Study On Construction Mechanics Of Asymmetrical Large-span And Small Clear Distance Tunnel

Mountain tunnel is an important infrastructure to improve transportation efficiency,which plays a very important role in China’s transportation industry.In some areas,due to the limited factors such as topography and geology,overall alignment and cost,it is necessary to use tunnels with smaller spacing.Compared with multi arch tunnels,small spacing tunnels have the advantages of simple construction technology,low cost and short construction period.In addition,with the increase of traffic flow,in order to save land and make the line smooth,it is necessary to increase lanes to meet the demand of traffic capacity.Therefore,the tunnel structure with large span and small clear distance is more and more applied to engineering construction.At the same time,in order to meet the design requirements of tunnel and utility tunnel or as bifurcation tunnel and escape tunnel,asymmetric tunnel structure should be adopted.Based on the tunnel construction project of Pingnan Road（Yongkang road Kangxian Road）in Longgang District of Shenzhen City,combined with the static problem of tunnel excavation and the dynamic problem of tunnel blasting vibration,this paper studies the construction mechanics of asymmetric large-span and small clear distance mountain tunnel under the condition of soft surrounding rock.This paper analyzes and summarizes the construction mechanical characteristics and construction technology optimization measures of asymmetric large-span and small spacing tunnel,and discusses the influence of blasting vibration of asymmetric large-span and small spacing tunnel on the lining of advance tunnel.The main research contents and achievements of this paper are as follows.（1）FLAC^3Dsoftware is used for numerical simulation.Combined with the static and dynamic problems of tunnel excavation,the numerical solution is compared with the analytical solution,which verifies the reliability of the numerical simulation method and the established model to simulate tunnel excavation.In addition,the numerical simulation results are compared with the measured data of the engineering case,which shows that the numerical simulation can reflect the actual situation.（2）Aiming at the static problem of tunnel excavation and support,this paper discusses the construction mechanical characteristics and construction technology optimization of asymmetric large-span and small clear distance tunnel under the condition of soft surrounding rock.The construction optimization measures such as the appropriate construction method,the best construction sequence and the reasonable reinforcement method of the middle rock column are obtained;This paper summarizes the interaction between left and right tunnels,the influence of asymmetry degree,and the mechanical characteristics and laws of tunnel construction under different site conditions,so as to provide reference for practical engineering cases.（3）Aiming at the dynamic problem of tunnel blasting vibration,the optimal blasting excavation sequence is proposed according to the asymmetric form;The influence of blasting vibration on the lining of the first tunnel is summarized;Combined with a variety of factors affecting blasting response,the single variable method is used to explore the response law and influence degree of different factors.At the same time,based on the uniform design method,the fitting formula of main influencing factors and response speed of blasting response is obtained,and the vibration velocity is predicted for blasting response,so as to adjust blasting parameters before blasting test and achieve the ideal blasting effect.