Development of a Multi-functional Physical Model Testing System for Deep Coal Petrography Engineering

Physical model testing is an important research tool for coal petrography engineering as it can solve many difficult problems associated with high risks and requiring long time periods to investigate with field studies. However, the accuracy of physical model tests can be reduced by problems with testing equipment, such as small model specimen size, poor airtightness and insufficient stress and pressure loading ability. To study the problems of coal petrography engineering in complicated stress environments, especially those in fluid–solid coupling, we designed and developed a multi-functional physical model testing system. The entire testing system consists of several specific sub-systems: loading, specimen shaping and installation, data monitoring and acquisition, pumping and gas injection, excavation simulating. The testing system can simulate complicated stress environments of coal-rock mass, and it can also be used to study the characteristics of strength-deformation, seepage-rheology and instability-failure under the conditions of gas–solid coupling and gas–liquid–solid multi-phase coupling. A load–unload experiment of air pressure and three-dimensional stress was conducted using the testing system. The experiment verified major technical indicators such as the loading capacity, sealing pressure and test precision, as well as operational stability of the testing system. The strain fields within the model specimen are well distributed and approximately linear with the stress. The stress of the specimen surface is approximately well distributed, and the specimen is subjected to uniform stresses. The testing system meets the requirements of the design parameters and has great potential significance to help reveal the scientific laws and inherent mechanisms of coal petrography engineering.