The Forecast And Analysis Of Ground Subsidence Based On The Excavation Of Changsha Metro

With the rapid development of China’s economy, subway excavation project has entered the stage of large-scale construction. However, more and more accident caused of underground excavation, ground subsidence caused by excavation affect more and more people’s attention. Underground excavation will result in disturbances to the surrounding soil, the soil stress release will break the stress balance of the original soil, the stress adjustment arising and deformation caused by construction disturbance formation is transmitted to the ground, causing soil properties and foundation support conditions changes, lead to the occurrence of uneven ground settlement and various modifications, will be severe affect the normal use and even occur collapse or bulge fracture. In recent years, many domestic and foreign excavation and construction of the subway in similar accidents frequently occur, causing significant economic losses and serious social consequences. The ground deformation caused by city tunnel construction will bring out negative impact on the environment, so the control of settlement is very important to the design and construction of a tunnel in quality management.In this paper we analyze the ground subsidence date which based on the shield-driven construction of Changsha Metro Line West Extension Wang Mei interval metro. First, we studied the lateral surface subsidence caused by underground excavation, Gaussian equation suggested by Professor Peck is one of the most popular-used methods to predict the soft ground movement induced by shallow tunneling work. Peck believes that ground settlement caused by construction is occurred without drainage, so the settling tank volume should be equal to the volume of ground loss. It is assumed that the formation losses are evenly distributed over the entire length of the tunnel, ground subsidence lateral distribution resulted by tunnel construction approximated a normal distribution curve. The application of this method in China should be carefully verified and evaluated since it was suggested based on case studies of limited areas. The regional differences in geological conditions, often leads to the settlement predicted by Peck formula does not correspond with the measured data, there is a big error. This paper improves the Peck formula and develops an applicable Peck formula for Changsha by focusing on the observed data of Shield Equipment & Project, introducing two correction coefficients by using the regression analysis method:the correction coefficient of the maximum surface subsidence αand the correction coefficient of the subsidence groove width β. And provide a reference for future subway construction of other lines. Then according to the measured subsidence data from December 20,2012 to July 15,2013, we discuss the changes principle of ground subsidence with time caused by the shield-driven tunnel construction by using of the various long-term forecasting model of the ground subsidence. We determine the most appropriate long-term forecasting model of the ground subsidence for this project by comparing the measured date with forecast date. Study results have important theoretical significance and broad application prospects.