In in-situ block shear tests, shear stress-shear displacement curve, shear stress-normal displacement curve etc. are usually obtained. Because characteristic points in these curves are not always distinct except failure point, it is difficult to estimate shear strength of rock mass for designing rock structure only from these curves. From these points of view, it is attempted to estimate shear strength in both in-situ block shear test and laboratory direct shear test by monitoring AE (Acoustic Emission). Consequently, it is found that shear strength which is estimated by monitoring AE in in-situ block shear test takes a lower value, and shear strength estimated by monitoring AE in laboratory direct shear test takes a higher value than peak shear strength obtained in in-situ block shear test. Also, shear strength estimated by monitoring AE in in-situ block shear test shows a tendency to be nearly equal to residual shear strength obtained in laboratory direct shear test.

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In order to investigate the effect of the intermediate principal stress on failure strength of rock and failure condition of rock under the multiaxial stresses, the true triaxial compression tests are carried out on two kinds of rocks, namely KIMACHI sandstone and OGINO tuff. For this test, a true triaxial compression testing machine using the cubic specimen was designed as shown in Fig. 2 and Photo. 1.
The main results obtained in this study are summarized as follows;
From the experimental results under the various combined triaxial compressive stresses, it becomes clear that the intermediate principal stress has an effect on the failure strength of rock, and the degree of its effect on the failure strength of rock is different for each rock. Also, under the multiaxial stresses including tension to compression stress field, the failure condition of rock can be expressed by Murrell's criterion rather than Drucker-Prager's one.

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[in Japanese]

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