非饱和膨胀土抗剪强度的试验研究

TESTING STUDY ON SHEAR STREANGTH OF UNSATURATED EXPANSIVE SOILS

膨胀土是一种特殊的非饱和土,经典的土力学理论在膨胀土问题中已显得无能为力。因此,用非饱和土力学理论来研究膨胀土问题在理论和实际两方面都具有重大意义。在非饱和土抗剪强度理论中,吸力的量测在工程实际中仍没有一种简单易行的方法。基于这种实际情况,试图通过其他间接的途径来代替吸力的量测,以确定非饱和土的吸附强度。对于膨胀土这种典型的非饱和土,膨胀力是其很重要的性质之一,它的大小受含水量的影响很大;另一方面,膨胀土的抗剪强度也随含水量的变化而不断地变化。进行了大量的膨胀力试验和抗剪强度试验,以确定膨胀土的膨胀力与吸附强度是否有一定的关系。通过对黑山土和梅山土的重塑试样试验得到的试验数据分析发现:膨胀力和含水量之间存在良好指数关系;粘聚力的对数和内摩擦角均随含水量的增大线性减小;非饱和膨胀土的吸附强度与膨胀力之间存在较好的线性关系,并在此基础上优化了非饱和膨胀土抗剪强度公式。

Expansive soil is of potential for shrinking or swelling which can be caused by the change of water content. The shear strength of expansive soil is one of the key issues of soil mechanics and further studies are required for the need of analyses including evaluation of the stability of slopes,design of foundations and earth retaining structures. However,the strength behavior of expansive soil is rather complex especially compared to other types of soils. In this paper,the swelling pressure and strength of two typical expansive soils respectively collected from Heishan of Liaoning Province and Meishan of Nanjing are systemically investigated using the methods of conventional soil tests in order to understand its physical and mechanical properties and damage behavior. Meanwhile,the relationship between the swelling pressure and shear strength parameters such as effective cohesion and effective angle of internal friction and initial water content of unsaturated compacted expansive soil is established based on experimental test results. The swelling pressure and shear strength of expansive soils decrease sharply and the volume increases greatly with increasing water content. The ratio of the strength caused by matric suction to the swelling pressure is constant. Therefore a new formula of shear strength for unsaturated expansive soils is presented.