钻孔剪切试验及其在黄土中的应用

Borehole shear test and its application to loess

钻孔剪切试验是一种通过在钻孔侧壁上进行直剪试验来测定土体黏聚力和内摩擦角的原位测试方法。阐述和总结了钻孔剪切试验的基本原理、试验和数据处理方法。为了评估钻孔剪切试验测定黄土抗剪强度指标的适用性,采用Iowa钻孔剪切试验仪实测了不同深度黄土的抗剪强度指标,并与室内三轴剪切试验(CU)和直剪试验结果进行了对比。试验结果显示,钻孔剪切试验用于测定黄土的抗剪强度指标时,抗剪强度与法向压力具有较好的线性相关性;试验黄土的钻孔剪切试验应力-应变关系曲线为应变软化型;钻孔剪切试验结果与室内三轴剪切试验(CU)和直剪试验结果相比,黏聚力降低,内摩擦角增大;均质黄土地层的钻孔剪切试验数据离散性相对较小,可采用"整体"破坏包线法对抗剪强度指标进行统计。

The borehole shear test（BST） is a direct shear test performed on the walls of a borehole in soil. The test is used to measure the cohesion and friction angle by destructing the soil along the circumference of the hole. The fundamental principle, testing method, and data processing method of the BST are introduced. To evaluate the applicability of this procedure to loess in Xi＇an, tests were performed to determine the soil shear strength parameters of loess at several depths by using Iowa borehole shear tester. The results of the BSTs are presented along with the results of laboratory triaxial consolidated-undrained（CU） tests and direct shear tests on samples obtained from each testing depth. The BST results are compared with the results from laboratory shear strength tests. It is shown that there is a good linear correlation between shear strength and normal stress. The BST stress-strain curves of the testing loess show strain-softening behavior. The BSTs yield the cohesion values which are lower than those from the laboratory triaxial consolidated-undrained（CU） tests and direct shear tests, but higher friction angle values than those from the laboratory triaxial consolidated-undrained（CU） tests and direct shear tests. The BST results obtained in homogeneous stratum have little discreteness, and thus a ＂global failure envelope method＂ can be applied to the statistics analysis of shear strength parameters.