土的各向异性和卸荷体缩

当三轴排水试验中的轴向荷重增加继而减退时，某些上的体积是收缩的，而不是膨胀的。这一看来是反常的现象实是土的各向异性所引起的。土的各向异性既源于原生又源于次生。而后者只有在各向不均等应力作用下才能反映出来。如果土样承受过的大小主应力比σ＿１／σ＿３较大，则土的次生各向异性更明显，试验结果表明，当σ＿１／σ＿３值约大于２．６后就会发生卸荷体缩。

Anisotropy and Volume-contraction of Soil due to Axial Unloading in CD Test

When axial load increases and then decreases in CD test, volume of some Kinds of soil is notexpanding but contracting.This unusual phenomenon,caused by the soil anisotropy. S0il anisotropyoriginates from both depeitional and induced anisotropy, and the latter can only come into being underanisotropic consolidation stress. The induced anisotropy of the soil sample is more obvious when theprincipal stress ratio（σ₁/σ₃）is higher. Experiments showed there exists soil volume-contraction due toaxial unloading in CD test as σ₁/σ₃ exceeds about 2.6.