Uralkali PJSC, Berezniki, Russia

V. S. Bespalov, Leading Engineer, Bespalov.VS@yandex.ru

The main factors affecting stability of interburdens at the Upper Kama Salt Deposit can be divided into geological and geotechnical influences. The geological influences are the structure and physical and mechanical properties of rocks, the depth of mining, and the thickness of beds and interbeds. The geotechnical influences are the stope width, the size of pillars and the presence or absence of backfill. At some deposits, one of the stability factors for overlying rock mass is folding. Historical data make it possible to analyze folding as the factor of failure in interburden layers at the Upper Kama deposit. One of the problems of mining operations at the Upper Kama Salt Deposit is instability of interburden crown since its failure leads to the transformation of rib pillars and, as acons equence, to the decrease of their load-bearing capacity. The influence of folding on the stability of interburdens in sylvinite strata is investigated. The factual observations prove that the lower layers of interburden and sylvinite left in its roof are unstable. On the available geological sections, the size of cut-in was determined for the most stable layers depending on the height of folds. The maximal cut-in sizes are in the anticlines. The known cases of local and blanket failures of interburdens were analyzed. The comparison with the actual condition of the mined-out space shows that anticlines up to 3 m high can cause local failure of interburden layers, and folding spread to 10 m can initiate premature blanket failure of interburdens. It is found that the lag of backfilling with respect to the interburden stability criterion in the actual procedure of determination of mining process parameters neglects sites where failure happens because of folding of interburdens.

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