In this paper, we have demonstrated that the rock mass mechanical properties of the basalt lava was evaluated by the numerical analysis with a homogenization theory. The basalt lava around Tokuyama underground power house at the upper part of Ibi River in Gifu prefecture, Japan, included cracks and fractures with slickenside and specific deforming structures that would be formed in the process of the plate accretion and faulting. It was feared that the deformation structures would adversely affect the stability of the underground power house. Therefore, we evaluated the mechanical properties of the rock mass including the structure by a method using a numerical analysis based on homogenization theory, and then performed excavation analysis of the underground power house with the calculated mechanical properties and compared the analysis result with the observed displacement around the underground power house. As a result, it was showed that the method was practical for the evaluation of such rock-mass properties.

1 Introduction

The mechanical properties of the rock mass are affected by the geometric characteristics of discontinuous surfaces and the characteristics of the rocks that constitute them. Therefore, in order to obtain the properties, it is required to conduct in-situ tests and laboratory tests that reflect the mechanical properties for rocks and rock mass, the geometric characteristics and scales of discontinuous. However, it is not always easy to evaluate the physical and mechanical properties of the rock mass with discontinuities and fractures of spacing and persistence difficult to reflect on in-situ tests. In order to solve this problem, it has been recommended to utilize the evaluation method of strength properties using the numerical analysis effectively. According to the previous research, the evaluation method using a homogenization theory has the advantage of being able to evaluate the strength of the rock mass including the cyclical cracks and fractures from the geometric information and the mechanical properties of the constitutional components for the targeted rock mass. However, there are few cases that applied to the evaluation of rock mass to conduct the excavation analysis for a large-scale underground cavern (Kyoya et al. 1999). Therefore, this paper demonstrates that the evaluation method can be applied to the excavation analysis for the underground power house construction at the Tokuyama hydropower plant in Gifu Prefecture, Japan.

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