Research On The Control Of The Retaining Structure Deformation Of The Deep Foundation Of Ningbo Metro Project

With the development of the economy, the urban buildings have continued to grow in terms of height and density. Meanwhile, with an increasing demand for the unban underground transit, a large number of metro stations are inevitably designed to have deep foundations underneath near the concentrated existing buildings, which makes the construction of the deep foundation increasingly restricted by the surroundings. The article takes the west extension of North Haiyanlu Station of Package TJ-VII of Ningbo Metro Line 1 as the research subject, gives an analysis of the water and soil change characteristics inside and outside of the foundation and the retaining structure deformation principles through a detailed theoretic analysis, calculation and arrangement of the monitoring data obtained from the poor geological and hydrogeological conditions of the deep foundation construction through the soft soil strata with high content of water in Ningbo, and finally proposes some effective technical measures for the deformation control during the deep foundation construction works through similar geological conditions.Starting from the basic principles of soil mechanics, the Article uses Foundation Retaining Wall Software(FRWS) to calculate and analyze the internal force and deformation of the foundation, monitor the entire construction process, collect the operation data, analyze and control the deformation. Based on the regression analysis of the numerous on-site monitoring data, it concludes that the retaining structure deformation caused during the construction of the deep foundation through the soft soil strata with high content of water in Ningbo mostly take on arc shape, namely the convex drum or a groove. The maximum deformation position descends with the excavation of the foundation downward and it normally remains at 3m to 5m below the excavation face. The ground deformation surface out of the foundation, the deformation surface of the retaining structure and the horizontal displacement surface of the strata near the walls out of the foundation turn out to be similarly irregular curve. The soil upheaval and plastic deformation of the soil in the foundation shall be caused by the excavation of the foundation, the deformation and extrusion of the retaining structure, the underground water pressure and the seepage of the underground water through wall toes and the weak sections of the diagram walls. During the construction of the foundation, the deformation of the retaining structure shall be determined by the designing schemes, foundation excavation scheme, quality of the strutting works, quality control capability in the construction works, the geological and hydrological conditions, and so on. The influence caused by the corner effect is small and the long side effect is also not an obvious cause for the deformation of the retaining structures.The deep foundation construction of the metro stations through soft soil strata is a systematic engineering, a race against time and space and a systematic works with an integration of the ground consolidation works, dewatering works, excavation works, strutting works and structure construction works. The process control shall be the priority among all the countermeasures for the foundation deformation, and the capability of the process control during the construction determines the effect of the measures. Therefore, during the foundation construction through the soft soil strata with high content of water in Ningbo, a good management of the time and space is the core spirit while the process control is the key.