Research On Deformation Law And Support Technology Of Ultra Long And Large Pipe Roof In Tunnel Under The Existing Highway

Pipe roof pre-support technology can limit the sink of surface and maintain thestratum stabl. In order to effectively solve the tunnel excavate problem of the large span,ultra-shallow, high underground water level tunnel under the highway, Pipe roofpre-support technology is used an auxiliary technique in tunnel excavation. The projectof JinCi tunnel under the highway is adopted as the example. The theories of elasticfoundation beam was applied to analysis the mechanical behavior and deformation ofpipe roof, and a lot of experiments such as deflection deformation and force of pipe roof,ground settlement, the force of special section were tested during the tunnel excavation.A three-dimension finite difference code (FLAC3D) was utilized to simulate theinteraction between pipe roof and tunnel excavation. Some advice about pipe roofdesign and construction were put forward by analyzing theoretical analysis results, thefield-test results and numerical simulation results. The main research content as follows:(1) The double-parameter elastic foundation beam (Pasternak) model had beenapplied to calculate the deformation curve and mechanical behaviors of the pipe roofduring the tunnel excavation in JinCi tunnel. The calculated results fitted the field-testvalues well. The deflection curves and force curves were compared by steel pipe ofdifferent buried depths and different diameter, and some suggestions were proposed.（2）A series of detailed field-tests were carried out in JinCi Tunnel and thedeflection deformation and force of the pipe roof were tested by level inclinometer tubeof60m and steel bar meter, and then working mechanism of pipe roof were discussedaccording to field-test results.(3) A three-dimension finite difference code (FLAC3D) wan employed to simulatethe interaction between tunnel excavation and pipe roof in JinCi Tunnel, the pipe roofwas simulated by shell element. Meanwhile, the tunnel construction process withoutpipe roof was also simulated and the two simulated results were compared. Thedeformation characteristics of surrounding rock were analyzed and the pre-supporteffect of pipe roof was evaluated.(4) This paper did a thorough research on the theoretical calculation, field test andnumerical simulation and the deformation characteristics and pre-reinforcing mechanism of pipe roof during the tunnel excavation was obtained. Some basis aboutdesign and construction of pipe roof pre-support technology were put forward.