DISCRETE-CONTINUOUS COUPLED METHOD FOR STABILITY ANALYSIS OF TUNNEL SURROUNDING ROCK

The discrete element method (DEM) is especially suitable for discrete materials such as soil or rock because of its excellent accuracy, and the finite difference method (FDM) is often applied to the analysis of geotechnical engineering because of its high computational efficiency. The discrete-continuous coupled method integrates the advantages of FDM and DEM and has been applied in the stability analysis of tunnel surrounding rock. However, the calibration of macroscopic and microscopic parameters of tunnel surrounding rock in this new numerical method has not been systematically studied. Meanwhile, the method for determining the discrete domain range in the coupled model of tunnel has not been fully addressed. Both issues require rigorous examination to establish a standardized method for the discrete-continuous coupled numerical model of tunnels. Therefore, the calibration method and size effect of rock mechanics parameters were first studied through direct shear tests and uniaxial compression tests using DEM. Subsequently, a discrete-continuous coupled model of tunnel was established, and the accuracy of the model was verified through comparative validation. Finally, the method for determining the optimal range of the discrete domain in the coupled model for tunnel was discussed. The results indicate that there is no direct correspondence between the macro and micro parameters of the surrounding rock, and they need to be calibrated through mechanical tests such as direct shear and compression tests that consider size effects. The criteria for stress continuity and displacement continuity were proposed, which can be used to prove the accuracy of the coupled model for tunnel. As the discrete domain expands, the displacement gradually decreases due to the reduction of boundary effects and converges to the correct value. However, the number of particles and relative computation time gradually increase, resulting in a decrement in computational efficiency. Considering the accuracy and efficiency of the calculation, it is recommended that the optimal discrete domain be 4R × 4R.