Back-filled Grouting Simulation Test And Grouts Diffusion Mechanism Research Of Shield Tunnel

As the key process of shield tunnel method, simultaneous grouting bring important influence on preventing the ground deformation, improving the impermeability of segmental lining, ensuring the early stability of the ling, composing theco-stressing of lining, slurry and formation. Based on a series previous study, model test indoor is adopted to study the effect of shield tunnel simultaneous grouting.In order to achieve a good grouting effect, the influence which is caused by the content of water-cement ratio, bentonite and water reducing agent to the properties of slurry such as viscosity, flow pattern, bleeding rate, compressive strength is studied. Besides, the grouting effect of material and sand samples is analyzed. Meanwhile, by introduced the fractal theory, the relationship between fractal dimension and porosity is also studied.According to the research demands, the shield tunnel simultaneous grouting three-dimension model test system is designed, which include grouting system, groundwater modeling system, drive system, experiment model box, test and data processing system. By this system, shield tail grouting, segment grouting, simultaneous grouting under the same geological condition and water, mud inrush condition can be modeled. The structure of grouting system can be dismantled, adjusted to simulate different conditions.According to the experimental phenomena, the diffusion form of slurry in the process of grouting and the variation of slurry flow rate is analyzed. Combining the theoretical calculation, some parameters are studied, such as filling rate of slurry λ, coefficient of over-excavation and slurry compressibility λ1+λ2, coefficient of slurry loss λ3, coefficient of slurry compaction and permeability m.After the test, by studying the shape of calculus, variations of earth pressure and pore pressure, the phenomenon is cleared that before permeated grouting and compaction grouting, filling grouting is prior. In this process, small particles of cement penetrate through the junction of slurry and sand. After the filling grouting, at the dual act of grouting pressure and gravity, the slurry further penetrates, the porosity of sand and diffusion capacity reduce, the grouting pressure rises. Because of the anti-percolation membrane formed at the surface of sand by slurry, downward pressure is produced to the sand. There is no clear dividing line between filling zone, permeable zone and compaction zone, which are the gradient mixture.