Study on Creep Mechanical Properties of Carbonaceous Slate in Muzhailing Tunnel

Carbonaceous slate is prone to creep failure under high in-situ stress, resulting in large deformation and cracking of tunnel support structure. Taking Muzhailing tunnel of Lanzhou-Chongqing railway as the research object, the creep mechanical properties of surrounding rock of Carboniferous slate tunnel were studied by uniaxial and triaxial creep compression tests, the creep law and aging characteristics of Carboniferous slate were analyzed, and the rheological model reflecting the rheological law of Carboniferous slate was established. The results present that the rock exhibits attenuation creep at lower stress level and isometric creep at a higher stress level. The creep failure of rock is characterized by brittle failure. There are obvious macroscopic fracture surfaces after the specimen is destroyed, and in most cases, it will be broken into blocks. By comparing the fitting curves of Burgers rheological model, rock nonlinear viscoelastic-plastic rheological model and nonlinear rheological model with fractional calculus, it is found that the fitting curves of Burgers rheological model and nonlinear rheological model with fractional calculus are very consistent with the test curves, which can well reflect the rheological law of carbonite. However, the study of nonlinear rheological model with fractional calculus is still in the initial stage, and the physical significance of parameters is not very clear. Therefore, Burgers rheological model can better simulate the uniaxial rheological curve of rock.