Study On Anti-Blowout Induced By EPB Shield Tunnelling Under High Water Pressure In Sandy Cobble Stratum

With the rapid development of economy in our country and the increasing of urban population, the urban road traffic problem is getting worse, so people gradually increase the development and utilization of underground space, with the fast development of underground rail transit construction, the underwater tunnel construction scale is also getting bigger, more and more urban traffic are in urgent need of building a large number of river, lake, river and subsea tunnel. Underwater tunnel in common use of shield construction, when the shield tunnel is located below the water level, the surrounding rock is sand and gravel stratum in rich water, high pressure water through soil compartment and screw conveyor to form concentrated seepage, driving the soil particles in the soil compartment to move together, it is likely to occur spewing phenomenon, we should take safe and effective measures to prevent blowout in the construction process. In this paper, based on the Lanzhou Metro Line 1 Aoshi area tunnel project (through under the Yellow River), through the muck conditioning test and numerical simulation, study on anti-blowout induced by EPB shield tunnelling under high water pressure. The main research contents and results are as follows:(1) The research status of blowout induced by EPB shield tunnelling and muck conditioning mechanism were comprehensively analyzed, providing a theoretical basis for anti-blowout research on the Lanzhou Metro Line 1 Aoshi area tunnel project, sampled sandy cobble stratum in Aoshi area, did analysis test of grading analysis and loose coefficient, the formation information of shield tunneling process is obtained, combined with the information of the construction site, such as the amount of slag to optimize the grouting system.(2) Tested and analyzed the viscosity and specific gravity of the bentonite slurry with various concentration, determined the optimal concentration of the bentonite slurry suitable for the construction, through the slump test, respectively to study effects of water ratio, foam, bentonite, foam and bentonite mixture on flow plasticity of sandy pebbles, providing reference for selecting additives for muck conditioning.(3) Mixed and stirred bentonite slurry and sandy pebble according to a certain volume ratio, conducted permeability test through the model barrel, obtained the permeability coefficient and maximum breakdown water pressure value of different ratio of muck, compared and analyzed the test results, optimized the grouting scheme.(4) Using FLAC3D software, selected various working conditions of the Aoshi area tunnel project, conducted numerical simulation of seepage induced by EPB shield tunnelling under high water pressure, obtained the distribution of water pressure in the spiral conveyor of shield machine and the influence of seepage on stratum, compared and analyzed the calculation results to obtain the most unfavorable situation.(5) Summarized the data generated by numerical simulation, compared and analyzed the most unfavourable water pressure and the maximum breakdown water pressure of permeability test to check up the effect of muck conditioning test, optimized muck conditioning scheme, it will effectively prevent blowout induced by EPB shield tunnelling under the Yellow River, providing theoretical basis and technical guidance for the design and construction of the Lanzhou Metro Line 1 Aoshi area tunnel project.