Rock cone penetration test under lateral confining pressure

To assess the effect the field stress on the in situ cone penetration test of rock, a series of laboratory cone penetration tests was conducted to study the fundamental relationship between the cone penetration test results and the state of stress of rock to be tested. Bidirectional confining pressures were applied on rock samples to reproduce the field stress state of the rock at the borehole wall. The test results show that the specimen under confining pressure shows a different failure mode and mechanical property. The fracture pattern of the specimen was affected by the lateral confining pressure. The load displacement curve under different confining pressures shows that the peak load and ultimate displacement tend to increase with increasing confining stress level. The minor confining pressure plays a dominant role in the process. The failure mechanism was analyzed, and attempts were made to relate the improvement effect of the confining pressure in this test to the increase in compression strength obtained in the conventional triaxial test.