| Nowadays,with the development of cities,there are more and more projects that tunnel underpass existing buildings.The impact of tunnel underpass construction under pipe curtain support on surrounding rock and existing buildings has always been a research hotspot.Previous research has been based on the absence of defects in pipe curtain construction,lacking research on the impact of pipe curtain construction defects on tunnel excavation.In order to study the impact of construction defects of ultra long pipe curtains on the construction of tunnel underpass overpasses,this article is based on the construction section of the newly built tunnel underpass overpass on the East Ring Road of Chongqing Railway Hub.Three methods,including theoretical analysis,numerical simulation,and on-site measurement,are used to analyze the displacement,stress,surface settlement,and displacement and stress data of the surrounding rock,as well as the pile foundation.The impact of tunnel underpass overpass construction on the surrounding rock and pile foundation is studied.The main research content and achievements are as follows:(1)This article first analyzes the theory of reinforcement with ultra long pipe curtains and proposes equivalent parameters for the reinforcement area of ultra long pipe curtains,in preparation for subsequent numerical simulations.Secondly,the settlement law of tunnel excavation under ultra long pipe curtain support was studied,and the ground settlement control reference value was obtained through calculation.Finally,based on the corresponding specifications for bridge pile foundation settlement control,a suitable pile foundation displacement control value for this project is proposed.(2)Using ABAQUS to establish a new tunnel underpass pile foundation model,by analyzing the maximum principal stress changes when the steel pipe top is not in place at the arch crown,arch shoulder,and arch waist of the ultra long pipe curtain,the most unfavorable position of the defect can be determined,and the most unfavorable defect length can be obtained.By comparing the impact of the most unfavorable defect situation and the defect free situation of ultra long pipe curtain construction on tunnel excavation.Research has shown that the surface settlement value of the surrounding rock in the case of defects has increased by 9.3% compared to that in the case of no defects.The arch settlement and surface settlement curves of the two tunnel structures are the same,and the displacement and stress of the pile foundation are minimally affected by defects.(3)Simulate the impact of tunnel excavation on surrounding rock and overpass when the positioning pipe of the ultra long pipe curtain deviates to varying degrees in three directions(up,down,and right)through ABAQUS.Research has shown that when the ultra long pipe curtain steel pipe experiences horizontal deviation,the surface settlement curve will experience horizontal movement in the opposite direction of the deviation;When there is an upper and lower deviation,the surface settlement curve at the same location has the same pattern.When the deviation is 2mm/m,the surface settlement value only has slight differences from the non deviation situation,and has no impact on the surrounding rock and pile foundation;When the deviation is 4mm/m,the surface settlement value shows a significant increase compared to when the deviation is2mm/m.The deformation of the pile foundation is manifested as the tilt deformation of the pile top close to the tunnel structure,and the pile bottom away from the tunnel structure,with no significant change in the stress of the pile foundation.(4)Analyze the tunnel excavation method and the diameter of the ultra long pipe curtain.Research has shown that compared to the step method,the construction of the double wall heading method reduces surface settlement by 9.5% and the vertical displacement of the pile foundation by 3.2%.When the diameter of the ultra long pipe curtain increased from 219 mm to 299 mm,the settlement decreased by 16.8%,and when the diameter increased from 299 mm to 400 mm,the surface settlement decreased by9.3%,indicating that the support effect of the ultra long pipe curtain gradually decreased. |
PDF Full Text Request