ABSTRACT
Major accidents at underground salt mines of PJSC «Uralkali», in most cases, lead to their total flooding. As a result, the need of detailed study of Verkhnekamskoe salt deposit geological features, in respect to oversalt rocks, appeared. First of all, abnormal complex zones in oversalt rocks and, primarily, in waterproof covering must be determined. A detection and investigation of local decompression zones, excessive fissuring and permeability of the rocks is significantly important while studying waterproof covering.
The paper introduces the method of weakened zones determination in waterproof covering. The method based on the joint application of geophysical and geomechanical approaches. The main idea is to obtain correlation dependencies between static and dynamic geomechanical properties, adjustment of dependencies using well logging data, to get distribution of compression wave velocity and acoustic impedance on the ground of 2D and 3D seismic data processing and, in final part, definition of zones with various consolidation degree in waterproof covering and salt rocks. Following this approach, it is possible to determine the values of uniaxial compressive strength, coefficient of elasticity, Poisson ratio and other characteristics in any point of waterproof covering.
The further geomechanical modeling of waterproof layers stress-strain state uses available values of physical and mechanical properties of rocks. The progression of ground movements and breaking zones in most weakened part of the mine at Verkhnekamskoe salt deposit is considered. The specific rock deformation rheological model implemented with finite element method was used. Physical and mechanical properties of salts and waterproof covering rocks defined from combination of geomechanical and geophysical methods were applied in geological-geomechanical simulation.
It is still not clear how dangerous weakened zones in waterproof covering and in salt rocks. From the usual point of view, weakened zones in waterproof covering are the reason of mines flooding. However weakened zones in salt rocks cause abrupt increasing of ground subsidence and possible destruction of hard rocks in waterproof covering as a result of higher loading of safety blocks. From the other side, even with low loading degree of safety blocks and solid rocks in salt layers, water-conducting cracks may appear due to weak strength properties of waterproof covering rocks.
