ABSTRACT

Salt deposits development is always associated with the risk of waterproof stratum failure resulting in hazardous fresh water inflow in mine openings. Due to high solubility of salts this could lead to flooding and collapse of mine as a result of uncontrollable water inflow increase. Process of flooding is usually accompanied by increased subsidence rate and sinkhole formation on earth surface. Estimation of negative consequences of mine flooding is based as a rule on earth surface subsidence surveys and a priori expected evaluations of rocks dissolution. Depending on different assumptions and taking into consideration actual data from geophysical research complex (seismic prospecting, gravity measurements, electrical exploration etc.) the results obtained could differ greatly.

Geomechanical model that describes the process of salt covering rocks failure during accelerated deformations associated with rock dissolution of upper part of salt strata is presented in the paper. The conditions of subsidence transformation into dynamic phase with sinkhole formation on earth surface are considered for the case of First Berezniki Potash mine flooding.

1 INTRODUCTION

The basic feature of salt and potash deposit underground mining is the necessity of water-proofness maintenance of sedimentary unit called waterproof stratum (WPS) which lies between the roof of upper layer extracted and bottom boundary of first (counting upwards) water-bearing horizon. This feature sufficiently complicates deposit exploration and mining, requiring the use of methods that exclude the possibility of water intrusion in mine. If the integrity of WPS is violated fresh or brackish waters erode fractures by dissolving salt rocks which leads to increasing of water inflow and flooding of mine.

Fresh water breakthrough results in intensification of earth surface deformations (Prugger, 1991, Baryakh A. A., Samodelkina N. A., 2017, Shiman, M. I., 1992) up to sinkholes formation of hundreds meters of depth during dynamic phase (Whyatt, J, 2008, Rauche, H, 2000). That of course presents a real danger for buildings and civil engineering infrastructure objects on earth surface (M. Van Den Eeckhaut, 2007, Waltham T, 2011, Gutiérrez F, 2014 and many others).

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