Characterization and analysis of optical-electrical-acoustic multi-parameter response of the whole process of loading typical rocks in coal measure formation

The deformation and fracture of rock under loading will cause changes in potential parameter information, and the dynamic capture of parameters can characterize the process of fissure generation, expansion, and closure, which is an important method for rock health evaluation. The article is based on the construction of a multi parameter testing system, which achieves synchronous collection of distributed fiber optic strain, electrode current, and longitudinal wave velocity of rock specimens under uniaxial loading conditions. Furthermore, a strength parameter characteristic relationship graph and parameter tomography imaging results are constructed to finely describe the spatiotemporal evolution characteristics of three typical rock types under full loading with multiple parameters. The experimental results show that there is good consistency between the time pressure curve and the multi parameter response curve. The distributed fiber optic strain with spiral arrangement shows a slow and stable growth during the primary pore compression and linear elasticity stage of the specimen, and a sudden and rapid growth during the crack generation and expansion stage. In this experiment, the distributed fiber optic strain values of sandstone, limestone, and mudstone under imminent fracture were 933×10^-6, 401×10^-6, and 3790×10^-6, respectively; The electrode current changes slightly during the compression and linear elasticity stages of the primary pores, but significantly decreases during the generation and expansion stages of cracks, and rebounds to a certain extent during crack closure; In the primary pore compression, linear elasticity, and rupture stages, the average longitudinal wave velocities of sandstone are 4.38 km/s, 4.39 km/s, and 1.26 km/s, respectively. The average longitudinal wave velocities of limestone are 4.83 km/s, 4.93 km/s, and 3.10 km/s, respectively. The average longitudinal wave velocities of mudstone are 3.65 km/s, 3.57 km/s, and 1.71 km/s. The energy value of the entire process of rock loading was solved, and a damage variable D was constructed to evaluate the degree of damage evolution of rock specimens. The D value of sandstone went through three stages: gradual increase, decrease, and sudden increase. The D value of limestone went through four stages: slow increase, rapid increase, stagnation, and sudden increase. The D value of mudstone went through three stages: slow increase, rapid increase, and sudden increase. Based on the results of distributed fiber optic strain testing, the fracture modes of rock specimens with different rock types were explored, providing assistance for the generation and propagation of cracks under load, as well as the prediction of potential fracture surface positions.