Study On Construction Sequence And Initial Support Parameter Of The Shallow Buried Tunnel With Small Interval And Unsymmetrial Loading

With the continuous advance of the construction in central and western regions,a large number of mountain tunnel appeared,and the neighborhood tunnel has been widely used in the construction of highway and railway for its convenience and economy.However the small spacing tunnel engineering geological conditions were worse,and usually accompanied with a shallow and bias.Improper construction sequence and initial support parameters may lead to large deformation of rock mass during the tunnel construction,even collapse accident,causing serious losses.Choosing a reasonable construction sequence and initial support parameters,ensuring the stability of the surrounding rock during tunnel excavation was a key problem in the construction and design of shallow bias neighborhood tunnel.To solve the problem,this paper took Cangnan County Zaoxi tunnel as the engineering background,the numerical simulation method was used to make system research.The main research contents are as follows:（1）The finite difference software FLAC^3D was used to research the influence level of the stability change of surrounding rock in shallow bias neighborhood tunnel by different construction sequence under the conditions of Ⅴ rock,and the influence in the change of surrounding rock displacement,stress and distribution of plastic zone caused by the different construction sequence and terrain bias angle was analyzed separately.A reasonable tunnel clear distance and construction sequence was obtained,providing a basis for the selection of shallow bias tunnel linear and construction scheme.（2）The stability change of surrounding rock of the excavated tunnel under different initial support parameters was studied,by analyzing on the change conditons of surrounding rock displacement,stress and distribution of plastic zone.The change regulation of surrounding rock stability with the change of supporting parameters was obtained,providing a basis for the optimization of supporting parameter.（3）The sensitivity analysis method was used to optimize the initial support parameters.The sensitivity of the displacement of control point and unit costs the excavated tunnel was analyzed under different initial support parameters.The optimized initial support scheme was obtained,and comprehensive comparing the optimized support scheme with optimized scheme verified the rationality of the optimized scheme and the feasibility of sensitivity analysis on support parameter optimization.This article stands at the front of blast sciences,using the latest numerical calculationand analysis method,studying on construction sequence,tunnel clear distance and initial support parameters of tunnel with unsymmetrial loading,possess a high application value,providing a validity measure for studying the stability of shallow bias neighborhood tunnel.