Studies On Grout Properties Of Backfill Grouting For Shield Tunnelling And The Influence On Ground Deformation

Shield method has been widely used in the underground engineering construction because of its unique advantages of safety, high efficiency and low disturbance, especially in the urban subway construction. However, tail void would appear inevitably between the soils and segment lining which will bring bad influence on surroundings and the stratum deformation is very distinct. So back-filled grouting becomes a necessary procedure since it can actively control ground displacement, reduce the disturbances of structures around and maintain the stability of shield tunnel. In this paper, the back-filled grout properties, ring distribution of grout pressure in void tail, grout consolidation test and numerical simulation about stratum deformation were studied and conclusions can be summarized as follows:(1)Grout properties was researched by orthogonal experiment design. Experimental analysis results shows that water-cement ratio, bentonite-water ratio, ash-cement ratio, cement-sand ratio, reducer-cement ratio all have great influence on the grout engineering properties. With the water content increasing, good flow ability of grout can be obtained, but grout physical stability worsening and leading to bleeding rate, shrinkage rate increasing. The more bentonite we use, the little bleeding rate and shrinkage rate we will get because of the water absorption.agent is an important material in single-fluid grout for adjusting physical stability.(2)A set of grout shrinking test was developed and research was studied about influence of grout pressure, soil properties around the tunnel, grout properties on the grout shrinkage rate. Under a certain circumstances, with the increase of grout pressure, shrinkage rate will increase also, but will not increase without limit. Grout has a strong ability of drainage in sandy soils since permeability coefficient of sand is bigger than clay. The most essential factor that affects the consolidation of grout is the grout properties. Only if we chose the best mixture ratio according to the construction environment can we control the proper grout shrinkage rate within a proper range.(3)Based on the continuity equations and momentum equations of Newton grout fluid, research on the ring distribution of grout pressure was carried out and distribution model was established considering the time-dependent characteristics of viscosity or not considering. Results shows that the variation of grout pressure along the ring is caused by the slurry weight and the shear stress and when the grout is flowing upward, slurry weight and shear stress will play a hindering role, on the other side, when the grout is flowing downward, slurry weight has a positive effect, while the shear stress, a negative effect. And if we take the viscosity degeneration into account, we will find that grout pressure at the same position is smaller than the one that without consideration of shear stress.(4)Shield tunnel construction process was simulated by a commonly used software ANSYS and grout pressure, grouting elastic modulus, grouting volume were analyzed to find the influence on stratum deformation. With the grout pressure, elastic modulus or the grouting volume increasing, the stratum settlement will decrease as a result, as for the effect of settlement control, grout pressure and grouting volume is more effective than the elastic modulus.