Strength Modeling and Experimental Study of Coal Pillar-Artificial Dam Combination after Wetting Cycles

To simulate the impact of the periodic wetting of the groundwater reservoir water level on the mechanical performance of the groundwater reservoir dam, we made a coal pillar-artificial dam assembly with a vertical interface, designed uniaxial compression tests with different number of wetting cycles, and considered two cycles as a gradient to explore the factors that affect assembly strength. We determined the strength model of coal pillar-artificial dam assembly in the groundwater reservoir after cyclic wetting and studied the mass variation induced by cyclic wetting. In addition, we analyzed the trends in the strength and deformation of the groundwater reservoir dam after cyclic wetting, proposed three failure modes, and clarified the internal mechanism for the cyclic wetting of the groundwater reservoir dam. The results demonstrated that with the increase in the number of wetting cycles, the internal water content, hydration reaction, and damage to the specimen were significantly enhanced and became more interrelated. The proposed cyclic wetting strength model of the groundwater reservoir dam can effectively represent the three-stage evolution law of the specimen strength curve. The compaction stage in the stress-strain curve of the cyclic wetting specimen is gradually extended, the straight line segment is shortened, the yield stage is also gradually lengthened, and the yield platform is obvious. The specimen failure patterns can be classified as unilateral columnar splitting, bilateral columnar splitting, and conical failure. The concrete will form ettringite and thaumasite with load-bearing capacity during the wetting process, and subsequently, C–S–H groups to invade the coal pillar.