Experimental Study On Creep Mechanical Properties Of Water Rich Carbonaceous Slate

Slate is formed by the shallow regional metamorphism of argillaceous rocks.Because of the complex stress history,the mineral composition and structure of the slate have complicated changes on microcosmic,and in macroscopic view,there are obvious inhomogeneity and anisotropy of flow twisting folds,flow cleavage and cleavage.With the development of tunnel engineering in the high altitude area of Western China,carbonaceous slate is a common rock mass in deep buried tunnel construction.The creep effect of deep water carbonaceous slate has become a difficult problem in tunnel construction in this kind of area,which is accompanied by many factors such as high ground stress,weak breakage of surrounding rock and underground water.Many domestic and foreign scholars have done a lot of research on the creeping of carbonaceous slate,and many valuable research results have been obtained.However,the creep mechanical properties of deep water rich carbonaceous slates are still worth studying and discussing because of the different environment of the tunnel surrounding rock.On the basis of previous studies,we collected samples in the mileage of large deformation during the initial support of the water rich carbonaceous slate tunnel.At the same time,the composition,microstructure,instantaneous mechanical properties and creep mechanical properties of carbonaceous slate were studied by electron microscopy,X diffraction,instantaneous mechanical test and uniaxial loading and unloading creep test.?1?Deep water rich carbonaceous slate is mainly composed of quartz?SiO₂?,muscovite?KAl2[AlSi3O10]?OH?2?,sodium feldspar?Na[AlSi3O8]?and a small amount of graphite?C?.Among them,there are microscopic pores formed by weathering of sediment in the single crystal of muscovite.The lubrication of water,the action of water wedge and the latent erosion result in the destruction of the mineral structure,the increase of the pore gap and the crack,which makes the rock macroscopic show that the uniaxial compression strength and the modulus of elasticity decrease,while the Poisson's ratio and the peak strain increase slightly.?2?Because of the rich water,the creep and creep rate of deep carbonaceous slates increase,especially for the increase of transient plastic strain and viscoelastic strain.At the same time,it can be seen from the strain axis of the constant strain rate curve that the deterioration of the water damage makes the creep of the rock nonlinear deformation and significantly reduces the long-term strength of the rock.Because of the anisotropy of rock,the above phenomenon is more obvious in axial aspect than in lateral aspect.?3?With the increase of the stress level,the deformation ability of deep water rich carbonaceous slate increases gradually,and the instantaneous deformation modulus increases gradually,and the creep deformation and the rate increase because of the mineral pore gap and the closure of the crack.In addition,there is a creep stress threshold value of?_k.When the stress reaches to?_k,creep deceleration creep and stable creep stage appear.At the same time,the lateral creep stress threshold is smaller than the axial creep stress threshold.?4?Based on the test results,the modified Xiyuan model considering moisture content and transient plastic strain is established by determining moisture content.Using the custom function of Origin software to fit the test data,the parameters of the model are determined,and the fitting degree is better.It can describe the law of the moisture content to the creep deformation reasonably.