Study On Statistical Damage Constitutive Model Of Deep Clay Rock In Tamusu

As a pre-selected surrounding rock for the high-level radioactive waste repository,the study of the mechanical properties and constitutive model of clay rock is of great significance.In this paper,the Tamusu deep clay rock is taken as the research object.Firstly,through macroscopic and microscopic tests such as point load tensile deformation test,uniaxial compressive deformation test,compressive deformation test with different confining pressures and microscopic deformation three dimensional CT scan test,the mechanical strength characteristics and damage characteristics of Tamusu deep clay rock are studied,and a modified nonlinear Mohr-Coulomb strength criterion is proposed to evaluate the strength of clay rock.Secondly,based on the revised criterion,a statistical damage constitutive model for Tamusu deep clay rock is established and the damage evolution law of clay rock is analyzed.In addition,a new brittleness evaluation method based on the statistical damage constitutive model is established to evaluate the brittleness characteristics of clay rock.The main research results have several aspects:(1)Macroscopic and microscopic tests were carried out on Tamusu deep clay rock,The results show that both the axial tensile and compressive strength of Tamusu clay rock are greater than the radial,and within a depth range of 200 to 800 m,the anisotropy index of clay rock is 2.57 to 1.34.As depth increases,the anisotropic characteristic of clay rock weaken;At a depth of 500 m,the uniaxial compressive strength of Tamusu clay rock is about 38.20 MPa.With the increase of confining pressure,the strength and deformation modulus of clay rock increase,the plastic deformation is more significant and the rate of post-peak stress drop is reduced,which shows a transition from brittle failure under uniaxial and low confining pressure to ductile failure under high confining pressure.After damage,the total number of internal pores increases and the proportion of large pore volume increases and becomes dominant.(2)A modified nonlinear Mohr-Coulomb strength criterion is proposed to evaluate the strength of Tamusu deep clay rock.The results show that the relationship between the internal friction angle and the confining pressure satisfies exponential function,which can reflect the nonlinear characteristics of rock strength.The modified nonlinear Mohr-Coulomb strength criterion based on the relationship has good nonlinear ability and applicability,and can accurately reflect the relationship between the strength and confining pressure of clay rock.(3)A statistical damage constitutive model for Tamusu deep clay rock was established.The results show that the statistical damage constitutive model for clay rock with consideration of damage threshold based on the modified nonlinear Mohr-Coulomb strength criterion can better simulate full triaxial compression stress-strain curves of Tamusu deep clay rock;During triaxial compression,the Tamusu deep clay rock is linear elastic at the initial stage of loading,and the damage variable is always 0.With the increase of axial stress,the clay rock starts from crack initiation to complete failure,the damage evolution rate first increases and then decreases,and the larger the confining pressure,the smaller the damage rate.Finally,the damage variable tends to 1.(4)A new brittleness evaluation method based on the statistical damage constitutive model is established to evaluate the brittleness characteristics of clay rock.The results show that the brittleness index has good applicability and can effectively and reasonably characterize the brittleness characteristics of rock;With the increase of confining pressure,the brittleness index of Tamusu deep clay rock decreases.This is because the existence of confining pressure inhibits the development of damage and the greater the confining pressure,the weaker the brittleness and the stronger the plasticity.