Effects Of Pre-stress On Cutting Loads And The Instability Of Excavation Interface Of Stratified Rock

The formation stress (pre-stress) of the rock has significant effects on the operating efficiency and security of underground engineering. The stability problem of the excavation face on the layered rocks is abstracted to the interfaces stability problem of the compressible transversely isotropic elastic half-space which is subjected to an impulsive line of traction on its otherwise free surface. Equations associated with infinitesimal time-dependent motion and the boundary conditions are listed with the fourth order elasticity tensors which are also deducted in detail. The connection between the material parameters frequently used in rock engineering and the parameters used in the specific strain energy function(by adding new invariant into Ogden's function)which is appropriate for the compressible transversely isotropic layered rocks, is set up according to the congruent relationship between the flexibility matrix and the fourth order elasticity tensors. The stability of the interface under impulse load is analyzed by calculating the speed of Rayleigh surface wave. Afterwards the critical stretch at which the surface wave speed vanishes is calculated in different materials directions using specific material parameters. And the most unstable material direction is pointed out. Finally, a 3-D FEM model is established to simulate the cutting process, with the failure effect of the rock. By using this model, a series of numerical simulations are performed with different formation stress. Based on the numerical simulation results, via modifying Evans formula, an improved formula is given containing the influence of formation stress.