Experimental Investigation of the Effect of Evenly Distributed Pore Pressure on Rock Damage

AbstractThe effect of pore pressure on rock damage is a core problem in underground engineering. In this paper, the pseudotriaxial hydromechanical coupling experiment system is utilized to carry out the physical model experiment of the pore pressure on the rock damage, and the effect of evenly distributed pore pressure on rock strength and pore structure is analyzed. Compared with natural rock sample before the pore pressure effect, the uniaxial compressive strength is reduced by about 35.24%. Pore pressure decreases the strength of the rock and reduces its ability to resist deformation. The stress growth rate at the prepeak stage of the stress-strain curve for rock sample after pore pressure effect decreases. The peak strength decreases, and the strain corresponding to the peak stress increases. The plastic deformation characteristics of the sample are obvious. After the sample has macroscopically broken, the decline rate of postpeak stress slows down, and the residual strength decreases. The rock gradually changes from brittle failure mode to ductile failure mode. Through scanning electron microscopy (SEM) test and comparison analysis, it is found that after the pore pressure effect, the surface of the rock sample becomes rougher. There are multiple pore and fissure concentrated areas in the rock sample. Compared with the sample before the pore pressure effect, the number of pores with an equivalent diameter in the range of 2 μm-3 μm increases significantly. The proportion has increased from 7.7% to 19.1%, and the number has increased from 1468 to 4454. A large number of small-sized pores (less than 3 μm) are generated in the rock sample after the pore pressure effect. Therefore, the overall pore content of the rock sample increases.