Experimental study of seepage characteristics before and after grouting and mechanical characteristics after grouting of fractured sandstone

This study aims to explore the seepage characteristics of fractured sandstone before and after grouting and the change rule of mechanical properties after grouting. Firstly, Rock Top multi-field coupling tester was used to conduct triaxial compression test on sandstone under different confining pressures at a constant rate of 0.02 mm/min to obtain fractured sandstone and conduct seepage test. Then, the self-developed grouting reinforcement system was used to reinforce the fractured sandstone, and the Rock Top multi-field coupling tester was used to conduct the triaxial compression seepage test on the fractured sandstone under different confining pressures. The results show that: (1) The permeability of fractured sandstone decreases significantly after grouting compared with that before grouting, with a decrease range of 24.26%-96.55%, but it is greater than the original rock permeability. (2) The permeability of fractured sandstone before and after grouting shows different periodic changes with the increase of hydrostatic pressure. When hydrostatic pressure reaches 40 MPa or above, the permeability difference within 5 MPa has a little effect on permeability, and the permeability curve tends to be horizontal. (3) After grouting, the fractured sandstone only exhibits brittle failure characteristics similar to the original rock only under 10 MPa confining pressure, but loses the brittle failure characteristics of the original rock under 20-60 MPa confining pressure, showing strong ductility failure and plastic flow phenomenon after the peak. (4) The peak strength and strain of the fractured sandstone after grouting both increase with the increase of confining pressure and show nonlinear variation characteristics satisfying the quadratic function relation. The peak strength ranges from 44% to 59% of the peak strength of the original rock. (5) The failure mode of fractured sandstone after grouting is mainly slip-shear failure, and new failure modes will appear under low confining pressure. With the increase of confining pressure, the failure effect weakens. (6) Scanning electron microscopy test on rock-slurry interface shows that ettringite and C-S-H (calcium silicate hydrate) gel are bonded to form stable hydration products, thus improving the bearing capacity of rock.