Study On The Ground Deformation Law Of Shield Tunnel In Ningbo Rail Transit

Shield construction technology has been widely used in urban rail transit projects with ahigh degree of mechanization, fast driving speed, relatively small perturbations on theformation and low environmental impact. Although, the disturbance of shield method is smallby compared with open-cut method,there has a certain disturbance on the around soil whichcan bring a series of adverse effects on close tunnels, pipelines, roads, buildings and structures.Since Ningbo soft soil has such special geological features as high water table, high soilmoisture, high compressibility, low intensity, high sensitivity and low permeability, therelacks study on the principles of impact on the surrounding environment made by shielddriving technology and lacks experiences on subsidence control and prevention technologyfor buildings and roads, many technical problems should be studied. Thererfore, this papertakes some sections in Line1and Line2of Ningbo rail transit as construction backgroundsand studies the deformation characteristics of surface and deep soil caused by EPB shieldconstruction in Ningbo area. The main contents of this paper include:1. Typical interval monitoring sections are selected, then combining the features ofFormation and shield construction parameters, single lateral surface subsidence features,double lateral surface subsidence features and vertical variation of surface subsidence of eachsection with shield forward are analyzed.2. Typical interval monitoring sections are selected, and the the features of formation andshield construction parameters are combined, the horizontal displacement of deep soil in thedirection perpendicular to the axis of the shield during driving are analyzed and the influencerange of construction of shield on surrounding deep soil are obtained.3. A total of100sets of singlet lateral surface subsidence data are statisticed, and theleast squares method and a linear regression curve are use to fit the measured sedimentationtank, then the results are compared with the prediction results by using the formula of Peck’s.Then, distribution and probability density of the width coefficient K of settlement trough andformation loss rate Vlare calculated inversely, and the recommended values are presented.4. The program of Flac3D is used to simulate excavation process of shield tunnel, andthe concept of equivalent layer is introduced to simulate mixture of slurry and soil aroundshield segment. Hardening slurry and slurry pressure dissipation process after the tail groutingis considered, the slurry pressure change equation under different grouting pressures arededuced by using theoretical and numerical calculation software. At last, the principles of theinfluence to the surface subsidence caused by the three factors of grouting, grouting pressureand earth cabin pressure are analyzed and, the measured values and the calculated values are compared.