Abstract

Studying stress wave propagation across fractured rock mass is crucial to estimate the safety of an underground construction. The universal distinct element code (UDEC) has been used in fractured rock masses for the discreteness of rock mass. In this paper, the calibration work of UDEC modeling on P-wave propagation across a single nonlinear joint normally is firstly conducted and the results match very well with the solutions by the time-domain recursive method proposed by Li (2012). Secondly, numerical studies of P-wave propagation across a single joint obliquely are carried out, Finally, parametric study is conducted for the effects of the joints spacing, the joint number, JCS and JRC on the transmission for the P-wave propagation across parallel joints. The results reveal that the magnitude of transmission coefficient not only decreases with the increasing of joints numbers but also related to the joint spacing, the JCS and JRC.

Introduction

In nature, rock mass usually consists of multiple planar fractures, such as cracks, joints, faults and weak intercalated layers. The presence of discontinuities makes rock masses discontinuous, inhomogeneous and anisotropic, and causes rock engineering greatly complicated. Studying stress wave propagation across fractured rock mass is crucial to estimate the safety of an underground construction.

The linear elastic model and nonlinear elastic model (BB model) usually were used to express the joint model. Nonlinear deformation may appear when the amplitude is large. According to the hyperbolic function, the BB model proposed by Bandis et al. (1983) has been widely used as a nonlinear model in the study. Analytical solution on wave propagation through single linear elastic joint in arbitrary angle was presented (Pyrak-nolte et al. 1990, Pyrak-nolte et al. 1996, Cook et al. 1992, Gu et al. 1996).

Based on time-domain recursive method, Li et.al (2011) established wave propagation equation across linear elastic joint to calculate the transmission coefficient and reflection coefficient when P-wave and S-wave propagation obliquely across a set of parallel joints, and the method can be also used in nonlinear joint (Li et al. 2012). In the numerical simulation, UDEC or 3DEC was used to study the law of stress wave propagation. Zhao simulated blast wave across rock include joints by Zhao (2002) used UDEC and AUTODYN-2D to simulated the law of wave propagation in jointed rock mass. UDEC was used to simulated the 1D wave propagation across joint by Cai (2004) and Zhao (2008), and the result showed the feasibility of UDEC to simulate wave propagation. Zhou (2011) study the rules of stress waves crossing fractures which have various attitudes. Transmitted law of joint considering various type of one-dimensional incident wave was studied(Wang et al 2006 and Yu et al 2009). SHI and LEI used 3DEC to simulated 2D wave propagation across joint. Based on continuous media discrete element method (CDEM) and discontinuous deformation analysis method (DDA), Wang (2009) and Zhang (2009) study the rules of wave propagation cross joints, respectively. In addition, research on transmission behaviors considering rough joint surface was studied by Ru (2008).

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