Study On Method Of Safety Evaluation For Rock Engineering Based On Failure Approach Index

Safty evaluation of surrounding rockmass is the key factor in the design and construction of rock engineering. It is of great significance to plan the scheme of the whole project in the stage of argumentation and program the excavation and providing method in the stage of construction. But now, at the local level, it is still of vital problem to be solved how to put forward a new scientific and practical method to accurately estimate the stress concentration degree of element in rockmass, to evaluate its damage degree, and to describe the evolution rule of the stability state. And at the same time, the concept of safety at the entire level is not clear in the engineering. And the corresponding evaluation method needs to be developed. In order to solve the problems put forward above, a new concept named FAI (failure approach index) and the corresponding evaluation method is proposed in this paper.The main study works and results are listed as follows:1. Based on the analysis of the relation between a stress point and the yield surface in the principle stress space, an index named YAI (yield approach index) is proposed in this paper. Furthermore, the other index named FD (failure degree) is put forward to describe the damage degree of surrounding rockmass based on the rule analysis of evolution of the plastic shear strain in the principle plastic strain space. So a new variable called FAI (failure approach index) can be attained based on the function of YAI and FD. Some cases are presented and the results indicate that the FAI field in surrounding rockmass can supply many important information for the safety assessment such as the range of plastic field, the stress concentration degree of every element under the complex stress state, the damage degree of every element in the excavation damage zone, and etc. And by analyzing the evaluation rule of FAI in the process of excavation, we can forecast the variation of extent and depth of the excavation disturbed zone, damage zone and failure zone in the process of excavation.2. In order to study the heterogeneous effect on the safety of surrounding rockmass, this paper suppose that the risk parameterω, which is the phase complementary parameter of YAI is the a stochastic variable in this paper which conforms to the Weibull's distribution and develops a new stochastic analysis method on safety of surrounding rockmass. An analyzing case is carried out. The application...