Research On The Relationship Between Stratum With Underground Water Level In Nanchang And Anti-floating Of Underground Composite Structure

In order to alleviate the urban road traffic pressure and to meet the development demands of urban rail transit underground rail transit constructions of first-tier cities and second-tier cities in china grows ever faster,which makes the deep foundation pit excavation scale of metro bigger.So it is particularly prominent to assure anti-floating safety reliability of underground structures of subway station in some cities with groundwater head high and rich,for example,Guangzhou,Shanghai,Nanjing,Wuhan and Nanchang.Connecting the underground continuous wall with the basement side wall of main body structure of station as a composite structure of the station,is one of the advanced technologies of underground structure anti-floating in deep foundation pit,and is also the most economic and effective method.At the present stage this type of underground composite structure anti-floating is also widely used in Nanchang subway station construction.Therefore,further studies on the characteristics and applicability of the anti-floating structure in Nanchang area have important theoretical significance and engineering application value for underground structure anti-uplift security research.This paper collected and summarized related literature and codes at home and abroad,analyzed the basement anti-floating measures adopted by the failure accident,compared the advantages and disadvantages of various anti-floating measures and their applicable conditions.On the basis of collecting data of a few large geotechnical engineering investigation projects,with analyzing the typical stratigraphic structure and geological features of Nanchang area,the comprehensive analysis of characteristics of Nanchang stratigraphic structure and hydrogeology are made,and relevance between the stratum with underground water level and surface water is discussed.and so on correlation;This paper presents the concept and relationship between the anti-floating water level and the structure design.Based on R/S analysis,the trend of groundwater development is predicted,and the historical trend of the water level of Ganjiang river in Nanchang is fitted and analyzed by linear fitting method,Theseresearches provide factual basis for further study of the characteristics of groundwater distribution and groundwater runoff in Nanchang and the further rational determine of the anti-floating water level of structure design.According to the analysis of accident and current situation,and based on the time phase and duty this paper put forward that classification of anti-floating water level must be carried out to make responsibility clear and design reasonable and well-documented.Types of anti-floating water level include site survey anti-floating water level,structure design anti-floating water level and structure anti-floating capacity water level;perpetual anti-floating water level and temp anti-floating water level.That designer gives structure design anti-floating water level is considered to be key to solve the anti-floating problem.The risk disclosure system for design is propsed in the paper.Based on survey data and design data of Dinggong south road subway station,to use underground continuous wall used and the main structure of station as the research object,the seepage and water pressure transmit lagging in two models are respectively analyzed in the pit construction phase and station operation phase by Geo-Studio software.The anti-floating stability design checking calculation for underground composite structure.Again is finished with anti-floating calculation formula in convention under the two conditions of site survey anti-floating water level and structure design anti-floating water level.Simulated calculation as to the underground composed structure is made with finite-difference software FLAC3 D in the process of excavation supporting to groundwater buoyancy recovery.From the analysis of displacement,stress and stability,it is proved that the underground composed structure becamed from connection between the underground continuous wall and the main structure of station can guarantee the long-term stability of the subway station,and has well future development.This paper proposed the theory of "water filled rubber ball blasting" to be applied in the study on mechanism of structural baseboard anti-floating effect.Anti-floating hydraulic transmission lag for impervious underground continuous wall is further demonstrated in theory.The theory provides theoretical basis for rationaldetermining anti-floating water level in the rich rain stage.By the theory it is proposed a practical significance technology that a water discharge gate installed in baseboard can be open to relieve buoyancy at anytime.