岩盤挙動の過去へのシミユレーション

Abstract

Simulation of rock behaviour going back to the past is proposed in this paper. Usually computer simulation is carried out solving partial differential equations as time goes by, that is, starting at tA and ending at tB with tA < tB. In the proposed method, computer simulation is performed from tB to tA. Analytical consideration may suggests that solution ascending time is similarly possible as that descending time. Numerical solution ascending time, however, has some difficulties because information of initial state is gradually dispersing as time goes by, therefore, very small difference of initial values at tB results in very large difference of solutions at tA. The difficulties in numerical simulation are discussed in this paper. For demonstrating and evaluating the feature of the proposed method, relaxation of rock stress is selected as an example case. A selected site is peripheral of Beijing, China where 100 million years ago a large rock mass was intruded and considered to cause large rock stress around the site. Supposing that rock stress continuously relaxed up to the present, a simulation back to the past is carried out obtaining material constants, then, simulation on to the future starting at the present is also carried out to estimate the creep strain after 10 thousand years. In the proposed method, only a model at the present is necessary. In the conventional simulation, however, requires modeling at the past which is considered to be more difficult and time consuming than modeling at the present. As stated in this paper, the proposed method has some difficulty in numerical solution, however, we considered this method is one of the promising methods to examine the long-term rock behaviour.