| With the improve requirements of transportation, more highway lanes are bound toappear, then the section of highway tunnels must be more large. During tunnelconstruction，tunnels with shallow, unsymmetrical loading,surrounding rock withrich water and some other geological problems, these caused difficulties to construct.This article take Yangang Tunnel as the background, the tunnel located at highwaywhich is shallow buried and over large cross section, it is along the Pearl River andfrom Guangdong to Shenzhen. The design, construction and monitoring measurementof shallow, unsymmetrical loading,super section and closely-spaced tunnel with richunderwater in Surrounding Rock is analyzed, at the same time, numerical simulationof tunnel construction method is done with the help of FLAC-3D, with a view tooptimizing the design and construction of the tunnel. The effects of bias ratio on rockpillar in the middle of tunnel with reasonable spacing and the stability of constructiondistance of palm face between left tube and right tube influence on surrounding rockand the middle rock pillars are revealed.Proceeding from the theory of percolation in rock, the effective stress ofpercolation consolidation process in surrounding rock and the change rules of porewater pressure are investigated, and explained the calculation principle of coupledpercolation and consolidation in FLAC-3D and the method coupling calculation.Combined with reality of surrounding rock with rich water at Yan Gang Tunnel,both side heading method for small spacing and over large cross section tunnel attypical section is used, the surrounding rock support structure of displacement andstress is monitored on-site, and monitoring results indicates that ground settlement,vault settlement, convergence displacement and support structure of stress are largedue to surrounding rock is disturbed often and rich water in surrounding rock wassoften. The section tends to be stable after excavated for about20days. Duringconstruction of right tube, the middle rock pillars of the left arch,its steel tensilestress value is large, temporary level support on both heading sides must be added,and meanwhile the inverted arch must be formed into closed ring in time.The dynamic construction process during the sector of Yangang Tunnel withshallow buried, unsymmetrical loading and rich underwater has simulated with thehelp of FLAC-3D.The simulation results indicates that during excavation the righttube has great deformation effect on the left tube surrounding rock, vault settlement,ground settlement and convergence displacement of left tube is larger than the righttube, it shown that the tunnel has apparent bias effect. The middle column rock plastic zone is small when using both sides heading method, bolt axial force near themiddle rock pillars is larger than the other parts. It should pay attention to blastingeffect on the middle rock pillar during construction, and meanwhile adding densityand length of bolt on middle rock pillar, pore-water pressure was reducing at bothsides when the excavation is finished. tunnel excavation is completed on both sides ofthe tunnel, pore water pressure at the edge corner wall and invert arch increasedapparently, thus weep hole should be laid in advance at the edge corner wall andinvert arch, releasing the pore water and reducing pore water pressure, preventing thebursting water.Combined with the Dongfeng Tunnel, CRD method, bench cut method and bothside heading method to construct, the stress of middle column rock, tunnel groundsettlement, distribute rules of vault settlement on left tube and right tube and trendingrules of side wall of plastic zone are simulated by the numbers, results showed bothside heading method can well control the parameters mentioned above. Throughresearch on optimize simulation, when the bias rate is1.16,1.25and1.5respectively,the minimum reasonable spacing between the left tube and right one is18m,24m and30m respectively, the right hole of the right wall has a large range of plastic zone atthis time, stability of sidewall is affected and the right wall must be strengthensupporting. Considering the terrain in actual situation, to design the distance ofmiddle rock with18m,on-site monitoring results showed it is a reasonable one, metrequirements stability of surrounding rock, so as to further verify the reliability ofnumerical simulation results. Based on three-dimensional simulation methodsimultaneously, the palm face distance between left tube and right tube tunnelinfluence on stability of the middle column rock is researched, calculations show thatwhen the distance between left tube and right tube is20m, construction over distanceis20m, vertical stress of the middle column rock is reduced apparently, to ensure thestability of surrounding rock, a reasonable distance should be over20m. |
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