Analysis Of Deformation Behavior Of Deep Foundation Pits In Soft Soil By Grading Excavation And Gradually Changing Supports In Hengqin Area

The deep foundation pit engineering in soft soil area usually affects the structure and surrounding environment,and the foundation pit construction parallel to the adjacent tunnel will cause the deformation of the foundation pit itself and the adjacent structure due to the influence of the geometric size and construction sequence of the foundation pit.Zone excavation is one of the effective deformation control methods at present.On the other hand,after the excavation of deep foundation pit is completed,the foundation pit enters the stage of back construction,and the original support needs to be removed gradually.The deformation of the foundation pit caused by the removal and replacement of bracing is not only related to the stability and safety of the foundation pit itself,but also has a greater impact on the surrounding environment.Most of the layout of the replacement bracing is determined according to experience,and the research on the method of the replacement bracing is relatively small.Based on an example of a deep foundation pit in Zhuhai City,this paper studies the influence law of the mechanical behavior of the deep foundation pit and its surrounding structures by the method of literature research,theoretical analysis and numerical simulation.The main research contents are as follows:1.Analyze the potential energy generated by the supporting piles,crown beams,and support beams under the action of active and passive earth pressure,and use the principle of minimum potential energy standing value to derive the formula for the influence of the length of the support beams on the lateral deformation of the support structure.2.Use Midas GTS finite element software to establish the three-dimensional numerical model of the project and simulate its construction process,including the foundation pit construction in different zones and construction sequences,and the construction process of basement floor and support replacement and removal after the foundation pit bottom slab pouring.3.The deformation of the supporting structure and the deformation of the adjacent tunnel under different excavation conditions are compared and analyzed.The influence of the excavation method and the excavation sequence on the retaining pile and the adjacent tunnelstructure is studied.The results show that the reasonable excavation sequence and excavation area should be selected to control the deformation of the foundation pit and the adjacent tunnel.4.Combined with the example of deep foundation pit engineering,the effects of different setting ratios and attributes of the replacement beams at the basement roof on the deformation and internal force of the deep foundation pit under the condition of dismantling and supporting are studied.The center distance of the support beam,the support ratio should be around 0.5 and the arrangement should be as close as possible.5.The engineering measures to control the deformation of the foundation pit are summarized and summarized from the three aspects of zoning excavation construction,replacement support construction and foundation pit construction in soft soil area.