Earthquake response analysis of a mine rubble deposit sites using NMM+DDA coupled analysis

This paper aims to analyze the scope and environmental impact of the mine deposit rocks sliding down when an active-fault earthquake occurs at the site in Tottori Prefecture, southwest Japan.

The authors analyzed the behavior prediction of waste rocks in earthquake using Numerical Manifold method (NMM) and Discontinuous Deformation Method (DDA) coupled analysis in this study.

The consideration of numerical analysis modelling at the site, i) the behavior of the bedrock as a continuum and the behavior of the waste rocks as a discontinuity must be coupled analyzed. ii) if the mine deposit rocks collapse due to the earthquake, it will be necessary to evaluate the impact on the surrounding area by risk of mine deposit rocks discharge (risk management), that is, to evaluate the scope and environmental impact of waste rocks falling down, the environmental impact, and its countermeasure costs. Since, an analysis method that can consider even large deformation (elastic-plastic behavior) of mine deposit rocks were required for this reason.

From these conditions, the authors solved the bedrock using NMM, which can solve stress-deformation analysis of discontinuous rock mass, and the waste rocks were analyzed by coupling them using DDA that can reproduce slope collapse phenomenon such as collapse shape, arrival time, and fall speed due to the earthquake.

Among active-fault earthquakes published by Tottori Prefecture (2015), the Level-2 earthquake motions used for evaluation of earthquake resistance adopted earthquake motions due to earthquakes caused by the Shikano-Yoshioka fault and the estimated active-faults in the southern part of Kurayoshi City. The waste rocks did not reach the river beyond the end retaining tailing dam as a result. A slight loosening occurred in the mine deposit rocks in the middle part of the slope corresponding to near the maximum inclination, and estimated that it would move downward though it was about 3 m or less.

The authors assumed the rock bolt insertion construction as a slope stabilization measure, performed the earthquake response analysis using the same seismic waveform, and confirmed the validity of the countermeasure., the displacement amount was reduced by 40 to 70% compared to the case without a countermeasure as a result.