Rheological And Mechanical Properties Of Carbonaceous Slate Under High In-situ Stress And Large Deformation Control Of Chamber Surrounding Rock

With the development of infrastructure construction,highways and railways are continously developing to the western mountainous areas.Large deformation of tunnel surrounding rocks,a quite common problem especially in mountain tunnels at high altitudes,is a complex mechanical behavior related to factors such as rock lithology,Geological Occurrence Conditions and in-situ stress conditions.Complex underground environment makes research difficult,and it is still of great significance to the study on the mechanical law of large deformation of surrounding rock and its supporting measures at present.Based on the large deformation of surrounding rock of Chang Ping Tunnel of Li Xiang Railway,in this paper the physical mechanics test and loading-unloading rheological mechanical test under high confining pressure are conducted,and the creep model of hardening damage adapted to creep characteristics of carbonaceous slate is constructed.The secondary development of creep model is carried out based on FLAC3 D.Combined with the monitoring results of large deformation disposal test of surrounding rock of Chang Ping Tunnel,the optimization of support scheme and numerical analysis of long-term stability of surrounding rock are presented,and the main research work of this paper is as follows:(1)Five different confining pressures(0mpa,10 MPa,20MPa,30 MPa and40MPa)were set up to test the triaxial compressive strength of dry and saturated carbonaceous slate samples,analyzing the stress-strain curve characteristics of the samples,the effects of water saturation and confining pressure conditions on the mechanical parameters of the samples,such as modulus of elasticity,Poisson's ratio,friction angle and cohesion.Brazilian splitting test was carried out on dry and saturated carbonaceous slate samples to obtain the tensile strength of dry and saturated samples.The cyclic loading and unloading tests under uniaxial and 40 MPa confining pressure were carried out on the saturated samples of carbonaceous slate to obtain the change rules of elastic modulus and plastic strain under different stress levels.(2)Three different confining pressures(0mpa,20 MPa and 40MPa)were set totest the rheological behavior of carbonaceous slate saturated samples,analyzing the creep and creep rate development of specimens under different stress levels.The strain separation of loading and unloading rheological curves is carried out,and the change rules of elastic-plastic strain and viscoelastic plastic strain of the samples under different stress levels are analyzed.Furthermore,the corresponding nonlinear hardening damage creep model is established based on the isochronous stress-strain curve.Based on the constitutive equation of creep model,the one-dimensional creep equation is derived,and the three-dimensional creep equation is further derived by introducing the yield function.The applicability of creep model is verified by identifying creep model parameters through origin,and the influence of different parameters on the creep,creep rate and accelerated creep of the model is further analyzed.(3)Based on the creep model established by rheological test,the corresponding nonlinear hardening damage creep model HDCVISC is built on basis of the CVISC model in FLAC3 D.The three-dimensional creep difference equations under different stress states are derived by setting the triple stress surface to establish the relationship between the lower limit of creep,long-term strength and strength.Under the development environment of Visual Studio 2010 C++,the secondary development of HDCVISC model is redeveloped,and the triaxial compression creep numerical simulation test is carried out by using hdcvisc model.The effectiveness of the secondary development of hdcvisc model is verified by comparing the indoor test creep curve and simulation creep curve.At the same time,the response effect of HDCVISC model on damage variable and elastoplastic state is further analyzed.(4)In view of the large deformation of surrounding rock and the damage of supporting structure in the field construction of Chang Ping tunnel,this paper analyzes the causes of the large deformation of surrounding rock,and monitors the displacement of surrounding rock and the stress of supporting structure in the large deformation test section of inclined shaft working area of Chang Ping tunnel.At the same time,it uses the invented pore water pressure device to monitor the lining water pressure,and analyzes the effect of large deformation support scheme on surroundingrock displacement control.Combined with the monitoring results,the pressure distribution of surrounding rock and the stress characteristics of support structure in the large deformation test section are analyzed,and the corresponding design and construction improvement measures are proposed.(5)The conduct of the chloride corrosion test on tunnel lining concrete is to obtain the changing rule of concrete compressive strength and corrosion time,to build a CEMC model which can reflect the corrosion time of concrete,to redevelop the CEMC model in FLAC3 D.According to the supporting project,the numerical model of Chang Ping tunnel is established.The shortcomings of the original support scheme and the large deformation support scheme are analyzed by numerical simulation.The control effect of SFRC lining material and section parameter optimization on the surrounding rock displacement is simulated and analyzed.The CEMC model is used to simulate and analyze the long-term stability of the tunnel support structure.The erosion effect of SFRC and the seepage effect of groundwater on the safety of the support structure and the long-term stability of the surrounding rock are analyzed.