Investigation of the real contact area of tensile fractures with different normal stresses and sizes by using pressure-sensitive films

Abstract

More than 240 experimental tests were conducted and the characteristics of real contact area of the mated tensile fractures were investigated by using pressure-sensitive films. The effects of normal stress, fracture size as well as rock type on the real contact area of mated tensile fractures were evaluated and discussed. The results show that the real contact area of the mated rock fractures has a parabolic increasing relationship with the normal stress ratio (the ratio of the applied normal stress on the fracture surface to the uniaxial compressive strength of the joint wall). Also, the size of the tensile fracture can affect its real contact area, and the larger the applied normal stress is, the more significant the size effect of the rock fracture on the real contact area is. Furthermore, lithology has a significant influence on the real contact area of the structural plane, which is also related to the applied normal stress. Under the same stress condition, the real contact areas of shale and granite fractures are the smallest, while that of green sandstone fractures is the largest. By analyzing the nominal normal stress and the real normal stress on rock fractures, it was found that even if the nominal normal stress applied on the rock fractures is only 1.5 MPa, the average real normal stresses can reach 20 MPa ∼ 45 MPa, which is about 15–30 times the nominal applied normal stress. The contact characteristics of tensile fractures were analyzed by adopting the cutting methods. It was revealed that within a mated tensile fracture, the smaller the JRC of an area is, the larger the real contact area will be. The results of this study are of great significance for revealing the characteristics and laws of the contact areas of tensile fractures, and the 248 sets of data specimens obtained from the tests can provide important support or reference for establishing mechanical models for rock mass contact.