Construction Monitoring And Numerical Simulation Analysis Of Deep Excavation Of Highway Tunnel In Deep Soft Soil Region Of Pearl River Delta

With the rapid development of China's economy and society,urban underground space has been widely used,and the scale and depth of excavation have also become larger.The construction of excavation has adverse effects on surrounding traffic and residents.In recent years,many major safety incidents of excavation have emerged in in coastal areas of China.The soft soil in the Pearl River Delta region has the characteristics of large water content,high compressibility and low bearing capacity.This puts forward higher requirements for the design and construction and engineering of foundation pits.The design and construction of deep excavation support faces many challenges.It is of great significance to study the deformation of deep excavation in areas of soft soil.Taking the deep excavation of a highway tunnel in the deep-thick soft soil area of the Pearl River Delta as an example,this paper firstly analyzes the physical and mechanical properties of the soft soil in this area through on-site monitoring and numerical simulation.Then the deformation and stress law of deep excavation in the soft soil area are studied based on the monitoring data.Finally,the construction optimization of excavation is analyzed and studied by using the three-dimensional numerical model for deep excavation of highway tunnel of the FLAC3 D software,which considers the space-time effect of soft soil.These works have great significance for guiding the construction safety of deep excavation of highway tunnel in the deep-thick soft soil area of the Pearl River Delta.The main research contents of this work are as follows:(1)The macroscopic engineering characteristics of the soft soil in this region were studied,and the basic physical properties and mechanical characteristics of the soft soil in this region were obtained through laboratory physical and mechanical tests and on-site in-situ tests.The test results show that the thickness of the soft soil in this area is 20 m,and that the void ratio,water content,plasticity index and liquid limit of the soil sample increase first and then decrease by depth,showing a soft plastic-flow plastic state,and that the sensitivity of soft soil in this area is high.(2)The monitoring data of the excavation of Chakeng Tunnel were analyzed,and the deformation and stress law of the excavation of the highway tunnel were discussed,and laid special stress on analyzing the change regulation of deep horizontal displacement of exterior-protected construction,surrounding ground settlement,steel support axial force and groundwater level.We fitted and analyzed monitoring data of the horizontal displacement of exterior-protected construction by using the least squares method and the control chart principle,and found the abnormal horizontal displacement of the exterior-protected construction.(3)FLAC3D was used to establish a three-dimensional numerical model for deep excavation of highway tunnel considering the time-space effect of soft soil.We chose three excavation stages,respectively completed excavation on the northwest side,completed excavation on the southeast side,and completed excavation of the whole excavation,and analyzed the deformation of the exterior-protected construction,the changes of support deformation forces and tunnel deformation caused by the excavation of the excavation of the tunnel.Then we compares the numerical calculation results with the monitoring data,and verified the accuracy and rationality of the calculation model.(4)Through the three-dimensional numerical model established by FLAC3 D,the construction process of deep excavation of highway tunnel is optimized,We simulated and analyzed six different foundation pit excavation and support methods,existing design and construction,no pillar piles method,adding the second support after excavation,excavation in sections,full reinforcement at the pit bottom,and 10 m reinforcement at the bottom of the tunnel.The results show that timely second steel support and construction floor in the excavation process of foundation pit have certain control effect on the deformation of the exterior-protected construction of the excavation,and that the tunnel excavation without the erect column piles deforms to the largest extent,and that the 10 m reinforcement at the bottom of the tunnel and the full reinforcement at the pit bottom can effectively control the deformation of the tunnel excavation.