Study On Numerical Simulation Of Pit Excavation Deformation In Soft Soil Area

To excavate deep foundation pit in soft soil areas is likely to cause serious deformation of the envelop enclosure,especially in the foundation pits complicated in structures with the pit-in-pit form.The soil stress state outside it's envelop enclosure is rather complex,the soil of which is not only the passive earth of the excavation at early stage,but also the active earth in the pits.However,due to the immature design method and difficult construction,it's easy to deform the structure,posing a negative effect on the surrounding buildings,or even bringing risks.It's rational to adopt the computer numerical simulation technology,because the traditional calculation method is hard to predict the deformation of the foundation pit and the surrounding soil.The paper takes the foundation pit in the soft soil area as the project background,integrating design,construction,monitoring and computer numerical simulation techniques together.It aims to conduct computer numerical simulation in two-dimensional and three-dimensional perspectives of the support process and excavation process of the foundation pit.Full consideration is given to the spatial effects of the composite soft soil stratum and the pit-in-pit envelop enclosure,as well as construction effects and other factors.The main tasks and conclusions are as follows:(1)The technical points of computer modeling of foundation pit engineering are introduced in details,while the construction process and simulation method of the modeling scope and boundary conditions,as well as the fundamental principle of the selection of soil mass and structural unit model are summarized.(2)Take the pit foundation project in a soft soil area as the background and establish the two-dimensional standard numerical model in order to simulate the excavation and support of the outer pit and the inner pit.By contrasting the measured values of the ground surface settlement and the literal sway of enclosure wall,the rationality of the model and parameters will be tested.The results of the simulation and actual measurement show that the pit excavation will cause serious ground surface settlement outside the pits.The influence of the excavation on the deformation of the foundation pit cannot be ignored.(3)Based on the calculation results of the foundation pit deformation of the standard model,two optimization programs for enhancing the prestressing force and increasing the passive soil reinforcement area of the basement are proposed.The results show that the efforts made in adjusting the support prestressing force and the passive soil reinforcement area at the bottom are helpful to control ground surface settlement to some extent,and the full reinforcement of passive soil plays a great role in controlling the settlement.Therefore,the optimization programs are of great significance.(4)Through the three-dimensional analysis,it's obvious spacial effect is showed in the pit excavation.The center position of the ground settling tank will move from the middle of the long side of the outer pit to the middle of the long side of the inner pit during the excavation process.The lateral displacement of the long side along the wall is much wider than that of the short side,and the length of the short side is short with inside corners at both ends,showing a distinct spatial effect.The deformation is not rather obvious,and the middle of the long side is close to the plane strain state,but with small constraint,the deformation is relatively serious.