Deformation Test And Working Mechanism Research Of Pipe-roof In Double-arch Tunnel Under The Existing Highway

Pipe roof pre-support technology, as an auxiliary technique in shallow tunnels excavation, has important function on preventing tunnel collapse, restraining ground movement and controlling ground surface settlement. Especially in the tunnels or other underground engineerings which pass cross-below the existing highways, railways and other structures, Pipe Roof Method was been widely applied because it has long pre-reinforced distance, high reliability, short construction period and other relative advantages. The working mechanism of pipe roof in shallow tunnels was been as researched object in this paper, and the longitudinal deformations of the pipe roof were tested by installation of a serious of strain gauges. Then, the theories of elastic foundation beam were applied to analyse the mechanical behaviour of pipe roof. A three-dimension finite difference code (FLAC3D) was utilized to simulate the interaction between pipe roof and tunnel excavation and the pre-support effect of pipe roof was evaluated. Some advice about pipe roof design and construction were put forward by analyzing the field-test results, theoretical analysis results and numerical simulation results. The main research content of this paper as follows:1. A series of detailed field-tests were carried out in Tujiangchong Tunnel of Chang-Ji expressway and the longitudinal deformations of the pipe roof were tested by a serious of strain gauges, and then the mechanical behaviour and working mechanism of pipe roof were discussed according to field-test results.2. Base on the principle of interacton between support structure and surrounding rock, a new elastic joint double-parameter elastic foundation beam model for pipe-roof in shallow tunnels was put forward and the solution of this model was given. Then the corresponding deflection equations,stress and strain formulas of pipe roof were deduced.3. The proposed elastic joint double-parameter elastic foundation beam model had been utilized to analyze the mechanical behaviors of the pipe roof in Tujiangchong Tunnel and the deflection curve, longitudinal deformation curve and foundation reaction curve were calculated. The calculated results fitted the field-test values well and it was indicated that the elastic joint double-parameter elastic foundation beam model was feasible to analyze the mechanical behaviors of pipe roof in shallow tunnels. 4. A three-dimension finite difference code, FLAC3D was employed to simulate the interaction between tunnel excavation and pipe roof in Tujiangchong Tunnel. The steel pipes were simulated by beam element and jet-grouting was simulated by enhancing the property parameter of surrounding rock pre-reinforced by pipe roof. The mechanical behaviour and deformation characteristics of pipe roof were analyzed in tunnel excavation. Meanwhile, the tunnel constructin without pipe roof pre-support was also simulated and the two simulated results were compared with field-test results. The deformation characteristics of surrounding rock and support structures were analyzed and the pre-support effect of pipe roof in shallow tunnels was evaluated.5. The deformation characteristics and pre-reinforcing mechanism of pipe roof in shallow tunnels were analyzed by field test, theoretical calculation and numerical simulation and the design and construction about pipe roof were discussed. Some advice about design and construction of pipe roof were put forward base on summarizing the existing experiences.