Hazard Prevention And Control Research In The Process Of Complex Foundation Pit Group Construction

With the rapid development of the domestic economy for many years in the city,the process of deepening, the city underground space development and utilization hasbeen more and more, at the same time, due to the rise of commercial development,many of the neighboring project started construction at the same time, lead to themutual spacing between foundation pit is small, and even the emergence of twoexcavation sharing a retaining structure, so that during the excavation of foundationpit have mutual influence.When this time, subway construction also obtained the rapid development in thecity, from the rapid demand for long-term planning and economic development of thecity construction, various commercial projects with rail transit station iscommunicated with each other, resulting in the formation of city commercial complexmode is a kind of trend, this combination is getting more and more domestic large andmedium-sized city recognition.City complex continuous built also makes the foundation pit engineeringcorresponding increasingly huge, huge project that consists of a plurality of adjacentcross, in space, composite foundation formed by the combination of both fromconstruction technology, project risk, mutual influence on surrounding environment orfrom the harm of view, than the single pit to complex times. So these complicatedexcavation group construction have become the new focus of the builders cityfoundation pit engineering concern, has become a very important research direction ofengineering and technical personnel.The research on complex foundation group (including the regional super largefoundation pit, two or more of the composite foundation and construction and rail transportation foundation or foundation group) as the main object, using acombination of theoretical analysis, numerical simulation, field measurement method,the multi-layer complex foundation pit engineering hazard in construction groupprocess (including foundation interaction and superimposition of the impact on thesurrounding environment), around the " group of the crater effect " to carry out thesystem research, the main research results are as follows:According to the combination form and position relation of the foundation pitexcavation group complex, the complex foundation group is divided into " pit-by-pit"," pit-beside-pit "," pit-in-pit " and other types;According to the actual engineering application, proposed "group crater effect "theory, and " theoretically harm group crater effect " and its mechanism, and on thebasis of previous research, discusses the causes of the surrounding soil and retainingstructure displacement near the influencing factors of the scope and the influence offoundation pit excavation.In a large complex project as the background of this research project, the use ofFLAC3D in the modified Cambridge model to establish a three-dimensional finitedifference simulation of construction process model, the model takes intoconsideration of foundation pit support structure, adjacent metro station structure andcomplex foundation group surrounding environment and other factors, numericalsimulation is carried out adjacent foundation pit excavation have synchronization.By theoretical analysis and data analysis results of numerical simulation of theeffect of the interaction, the foundation pit excavation process between the complexand superposition effect on the surrounding environment, including the complexfoundation pit excavation of the foundation pit retaining wall displacement,displacement and internal force characteristics influence, after the construction offoundation pit has built on the influence of foundation pit structure, foundation pitexcavation has been built on the structure of the drift hazards, and complexfoundation pit excavation group camera fold effects on surrounding soil displacement. Based on analysis of the " group of the crater effect ", the hazard controlmeasures: Excavation in the plane partition method and conditions, in order to makethe most of the surrounding environment protection as the standard, in order to takeoptimal excavation; The bottom soil retaining wall structure increases especially toesoil stiffness way to reduce soil deformation; The outer enclosure structure byincreasing the overall stiffness approach to coordinate the deformation of retainingstructures; The reasonable arrangement of construction sequence, deformation controlstructure, such as the use of both sides of foundation pit excavation synchronouscoordination mode, so that the deformation complete foundation pit bracing structure;To the pit on the pit and pit in the case of pit, as far as possible the use of symmetryand balance the construction measures, ensure that the foundation of entire forcebalance.Will use theoretical analysis, numerical simulations of the hazard controlmeasures applied in the background of engineering, and the field test methodvalidation, results show that, the relevant control measures to effectively control thedisplacement of deep foundation pit and surrounding environment, application of thetheory is successful. Confirmed in the background of this research project, and willharm the application of control theory in another complex foundation pit construction,also achieved good results, show that the method effectively ensure the complexfoundation in the foundation pit retaining structure and surrounding environment, soas to be able to escort for the smooth construction project, but also accumulatedvaluable experience for similar engineering construction in the future.