Causes of rock deformations on the contours of mine workings under the action of blast waves

Abstract

Blast wave influence on rock stability in mine openings is given an account of. Results of mathematical modelling of a dynamic stress field created in the massif due to wave interaction with the mine opening have been analysed. A stress field influenced by short wave blasts has been studied. Equations of dynamic balance for theoretically elastic environment, supplemented with boundary and initial conditions for the corresponding components of stress tensor, serve as the basis of a mathematical model developed by V.V. Karpenko and G.A. KoIton. The set of 5 equations was solved using S.K. Godunov numerical technique. Input data are assumed on the basis of the mining conditions at the Severniy (Northern) mine (blast hole diameter - 76 mm; blast type - granulite AC-8). A particular case of blast influence at 10 m range between the charge and the gallery roof (r =370) has been studied. Distribution diagram parameters of the forward-moving elastic wave compression phase have been determined using analytical dependence for a cylinder-shaped charge blast (amplitude σ o = 9.6 MPa, period of time t - 1.2 ms, speed C 1 - 4500 m/s). It has been demonstrated, that form the direction of the forward-moving wave, refracted and diffracted waves create in the massif an extensive zone of radial tension stress, peaking at 1.6 at the distance of 0.8-1.0 R from the contour. In lateral areas, the blast wave produces concentration of tangential compression stresses up to 1.6 σ o . An estimation of mine destruction caused by the energy of dynamic development has been given. Besides dynamic compression and tension stresses, repeated blasts and impulse stress load and relief on the massif also influence stability of the mine openings. An estimation of rock stability criteria at the entry contour during joint action of static and dynamic stresses has also been given.