Modeling the dispersion of size reduction of rock during blast-induced failure of a rock mass surrounding an excavation

Abstract

The polarization-optical method of examination, which makes it possible in combination with physical modeling, to obtain voluminous information on the process of blast-induced failure of rock, has come into widespread use in studying this process [i]. To produce processes equivalent to natural processes in a physical model, it is necessary to establish criterial relationships between basic parameters and to carry out these relationships in experiments. Komir et al. [i] and Sushkov et al.[2] present criterial relationships between basic parameters of the failure process of a uniform isotropic rock mass.They were derived on the basis of a static strength model using Griffiths' criterion to determine the moment of crack initiation.The criterial relationships assume the fulfillment of established relationships for the size of the cracks, their distribution density in the mass, the propagation rate, and the specific surface energy in the material in nature and in the model.It is established that the dispersion of the size reduction of a uniform rock mass by blasting, which is closest to that in nature, can be obtained in models formed from commercial glass.This material satisfies most fully the relations between the scales of the specific surface energy and the time required for the failure process and the scales of the quantities describing the elastic wave field of stresses, which assumes the form:where lj, lo, 10, It are, respectively, the scales of the specific surface energy, stresses, and densities and the time scale of the failure process, IL is the geometric scale, and Ic is the scale of the propagation rates of the elastic longitudinal waves, respectively.Average mechanical characteristics of the model material and certain rocks are presented in Table i. Their analysis demonstrates that relationships (i) and (2) can be satisfied, if commercial glass is used as the model material.In this case, the dispersion of the size reduction of the mass surrounding the excavation, which is similar to that in nature, can be produced in the models.The linear dimensions of the lumps in the model and in nature are related in terms of geometric scale.It should also be noted that in conformity with equality (i), the stress scale for the commercial-glass models is unity, and coincides with the scale for the elastic modulus in terms of the similitude criterion for elastic wave processes [I], i.e., En (3) ~o '= ~j = ~E = E~ where I E is the scale of the elastic moduli, and E n and E m are the elastic moduli of the natural material and the model material, respectively.We can conclude the coincidence of the elastic-moduli scale for the glass and rock from comparison of the mechanical characteristics of the materials, which are presented in Table i. Coincidence of the modeling scales (for E in the case in question), which are defined in terms of similitude criterion, with scale values computed for direct comparison of the characteristics analyzed also confirms the correct selection of the model material.V. V. Kuibyshev Military Eng...