Study on Similar Material Ratio and Mechanical Properties of Surrounding Rock in Underground Coal Gasification

To provide a reference for the model tests of UCG, river sand was used as the aggregate, cement and gypsum was used as the cementing agent according to the similarity principle, and a combination of comprehensive test and orthogonal test was applied to obtain the suitable ratio of similar materials for the surrounding rock. The mechanical properties and damage variation law during uniaxial compression are studied and analyzed. The results showed that the compressive strength of similar materials with different proportions is between 0.71 MPa and 2.1 MPa, which provides a reference for the selection of similar materials for surrounding rock of UCG. There are four groups of similar proportions of similar specimens, which meet the theoretical requirements and can be used in model tests. The compressive strength decreases with the increase of sand binder ratio, and with the increase of cement gypsum ratio, the compressive strength of the specimens first increases and then decreases. The failure modes of specimens are mainly shear failure and splitting. The main stages of damage increase of similar specimens under uniaxial compression can be divided into three categories, namely, the stage before peak stress, the stage after peak stress and the stage before and after peak stress.