Development of approaches to calculation of the stress-strain state parameters of the rock mass based on the results of deformation measurements at the borehole bottom

To ensure safe conditions for mining of mineral deposits, information on the stress-strain state of the rock masses is necessary. There are a few methods to obtain this type of information. One of them, which has found wide application at mining enterprises, consists in using the characteristic of elastic restoration of the shape and dimensions of the rock mass element when its connection with the main mass is forcedly broken (the doorstopper method). For its correct realization, a mathematical tool is required that allows the transition from stresses at the borehole bottom to stresses in the rock mass without the use of empirical coefficients. The paper presents the results of developing a mathematical tool to calculate the stresses acting inside the rock mass and determined based on the doorstopper method. The possibility of using empirical coefficients (the concentration coefficient and the axial stress influence coefficient) obtained during long-term in-situ and laboratory studies for the transition from stresses at the borehole bottom (flat stress state) to stresses inside the rock mass (volumetric stress state) is shown. An approach for calculating the components of the stress tensor in the bottomhole plane of three mutually perpendicular boreholes through the deformation values of a four-sensor socket is proposed. The approach for transition from the directions and magnitudes of stresses on the measurement plane to the direction and magnitude of the main stresses inside the rock mass is given.