The purposes of this research are to clarify problems of seismic assessment of discontinuous rock mass and to search a solution to the issues. Therefore, the shaking tests were conducted on a slope model made of stacking metal hexagonal rods simulating a discontinuous rock mass, and the vibration condition of collapse and the collapse forms were estimated using various analysis methods. In this study, the collapse mode was predicted from the displacement and acceleration response and strain distribution calculated by equivalent continuum finite element method as Multiple Yield Model (MYM) introducing cyclic loading elastic-plastic deformation characteristics of rock joints. The results were compared with experimental results to discuss the applicability of the analytical method and its issues.
Slopes adjacent to important civil engineering structures such as major roads and nuclear power plants require high seismic safety, so dynamic FEM analysis is used to evaluate slope stability. In general, the stability of rock slopes is evaluated by numerical analysis assuming that the rock mass is a homogeneous elastic body. However, it is known that rock masses are discontinuous and have discontinuities such as nodes and fractures, and that the mechanical behavior of rock masses is strongly influenced by the mechanical properties of discontinuities such as direction, inclination, spacing and series of nodal groups and geological conditions. Therefore, it is important to consider discontinuities in the evaluation of seismic performance.
In this study, vibration tests are conducted on a model of discontinuous rock mass, and various evaluation methods (static/dynamic, conventional/numerical, continuum analysis/discontinuum analysis) are compared to clarify the issues of seismic evaluation of discontinuous rock mass and to discuss a reasonable evaluation method.
The authors have proposed nonlinear deformation characteristics dependent on the normal stress of rock discontinuities during unloading and loading processes, and introduced them into the multiple yield model (MYM), a type of equivalent continuum analysis using the finite element method that can consider the distribution and deformation characteristics of discontinuities. Using this model, we have performed the simulations of the observed waves on the ground foundations of large structures during the 2005 off Miyagi Prefecture earthquake and the 2013 off the Pacific coast of Tohoku earthquake (Iwata et al. 2013). The results show that proper modelling a rock discontinuity can evaluate the seismic behavior that cannot be reproduced when the rock mass is assumed to be elastic, and the validity of the analytical method and modelling is checked. In this paper, the failure mode is predicted from the displacement/acceleration responses and strain distributions using MYM, and the applicability and issues of the analytical method are discussed by comparing with the experimental results.
