黄土的钻孔剪切试验特性研究

为研究钻孔剪切试验在黄土中的应用效果，在西安东郊典型的Q₃黄土中进行不同首级法向应力和不同法向应力增量条件下钻孔剪切试验。试验结果表明，抗剪强度随法向应力增大呈曲线形式增大，存在某一临界法向应力值，超过该值后抗剪强度与法向应力之间呈良好的线性关系，能较好地符合摩尔-库仑强度准则，所测得的抗剪强度参数相差较小；在分级加载试验中，法向应力增量越小，达到同一法向应力时的抗剪强度越大；分别加载试验与分级加载剪切试验相比，在相同法向应力下测得的抗剪强度值偏小，随法向应力增大，偏离程度增大；当法向应力较小时，剪切齿难以压入硬土中，导致所测得的黏聚力偏小、内摩擦角偏大，为此建议开发适合不同软硬土质的剪切板，并增加法向位移观测系统，用于判断法向应力施加过程的齿尖压入孔壁情况。

Characteristics of borehole shear test of loess

To study the application effect of the borehole shear test on loess, a series of tests under different primary normal stress and different normal stress increments were carried out on the typical Q₃ loess in the eastern suburbs of Xi''an. The test results show that shear strength increases in a curvilinear trend with the increase in normal stress, and there is a critical normal stress value. Beyond this value, there is a good linear relationship between the shear strength and normal stress. It is in good agreement with the Mohr-Coulomb strength criterion, and the measured shear strength parameters have little difference. In a multi-stage loading test, the smaller the increment in normal stress, the greater the shear strength associated with the same normal stress. Compared with the multi-stage loading test, the shear strength measured by the single-stage loading test under the same normal stress is smaller, and the deviation degree increases with the increase in normal stress. At low normal stress, it is difficult for the shear teeth to be pressed into hard soil, resulting in low cohesion and a large internal friction angle. Therefore, it is suggested that shear plates should be developed to suit different soft and hard soils and a normal displacement observation system should be added to judge the press of the tooth tip into the borehole wall during the application of normal stress.