Research of In-situ Borehole Shear Test of Loess

It is very important to accurately obtain the in-situ shear strength parameters of loess for loess engineering. In this study, borehole shear test (BST) was applied to test the shear strength parameters of loess on a loess landslide in Xi'an. The suitable drilling method in loess site was proposed, and a micro displacement-shear strength measurement system was added on the basis of the original Iowa borehole shear test to accurately measure the normal displacement and shear stress. The results of BST and direct shear test were compared. The results show that the improved equipment is more visible and controllable; the normal stress is proportional to displacement, which indicates that the soil is in the stage of quasi elastic deformation. To ensure the reliability of the results, the time for consolidation under the first stage of normal stress needs 10 min while 5 min meet the requirement in the subsequent stages. Compared with the direct shear test, the internal friction angle measured is larger for 40.8% on average while cohesion is 12.7% smaller. The borehole shear test shows a good performance on the test of the shear strength parameters of loess in-situ.