ABSTRACT

Joints and fractures contained make rock mass complex mechanical and hydraulic properties. The randomicity of fractures shape factors (fracture orientation, dip, trace length, width, and spacing) is considered and Monte-Carlo simulation technique is adopted to develop the digital fractured rock mass model, which can be combined with numerical methods to solve practical engineering problems. FEM is adopted to simulate the mechanical and hydraulic properties of rock mass with different scales. Identifying representative elementary volume (REV) is a fundamental problem in studying rock mechanics and rock hydraulics, and it is a quantitative criterion for identifying if equivalent continuum approach is available for rock engineering problems and what the REV size is if it exists. On the basis of numerical modeling results, REV of fractured rock mass is discussed. The results show that REV size can be determined by the method in this paper and it can reflect the size effect of mechanical and hydraulic properties of rock mass. In addition, for the different research objects, such as mechanical property and hydraulic property, there exists different REV size.

1 INTRODUCTION

Natural rock masses consist of intact rock matrix and fracture systems, including faults, joints, fracture zones and other types of geology structures. The fracture systems with different sizes and rich fractures have a significant effect on the mechanical and hydraulic properties of rock masses. It is the presence of the fracture systems that makes fractured rock masses one of the most complex materials. So whatever methods are adopted to study the engineering properties of rock masses, fracture systems must be included in the analysis process in order to obtain the results as rational as possible.

With the development of computer and its related techniques, numerical modeling has been effective method in solving rock mechanics and rock engineering problems, and fruitful achievements have been obtained. It is predictable that numerical techniques will be one main research issue in the study of rock mass properties. One of the main tasks of numerical modeling in rock mechanics is to be able to characterize the fracture systems (geometry and behavior) in a computational model. The parameters of rock masses are often difficult to be determined. Experiment is effective method, but it has some disadvantages. On one hand, only small rock samples, regardless the fractures and joints in rock masses, can be investigated by laboratory experiments. Obviously the results cannot show the true nature of rock mass. On the other hand, in situ tests to determine the engineering properties of rock mass are difficult to be put into practice, time-consuming and expensive. Some empirical or semi-empirical methods (Richard, 1996; Hoek et al., 1997; Sing, 1999; Smith, 2004; Ramamurthy, 2004; Cai, 2004; Singh 2005;), such as RMR (Goel et al., 1995), RQD, Q-system, Hoek-Brown strength criterion, were provided to evaluate engineering properties of rock mass and classify rock mass. These methods have been adopted in rock engineering successfully, but they often can not identify all the mechanical and hydraulic parameters of rock mass.

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