Monitoring of waterproof pillars at salt deposits

As per the Federal Norms and Regulations on Industrial Safety, salt mine fields are divided into waterproof sites using waterproof pillars. This measure is aimed to prevent mines from flooding by means of waterproofing of mine sites to withstand probable damage of impermeable strata and influx of oversalt water. In operation of a mine with waterproof pillars created, the mined-out part of the mine field can be closed up by constructing brattices in underground rooms and by filling the mined-out voids with mineral brines. Owing to solubility of salts, waterproof pillars get affected by brines and degrade. For this reason, before completion of all operations in a mine, it is required to monitor condition and dimension, as well as physical properties of waterproof pillars that separate the closed-up and operating areas in a mine. The control over condition of waterproof pillars using methods which can cause damage to them (for instance, drilling) is inadmissible; thus, it is reasonable to monitor possible changes in dimension and physical properties of salt rocks in pillars with time with the help of the nondestructive inspection—geophysical exploration. This study aimed to select and justify an NDT procedure for the width and physical properties of waterproof pillars in salt mines. The analysis of applicability of geophysical exploration techniques in geotechnical conditions of salt rock deposits yields that the most promising method in this case is underground seismics. The implemented research with numerical modeling and field studies enabled justification of an underground seismics procedure for the investigation of waterproof pillars. The procedure uses P- and S-waves, and engineering seismology equipment with little modification of attachment of seismic sensors. It is demonstrated that the procedure is serviceable in monitoring time changes in width and in physical properties of waterproof pillars.The authors appreciates participation of Doctor of Engineering Sciences, Professor V. N. Aptukov (VNII Galurgii JSC, Perm State National Research University), Candidate of Engineering Sciences V. A. Voroshilov (VNII Galurgii JSC, Perm State National Research University) in this research.