Numerical Analysis of the Effect of a Fault On Blast-induced Wave Propagation

Sharafisafa, M. (Amirkabir University of Technology) | Mortazavi, A. (Amirkabir University of Technology)

OnePetro 

Rock masses consist of intact rock and discontinuities such as faults, joints and bedding planes. The presence of such discontinuities in rock masses dominates the response of jointed rock masses to static and dynamic loading. This paper focuses on the propagation and dynamic effects of blast waves in faulted rock masses. In order to investigate the effect of faults, a numerical simulation was conducted. The 2D distinct element code (UDEC) was used to model fault effect on rock failure and stress distribution through the rock mass due to blast wave propagation. The blast loading history was simplified and applied to the blasthole walls. Accordingly, the interaction of explosive energy transferred to the rock mass from the blasthole pressure was examined as a function of distance to the fault plane from the blasthole. A Mohr-Coulomb material model was used for host rock to allow for plastic failure calculations. The conducted numerical study describes the role of fault in blasting in a qualitative manner. On the other hand, a free face boundary was considered as a common blast operation which is conducted in surface mining.



1. INTRODUCTION

The process of rock fragmentation by blasting is a complicated phenomenon which is controlled by many variables and parameters. Considering all this parameters in a single analysis is not possible at the present time, especially when some of them are not clearly understood yet and the effect of others is difficult to quantify. In most blasting practices, empirical or semi-empirical techniques are used for blast design and fragmentation analysis. These techniques are based on information obtained for certain range of rock types and blasting conditions and cannot be generalized for all blasting conditions. With regard to the limitations of empirical methods, numerical methods are viable tools to further understand and illustrate the fragmentation process. Application of numerical methods in blasting allows for consideration of complex boundary conditions, material non-linearity, dynamic material behavior, geometric non-linearity and complexity associated with blasting operations. The nature and degree of heterogeneity of the rock mass is very important in blast design. That is, discontinuities such as joints, bedding planes, faults, and soft seams can allow the explosive''s energy to be wastefully dissipated rather than perform the work intended. In some cases, the discontinuities can dominate the fracture pattern produced by the explosive, and the influence of the structural geology often overshadows that of the rock''s mechanical and physical properties. Best fragmentation is usually obtained where the face is parallel to the major discontinuity set [1 J. The last few decades have seen a variety of numerical studies on the blast-induced waves and their propagation in rock masses with much efforts being placed on the study of dynamic responses of continuous rock masses under blast loading [2,3 J. However, rock masses encountered in reality generally contain geological discontinuities (e.g. joints, faults and bedding p1anes).The properties of rock masses are determined by both the properties of the intact rock and the discontinuities [4,5].