原位置せん断試験で得られる均質な岩盤の変形・強度特性

Abstract

To investigate the fracture process and to interprete the strength parameters of the homogeneous soft rock mass obtained by the in-situ block shear test, two dimensional finite element simulation study has been conducted under the assumption that the rock mass behaves as the strain softening material. At the same time, three dimensional physical model experiment has been performed using plaster as the modeling material. Main results are as follows:(1) Results of the in-situ shear test obtained both by the simulation and model study were expressed as the linear curve in the σ-τdiagram, and the value of the shear strength indicated from these data lay between the peak shear strength and the residual shear strength esitimated from the triaxial tests.(2) In the model study, three types of shape on the shear load versus vertical displacement curve, depending on the vertical stress level, were recognized.(3) In the simulation study, progressive failure has started from the early stage of loading and in accordance with this, load-displacement curve bent from the straight line observed in the inital loading stage. Similar tendency for the corresponding curve was recognized both in the field tests and in the model study.(4) The corrugated shaped fracture surface located deeper than the assumed shear plane was observed in the field experiment as well as in the model study. It was also found in the model and in the simulation study that the thickness of the yield zone developing under the fracture surface was not uniform.