Mechanical Behavior In Neighborhood Tunnel Based On Displacement Back Analysis

The expanding of city construction and the continuous rising of the people’s living standard have raised higher requirements for transportation.Because of the complicated topographic and geologic condition,the traditional separated tunnel already can’t satisfy people’s growing traffic demand.Neighborhood tunnel arrangement has been widely used in mountainous Southwest China.However,the middle rock thickness of neighborhood tunnel is far less than the separated one,the stress fields of two tunnel overlap each other which combined into a complicated stress and deformation distribution in middle rock.In addition,poor geological conditions such as shallow buried,high slope are encountered during the excavation process,is easy to cause the collapse,roof caving and surface subsidence.Therefore,geological investigation should be done before design and construction.Choosing a reasonable construction method and Supporting system means a safer construction and more efficient excavation for unsymmetrical loading neighborhood tunnel.This paper is based on Dashiling tunnel of Jiangluo expressway in Guangdong province.The formula of rock pressure in unsymmetrical loading neighborhood tunnel is given by theoretical analysis and a combined method of numerical simulation and field measurement is used to optimize the excavation procedure.The following research results are obtained:(1)According to the code for design of road tunnel and forerunners’ relevant theories and methods on surrounding rock pressure,the formula of rock pressure and lining internal force in unsymmetrical loading neighborhood tunnel is derived.The calculation and analysis are carried out according to the engineering example.The results show that with the increase of buried depth,lining bending moment changed from tensile to compressive in the inner edge of arch and lining axial force of deep buried side is bigger than shallow buried side.(2)Orthogonal experimental design is adopted to constitute study examples,and Artificial neural network is trained based on displacement back-analysis approach of numerical simulation.Simulation results are compared with field monitoring results and errors are controlled to ensure the accuracy and reliability of rock parameter.(3)Based on finite difference method,numerical models were established,different excavation procedures of existing tunnel and following tunnel are discussed respectively.Though the plastic zone of surrounding rock and the development law of stress and deformation,it turned out that the middle rock should paid more attention to monitoring and reinforcement in the middle and bottom part.By contrast,the reasonable excavation procedures of existing tunnel and following tunnel is shallow pilot drift first,deep-buried pilot drift follow and then the last section.