土体钻孔剪切仪自动化改造及应用研究

Automatic transformation of soil borehole shear equipment and its applications

针对现有钻孔剪切仪存在的缺点,对既有土体钻孔剪切仪进行自动化改造。为评估改造后的钻孔剪切仪测定土体抗剪强度的适用性,以光谷创新基地黏性土及广佛环线琶洲站残积土为研究对象,利用改造后的钻孔剪切仪进行大量钻孔剪切试验,得到原状黏性土和残积土(原状、短时(2~3 h)浸水及24 h浸水)的抗剪强度参数。从多方面对钻孔剪切试验与直剪试验结果差异性进行分析,以南京禄口机场站粉质黏土为对象,重点对法向压力的影响进行分析。结果表明:黏性土和残积土的钻孔剪切试验数据的线性相关性良好。短时(2~3 h)浸水后,残积土黏聚力减少15.28%~40.45%,钻孔上部土体内摩擦角增大17.35%~30.90%,钻孔下部土体内摩擦角减少4.83%~8.75%。24 h浸水后,残积土黏聚力减少45.10%~69.33%,内摩擦角减少52.14%~69.87%。通过对比发现,钻孔剪切试验相比于室内直剪试验得到的黏聚力小,内摩擦角大。通过对南京禄口机场站粉质黏土抗剪强度参数随法向压力的变化规律分析,发现法向压力由30 kPa增加至50 kPa时,黏聚力增大了2.88倍,内摩擦角减少了约41.6%。研究成果可为钻孔剪切仪在土体中的应用及法向压力选择提供参考。

In view of the shortcomings of the existing borehole shear equipment,the existing borehole shear equipment was transformed automatically.In order to evaluate the applicability of the modified borehole shear equipment to measure the shear strength of the soil,taking the cohesive soil of the Optics Valley Innovation Base and the residual soil of the Pazhou Station of the Guangfo Ring Line as the objects,a large number of borehole shear tests were carried out using the modified borehole equipment.The shear strength parameters of undisturbed clay soil and residual soil(undisturbed,short-term immersion and 24 h immersion)were obtained.The differences between the results of borehole shear test and direct shear test were analyzed from various aspects.Taking the silty clay of Nanjing Lukou Airport Station as the object,the influence of normal pressure was emphatically analyzed.The results show that the linear correlation of the borehole shear test data of clay soil and residual soil is good.After short-time(2~3 h)immersion,the cohesion of residual soil decreases by 15.28%~40.45%,the internal friction angle of upper soil of borehole increases by 17.35%~30.90%,and the internal friction angle of lower soil of borehole decreases by 4.83%~8.75%.After 24 h immersion,the cohesion of residual soil decreased by 45.10%~69.33%and the internal friction angle decreased by 52.14%~69.87%.Through comparison,it is found that the cohesion values obtained by the borehole shear test is smaller than that obtained by the direct shear test,and the internal friction angle is larger.Through the analysis of the shear strength parameters of silty clay at Nanjing Lukou Airport Station with the change of normal pressure,it is found that when the normal pressure at all levels increased from 30 kPa to 50 kPa,the cohesion values increases by 2.88 times and the internal friction angle decreases by about 41.6%,which better explains the difference between the results of borehole shear test and the direct shear tests.The research results can provide reference for the application of soil and the selection of normal pressure.