ABSTRACT:

Due to complexity of soil rock itself and an environment in which soil rock lies, there are a lot of stochastic elements concerning with stability of surrounding rock for underground roadway that lies in soil rock. It is necessary to study stability reliability degree for surrounding rock of the roadway in soft rock based on design methods of safety coefficient. A key issue that must be solved is how to establish a model to calculate reliability degree while reliability analysis was done. Based on stress distributing mechanics of surrounding rock of underground roadway and characteristics of soft rock in itself, calculation methods for resistance force and load of surrounding rock of underground roadway lied in soft rock that was supported by shotcrete and rockbolt were researched while mechanical media of the son rock were belonging to layered structure mechanical media and approximately continuous media respectively. One model was verified by an example.

I.
INTRODUCTION

Research on son rock issue always is one focus in geotechnic engineering area. Due to complexity of various physics and mechanics characteristics of soft rock, there are a lot of arguments on definition and classification of soft rock since a long time ago. Based on synthetically researched results on various definition and physical & mechanical characteristics, especially the mechanics of deformation of soil rock, kinds of soft rock was classified into geological and engineering soft rock after essential characteristics of soft rock was grasped in literature[¹] in the later of 90s'. The engineering soft is a engineering rock mass that can arises large plastic deformation while a engineering force was acted on it. There is uncertain in their physical and mechanical parameters. Mechanical behaviors of surrounding rock of underground engineering in soft rock are more complex than in ordinary rock-mass. Mechanical behaviors of the former arise non - linear characteristic. Non-linear mechanical design methods must be adopted in their design theory. While the underground engineering is devised, besides carrying out certainty analysis, it is necessary to adopt reliability analysis methods that will express stability degree by probability to take into the randomness of mechanical parameters and behaviors.

2.
BASIC STOCHASTIC ELEMENTS OF UNDER-GROUND ENGINEERING IN SOFT ROCK

Stochastic elements of underground engineering in soft rock radically have two kinds, namely components, physical & mechanical parameters and deformation principle of soil rock. 2.1 Randomness of physical and mechanical parameters The component of soft rock concerns with slime. Its main components are slimy minerals, including Kaolinite, Montmorillonite, Illite. Based on engineering experience in a coal mine, variability of contents for slime in soft rock is very much remarkable at different area in the same project and strata. Slimy mineral is main element that influences mechanical characteristic of soft rock. The variability of contents for slimy mineral is one element that results in the variability of mechanical characteristics for soft rock. For example, it is found that average content for slimy mineral of soft rock in different area of a project for one coal mine.

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