Assessment of the stress state of a rock mass using the blasting and vibroacoustic methods

In order to ensure safety at the level of -250 m in the Gubkin mine of KMAruda, the following activities were performed: assessment of the rock mass susceptibility to rock bumps using the vibroacoustic method, as well as determination of the stress state of the rock mass with the blasting method. As the result of experimental studies using the vibroacoustic method, a decrease of the stress state of the rock mass was found to vary from 17.5–92.5 MPa (at the entry contour) to 10–30 MPa at the distance of 1.8 m from the wall. The blasting method used at the level of –250 m of the Gubkin mine revealed that the stress state of the rock mass at the bottoms of the cutting and auxiliary holes is 21.9–33.5 MPa, while at the bottoms of the outer and trimming holes it varies within 55.7–65.1 MPa. The blasting and vibroacoustic methods for determining the stress state of the rock mass are similar in the physics of the process. When exposed to the detonation products or the drilling tools combined with the static rock pressure, a certain volume of rock mass is destroyed. The greater the static rock pressure, the greater the volume of destruction is under the same dynamic loads. Taking into account an increase of the stress state from the center towards the outline for the rock face plane, a numerical assessment of the stress state at the entry contour after blasting of the cutting, auxiliary and outer holes was carried out based on a theoretical formula. The calculations using the formula and based on the test data coincide, which indicates creation of residual stresses within the rock mass due to the sequential detonation of the explosive sets in the blast holes.