Optimization Simulation Studying Of Dadingshan Tunnel Pipe Roof Advance Support Parameters And Construction Scheme

In order to prevent tunnel collapse,restrain ground movement and control ground surface settlement when tunnels would be constructed in soft or weak geology stratum,several pre-reinforcement methods of heading have been development.One of such methods is the pipe roof reinforcement method.This method consists on installing,prior to the surrounding of tunnel,a series of pipes,the ground in between the pipes is stiffened and the pipes are connected,creating a kind of 'umbrella' above the area to be excavated.This technique combines the advantages of the modern forepoling system with the grouting injection method.In other words,the improvement of the mechanical characteristics and the impermeability of the ground around the tunnel can be achieved simultaneously.This paper is based on the orthogonal experimental design to tunnel construction under the condition of the forepoling of the pipe roof stability of surrounding rock and different construction schemes of examining index as the research object,expecting to providing the scientific reference basis for the design and construction of underpass type tunnel.The main contents are as follows:(1)Study abroad abase on loose sediment multi-arch tunnel,focuses on the research status of Loose Stratum large section tunnel excavation and tunnel construction technology through the existing road,summarizing the kinds of advance support and lead pipe-shed support actuality,It elaborated pipe roof numerical analysis research status.(2)For surrounding rock stability analysis,analyzing the influencing factors of surrounding rock,presenting in the form of mechanical mechanism about surrounding rock instability factors,discussing the instability criterion of surrounding rock,it is reasonablely regarded feature points displacement catastrophe as surrounding rock instability factors according to contrast about that.Learning basic rock pressure tunnel theory,considering the depth,rock conditions of tunnel,it clears the tunnel excavation pipe roof loads and loads range.(3)There are so much the factors of surrounding rock stability for the construction of the tunnel project.It is necessary to introduce orthogonal design.This article stresses it is reasonable,scientific,rigorousness to applly orthogonal design on multi-factor matter.It describes the design theory,the relevant principles and basic steps on orthogonal experiment.V And in accordance with the actual situation of the project,drawing on orthogonal experimental design analyzing on affecting the stability of surrounding rock significance.(4)Introducing FLAC numerical analysis software to build finite element model and according to DaDingShan tunnel project,this article reasonably selects surrounding rock parameters with finite elements numerical simulation to study pipe length,pipe diameter and line spacing.What is more,it summarizes the rules and size of crown settlement,plastic zone volume and displacement of the tunnel to determine optimal parameters.Secondly studying under the influence of CD Excavation,three steps and the whole section excavation scheme on surrounding rock deformation,optimized construction scheme is chose combing with practical engineering.