Research On Key Techniques Of Construction Of Deep Foundation Pit Super Deep Rock Embedded Diaphragm Wall In Floodplain Of Yangtze River

With the development of China’s economy,rapid urbanization has increased traffic pressure.First-and second-tier cities,including Nanjing,have built subways to ease traffic congestion.Research has become a hot spot.The Hexi area of Nanjing is located in the floodplain of the Yangtze River.The properties of stratum engineering are poor.The risks of channel formation stability,stratum deformation,and lifting of extra-long and overweight steel cages during the construction of ultra-deep rock-inserted underground continuous walls are greater.The key technology of rock-socketed underground diaphragm wall construction was researched,and how to take reasonable measures to reduce construction risks and improve the construction quality of underground diaphragm wall was analyzed under the geological conditions.Based on a station project on Nanjing Metro Line 7,this paper analyzed and researched the key technologies for the construction of ultra-deep rock-inserted underground continuous walls of subway stations in the Yangtze River floodplain area through theoretical analysis,numerical simulation and on-site monitoring and measurement.jobs:(1)Based on the study of engineering geology in the Hexi area of Nanjing,analyze the major and difficult points in the construction of ultra-deep rock-inserted underground continuous walls in the floodplain of the Yangtze River,analyze the necessity of soil reinforcement and test the effect of triaxial reinforcement of this project Shaft reinforcement effect.(2)Based on the geological conditions in the floodplain of the Yangtze River,carry out work such as the selection of groove-forming equipment,the design of theratio of protective mud slurry,and the selection of guide wall type.A variety of groove construction quality control techniques are adopted to ensure the stability of the groove formation and the verticality of the groove wall of the ultra-deep rock-inserted underground continuous wall construction.The numerical model was used to establish a three-dimensional numerical model to predict the deformation of the underground continuous wall construction in the underground floodplain area.It was concluded that the settlement of the ground caused by the construction of the underground continuous wall in the case of cemented soil mixing pile reinforcement was 55 m.Carry out safety check calculation for the processing and hoisting of the ultra-deep and heavy-weight reinforced cage construction of the ultra-deep underground continuous wall,and analyze the safety of hoisting construction under the existing engineering conditions.This paper studies the arrangement of the lifting points of the special-shaped steel cage and the reinforcement technology of the steel cage in this project,especially introduces the splicing scheme of the main and auxiliary cages of the Z-shaped steel cage.(3)The processing and hoisting of the ultra-long and heavy-weight reinforcement cage,one of the key procedures for the construction of the ultra-deep underground diaphragm wall,was studied.The “one” and “L” reinforcement cages in this project were calculated through theoretical calculation,numerical simulation,optimization,selection and discussion Cage reinforcement technology,study the Z-shaped steel cage main and auxiliary cage split hoisting scheme and slot joining technology.(4)Compare and select the joint selection of the underground continuous wall in the underwater concrete pouring,one of the key processes of the construction of the ultra-deep underground continuous wall in the floodplain area,choose the combination joint of I-shaped steel waterproofing steel plate and joint box suitable for this project and introduce the The main points of joint application;multi-channel underwater concrete pouring anti-circulation technology.(5)Through the vertical deformation monitoring of the surrounding surface,the deformation of the surrounding stratum during the wall construction process is analyzed,and it is concluded that the cement-soil mixing pile construction has little disturbance to the outer stratum at 1.7 times the depth of the foundation pit,and the stratum near the centerline of the foundation pit is more susceptible to construction disturbance;Thesurface settlement caused by the construction phase of the underground continuous wall accounts for more than 65% of the entire construction phase.The ultrasonic groove formation test shows that the key technology application effect in the groove formation is better.