Dynamic Response And Optimize For Deep Crossing-shaped Foundation Construction

Under construction in Changchun North Station light rail and subway excavationengineering is Changchun City Light Rail Transit Line1and Metro Line4of thetransfer station. Light rail pit length of205.8m, width of20.8m, the deepest foundationpit depth of10.5m; the subway excavation pit length of143.4m, width of20.5m, pitthe deepest depth of17m. Two pits was62.71°angle crossing-existence and throughthe strata of Quaternary alluvial clay and sand strata. The paper focuses on the deep pitof clay sand formation cross heterosexual construction, rely on the transfer stationfoundation pit of the Changchun City Light Rail Transit Line1and Metro Line4, andcomprehensively analyze deformation and internal forces of support system and itsengineering countermeasures and construction safety assessment of the stickysand-deep excavation of the land layer crossing-shaped by some measures which aretheoretical analysis, numerical simulation, field monitoring and so on, the mainresearch content and results are as follows:(1) Pile is one of the most important foundation pit structure, and choosing itsdiameter play a prominent role on the deformation and stress of the pit during theconstruction process. Deep foundation pit of the cross heterosexual envelope systemfor the transfer station of Changchun City Light Rail Transit Line1and Metro Line4,which has been carried out a systematic numerical analysis, and analysis showed thatthe envelope pile’s diameter increase from1000mm to1200mm can significantlyimprove overall stiffness of envelope structure, effectively block local adversemutations of the piles and avoid the loss of damage to the piles and fencing-work.Therefore recommended that in the crossing-opposite parts of the envelope piles’ diameter is1200mm, the rest can be1000mm.(2) Research to deep foundation construction dynamic response of Changchunsubway clay and sand formation crossing heterosexual, study and analysis to carryingout excavation of two different construction programs that is first subway excavationof foundation pit to light rail pit excavation and first light rail excavation of foundationpit to subway pit excavation, the pit soil deformation and maintain the system forcecharacteristics, the analysis shows, excavation to select the construction of light railafter subway pit program, to a certain extent, effectively use of time and space effect ofexcavation pit, envelope of crossing-profiled section stress redistribution effect issignificant, so the recommended preferred light rail excavation after the subway pitexcavation.(3) The support system is not only an important guarantee of the safety of deepfoundation construction，but also play an important effect on long-term stability of thestation structure. Under meeting foundation stability requirements, using numericalsimulation, study to the foundation force and stability by cross-profiled sectiondiffer-support vertical layers, studying show that, where appropriate, apply layers ofsteel support pre-stressed conditions, it is subway pit with three steel support and railpit with two steel support to meet the deformation, stress and strength requirement ofthe pit structure.(4) comprehensive assessment of excavation, support and envelope system designmethod the effect to the deformation of the foundation pit and the dynamic response inconstruction process, combined with the existing engineering practice and relevantnorms, determine excavation monitoring and warning and control value of Changchunmetro cross-shaped parts of the layer crossing heterosexual clay and sandy soil deepfoundation. Tracking the construction process of deep foundation, taking upconstruction of the crossing-heterosexual dynamic monitoring, on-site monitoring dataanalysis showed that the recommended optimization of the crossing-Shaped deepexcavation is scientific and reasonable.