Study On Deformation Law And Influencing Factors Of Foundation Pit Excavation In Soft Soil Area Of Tianjin

With the rapid development of urban rail transit, more and more cities and regions in China began to build subway, and a large number of subway deep foundation pit constructions sprung up. China is a country with a vast territory and a variety of urban geological features which make the foundation pit engineering has a strong regional characteristics. Therefore, the design and construction of foundation pit should be adapted to local conditions and it’s very important to study the design and construction of foundation pit in a certain area with similar geological condition. This paper is based on the foundation pit engineering of Metro Line 5 and Line 6 in Tianjin soft soil area. From the engineering practice, with the field monitoring data analysis, mathematical statistics, numerical simulation, theoretical analysis and other means, the deformation law, deformation mode, deformation influencing factors and other related issues of foundation pit retaining structure and ground surface in Tianjin soft soil area are studied in depth. The main research contents are as follows:(1) Compare the monitoring data of the projects based on in this paper with the scientific theory of similar projects and the statistical analysis results of the monitoring data at home and abroad.(2)A database of 32 case histories of foundation pits of Metro Line 5 and Line 6 in Tianjin soft soil area is presented. The deformation characteristics and development law of surface settlement of deep foundation pit in soft soil area of Tianjin are studied. Based on the monitoring data and analysis results, suggestions on design and construction of deep foundation pit in soft soil in Tianjin area are put forward.(3) The relation between the influence factors of foundation pit deformation and the maximum lateral displacement of foundation pit support structure and the maximum surface settlement behind wall is studied. Based on the gray relational theory and monitoring data, the sensitivity of the deformation of foundation pit to influence factors is studied; in addition, the main influence factors and secondary influence factors of foundation pit deformation are determined.(4) According to the actual situation of projects, a standard model is established. A total of 21 models in 5 groups are set up by variable control method based on the standard model. The effects of foundation pit depth, aspect ratio, insertion ratio, thickness of diaphragm wall and support stiffness on the deformation of foundation pit are studied and the deformation law of foundation pit under the change of single factor is obtained.(5) Based on the numerical simulation method, foundation pit angle effect is studied. The influence of pit angle effect on different position of long side of foundation pit is quantitatively studied and the influence range of pit angle effect is accurately determined through introducing the concept of influence coefficient of pit angle effect Ks. The variation law of the influence range of pit angle effect is studied in the form of the different foundation pit geometry, the insertion ratio of the diaphragm wall, the supporting stiffness and the thickness of the diaphragm wall.