Morphological Features of Fractures Developed by Direct Shearing of Intact Granites after Water Cooling Cycles

Abstract

Rock fractures are considered as favorable objects for enhanced geothermal development. The fracture morphologies play an important role in enhanced geothermal development. Therefore, the study of fracture morphologies has a certain guiding significance for the geothermal reservoir. Water cooling and water cooling cycles can change the morphology of fracture surfaces formed by the shear failure of intact granites. To date, however, there is little work on the effect of water cooling and water cooling cycles on the morphology of fracture surfaces formed by direct shearing of intact granites. In this study, the direct shear tests of intact granites treated by water cooling cycles at different temperatures were conducted, and the variations in the laws of shear strength of intact granites and morphologies of fracture surfaces with temperature or cycle times were analyzed. Test results showed that the shear strength and shear stiffness of intact granites decreased nonlinearly with the increase of temperature or cycle times, but the height and apparent dip angle of asperities on the fracture surface increased with the increase of temperature or cycle times, and the overall uniformity of the fracture surface was improved. The height distribution frequency of asperities on fracture surfaces can be divided into four types: right-biased peak type, left-biased peak type, left-biased middle peak, and left-biased flat peak. The asperities on the fracture surface formed by the shearing of intact granites have asymmetric characteristics. The maximum apparent dip angle and average apparent dip angle in the reverse shear direction are larger than those in the shear direction, and the initial contact area ratio between the shear direction and reverse shear direction is in the range of fluctuation between 1.4 and 2.