Abstract: To further explore the fracture initiation mechanism of fracture grouting in typical sandy mudstone from Huainan and Huaibei mining areas in China, a conventional triaxial fracture grouting test device was developed, and the model test of fracture initiation pressure of slurry fracturing in similar material of sandy mudstone was carried out. Based on the test results, the influences of rock strength and stress state on grouting fracture initiation pressure and fracture propagation pattern were analyzed, and the fracture initiation mechanism of fracture grouting in sandy mudstone was revealed. The results show that there is a positive correlation between the initiation pressure and the compressive strength of rock; the larger the compressive strength of the rock is, the more complex the fracturing path is. The sensitivity of fracture initiation pressure to confining pressure is much greater than that of axial pressure; the larger the stress difference Δσ =σV −σH is, the more regular the fracture shape is. Under the triaxial condition of pore pressure, the rock tensile strength determined by slurry fracturing method in sealed open hole section is approximately 2.5 times the uniaxial tensile strength. The research results can provide a reference for the design and construction of fracture grouting in similar rock strata in the future.

Key words: sandy mudstone, conventional triaxial test, fracture grouting, fracture initiation pressure, model test