Comprehensive Construction Technique For Subway With Small Distance And Low-Buried Locating Under Pedestrian Bridge

Recent years,with the construction of large and deep-buried structures and subway,especially the quantities of foundation strengthening of ancient structures in the world are a lot.Sometimes,the reconstruction,storey-adding and increase of working load for the existing structures need underpinning technique.So,at present,the work quantities of underpinning of all countries in the world increase a lot,and the underpinning technique has a dramatic development.With the development of construction,the quantity and scale of underpinning technique of our country have increased continuously.Considering underpinning technique, such as foundation pressure deviation rectify method、static pressed pile method、lime pile method、pressure increase rectify method and so on,all have great innovation and characters.The linear section of contract 23 of the first-phase of Shenzhen subway project locates under Shennan Street,which is the most busy traffic road of Shenzhen City.The tunnel runs through under two pedestrian bridges and its depth is between 7.5～18 meters.The four piers of the two pedestrian bridges lie on the right upward side of the tunnel.So,while constructing,in order to prevent the possible danger caused by too much sedimentation of the piers,we adopt upper steel pipe pile underpinning of beam to reinforce the foundation of the pedestrian bridges,as well as take reinforcement measures in the tunnel,to assure the pedestrian bridges can be used safely.The tunnel locates in stratum and sand layer where are rich of water,and its underground water level is much higher than the construction water level.Affected by the water,the tunnel may easily soft plastic collapse and this will impact the safety and quality of construction seriously.In according to the different geology and hydrology,we adopt the comprehensive lowering water technique of well precipitation and waterproof curtain to make tunnel construction work on the condition without water.Meantime,the surface sedimentation,industrial area and existing buildings aside of the tunnel are within the design scope.The left line,which opposite the right line sectional tunnel SK14 +958.039～SK15 +218.524,is an existing tunnel.The distance between the two lines is 13.2 meters,while the thickness of the rock pile is 6.6 meters and the thickness of rock in people prevention is only 4meters.The geology of this section is classⅢsurrounding rock.In order to make sure of the safety of the construction and the existing tunnel of the right line,we adopted "the method of reducing vibration with interference promptly" to control blasting and we have made good effects.The integrated construction technique of small distance and low-buried subway which run through under pedestrian bridge has been proved to be feasible in theory.And through the control and actualization of related techniques,we proved the advantage of this technology in practice.According to the actual construction progress of this project,the technology adopted by this article has expedited the construction schedule,as well as it has saved the investment,completed the construction task successfully and achieved the anticipative purpose.