Micromechanical mechanisms of grouting reinforcement in rock joints and microstructure optimization of grout-rock bonding interfaces

The microstructure and its mechanical properties of grout-rock bonding interfaces fundamentally control the macroscopic deformation and failure behaviors of grouted rock joints. In this paper, a series of macroscopic direct shear tests, microscopic SEM scanning tests and nano-indentation tests were carried out on grouted jointed sandstone specimens. The macroscopic shear mechanical strength parameters, shear failure modes, microstructure characteristics of grout-rock bonding interfaces and micromechanical properties of the interfacial transition zone of the specimens were obtained, and the modification and optimization mechanisms of grout-rock bonding interfaces by using new grouting materials such as ultrafine cement and nano-SiO2 were discussed to overcome the microdefects in grout-rock bonding interfaces resulting from the ordinary Portland cement grout. The results show that the grout-rock interface at the microscale is characterized by high porosity and low strength interfacial transition zone with a certain thickness(about 10-30 μm). The interfacial transition zone is the weakest link in the composite structure of grouted rock joints, and there is a positive linear correlation between the microscopic indentation modulus and microscopic indentation hardness with the macroscopic cohesive force of grouted rock joints. The new grouting materials of ultrafine cement and nano-SiO2 can optimize the microstructure of grout-rock bonding interfaces, reduce the thickness of the interfacial transition zone, thereby improve the micromechanical properties of the interfacial transition zone and the macroscopic cohesive force of the grouted joints, but have little influence on the internal friction angle of the grouted joints. © 2020, Science Press. All right reserved.