Study Of Construction Mechanical Behavior Of Super-Large Cross-Section Shallow-Buried Bias Tunnel Excavated By Two-side Drifting Method

At present, super-large cross-section flat tunnels that cross-sectional area ismore than150square meters are still quite rare in all Chinese road tunnels.Since the cross-section is super large， compared with usual tunnels, the flatrate is much higher， the buried depth needed to form collapsing arch is muchdeeper，during construction, a little bit careless would easily lead to accidents,like collapse and roof falling. Hence, earth surface settlement and rockdeformation were not only under harsh control during construction, butconstructed rapidly as well, which put forward a higher requirement fortraditional construction method.This thesis will further study on construction mechanics behavior ofsurrounding rock，tunnel lining，temporal support and system anchor ofsuper-large cross-section shallow-buried bias tunnel excavated by two-sidepilot drifting method, on the background of domestic rare large-span andsuper-large section tunnel---ShenHai Highway extension project QianOuTunnel and based on the research methods that Combining in-site test withstatic finite element analysis. Some main research fruits and conclusions areobtained as follows:1. Excavation displacement deformation of the pilot tunnel in the first halfof section accounts for25%of the total deformation, which is the controlprocess of surrounding rock deformation; in the process of excavation, themaximum transverse horizontal stress of lateral temporary invert of left andright side has amounted to19MPa, while staging invert only hit1.43MPa,hence, the force it born could not be taken into consideration. the biggeststress of vertical temporal support appeared at the deep-buried vault, whichamounted to34.8MPa; the average earth surface settlement of10-meter stepconstruction method was1.9%smaller than that of20-meter’s; thecorresponding displacement discharge coefficients of middle and upper coresoil were22.66%and21.08%, respectively, stability of work plane canbenefit from left-right pilot tunnel with10-meter step and core soil with 20-meter step. the tolerance of earth surface displacement between1-meterprogress construction method with excavation speed promoted and2-meterprogress construction method was only standing at0.4%. While1-meterprogress construction method would cause largest first main stress, amountingto1.7MPa, at the dangerous points of left vault, which was18%higher thanthat of2-meter progress construction method. Therefore,2-meter progressconstruction method was more reasonable.2. New stress field caused by excavation is marked differ from originalstress field. No connection zone is formed, which fully reflects that when Hequals to2.07D, smaller than ruled shallow-buried boundary value, vault canstill form strata arch to sustain the stability of surrounding rocks.3. Affected by bias, the subsidence maximum occurs in the tunnel on thedome at the surface, on both sides of the surface subsidence became smallerand smaller, buried side is greater than the shallow side, showing a clearsettlement trough phenomenon, buried deep within the tunnel side of thesettlement value22mm, the shallow side of the settlement value of14mm, theburied side convergence is4mm, the shallow side of the convergence value of13mm; buried side the stress is significantly greater than the shallow side ofthe force; surface subsidence of first excavation of the buried side is smallerthan first excavation of the shallow side1.37%, the first principal stress in theleft dome points (risk points), a small3.5%, the first excavation of buried sideof the first stress value of1.4MPa, the focus to consider the impact of surfacesubsidence obtained excavation of buried side is more reasonable.