One Dimensional Consoilidation Analysis Of Saturated Soft Soil Foundation Under Complex Cinditions

In recent years,the rapid development of urban rail transportation,new foundation pits adjacent to the underground tunnel is a common engineering situation,the impact of foundation pit construction on the surrounding environment has attracted widespread attention.Actual engineering and research at home and abroad have shown that the deformation of the envelope and surrounding strata caused by pit precipitation can reach the centimetre level and can pose a certain threat to the safety of existing buildings(structures),and recommendations are given for pit deformation control.As the underground space becomes more crowded,foundation pits are often adjacent to existing tunnels,but the deformation of the adjacent tunnels parallel to the foundation pits under precipitation conditions has rarely been studied,and the deformation characteristics of existing tunnels under such conditions are not yet known.This paper therefore analyses the deformation characteristics of existing tunnels parallel to the pit under precipitation conditions,using both scaled-down model tests and numerical modelling methods.Specifically,this paper firstly establishes a reduced scale model based on the similarity ratio principle for the actual project,and then conducts a study on different precipitation depths and different pit widths to investigate qualitatively the changes in water level,pore pressure,surface settlement,pore pressure,earth pressure,effective stress,longitudinal and crosssectional bending moments of the tunnel outside the pit.ground investigation report using the modified Moore Cullen principal structure to establish a three-dimensional numerical model for numerical analysis,after using the measured data to verify the correctness of the numerical model,using the orthogonal table to screen the maximum influencing factor,while the factor was then subjected to univariate analysis,and based on the analysis of different precipitation depths in the indoor model tests,the study was extended to analyse different ground link wall insertion depths,stiffness,tunnel burial depths,etc.The effect of different factors on the force deformation of the adjacent tunnel under precipitation conditions is analysed.The reduced scale model tests and numerical calculations in this paper have led to the following conclusions:(1)As the precipitation progresses,the shape of the precipitation funnel becomes apparent and a ’shoulder’ type of ground settlement occurs outside the pit.The total pressure at the top of the tunnel vault decreases and the effective stress increases,resulting in a "concave" vertical settlement of the tunnel.Due to the presence of the precipitation radius,the closer the tunnel is to the centre of the precipitation during the precipitation phase,the greater the settlement value,which disappears when the excavation is carried out,and is greatest in the middle of the pit.The depth of precipitation and the increase in the width of the pit can cause an increase in tunnel bending moment,with the maximum negative bending moment occurring at the 90° arch waist and the maximum positive bending moment occurring at the top of the arch,and the vertical diameter of the tunnel decreasing and the horizontal diameter increasing due to precipitation,i.e.the tunnel shows a "horizontal duck egg" deformation with vertical flattening and horizontal stretching.(2)The difference between the water level inside and outside the pit caused by the precipitation caused seepage,which led to a "cantilever" lateral shift of the ground link wall towards the pit,which in turn caused the settlement of the soil outside the pit,while the friction between the piles and the soil limited the settlement of the soil around the ground link wall,so the maximum value appeared at 12 m outside the pit,while the settlement of the ground surface outside the pit from the bottom upwards The ground settlement outside the pit accumulates from the bottom to the top,showing a "groove-like" pattern.The maximum horizontal displacement of the tunnel caused by the precipitation occurs within 25 m outside the pit,and the deformation pattern of the left and right arches,the top and the bottom of the tunnel shows a "large in the middle and small in the sides".(3)Using the maximum vertical displacement of the tunnel as the evaluation index,the analysis of variance found that the vertical displacement of the tunnel was greatest when the insertion depth of the ground link wall was 22 m,the net distance d between the tunnel and the foundation pit was 7m and the burial depth of the vault was 14 m,in the actual project when the adjacent tunnel was closer to the foundation pit and the burial depth was shallower,the insertion depth of the ground link wall should be increased.Analysis of variance found that the depth of insertion of the ground link wall is the main factor affecting the vertical displacement of the tunnel,when the ground link wall is at different insertion depths,the vertical displacement of the tunnel vault z to the soil body with the increase of the depth of insertion of the ground link wall and reduce,and the deeper the soil body displacement value is smaller,the maximum displacement appears in the(-5,0)soil body interval;precipitation depth and tunnel burial depth can cause significant deformation of the tunnel The impact of the ground link wall stiffness is minimal,and the actual project can reduce the impact of construction on the surrounding environment by appropriately deepening the length of the ground link wall,the thickness of the ground link wall is of little significance for structural deformation control.At the same time,during the precipitation process before the construction of the foundation pit,extra attention should be paid to the depth of precipitation to avoid excessive deformation of the adjacent tunnel caused by overfall,which may cause safety risks to the operation of the existing tunnel.