Experimental Study on Uniaxial Compression Failure Characteristics and Mechanical Properties of Composite Aquiclude Rock

Composite aquiclude rock is an important part of the water barrier layer of coal seam floor, and its mechanical properties and failure characteristics have an important impact on the safety of coal seam mining. In order to explore the uniaxial compression failure characteristics and mechanical properties of composite aquiclude rocks, the mineral composition and microstructure of the composite cement rock were measured by XRD and SEM. Using a WAW-1000D electrohydraulic servo universal test system, uniaxial compression tests were carried out on samples of four structural types, namely, mudstone/siltstone, mudstone/fine sandstone, fine sandstone/siltstone, and siltstone/mudstone/fine sandstone composites soaked in saline water with various immersion periods and pH values. The experimental results show that the failure of composite rock samples was mainly concentrated in the mudstone part. With the increased proportion of soft rock in the structure, the rock samples exhibited changes in tensile, X-shaped conjugate inclined plane shear, and single inclined plane shear failure modes. The overall compressive strength of composite rock samples decreased with immersion time, and their failure mode shifted from shear to tensile with increasing immersion time. The strength-weakening effect of high-salinity water with different acidity and alkalinity on composite rock samples was significant. The increased pH promoted the tensile failure-shear failure-tensile failure evolution. The results of this study can provide important experimental data and theoretical basis for the stability control of composite aquiclude rock in coal mining.