土的压缩、固结与地基沉降

oedometer
2 Compression curve/压缩曲线
F h F (h s) 1 e0 1 e1 e0 e1 s h 1 e0
s e1 e0 (1 e0 ) h
3 compression coefficient av/压缩系数
e1 e2 de av , p2 p1 dp
p>pc, lack consolidation（欠固结） P=pc, normal consolidation （正常固结） P<pc, overconsolidation （超固结）
Determine pc
1.2 compressible deformation calculation/单向压缩量的计算
1 Compressibility/土的压缩性
1.1 Consolidation Test and compression characteristics/土的固结试验与压缩特性
1 Consolidation test Assumption:
• Load distribution-uniform • Stress distribution(in different height)-the same • Lateral deformation-0 • The area of the sample section-unchangeable • Solid soil-uncompressible oedometer
Hale Waihona Puke 4 compression index Cc/压缩指数
Cc
e1 e2 (e e ) 1 2 p2 lg p2 lg p1 lg p1
e1 e2 de Cc p dp lg lg pc p
de C c av dp p
Stress History Effect—
§ Compressibility, consolidation and settlement 土的压缩、固结与地基沉降
•Compressibility /土的压缩性
•Consolidation /土的固结
•Settlement /地基沉降
• Introduction / 概述
Compressibility and consolidation can be distinguished as: · compressibility –volume changes in a soil when subjected to pressure –giving AMOUNTS of settlement · consolidation -rate of volume change with time –giving TIME to produce an amount of settlement required These are distinct from: 1. compaction which is the expulsion of air from a soil by applying compaction energy. 2. immediate or undrained settlement which is the resultant deformation of a soil under applied stresses without any volume change taking place
on the flatter portions( 2 and 3) and volume changes can increase or decrease with changes in effective stress.
e0 e1 p av p 1 s h mv p h p h 1 e0 Es mv av coefficient of volume compressib ility / 体积压缩系数 1 e0 / 压缩模量
1 e0 Es Compressib le mod ulus av
•Only compression in vertical，Deformation due to void volume decrease
F h F (h s) 1 e0 1 e1 ei av s e0 e1 h 1 e0
hi hs hi 1 hs hs
MPa , kPa
1
1
av1-2<0.1Mpa-1, 0.1≤av1-2<0.5Mpa-1, av1-2 ≥ 0.5Mpa-1,
Low compressibility /低压缩性土 Middle compressibility/中压缩性土 High compressibility /高压缩性土
1.3 Effective stress plot
The soil is described as normally consolidated when its state exists on the steeper line (1 and 4) and the effective stress can only be increased with subsequent reduction in volume because decreasing the stress takes the soil state away from the normally consolidated line. This line is often referred to as the virgin compression curve or line as any change of effective stress along it will be for the first and only time whereas any number of unload/reload paths could be followed. The soil is described as overconsolidated when it occurs