Experimental and numerical investigation on the short- and long-term mechanical properties of mylonite before and after grouting reinforcement

Accurate determination of physical and mechanical properties of rock mass is essential for stability evaluation and structural design. To evaluate the stability of bridge foundation buried in the mylonite, a series of laboratory experiments about the short- and long-term properties were studied, and the grouting effect by the mixture of cement slurry and rock was also discussed. Then, numerical analysis was carried out to discuss the factors affecting the stability of the bridge foundation. Results show that the strength and deformation modulus are 0.32 MPa and 26.65 MPa for the natural rock cores. From the results of triaxial compression tests of the reconstituted specimens, the increasing of confining stress can strengthen the rock mass, leading to the improvement of strength and deformation modulus. The deformation of specimens under step loads includes instantaneous strain, visco-elastic deformation, and steady-state creep stage. A further increment of stress may result in ductile failure. In addition, the grouting samples with different filling ratios of cement slurry were studied, indicating that affected by the property of cement slurry, the strength increases linearly with the filling ratio, and the deformation modulus increases exponentially with that. The strength was significantly improved than natural rock core. Besides, the effect of grouting on the stability of bridge foundation was also investigated by FEM, which indicated that less deformation of cushion cap and piles was observed. Therefore, it reveals the effectiveness of the method to guarantee the safe construction of the bridge pier.