Effect Of Pit-in-pit On Behaviors Of Excavation

For recent years, with the development of Chinese economy, the process of urbanization is faster and faster. As the exploitation of underground space and the high-rise structures in urban, a large number of foundation pits have appeared lately.Currently, studies at home and abroad about "pit-in-pit" are extremely scarce. Because of the difference in size of bearing platform, or the need of building basement, the foundation pits differ in the bottom depth, secondary stepped foundation pit (also called "pit-in-pit") or even multi-class foundation pit often appears. Excavating subordinated pit will change secondary stress field which caused by construction of super ordinate pit, and which result in stress redistribution, in addition, the overall stability of the pit isinfluenced. The circumstance mentioned above might lead to the deviation of retaining piles and great affection on the surrounding environment Even worse, it may lead to foundation pit's failure and destabilitization. Therefore, the study on pit-in-pit should be paid attention.By comparing between the results from two typical pit-in-pit in PLAXIS program and orthogonal experimental design software Orthogonality Experiment Assistantâ…¡, the influence rules of pit-in-pit on behaviors of excavation are analyzed, and designs of retaining system of local deep excavations in foundation pits were summarized systematically. The major works of this thesis are carried out as follows.1. Based on Finite Element Method, the traits of two typical kinds of pit-in-pit are analyzed A detailed discussion of individual factor on deformation of foundation pit is carried out and the interaction between two class foundtion pits are reported. In the case of smaller pit-in-pits such as elevator shaft or engineering well, effect of individually factors on deformation of foundation pit and exterior-protected construction internal force are discussed in detail by changing distances between inner pit-in-pit and foundation pit, excavation widths and depths of pit-in-pit In the case of bigger pit-in-pits, the interaction rules between two class foundation pits are rqported by changing the characteristics of the soil, the width of platform, the stiffness of the support and design parameters of foundation pit.2. This thesis adopts Orthogonal Experimental Design. Utilizing the deformation of exterior-protected construction which is obtained from the model of Finite Element simulation as investigating object, and based on the appropriate level of factor figure, we select the suitable orthogonal array, the numerical simulation experiment is carried on. The sensitivity of parameters can be evaluated.3. Relevant factors of retaining system of pit-in-pit such as water pressure, earth pressure, construction overload and effects of excavation of pit-in-pit are discussed based on computing depth of foundation pit. Designs of retaining system of local deep excavations in foundation pits are summarized systematically,and the characteristics, applicability, and design features of retaining system are discussed.4. Taking the Fujian Grand Theater engineering as the project example, the correctness and accuracy of result from numerical calculation can be verified, and then some meaningful conclusions and recommendations for design and construction of multi-stage foundation pit are proposed.