Research On Dynamic Mechanical Properties Of Multi-arch Road Tunnel Based On The Visco-efasticity Plasticity Mechanics Model

With the increase of highway construction, Multi-arch Road Tunnel is widlyused as a new large span tunnel. This type of tunnel has many features suchas large-span excavation, larger surrounding rock pressure, easy to producebias pressure, shallow buried depth, more disturbance to surrounding rock,complex construction processes, complex structure and so on. Multi-archRoad Tunnel excavation and supporting are more complex than separatedtunnel and tunnel with small interval.The geotechnical materials have the characteristics of creep according tothe NATM basic idea. After excavating of tunnel, it takes some time fromdeformation of surrounding rock to its failure. The time includes excavationface advance surrounding rock pressure gradually release time effect and rockrheological effect. The classical theory of elastic-plastic deformation considerthat：after the excavation of tunnel，deformation release of no supportingcaverns is instantaneous to processing which can not reflect the timeeffect.Only considering of the rheological properties of surrounding rock canreflect the formation and supporting structure interaction characteristics whichcan determine a reasonable initial support and second lining timberingopportunity.This paper takes Jilin province Yumujiang Ditch Multi-arch Road Tunnelas engineering geological background. Meanwhile using the numericalanalysis software FLAC3D basing on the finite difference method analysisconstruction process of Multi-arch Road Tunnel. This paper Mainly discussesthe stress and strain relationship between excavation footage or face advancedistance of tunnel and surrounding rock and supporting structure. The contents and the results of numerical analysis are as following:(1) Creep model in the FLAC3D is used as analysis model. Referencing tomonitoring measurement of Yumujiang Ditch Multi-arch Road Tunnel,Multi-arch Road Tunnel creep parameters were obtained by using ofdisplacement anti-analysis. The parameters include Kelvin shear modulus, itscoefficient of viscosity, Maxwell shear modulus, and its coefficient of viscosity.(2) This paper analysis construction process in different constructionscheme and different mechanical models. At the same time This paperrecords stress, displacement, internal force of the support structure andunbalance force of each construction process. We get conclusion through toanalysising the recorded data each comparative as following: Based onvisco-elastoplastic model the calculated surface displacement, vertical crowndisplacement were larger compared with based on elastoplastic model; basedon visco elastoplastic model the calculated convergence based onelastic-plastic deformation is smaller than based on elastic-plastic model;based on visco-elastic plastic model the calculated internal displacement ofsurrounding rock curve are in parallel, based on the elastic-plastic mechanicsmodel the calculated internal displacement of surrounding rock changingcurves are crossing each other, but nearing the free surface measuring point’sdisplacement converges to zero.(3) This paper analysis space effect as to Multi-arch Road Tunnelconstruction process.using Using the same construction schemes of differentmechanical models, the same mechanical model different constructionschemes the same mechanical model, different construction schemes ofdifferent mechanical model.This paper through to analysising vault verticalstress and displacement relationship between excavation footage or faceadvance get conclusion as following:based on visco-elastoplastic model threeheading construction scheme, vertical crown stress and vertical displacementinfluence range of about1.5times the single hole span as to excavationfootage or face advance distance. (4) This paper analysis time effect as to Multi-arch Road Tunnelconstruction process. Based on visco-elastoplastic model, This paper carriieson comparison Analysising in he same construction schemes of differentmechanical models, the same mechanical model different constructionschemes the same mechanical model, different construction schemes ofdifferent mechanical model，we get conclusion as following: based on thesame construction scheme，the greater the vertical crown displacement vaults,the longer the time interval between construction process; vault vertical stressconverges to the same stress with time gradually in the three headingconstruction method, vault vertical stress size’s order according to the processtime interval:5days interval>8days interval>10days interval.