Research Of Tunnel Excavation Risk And Settlement In Water-enriched Soil Layers Of Qingdao Metro

During the process of tunneling, the tunnel will inevitably disturb thesurrounding rock, the mechanical equilibrium state of the adjacent formation willchange continuously. And also excavation will induce deformation of the adjacentrock towards the free face known as convergence deformation which causes settlingof ground simultaneously. When meet water-enriched soil layer, it may be appearsudden water gushing, poured sand in the excavation or causing the groundsubsidence. Drainage method and the technology of pre-reinforcement in advancefeatured with pumping water from the inner pipe is the most universal methods in thesubway construction in our country. But excessive drainage method may induce thelarge-area subsidence of ground surface and cause great negative impact to theenvironment. When By the technology of pre-reinforcement in advance, because ofgeological conditions are not clear or the construction technology not mature, tunnelexcavation cannot smoothly. There have some stratum contain which abundant waterin Qingdao metro, the existence of the surrounding buildings and pipelines,requirements strictly control the strata settlement, reduce the risk of excavation. Thispaper study the research of tunnel excavation risk and settlement in water-enrichedsoil layers of Qingdao metro to provide the guidance of safety for tunnel constructionof QingdaoThis paper is on the basis of large number of previous research in domestic andforeign tunnel collapse event, analysis the cause of the event and collapse mechanism,The key research is of six events in Qingdao subway since start working, alsosummarizes the collapse type, the mechanism of landslides, influence factors andcomprehensive prevention and control measures; According to the water-enriched soillayers in Qingdao subway, this paper expounds the technique of horizontal rotary jetgrouting piles applied in rock Ⅵ of Baoer station-Hexi station; adopts the FLAC3Dascomputer tool which is a three dimensional explicit finite-difference program forengineering mechanical computation. Simulate the rule of Strata and the plastic zone.Considered the coupling effect, to establish fluid-mechanical-settlement modelsin the process of tunnel construction. Thesis simulates the process of seepage,mechanical, settlement. Analysis strata settlements in process of precipitation andexcavation. In the construction of horizontal rotary jet grouting piles, this paperillustrates the of deformation inside hole, deformation of the ground surfacesettlement on the course of the tunnel crossing the dormitory building.Summing up the above content, draw the conclusion:(1) because of the drilling Angle control between pile still not mature, thehorizontal rotary jet grouting piles can’t form the waterproof curtain, but thecomprehensive effect are superior to pipe roof and have good advantage in surfacesubsidence and collapsed.(2) Numerical simulation results show that the precipitation radius is about50m,formation of the surface subsidence caused by water is about20mm. In the process oftunnel excavation, when the right excavation is completed, the maximum surfacesubsidence is about31.2mm, surface subsidence is symmetric distribution center lineabout tunnel. When the left tunnel excavation is completed, the largest surfacesubsidence is about38.13mm, the simulation results consistent with the testingresults. In the process of tunnel excavation of the left line, the range of surfacesubsidence further expansion. The influence of surface subsidence stack with eachother, the surface subsidence has obvious influence on the width of the slot for about70meters.(3) Monitoring data show that the largest deformation rate occurred in uppersteps when excavation, the rate of change decreased after cyclication. The groundsurface settlement and building settlement uplift in construction process of horizontalrotary jet grouting piles, when the project through, due to the influence of groundwater erosion, the ground surface settlement continues to decline, nearly11months bemore stable, This shows that groundwater loss is the main factors to stratigraphicsedimentation when tunnel excavation. The biggest ground surface settlementaccumulated to37.99mm, compared with5.30mm vaults settlement-small changes,the result indicate that level rotary spray in strata have good reinforcement effect;Building settlement and surface subsidence rule changes almost the same, the biggestaccumulative change was19.05mm.