Research On Ground Surface Subsidence Laws Of Compound Stratum During Underground Tunnel Construction By Shield Method

Shield tunnel method is one of the major methods of subway construction which occupies a dominated position in the underground construction in the world. However, shield tunnel construction could inevitably cause some disturbances on the stratum by causing the ground surface subsidence which has an negative impact on nearby buildings and infrastructures. In this thesis, theoretical analysis, field measurement and numerical simulation study methods are used to launch the research regarding"the ground surface subsidence induced by shield tunnel during underground constructing".Through these three methods which complement and verify each other, this research reached to the influencing factors and their changing laws of the ground surface subsidence, which lays the foundation for predicting, controlling and further studying the ground surface subsidence induced by shield tunnel. In specifics:Through the elastic and plastic analysis of the stratum around the shield tunnel, this research gained the conclusion that'the stress change caused by the stratum loss is the main reason causing the ground surface subsidence'. Then, the main influencing factors of ground surface subsidence were analysed. According to the similar theory, the similar criteria of calculating the ground surface subsidence was deduced which created basic theoretical conditions for both numerical simulation and field measurement of the further studying on ground surface subsidence.Based on the M.M. PROMOJIYFAKONOV theory which was used to state the mine roadway plats pressure, and combined with th??ological conditions and the measured ground surface subsidence data from compound stratum with rock and soil in Guangzhou, this research studied the height of the arching effect of shield tunnel which provides a predicting method to determine whether the ground surface subsidence will happen or not. Research showed that: the arching effect has great influence on the ground surface subsidence caused by shield tunnel——if the arch can be formed in stratum, the largest subsidence will be small, the affected subsidence scope will be limited, and the curve of subsidence will be gentle; on the contrary, all reversed.The research derived the formula for calculating the value of ground surface subsidence by studying the changes of"subsidence trough"with time and space during shield promoting, which brakes through the troditional research model of"subsidence basins"(deformation). This method then were used in the measured analysis and numerical simulation study of subsidence. By adopting the similar criteria to study the ground surface subsidence induced by the shield tunnel from the perspective of four-dimensional (3Dspace and time), the measured data are analysed which are from the shield project of ZHU-KE area within the third line of Guangzhou Subway. A simple and effective equation S ? ke? k X?e?kL which is the first formula reflecting the continuous dynamic changes of the ground surface subsidence in the four-dimensional space.was regressed from the data analysis. By this equation, once"the distance between the points of the settlement monitoring on the tunnel's both sides and the center line of the tunnel","the promoting time and length after the shield machine crossed the monitoring section"and"the stratum's attribute and depth of the tunnel"are available, it is possible to derive the similar ground surface subsidence rule. This research result can be used for predicting the ground surface subsidence induced by the shield tunnel in Guangzhou area.The finite element software ANSYS was used to build a four-dimensional dynamic finite element model to simulate the process of shield promoting. This model analysed the changing law of"subsidence trough"in the transect section on tunnel axis thus to determine the shape of the ground surface subsidence;. This model was also used to derive the calculating formula between the ground surface subsidence value and its distribution with impact parameters. All these foundations can be used to regress the measured data.The law of the ground surface subsidence gained from numerical sim??ion and practical study inosculated well with the actual situation of the project. These law can be used to predict the latter and final settlement value through the coefficients regressed from the pre-measured data (or use relevant parameters of similar stratum for reference).Finally, the research results of this thesis were used to comparatively study the project of Shenzhen subway which which shows that,: once the parameters in the early stages of construction are gained, it is possible to calculate and predict the law and the final value of the ground surface subsidence, the predict results could be further improved by more pre-measured data. These research results have great significance in guiding construction and in early control of the subsidence.