Study On Steel Arch Supporting Of Cai-Gu Tunnel

Steel arches, with its higher strength and rigidity, withstand loads of surrounding rock intime, quickly following on surrounding rock supporting role to play, and other advantages, arewidely used in the design and construction of soft surrounding rock tunnel. But the supportingprinciples of steel arches and factors affecting their supporting effect still need to conduct anin-depth study, This article relies on CaiGu tunnel in rebuilding project of the313highway inGanSu Provincial, on-site test of steel arches, using convergence confinement method tostudy interaction between the primary supporting structure and surrounding rock andnumerical simulation of steel arches supporting effect for a more systematic study, obtainedthe following results:1. The research results of convergence constraint method, show that largest supportingresistance of I20a steel arch is16%larger than I18steel arch; Steel arch,with supportingspacing increases, the maximum bolting force fells sharply, and effective support spacing isbelow1.2m.2. Numerical simulation shows that, because of the steel arches, rock bolts located in acertain range of the tunnel arch are under compression. Different support parameters of steelarch effect on surrounding rock plastic zone distribution range is small, improve the steel archsupport parameters, can effectively reduce the steel frame, the stress of the shotcrete, improvestress conditions of the supporting structure.3. According to field tests and numerical simulations, as the main structure of primarysupport, the steel arches are overall under pressure, the maximum axis force are happened inarch crown, gradually reducing its value from arch to the side wall; The maximum momentare happened in side wall, and positive and negative bending moments alternate frequently(-30kN.m~+30kN.m), reflecting the side wall-beam-arch stress complex, combined withstability prediction for the steel arches, recommendations of excavation width of stairs underconstruction process control. 4. Integrated convergence confinement method and numerical simulation, interactionbetween steel arches and shotcrete, improving the parameters of steel arch support or increasethe shotcrete thickness can reduce the internal force of steel arch-shotcrete combination;According to supporting effect, in CaiGu tunnel, I20a steel+0.26m in initial support oftunnel shotcrete support form is available, but the level of steel stress is low, It is suggestedthat support spacing should be increased to0.75m or use support spacing0.75m I18-steel+0.36m form of shotcrete support.