Study On Applying The Key Technology Of Super Deep Underground Continuous Wall In The Rail Transit Project Of Soft-earth Area

Diaphragm walling is an important construction process in the urban rail transit construction.It is mainly adopted to enclose the underground station,separate confined water and support the foundation pit.With the development of the city,the excavation depth of the foundation pit in the construction of urban rail transit station has been deepened because of its performance demand.So,the diaphragm wall is also deepened,which is wildly used in the enclosing structure of the rail station.The underground diaphragm wall is hereinafter known as diaphragm wall.It has certain rigidity and impermeability,and its construction process is to firstly use a channel equipment to stabilize the groove wall of the groove and excavate toward underground along the design axis for the forming of groove section,whichin the reinforcement cage is inserted and the concrete is poured in.In the soft soil areas such as Shanghai and Jiangsu,there are thick mucky soil and sandy soil in the soil layers,which contains large and high-lever groundwater.Under this condition,traditional construction process for the ultra-deep diaphragm wall with a more than 60 m depth may confront many problems,including groove wall collapse,concrete streaming,out of position of steel cages,water leakage of diaphragm wall and even water-gushing and sand-gushing.Taking the 64 m ultra deep diaphragm wall of the subway station in a city as an construction example,this paper studies the test groove-forming situation in the experiment,the reinforcement of groove wall,mud indicators,vertical degree of the groove,the hoisting of large weight steel cages,cleaning of bottom detritus by air-lift cycling method,anti-streaming measures for the junction and underwater pouring quality of concrete.During the study,the mean of combining theory with practices is adopted,and methods of experiment analysis and empirical study have been used.Finally,this pater summarizes key techniques available for similar soft soil areas,comprising enforcement measures for the stability of ultra deep diaphragm wall,indicators of mud performance control,methods of bottom detritus control,lifting technique of large-size and large-weight steel cage,underwater concrete pouring and anti-streaming conjunction type,which will provide technical reference for the construction of ultra deep diaphragm wall of urban rail transit in the Shanghai,JiangSu and other cities with rich-water or soft soil layers.