Study On Damage Softening Behavior Of Fractured Surrounding Rock And Interaction Between Surrounding Rock And Support Structure

In the underground engineering rock,non-penetrating fractured rock mass is more common.Due to the weathering and other factors,the stability of the underground rock mass is poor,and the failure mode is different from the general rock engineering.Fractured rock mass has the characteristics of complex mechanical and non-linear characteristics,it is more difficult to construct a nonlinear mechanics model which can accurately describe the evolution of fractures.It is more difficult to describe the post-peak strain softening behavior of fractured rock mass.Due to the role of cracks and structural planes,shallow depth of the surrounding rock generally show a strain softening behavior,and the lack of in-depth understanding of the designer,will lead to safety incidents.The stability of the support structure,the failure mode of the surrounding rock,the interaction behavior of the surrounding rock and the supporting structure and the optimal support time are the important problems in the underground engineering design of the fractured rock mass.All these problems are related to the constitutive model of the surrounding rock The Therefore,it is of great practical significance to construct the strain softening model of surrounding rock under the condition of evolution of fracture.However,this paper,based on the previous research,prepares the built-in three-dimensional fractured rock specimen according to the similar material theory,and makes a study on the fracture and softening behavior of the surrounding rock.Based on the indoor experiment,the FLAC3D numerical software was used to simulate the development of single and multiple fissures and the failure mode,and the number of fissures and the number of fissures were calculated.The results showed that the fracture volume and the softening model were established under the two factors.The fracturing development model is established by using the computer programming language to study the fracture visualization model.The damage softening model of the rock mass under the development of the fissure is established,and the characteristic curve of the supporting structure is calculated.And the influence of the fractured rock mass on the surrounding rock-support interaction is studied.The main beneficial conclusions are as follows;(1)through the preparation of fractured rock mass similar materials and indoor triaxial strength test specimens,the fracture number and confining pressure on the compressive fracture rock peak strength,residual strength and softening characteristic parameters such as the influence law of the fractured rock mass strength reduction factor was established and the crack rate of function relationship;(2)in the finite difference software FLAC3D using Fish language in terms of quadratic programming development,constructing an improved numerical calculating model of fractured rock mass,and realize visualization of the fractured rock mass destruction;(3)based on the theory of damage statistics,constructed the distribution characteristics of rock fracture parameters and the function relation between the damage factor of fracture rock,based on the Mohr-Coulomb(hereinafter referred to as the M-C)and Drucker Prager(hereinafter referred to as D-P)yield criterion,established the mathematical model of the fractured rock mass damage and strain softening;(4)through the calculation and analysis of the displacement and stress of the surrounding rock of the tunnel fracture,the displacement and stress development of the fractured surrounding rock during the excavation of the tunnel are obtained.(5)the fine 3 d numerical model is established in the FLAC3,the cable element simulation anchor structure of the tunnel in the fracture of surrounding rock type binder bolt axial force response law of tunnel in the fracture of surrounding rock is given binding type anchor mechanics characteristics specific change rule;(6)the theory of convergence constraint,and the fracture stress state of surrounding rock in the process of tunnel excavation supporting development change rule of calculation and analysis,the fractured surrounding rock stress state,the development situation of crack calculation model,the change of the surrounding rock stress and surrounding rock,after the peak strain softening coefficient relationship was not significant,but with the surrounding rock pressure,lateral pressure coefficient changes occur more obvious change;(7)to big reed ditch tunnel project as an example for numerical calculation,get in the process of the excavation support-support interaction characteristic curve and displacement of surrounding rock characteristic curve,contrast damage strain softening model and ideal elastic-plastic model calculation results,and compared with the field measured data analysis,for the corresponding tunnel fracture of surrounding rock deformation and safety analysis provides a reference.