In this paper, the characteristics of stress wave propagation are investigated and the response of the plane of weakness in e entire rock mass subjected to spherical wave has been analyzed. Both the characteristics and response are studied with the factor of safety and energy criterion respectively. Results of the investigation show that the two criteria are consistently in agreement, and their limitations are also obvious. Both criteria have been systematically used to evaluate the response of the weakness plane of the entire rock mass. Results of a study using the criteria on two examples are presented. It is concluded that the methods are reasonable and effective In response assessment.
Underground blasting generates intense shock waves that can damage other adjacent underground and surface structures. The shock intensity depends on the quantity of explosives used and the distance between the detonating source and the structure under assessment. Between them is the rock mass, and it is well known that shock waves induced by such blasting will attenuate significantly as it travels and spreads through them. These waves will eventually become stress waves, and they play an important role during the breakage of rock (Rustan, 1983). Natural rock mass is non-homogeneous; many discontinuities exists including the interfaces between rock layers and rock mass weakness planes, such as faults, joints and cracks, which can seriously impede stress wave propagation. These discontinuities are source of dissipating energy. Therefore, study of the characteristics of stress wave propagation through structure weakness planes is important both in theory and in practice. This is especially critical in the choice of blasting parameters and in increasing operation efficiency. The Influence of the interface in rock mass has been accorded increasing attention in studies relating to safety in rock and soil engineering in a dynamic environment. In the early 1960's. Rinehart investigated the relationship between the incident, reflected and transmitted wave for a completely cohesive interface. However, for some structure weakness planes. the shear force induced by stress wave components will cause the interface to slip. Thus, structure failure occurs when the blasting stress waves, which are mostly compressive stress waves, passes these planes at an incident angle (e.g. obliquely). However, for spherical wave induced by blasting, the angle of incidence is different at each peints of the interface, and the coefficients of reflection and transmission are correspondingly different. Using previous analytical approaches, inconsistencies arise because some areas are estimated as safe but some are known to slip along the interface. The influence on the entire plane of structure weakness and how sliding along the interface are ignored. This paper addresses some of the outstanding problems encountered by researchers and attempts to resolve them accordingly.
When a P-wave travels to a cohesive interface between two different media,some of its energy is transmitted and some are reflected. Fig.1 shows four new waves, and in which there are two P-waves. The incidence point is O.
