other factors on void ratio-pressure relationship
t=7days Void ratio, e t=1days t=14days
Pressure, logp
Effect of load duration
Virgin compression
Void ratio-pressure plots (e-logp curve)
e1 Void ratio, e e2
Compression Index 压缩指数 Cc=(e1-e2)/(logP1-logP2)
Cc<0.2 low, 0.2<Cc<0.4 medium, Cc>0.4 High
Swell Index 回弹指数
Ss
Secondary consolidation settlement
Time-deformation plot during consolidation for a given load increment
One-dimensional laboratory consolidation test