Taking the foundation pit project of Tanggu Station on Line B1 in Binhai New Area,Tianjin as the engineering background,where the confined aquifer water level is significantly lower than the phreatic surface,cross-layer seepage effects were identified under dewatering-excavation interactions.A numerical model simulating deep excavation processes was developed to predict deformation behaviors of retaining structures at different excavation depths,while investigating settlement evolution patterns of adjacent existing buildings.By considering cross-layer seepage characteristics of confined water,the fluid-solid coupling method was employed to analyze the impact of construction suspension at various excavation phases on soil reconsolidation and subsequent building settlements induced by confined water migration.
In order to study the advantages of shaped charge blasting over traditional smooth blasting in multi-joint tunnels,four models of double hole smooth blasting and shaped charge blasting were established to study the influence of the angle of joint and hole connection on the overcut and undercut of multi-joint tunnels,and to explore the dangerous position in the tunnel section blasting excavation.The research results show that smooth blasting shows great damage in multi-jointed shale tunnels,resulting in a significant increase in overcut and undercut.Especially when the connection direction of the hole and the joint is 45°,the amount of overcut and undercut generated by smooth blasting is the largest,reaching 1 436 cm2.Therefore,special attention should be paid to such angle conditions in the blasting scheme design.Shaped charge blasting has less damage to surrounding rock in multi-jointed shale tunnels,and can effectively reduce the amount of overcut and undercut in blasting.The average amount of overcut and undercut in the tunnel is reduced by 1 090 cm2,especially in the 45° angle model,compared with the smooth blasting,the reduction is 1 161.4 cm2,showing a significant optimization effect.To sum up,the application effect of shaped charge blasting in multi-jointed shale tunnels is obviously better than that of traditional smooth blasting,which can not only effectively reduce the damage of surrounding rock,but also significantly reduce the amount of overcut and undercut,thus improving the safety and efficiency of tunnel construction.Therefore,it is suggested to preferentially use shaped charge blasting technology in practical engineering.
With the advancement of rail transit technology,shield machines are increasingly used for pile grinding construction to undercross existing structures.Improper parameter selection may not only damage shield machine but also lead to secondary disasters such as ground collapse and existing structural damage.To enrich domestic construction experience in EPB pile grinding,we systematically summarize the construction techniques for shield machines passing underneath row piles in soft soil formations using small-angle cutter,based on practical construction cases.The paper details key information including construction challenges encountered,countermeasures implemented,and critical tunneling parameters during the construction process.This work provides robust technical support for accumulating pile grinding experience within the industry and offers practical case references for similar engineering projects.
Due to its unique geological structure and surface morphology,karst geological areas often encounter hydrogeological problems such as sudden water inflow,which pose potential threats to the stability and safety of urban tunnels.This article combines on-site monitoring and numerical simulation methods to explore the impact of karst geological sudden water inflow on urban tunnels,and proposes corresponding grouting for water blocking scheme.The research results indicate that the deformation during the entire monitoring period can be divided into three stages based on the rate of change in deformation at different locations:rapid change stage,slow development stage,and stabilization stage.When the water head of the dissolution chamber is 10 m,it can be used as the critical water head value of the dissolution chamber.When the water source pressure exceeds 0.5 MPa,a sudden water inflow occurs in the tunnel,and as the water source pressure increases,the amount of sudden water inflow continues to increase.When the thickness of the filling material is less than 10 m,a sudden water inflow occurs in the tunnel,and as the thickness of the filling material decreases,the amount of sudden water inflow continues to increase.The grouting for water blocking scheme was adopted to timely treat the leakage water during tunnel excavation and support,effectively ensuring construction quality,reducing idle waste of construction personnel and mechanical equipment,and saving costs.
The steel trestle has become an important technical means to solve the construction difficulties such as the limited working space of the deep foundation pit with cover and cut-top down method,the excavation of the foundation pit and the difficulty of transportation of construction materials because of its convenient installation and disassembly and easy recycling.In this paper,the design and construction of steel trestle for deep foundation pit in water-rich sand layer are studied.The connection form between steel pipe column top and Bailey beam is discussed,and the'slope type'connection end is developed accordingly.The connection end is welded after the steel pipe column is excavated,which ensures the installation accuracy of the steel trestle and improves the construction efficiency.In order to optimize the construction method of pile column support,the steel pipe column and the anti-pulling pile reinforcement cage are reliably connected by the pre-insertion method,and then hoisted to the design elevation on the construction work surface,which ensures the verticality of the anti-pulling pile and the steel pipe column.The Bailey beam of the steel trestle and the support between the steel pipe columns are excavated with the earthwork and installed in sections and layers,which ensures the overall safety and stability of the steel trestle.With the help of Midas finite element analysis software,the main components of the steel trestle and the stability of the steel pipe column are numerically simulated.The results show that the steel trestle is safe and reliable and can meet the construction requirements.
