Study On Mechanical Characteristics Of The System Of Support And Surrounding Rock

In recent years,subway,high-speed railway,highway and other transportation infrastructures have entered a large-scale construction period in our country.As an important carrier of traffic engineering,the sharply increasing of the number of tunnel engineering and the merging of technical issues in tunnel construction have led that the construction theory of tunnel engineering has obviously lagged behind the engineering practice.The cognition depth of the mechanical characteristics of the system of support and surrounding rock interaction directly determines the scientificity,safety and economy of the design and construction in tunnel engineering.Therefore,to clarify the mechanical evolution process and main characteristics of the system of support and surrounding rock,a series of in-depth studies based on three prolems,which are the time-space effect of surrounding rock deformation caused by excavation disturbance,the three-dimensional analysis method of the mechanical response of surrounding rock and the mechanical mechanism of support system-surrounding rock interaction,will be conducted with the methods of statistical analysis,numerical simulation,theoretical analysis and laboratory test in this paper.Furthermore,a new method of determining the stiffness of supporting structures in tunnel engineering is proposed.The main research results are as follows.(1)The excavation disturbance effect is the fundamental driving force of the mechanical evolution of the system of supporting structures and surrounding rock.The four-stage law of surrounding rock,which is accelerated deformation,rapid deformation,slow deformation and deformation stability respectively,is universal regardless of the strata structure charcteristics and the phusical and mechanical parameters of surrounding rock.In addition,the evolution of the surrounding rock deformation has significant self-similarity,which is determined by the periodic characteristics of the superposition of tunneling effect.The deformation at the crown is the key index evaluating the safety of surrounding rock,and the calculation foumula adapting to predict the deformation at the crown is fitted according to the surrounding rock deformation results under the condition that the lateral pressure coefficient is equal to 1.(2)Providing that the strata is considered as semi-infinite or infinite elastic body,three-dimensional mechanical models of the mechanical response of surrounding rock for deep and shallow buried circular tunnels are established respectively through simulating the excavation effect using equivalent stress.Based on Mindlin's solutions and Kelvin's solutions,the integral formula of deformation and stress are derived.Then the corresponding calculation programes were compiled on the basis of Mathematica and the effect of the face stress release and the wall stress release on the deformation was analyzed.At last,through the comparative analysis with the numerical simulation results,the rationality of mechanical models and the accuracy of analytical method are proved.(3)The general and special concept of tunnel support system has been proposed.And the support effects of various supporting structures and their roles in the process of mechanical evolution of tunnel construction are clarified.The initial support is the main structure bearing the surrounding rock load.The composite support with high-strength reinforcing lattice girders embedded in concrete is characterized as high-strength and large-deformation because of the application of high-strength bar,so it is able to satisfy the supporting demand of special geology and soft rock.Under the combined disturbance effect and intervention effect,the evolution of surrounding rock deformation still shows four-stage law.(4)Based on the study of the evolution law of surrounding rock deformation and the mechanical mechanism of the support-surrounding rock interaction,combined with the statistical analysis of a large number of monitoring datas of deformation and stress,the basic characteristics of the mechanical evolusion process of support-surrounding rock interaction are summarized.Following the principles of consistency,universality and typicality,three key nodes including the tunnel face,the construction position of preliminary support and the construction position of secondary support are determined and then the whole process of support-surrounding rock interaction is divided into four stages.Subsequently,the action characteristic,key question and key point of each stage are summarized according to the existing results.(5)Based on the basic characteristics and three-dimensional mechanical model of support-surrounding rock interaction,a new method of tunnel support design is constructed in term of support demand of surrounding rock.And after the quantitative index of rigidity demand of surrounding rock is obtained by the new method,the design scheme can be improved through the feedback analysis of monitoring data.To make it easier to apply in practical engineering,a quick design sheet of tunnel support including important parameters in each analytical step is construnted.In future,the accuracy of the stiffness value of supporting structure will be improved with the progress of theoretical research and computing technology because of its convenience and open.