Shear mechanical properties of rough-walled joints of red sandstone under real-time temperature

The shear mechanical properties of joints under real-time temperature are important factors affecting high geothermal tunnel excavation and deep mining. In order to investigate the shear mechanical properties of red sandstone rough joints under real-time temperature, based on the three-dimensional morphology parameter proposed by Grasselli as the quantitative standard of roughness, we carried out experimental research on the shear mechanics of different rough joints in red sandstone under real-time temperature by using the GDW–50 high and low temperature test chamber and the YZW30–LT2 microcomputer-controlled rock shearer to an-alyze the impact of real-time temperature and roughness on the shear mechanical parameters of red sand-stone joints such as shear curve, abrasion characteristics, peak shear strength, and so on. We analyzed the effects of real-time temperature and roughness on the shear curve, wear characteristics, peak shear strength and other shear mechanical parameters of red sandstone joints. The results show that the growth of peak shear strength with temperature can be divided into two stages: 25–75 ℃ stage, the temperature in-crease leads to the increase of microcracks, resulting in a predominantly thermal cracking effect, and the overall trend of peak shear strength is decreasing; 75–150 ℃ stage, the temperature increase is pre-dominantly thermal expansion, and the effect of thermal expansion is greater than that of thermal cracking, with an overall trend of peak shear strength growth; temperature threshold is 75 ℃, and the coupling of temperature and roughness exacerbates the threshold temperature phenomenon. Smaller roughness leads to the joint surface shear process is dominated by frictional slip, the threshold phenomenon is not significant. Larger roughness causes the joint surface shear to be dominated by shearing behavior through the base of the bulge, and the generation of microcracks makes the bulge shear easier, resulting in a more significant threshold phenomenon. With the simultaneous increase of roughness and temperature, both contribute positively to the peak knuckle surface shear strength. The wear ratio of the nodal surface showed a linear relationship with the increase of temperature and roughness, and the roughness of the nodal surface had a more significant effect on the nodal wear ratio, with the increase of roughness, the maximum increase of the wear ratio amounted to 60.09%; while with the increase of temperature, the increase of the wear ratio was only 20.91%.