The problem of selecting the most effective device for creating concentrating stresses on the borehole contour when using non-explosive destructive mixtures (NDM), allowing to create a main crack between contour boreholes in a row and to save the roof of the chamber from groundwater breakthrough into the excavated space, is considered. Laboratory studies carried out on samples of gypsum powder monolith and natural gypsum blocks of an underground mine confirmed the theoretical data on the effectiveness of using twin metal inserts for directional fracturing of gypsum rocks using NDM.
The parameters of the environmentally friendly method of directed cracking of sedimentary rocks with the use of non-explosive destructive mixture (NDS) are substantiated. This method provides increase of stability of the underground chambers roof and preservation of the earth surface from collapse. The calculation of the distance between contour boreholes when conducting ventilation excavations at the gypsum deposit is carried out. An engineering method for calculating the parameters of contour blasting with LDC has been developed.
The results of studies to establish the degree of influence of the relief of the earth surface on the stress-strain state ("SSS") of the rock massif and the parameters of mine workings allowed to identify coefficients of influence of the surface relief on the SSS of the massif, representing the sum of relative stresses from the weight of rocks and additional loads caused by different configuration of the surface relief, whose value functionally changes depending on the distance to the place of observation and the shape of the relief according to the power law, and which should be considered when determining the parameters of underground mine workings.
The efficiency of the method of directional cracking of gypsum rocks using non-explosive cement-based fracture mixture (NBRM) can be increased by the developed design of stress concentrators in the form of two parallel metal plates. Design formulas and graphs of directional crack development between boreholes in time are presented.
