The authors have developed a new dynamic direct shear test machine, for the purpose of investigating the response to the earthquake motion of rock discontinuities. We conducted a large number of dynamic direct shear tests for the rock discontinuities. Test specimens are Limestone joint, Sandstone joint and Mudstone bedding plane of natural discontinuity made by boring-core, and artificial discontinuities made of mortar. By these test results, we examined dynamic shear strength and dynamic shear deformability of rock discontinuity.

The authors defined dynamic peak shear strength τp(d) by the results of Multi-stage amplitude dynamic direct shear tests. Then, we investigated comparison of dynamic shear strength and static shear strength, and dependence on frequency for dynamic shear strength. It is clear that dynamic shear strength exceeds static shear strength for relatively rough planes, and dynamic peak shear strength τp(d) does not depend on the frequency in the range from 0.1 Hz to 3.0Hz

Also we defined the dynamic diagonal shear stiffness Ksd(d) and attenuation h. Furthermore, we examine the stress dependence and frequency dependence of these dynamic deformability parameters. We defined skelton curves and modelled it by hyperbolic function. It is Clear that both the dynamic diagonal shear stiffness Ksd(d) and attenuation h, have a dependance about normal stress an and shear stress amplitude.

1 General Introduction

Many rock discontinuities are distributed in hard rock such as bedding planes or joint planes, and influence the strength and deformability of the rock mass. In recent years, dynamic analysis method for rock foundations such as for very important facilities and on large rock slopes was required. With regard to this dynamic analytical method for discontinuous rock mass, the problems due to the conventional elastic analysis methods being insufficient are pointed out, but a new analytical method for rock foundation and rock structure has been proposed in recent years (Iwata et al., 2012; Yoshinaka et al., 2012).

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