Shear Characteristics of Rock Containing Weak Planes (2nd Report)

Abstract

In estimating the shear strength of rock mass, the weak planes contained in the rock mass must be taken into consideration. Therefore, a direct shear testing machine has been developed to perform the experiment. A preliminary research has been done which is described in the previous report.In this study, a practical research is carried out by using the direct shear testing machine and the results obtained are summarized as follows:(1) In the direct shear test, the shear load is applied at the desired normal stress. The shear stress becomes maximum at the point of failure strength and reaches finally a value of residual shear strength. The normal stress is then increased as predetermined, and again the shear load is applied. This procedure is repeated, and the testing method is called as multistage shear test.The values of residual shear strength obtained from the multistage shear tests have little difference to those obtained from the usual shear tests.(2) The direct shear tests are conducted on the rock specimens collected in the vicinity of places where the in-situ block shear tests have been done, and the results obtained from the direct shear tests are compared with those obtained from the in-situ tests. Consequently, it is found that the values of peak shear strength obtained from the in-situ tests lie between the values of peak shear strength and residual shar strength obtained from the direct shear tests. From this finding, it is clear that the direct shear tests is useful for estimating the shear strength of rock mass.(3) The rock specimens are collected from many working sites, and the tests are carried out.The experimental values indicating the relationship between residual shear strength and normal stress are scattered in the same rock type, because the rock specimens collected from different places are classified into the same rock type, and those collected from the same place are not homogeneous. But, it is recognized that the experimental values in the same rock type have a tendency to be expressed by Jaeger's equation.