Impact of corrosion of cast iron tubing on residual strength of mine shaft lining

Vertical shafts in all mines are the main accesses to mineral bodies and the most critical structures to connect the ground and underground infrastructures into a unified system. Lining of vertical shafts is an essential element that ensures strength and safety of the mine structure. One of the most common types of lining in vertical shafts is the cast iron tubing capable to provide high strength, waterproofness and endurance. Nonetheless, in vertical shafts in potash mines, favorable conditions form for intense corrosion processes. Highly mineralized brines of sodium and potassium chlorides, high content of salt dust, and increased temperature and moisture boost corrosion development. As a result, the signs of spongiosis or spongious corrosion appear on the surface of cast iron liners. For this reason, longterm operation of mine shafts results in significant alteration of physical condition of cast iron in the liners. The decrease in the nominal wall thickness and length of a cast iron liner because of the chemical corrosion affects the strength, damp proofness and load-bearing capacity of the shaft lining. Later on, this can lead to the loss of operational efficiency of the tubing support. The authors estimate the corrosion wear of the cast iron tubing components in shafts in salt mines and determine the actual residual wall thickness and length of the cast iron liners by instrumental measurements. The mathematical model is presented for determining the stress–strain behavior of a tubing support in the tubing—concrete lining–rock mass system at different deviations of the tubing geometrics from the nominal values. Prediction of a corrosion process in time is made together with the estimate of the load-bearing capacity of tubing.