Study On The Size Effect Of Mechanical Properties Of Jointed Rock Mass By Discrete Element Simulation

With the rapid development of the national economy,the construction of a large number of rock engineering projects has greatly promoted the study of the mechanical properties of rock mass.However,due to the natural complex characteristics of rock mass,people can not accurately and effectively predict and then control the mechanical response of rock,resulting in rock engineering disasters are still frequent.Which is of great value to the correct assessment of the mechanical properties of jointed rock mass.The size effect is one of the inherent properties of rock mass,and the correct understanding and mastery of the regularity of rock mass size is the key of rock engineering design and numerical calculation.Based on the numerical simulation of 3DEC software,this paper studies the size effect and its influencing factors of jointed rock mass mechanics,and the main work and achievements are as follows:(1)Based on the uniaxial compression test,the variation law of the strength and deformation parameters of the jointed rock mass and the rock mass size is explored.The results show that the uniaxial compressive strength of the jointed rock mass decreases with the increase of the size of the rock mass,and its size effect rule follows the negative exponential function,while the strength characterization unit size REV is basically 11.5 times the joint spacing(11.5ld).The deformation modulus decreases with the increase of the size of the rock mass,and the law of size effect is obvious,the deformation REV is 9 times of the joint spacing.(2)Based on the triaxial compression test,the variation law of the shear strength parameters of the jointed rock mass and the size of the rock mass are studied.The results show that the cohesion of the jointed rock mass decreases with the increase of the size of the rock mass,and the relationship law of the size effect is negative exponential function,the cohesion REV is 9ld.There is no obvious relationship between the friction angle and the size of the rock mass.(3)Based on the triaxial compression test,the variation law of the size effect of the joint mechanics parameters with the confining pressure is discussed.The effect of confining pressure makes the axial compressive strength of jointed rock mass be improved,the deformation property can be promated and the post-peak ductility is increased.With the increase of the confining pressure,the sensitivity of the size effect of the axial compressive strength of the jointed rock mass increases and the strength REV decreases.The deformation modulus varies little with confining pressure,under all levels of confining pressure,the size effect of deformation properities and deformation REV of jointed rock mass are basically the same.(4)From the aspects of rock material properties,the influence of rock material parameters and joint material parameters on the mechanical properties and size effect of jointed rock mass are discussed.The author believes that the greater the ratio of the "rock mass strength parameter/joint strength parameter",the smaller the proportion of rock in uniaxial compressive strength of jointed rock mass,and the larger the proportion of joint,and the larger the ratio,the greater the sensitivity of the size effect of jointed rock mass,the smaller the intensity REV.And the deformation properties of the joint rock mass have a "short plate effect",which is controlled by the deformation parameters of the joint,the material parameters of rock and joint have little effect on the size effect of deformation of jointed rock mass.(5)From the perspective of geometric properties of rock mass,the influence of joint geometric parameters on the mechanical properties and size effect of jointed rock mass are discussed.The influence of joint geometric parameters on the mechanical properties of jointed rock mass is not absolute.The geometric parameters of the joint directly affect the mechanical properties of jointed rock msas,the influence of joint geometry paramaters on the size effect of intensity property is very prominent,but the geometric paramaters of the joint have little effct on the deformation properties of jointed rock mass.