Study On Impacts On Deformations Of Metro Tunnel Induced By Overcrossing Excavation Considering Effects Of Soil Reinforcement And Excavation Sequence

In order to solve the increasingly serious problem of urban traffic congestion,China has increased the construction of urban traffic infrastructure in recent years.During the construction of urban transportation facilities,the retaining structures construction,soil reinforcement and excavation for the road tunnel crossing the existing subway will cause deformations of the underlying existing subway shield tunnel,which may bring potential dangers to the normal operation and safety of the subway service.Based on the excavation project of Wenling Road overpassing the underground section of Yaoxiang Road Station～Huolidao Station of Metro Line 4 in the rapid reconstruction project of Chunshenhu Road in Suzhou,the deformation characteristics of surrounding soil and underlying existing metro shield tunnel induced by the construction of Metro Jet System(MJS)piles and triaxial cement mixing piles are analyzed by means of field measurement and finite element calculations.And the influence of different soil reinforcement and excavation methods on the deformation of existing subway shield tunnel are studied as well.The main research contents and results are as follows:1.Based on the field measurement,deformation characteristics of underground metro shield tunnel and soil layer caused by overhead MJS reinforcement construction are studied and analyzed.During the construction of MJS piles,the pore water pressure(increment,the same later)of soil layer and the earth pressure(increment,the same later)decrease with the increase of the distance from the constructed piles;The horizontal displacement of deep soil decreaseys with the increase of the distance from the constructed piles,with direction away from the constructed piles;The vertical displacement of the ground surface is upwards at the initial stage of construction,and then begins to fall gradually and turns into subsidence;As for the layered settlement,the soil around the shallow and bottom depth of the pile heaves and gradually settles after the completion of construction.The vertical deformations of metro shield tunnel vault,track bed and arch waist within and outside the construction scope of MJS piles are generally upwards and downwards respectively,and the convergences of horizontal clearance are compression and tension respectively;The vertical deformation and horizontal clearance convergence of arch crown,track bed and arch waist are generally small,all of which do not exceed the control values.2.Based on the field measurement,deformations of underground metro shield tunnel and soil layer and the corresponding changing pattern caused by triaxial cement mixing pile construction are studied and analyzed.During the construction of triaxial cement mixing piles,the pore water pressure decreases with the increase of the distance from the construction piles;The horizontal displacement of deep soil is towards the direction of piles,and gradually decreases with the depth;The surface settlement decreases with the increase of the distance from the construction piles;The vertical deformations of crown and waist of metro shield tunnel are downwards,the vertical deformation of track bed is generally upwards(for section outside the construction scope of the triaxial mixing pile,the deformation pattern shows an initial subsidence,followed by an upward deformation),and the convergence of horizontal clearance is sorted as stretch;Generally,the vertical deformation and horizontal clearance convergence of arch crown,track bed and arch waist are smaller than the control values.3.Based on finite element modelling,deformations of underground metro shield tunnel under real soil reinforcement and excavation condition and the corresponding changing pattern are studied and analyzed.The numerical results show that the maximum upwards movement of metro shield tunnel is 4.8 mm,which is under the control level;The vertical deformation along the metro tunnel shows a "bow-shaped" pattern;The numerical results of tunnel deformation and its changing pattern are consistent with the measurement,proving the accuracy of the model and material parameters adopted.4.Based on finite element modelling,influence of nine hypothetical soil reinforcement and excavation methods on metro shield tunnel deformation are studied and analyzed.The stimulated results indicate that adopting soil reinforcement within excavation,pit and block dividing method,reducing block dividing excavation area and block excavation perpendicular to the tunnel axis are conducive to reducing the deformation impact on the underlying metro shield tunnel.