ABSTRACT

A numerical code RFPA2D (Rock Failure Process Analysis), was used to simulate the initiation and propagation of fractures around pre-existing cavities in brittle rock. The dynamic loadings were applied to the rock specimens to investigate the mechanism of fractures evolution around single cavity. In addition, the evolution and interact of fractures between multiple cavities was investigated. The numerical simulated results reproduced tensile and remote fractures due to dynamic loading. Moreover, numerical results suggested that both the compressive wave and tensile wave could influence the propagation of tensile cracks. Especially the reflected tensile wave accelerated the propagation of tensile cracks.

INTRODUCTION

The stability of cavities due to static loading had long been the subject of intensive studies in mining and civil engineering. Extensive research was done on fractures evolution around a single pre-existing cavity (Hoek 1962; Lajtal 1975; Ewy and Cook 1990; Carter et al. 1991). However, few works focused on the fractures evolution surrounding cavities under the condition of dynamic loading.

Although many numerical methods, such as finite-element, boundary-element, finite-difference and discrete-element methods did well in simulating non-linear behavior in rock deformation, most of them were not physical modeling of the non-linear behavior of brittle rock, and did not demonstrate the progressive failure due to heterogeneity of rock, which resulted in non-linear behavior. Therefore, a more reasonable numerical code RFPA2D (Rock Failure Process Analysis) was introduced (Tang et al. 1993; Tang and Kou 1998;). In addition, this code had been developed to study the dynamic failure process of rock, considering the effect of strain rate on the strength of rock (Chau et al. 2004; Zhu and Tang 2006).

This paper aimed to simulate the evolution of dynamic fracture initiation, propagation around pre-existed cavities in brittle rock. The evolution and interact of fractures between multiple cavities was investigated.

2 BRIEF DESCRIPTION OF RFPA2D

RFPA2D code could be used to model the observed evolution of damage or crack initiation, propagation and coalescence in brittle materials by allowing the linear elastic elements to fail in a brittle manner. The method was used for modeling progressive failure and associated seismicities in brittle rock.

Instead of using a fracture mechanics approach where fracture propagation was controlled by the fracture toughness and was related to a stress intensity factor at the advancing crack tip, a failure approach was adopted in the code, RFPA2D, where microfracturing occurred when the stress level in an element satisfied a certain strength criterion (Tang 1993). In the present in investigation, both tensile and shear failures were considered in the analysis. An element was considered to have failed in the tension mode when its minor principal stress exceeded the tensile strength of the element (Eq.1), and to have failed in the shear mode when the shear stress satisfied the Mohr–Coulomb failure criterion (Eq.2):

  • (Equation in full paper)

3 MODEL DESCRITPION

There were four types of models provided in this study. 1) Single circular cavity with vertical dynamic compression; 2) Single circular cavity with both vertical and horizontal dynamic compression.

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