Justification of Secondary Mining of Potassium Reserves
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__________________________ MINERAL MINING ________________________________ TECHNOLOGY
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Justification of Secondary Mining of Potassium Reserves A. A. Baryakha*, N. L. Bel’tyukova, N. A. Samodelkinaa, and V. N. Toksarova a
Mining Institute, Ural Branch, Russian Academy of Sciences, Perm, 614007 Russia *e-mail: [email protected] Received April 14, 2020 Revised April 20, 2020 Accepted May 29, 2020
Abstract—The article discusses feasibility of secondary mining of natural–manmade sylvinite seam KrII* in the Upper Kama Potassium Salt Field. The full scale tests of large samples were carried out to determine mechanical properties of seam KrII*. Mathematical modeling provides estimates of load exerted on nonuniform safety pillars after secondary mining. The authors propose alternative flow charts for the secondary mining of natural–manmade seam KrII* to ensure safety and reasonable efficiency of production. Keywords: Safety pillars, stopes, natural–manmade seam, secondary mining, full scale testing, loading rate, mathematical modeling. DOI: 10.1134/S1062739120036690
INTRODUCTION
In the world practice, secondary mining is performed mainly at ore deposits as complete or partial extraction of ore reserves from safety pillars of primary room-and-pillar [1–3]. Such technology, or two-stage mining, can be applied in potassium salt deposits, in particular, in Russia’s largest Upper Kama potash deposit [4–8]. Salt mining requires safety of waterproof strata to be preserved to separate mined-out voids and aquifers. At the first stage of mining, wide and “tough” safety pillars are established. Then, after backfilling, ore reserves are partly extracted from these safety pillars. However, the room-and-pillar system with two-stage mining has not been widely used in potassium deposits. The reasons are both economy and technology: minimized time lag between the backfilling and stoping operations, poor condition of development headings after the first mining stage, etc. [4]. Extraction ratio was enhanced in some sites of the Upper Kama deposit through the use of “yielding” safety pillars (Fig. 1). The pillars in this case had the life tie not longer than 1.5–2.0 years [9] and lost their stability afterwards completely. Smooth subsidence of waterproof strata without breaking its integrity was maintained by adjusted advance rate of the stoping front. Experimental access to earlier mined-out area with “yielding” pillars in Berezniki Mine 2 showed partial and complete filling of stopes in the seams AB and KrII due to deformation of the yielding pillars and filling of the stopes with enclosing rocks. It can be assumed that a continuous thin natural– manmade layer with transient mechanical properties is formed (Fig. 2). This secondary natural– manmade seam KrII* with sufficient thickness and strength
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