Study On Characteristics Of Deep Excavation Utilizing Pile Wall And T-Diaghram Wall In Hangzhou Soft Clays

With the development of economy and the acceleration of urbanization in China, various underground building and infrastructures are being constructed, which means more and more excavations need to be built. The influence on itself and surrounding environment is the keen important research content of deep excavation. Many researchers have reported a number of case histories and gained many valuable conclusions. Due to its regional characteristics, the research of excavation in other area may be not suitable for Hangzhou cases. Meanwhile, as a novel structure, T-diaphragm wall has the advantage to increase the stiffness of retaining wall which could control the deflections better. However, a fundamental study of this type of structure is relatively limited and infrequently reported in the literature.This research has studied the characteristics of deep excavations utilizing pile wall and T-diaphragm wall. In order to learn the deformation rule of pile wall excavations, the data of similar excavations are collected, observed performances of one excavation in Hangzhou are also analyzed. Through the method of numerical simulation and comparative analysis of the engineering application, deformation characteristics of T-diaphragm are studied. The main contents of the result are as follows:1. A database of10case histories of deep excavations in Hangzhou soft clays is reported. Deformation behavior of deep excavations supported by continuous pile wall is analyzed based on the deformation data. The range and mean value of the maximum lateral displacement of wall are proposed. Factors such as stability number, the system stiffness, the factor of safety against basal heave which affect the maximum lateral displacement are studied. The range and mean value of the maximum ground settlement are also analyzed. A range is proposed to describe the boundary of ground settlement based on the analysis of ground settlement profile. Many figures obtained through these analysis offer a practical approach for geotechnical engineers to predict deformations of deep excavations in Hangzhou soft clays.2. Measurement analysis is carried out on one excavation which locate at the old urban of Hangzhou. The observed results show that maximum lateral displacements of the inclinometers fall in the range proposed by the previous analysis. Distributions of surface settlements and longitudinal settlements are analyzed. The monitored ground settlements fall within boundary range reported by the summative analysis. Internal force variation of the horizontal struts are analyzed based on the collected data. Earth and pore pressure changes caused by excavation are also studied.3. Finite element method is used to analyze the typical retaining behavior of the T-diaphragm wall. Both a slicing finite element model and a3D simplified finite element model are proposed to simulate the excavation supported by the T-diaphragm wall. Deformation behaviors including the wall deflection and ground settlement due to deep excavation are investigated in detail. By performing a series of parametric studies, the influence of the geometry size of the T-diaphragm wall are investigated. After analyzing the3D simplified model, the study of deformation characteristics of both long side and short side retaining wall have been finished."Three-dimensional effect" and changes of wall’s corner stiffness which affect the deformation are also analyzed. The studied results are compared with the monitored data which provide a reference for the design and construction of the T-diaphragm wall.