Application of geophysical methods for the assessment of the condition of rib pillars between large cross-section rooms in potash mines

After mining-out, large cross-section rooms are backfilled with slurry using hydraulic method, and brines are then removed from the hydraulic fill. During backfilling of large cross-section rooms, salt precipitate develops because of cooling of slurry and NaCl-KCl disbalance. As a result, the hydraulic fill brine can dissolve pillars left between the large cross-section rooms. As a consequence, during backfill of large-cross section rooms, their walls are exposed to leaching and degradation under the impact of brines and because of solubility of salts. For this reason, up to full backfill of large cross-section rooms, it is required to supervise their condition and dimension, as well as the physical properties of pillars separating the large cross-section rooms from the operating rooms in a mine. It is critical to eliminate disintegration of the rib pillars of large cross-section rooms, and, therefore, the use of the methods which can disintegrate them (for instance, drilling) is unacceptable. It is only possible to stick to the nondestructive control of the condition of the rib pillars using geophysical methods. The geophysical methods allow monitoring condition of the pillars fencing the large cross-section rooms. The aim of the research was to develop and substantiate a methodology for determining the actual width and physical properties of the pillars separating large cross-section rooms from other mine openings. The analysis of capabilities of geophysical methods in handling this mining problem in the conditions of a potassium salt deposit, and the authors’ own studies show that the most promising methods for this purpose are ground penetrating radar and seismic survey. The implemented full-scale research trialed and validated the integrated application of GPR and seismic surveying. The article demonstrates the operability and efficiency of the mentioned combination of geophysical methods allowing controlling the thickness of the rib pillars between large cross-section rooms. The features of the seismic survey data processing to suppress reflections from geological levels and to distinguish reflections from the walls of large cross-section rooms are described.