基质吸力对非饱和土抗剪强度的影响

在自然界和工程实践中遇到的土大多数是非饱和土,研究吸力对非饱和土抗剪强度的作用,对于工程实践具有重要的意义。通过压力板仪和直剪仪组合试验,探讨了击实土抗剪强度和基质吸力的关系。试验结果表明：凝聚力在饱和度为40%-60%时最大,而内摩擦角则随饱和度增加而有所减少。进一步对比土-水特征曲线与抗剪强度的关系,并整合前人研究成果,指出了非饱和土中吸力对其抗剪强度影响的规律。对于无黏性土,在边界效应区不产生假凝聚力,且内摩擦角不变;在过渡区与非饱和残余区,假凝聚力和基质吸力的关系存在峰值且变化较大,内摩擦角则随吸力增加而增加。对于黏性土,残余体积含水率所对应的最小吸力可能是影响抗剪强度的界限值,小于此吸力值,φb可近似为常数。但在非饱和残余区,凝聚力将随土状态路径的不同而变化。对于重塑土,凝聚力降低;而对于原状土,则凝聚力可能不变或增加。

Influence of matric suction on shear strength behavior of unsaturated soils

It is evident that unsaturated soils are usually encountered in nature and engineering practice. Hence, the understanding of unsaturated shear strength behavior is necessary. The shear strength behavior of unsaturated soils is investigated on the basis of pressure plate test and direct shear test. The results show that the angle of internal friction decreases with increasing degree of saturation and the cohesion attains its peak value at degree of saturation 40 % ? 60 %. According to these results, the unsaturated shear strength behaviors of non-cohesive and cohesive soils are demonstrated. The internal friction angle of non-cohesive soils increases with increasing matric suction; and the pseudo-cohesion attains its peak value in primary transition zone and then decreases. The cohesion of unsaturated cohesive soils increases with increasing matric suction until threshold suction reaches. The threshold suction is the minimum suction at the residual zone of unsaturation. The cohesion of unsaturated cohesive soils can be predicted before the threshold suction, because value is approximately constant. Moreover, the state paths influence cohesion in excess of the threshold suction.