Study On Mechanism Of Deformation And Destruction For Building Foundation And Pipeline Engineering In Loess Areas With Excavated-filled

Based on the development strategy of “make the central part less dense and expand the city,and build cities on mountains” under implementation in Yan’an,Yan’an New District was started construction in 2012,and in terms of scales of “cutting mountain for city building” in the collapsible loess area,the construction project of New District is now the world’s largest geotechnical engineering project,and it is also the first case in the history of the world city building;because the fill area in the construction site is quite large,with great filling thickness and high grade of loess collapsibility,the core problems encountered at the beginning of construction project of cut-fill site is the unforeseeable sedimentation problem caused by cutting and filling the foundation.In the middle stage of construction,the main problem lies in the deformation of ground buildings on the cut-fill site.The main problem of the latter stage of the construction is the long-term security and stability of subgrade and foundation.So the foundation selection of subsidiary building(structure)will be the most critical part affecting the safety of the building built in cut-fill site.Relying on “Research on Major Geological and Geotechnical Engineering Problem of Construction in Yan’an Loess Hilly and Gully Area”,as a subject of “Major Scientific and Technological Innovation Project in Shaanxi Province”,“Research on Key Technology Demonstration for Construction Engineering of Yan’an Loess Hilly and Gully Area(Yan’an New District)”,a subject supported by “Twelfth Five-Year National Science and Technology Program”,the subject of “Research on Foundation Damage Mode and Mechanism of Buildings in Fill Area(2015KTZDSF03-02)” which supported by “Innovation Chain of Key Industries in Shaanxi Province-Social Development Field” and so on,we have conducted systematic research on the deep foundation and shallow foundation of building in the cut-fill site and the damage mode and deformation mechanism of pipeline engineering during the construction of Yan’an New District,and the main research contents are as follows:(1)The author independently developed the model test device for piled raft foundation and raft foundation in the loess cut-fill site.By systematic study on the raft foundation in and pile foundation in piled raft foundation and the pile foundation,the author compared piled raft foundation and raft foundation in terms of the load and deformation characteristics and adaptability in the cut-fill sites,which provided the basis for the foundation selection and optimization design of buildings in the loess cut-fill sites;meanwhile,the author proposed subgrade settlement control measures,building foundation design principles and deformation control measures for loess cut-fill site.(2)According to the similarity theory,the author independently developed straight-buried pipe and utility tunnel test device in the loess cut-fill site.The author is the first one who studied the impact of settlement on the pipeline project after the foundation cut and fill is finished in the loess cut-fill site through the physical model test and generalized the laws for the load and deformation damage of pipeline engineering(straight buried pipeline and utility tunnel)in the loess cut-fill site,providing the basis for the selection and deformation control of the pipeline project in the loess cut-fill site.(3)The physical model test is verified and supplemented through numerical simulation and so on.The author compared and analyzed the deformation and load conditions of raft foundation,piled raft foundation,straight-buried pipe and utility tunnel with different cut-fill surfaces,and summarized the influence of angle of cut-fill surfaces on the foundation engineering and pipeline engineering.The author was the first one proposing that the angle of cut-fill surfaces shall be taken as a factors influencing the selection and design of the foundation of the building and the pipeline project,providing references to the selection of slope angle of cut-fill parts and the design of foundation engineering and pipeline engineering in the cut-fill sites.(4)Based on the results of model test and numerical simulation,through the theoretical analysis and deduction,the author constructed the mechanics model of the deep and shallow foundation and the pipeline engineering of buildings in the cur-fill areas,and discussed the control method and the standard control measures for sedimentation in the loess cut-fill sites;meanwhile,the risk identification method and early warning criterion are put forward from the aspects of foundation treatment,structure selection and structural design and so on.The research results in this paper have some reference significance for the construction of the loess cut-fill site,especially for the the foundation engineering and the pipeline engineering construction.