Effect of dynamic rock pressure redistribution on the formation of instable rock zone in mines

The causes of roof rock caving in underground mine workings of the Dzhezkazgan copper ore field have been analysed. The results of the ultras sonic test on the rocks of the extraction chamber immediate roof and interchamber pillars are presented. The thickness of the insecure rock zone in the roof and pillars is determined. The influence of static stresses on the possibility of roof rock failure under blasting conditions has been evaluated. It has been found that besides the static stresses and seismic waves of communition blasting, dynamic loads at rock pressure redistribution exert an appreciable effect on the formation of insecure rock in the near—contour rock mass. The dynamic rock pressure redistribution during rock blasting in the face is attended with the formation of intense load relief waves. The values and directions of the resulting dynamic tensile stresses are determined. It is shown that with increase in the depth of the underground mineral mining the load relief waves will produce an increasingly pronounced effect on the formation of the insecure rock zone in the near-contour rock mass.