Research and development of testing apparatus of coal solid-gas coupled meso-mechanics

A coal solid-gas coupled meso-mechanical testing apparatus has been developed, which can be used to study the law of deformation and destruction of gas-bearing coal. Some key technical issues, such as sealing method, light transmitting mirror technique, etc., have been further analyzed. The apparatus is comprised of loading system, gas charging system, microscopic observation system and acoustic emission monitoring system. Compared with the current meso-mechanics apparatus, it has the following advantages. Firstly, three types of force state are provided including uniaxial compression, plane strain and triaxial compression (σ2=σ3). Secondly, several measuring methods are offered, and the real-time observation of the micro-structural images and the collection of stress-strain and acoustic emission signals are realized during experimental process. Thirdly, it is gas-tight and exploding endurable, which makes it similar to actual testing environment. Fourthly, the structure is very simple, low-cost and high reliability. The meso-mechanics experiments have been carried out using this apparatus under gas pressure of 1.0 MPa and confining pressure of 1.0 MPa (σ2=σ3). And the apparent images and acoustic emission characteristics in failure process of coal specimens have been obtained. The formation process of tension cracks and their propagation in regional areas before and after failure have been analyzed. It is shown that the testing apparatus can provide a new and practical test method for solid-gas coupled experiments.