Research On Supporting Mechanism Of Composite Structure Of Freeze-sealing Pipe Roof In Gongbei Tunnel

The Gongbei Tunnel of the Zhuhai connection highway of the Hong Kong-ZhuhaiMacao Bridge project is crossing the Gongbei Port,with unique geographical location,sensitive political factors,complex geological conditions,intensive surrounding buildings and huge project risk.An innovative super-large section shallow buried tunneling method under the support of pipe roof and horizontally controlled frozen is adopted in the Gongbei Tunnel to successfully cross the sensitive building.At present,there is little systematic research on super-large section shallow buried tunneling method under the support of composite structure of freeze-sealing pipe roof.Its principle and mechanism,parameters and control,methods and rules of force and deformation require systematic research.In this paper,the supporting principle,key parameters,control methods,mechanical properties,environmental impacts on the composite structure of freeze-sealing pipe roof are studied,the main results are as follows:(1)The key parameters affecting the safety,durability and economy of pipe roof engineering such as pipe segment length,pipe jacking diameter and pipe jacking wall thickness of the composite structure of freeze-sealing pipe roof are determined;on-site artificial frozen soil mechanical test is carried out to obtain key parameters such as shear strength,elastic modulus,Poisson's ratio,internal friction angle and cohesion and their variation with temperature;the water sealing and frost heaving properties of artificial frozen soil curtain are studied to determine the reasonable thickness of frozen soil curtain;the in-situ test is carried out to study the distribution law of temperature field of the frozen soil curtain,and obtain the reasonable control temperature of the frozen soil curtain.(2)The coordinates of the head and tail center of the pipe jacking segment are determined,the control method of space curve pipe roof trajectory is proposed,the trajectory accuracy of the pipe jacking is analyzed,the reliability of the control method is verified;two control methods,i.e.key position heat control and reduce cold energy control of the artificial frozen soil curtain thickness are proposed,and the rationality of the control method is verified through in-situ test.The super-large section shallow buried tunneling method under the support of the composite structure of freeze-sealing pipe roof is optimized,and reasonable safety control measures are proposed.(3)The properties and parameters of freeze-sealing pipe roof are considered respectively;by means of numerical calculation,the mechanical properties of the composite structure of freeze-sealing pipe roof in large section shallow buried tunnel under the support of composite structure of freeze-sealing pipe roof are analyzed to obtain the force law of the composite structure of freeze-sealing pipe roof,and the bearing capacity of the composite structure of freeze-sealing pipe roof is analyzed to verify the reliability of the composite structure of freeze-sealing pipe roof.(4)By setting the monitoring data such as surface deformation,tunnel deformation and groundwater level change on site,the deformation regularity of the upper surface and buildings of tunnel under the conditions of group pipes jacking,large section long distance horizontal control freezing and super-large section multi-layer time step threedimensional excavation is analyzed,and the law of influence of shallow buried tunnel on the environment under the support of composite structure of freeze-sealing pipe roof is grasped.