Study On The Influence Of Back-fill Grouting To Tunnel And Surface Subsidence In Shield Tunnel

Shield construction method has been widely used in soft soil area subway tunnel construction because of the unique characteristics and advantages of quickness, goodness, economy and safety, etc. But stratigraphic excavation inevitably lead to displacement of Earth’s surface and deformation of surrounding rock cavern. When the displacement and deformation exceeds a certain limit, this will be threat to the safety of surrounding buildings and underground pipelines. Thus, the study on effect on the tunnel and ground subsidence in the process of shield tunneling is very important. Now, many scholars have make a lot of research on the various factors, But there are still many problems and deficiencies, theoretical studies clearly lags behind the engineering practice, shield construction remains largely dependent on experience. There are few experts conduct on grouts diffusion law and segment pressure caused by grouting, when considering the grouts viscosity variation of back-filled grouting.This paper research the surface subsidence, rock deformation and force of support structure in the shield tunnel grouting, analyzes grouts diffusion and pressure transmission mechanism and the stability of supporting structure in back-filled grouting, and compare the shield zone monitoring data of Changsha City Subway with the numerical simulation results. The results can be the reference for the engineering application of grouting. The main content and results in this paper are as follows:(1) Derive and analyze diffusion law and segment pressure of back-filled grouting: Experimental research was carried out for time-dependent characteristics of grouts, which confirmed that grouts of commonly used water-cement ratio conforming to bingham fluid.According to the exprimental results,viscosity of grouts with different water-cement ratio increase greatly as grouting time increasing. Cement slurry diffusion radius and segment pressure caused by grouting all relate to viscosity variation. After considering viscosity variation of grouts, diffusion radius and pressure on segment are also smaller than the result of fixed viscosity. And the diversity gets obviously as grouting time increasing.(2) Through analysis the surface subsidence monitoring data of Changsha City Subway shield zone during the shield construction, it is concluded that surface subsidence law in the process of shield tunneling, and to assess the rationality of the subsidence and the construction parameter settings, and then to provide technical support for other shield construction parameter settings.(3) To numerical simulation the typical cross section of Changsha City subway shield zone, we can know that stratum settlement laws, influence scope and characteristics of the force supporting structure under the different pressure conditions grouting, and compare with measured values and the empirical formula calculated value to verify the correctness of numerical analysis, confirmed the three-dimensional finite element numerical simulation method used in this paper is reasonable to simulation shield tunnel construction, and grouting pressure has a decisive role to reducing surrounding rock deformation and surface subsidence, using non-uniform grouting pressure can get more reasonable results.