ABSTRACT:

In the present study, a verified material model for rock mass which includes damage evolution, modified strength criterion and equation of state, together with a numerical model, is used to investigate the effects of charge loading density, charge distribution and charge chamber geometry on underground blasting induced stress wave propagation in a rock mass. The numerical model is coded and linked to a commercial program Autodyn3D as its user's subroutines. Parametric calculations on peak particle velocities of stress wave generated by underground explosion in chambers with different geometries and different loading densities are performed. Based on the numerical results, new relations that take into considerations of charge loading density, explosive distribution pattern and charge chamber geometry are proposed to predict stress wave propagation in the rock mass.

I.
INTRODUCTION

Common methods in engineering to predict intensities of stress wave propagation in a rock mass to blasting loads are usually dependent on some empirical or semi-empirical formulae. These empirical formulae are usually obtained by different authors based on their own collection of data from different sites (Dowding 1996). Some empirical formulae consider the effects of loading density and the approximate properties of the surrounding rock mass (such as soft or hard). However, other factors, such as shapes of the chambers, distribution patterns and locations of explosives are not considered in these empirical formulae. Investigation of these factors by conducting field blasting tests is very expensive, sometimes it is not possible due to the environment and safety constraint. Thus, numerical calculations with validated numerical model provide an alternative way to investigate the effects of these factors on stress wave propagation. In most previous studies, continuum damage models with assumption of isotropy are used (Yang et al. 1996; Liu and Katsabanis 1997; Hao et al., 1998). Although the isotropic assumption is often sufficient and can give reasonable prediction of rock mass behavior under blasting loads, it is a simplification of a naturally anisotropic problem. An anisotropic damage model with stochastic initial damage and damage evolution was developed by the authors (Hao et al., 2000) to analyze blasting-induced stress wave in a rock mass. It was shown that the anisotropic model gives more accurate prediction of underground blasting-induced stress wave propagation than the isotropic models. In this paper, the calibrated anisotropic damage model, which includes the stochastic initial damage, damage evolution, modified strength criterion and equation of state (Hao et al., 2000)' is used to perform parametric studies. The effects of loading densities, charge distribution, chamber geometries and chamber volumes on stress wave intensities in a rock mass are investigated. The numerical results are used to derive some semi-analytical formulae, which include the effects of various explosion conditions, to predict PPV of stress wave in the rock mass.

2.
NUMERICAL MODEL

The numerical model, which was developed and validated by authors (Hao et aI., 2000), is used in the present study. Following briefly introduces this model.

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