Experimental study on mechanical properties of the non-equal-size rock-coal composite specimens

The residual coal pillar and roof strata of strip mining in coal mine constitute a joint bearing body, which can be simplified into " T " shaped unequal size rock-coal combination sample in laboratory test. In this paper, the uniaxial compression test of the composite specimen is carried out to explore its mechanical properties. The results show that both sides of the specimen sandstone can share part of the load. As the width ratio h of rock and coal increases, the peak load of the composite increases, but the effect is limited. When h reaches 2.0, the " bending " deformation on both sides of the sandstone is prominent, which aggravates the damage of the combined coal sample and reduces the bearing capacity. The acoustic emission characteristic signal of the rock-coal composite sample can be divided into four stages : calm, fluctuating rise, growth and steep increase. With the increase of h, the acoustic emission signal is more obvious, the failure time of the composite sample is prolonged, and the failure mode of the sample is changed from spalling failure to spalling-ejection mixed failure.