Study On The Grouting Control Of Deformation Of Tunnel Due To Deep Excavation In Close Proximaty

With the continuous progress of urbanization,a number of foundation pit excavations adjacent to subway structures had been carried.The unloading of excavation will inevitably cause deformation of adjacent subway structures.There are strict requirements of displacement control for subway structures.If the deformation of the subway structures was too large during foundation pit excavation,it would affect the safety of the subway structure.In view of this problem,based on a foundation pit project,the study of grouting control technology of tunnel displacement was carried out in this paper.The main researches carried out are as follows:(1)Field grouting tests had been carried out to study the horizontal displacement and excess pore water pressure distribution around the grouting zone.It was found that the excess pore water pressure was basically dissipated one day after the end of the grouting.The uneven distribution of the slurry was observed after the grouting.A new finite element simulation method was proposed,in which the non-uniform expansion of grout,the dissipation of excess pore pressure and the overconsolidation effect of the site were considered.The unloading effect of foundation pit excavation will reduce the effect of grouting.This method can be used to calculate and predict the grouting effect according to the actual grouting amount.(2)Based on the soil conditions in Tianjin area,the influence of different soil strength and stiffness on the grouting effect was analyzed.It is concluded that the soil stiffness parameters are the main factors influencing the grouting effect.The distribution law of horizontal displacement of soil surrounding the grout was studied and the influence of grouting quantity,grouting distance,grouting depth and other parameters were analyzed.There is a linear relationship between the grouting amount and the displacement of the surrounding soil.The maximum displacement of the soil around the grout appeared near the top of grouting zone,and gradually moved up with the increase of grouting distance.(3)On the basis of the grouting deviation tunnel test,finite element simulation and parameterized analysis were carried out.There is a linear relationship between the grouting amount and the displacement of tunnel.The relationship between grouting effect without tunnels and the effect of grouting for correcting horizontal displacement of tunnels was established.The concept of grouting efficiency and the effective range of single hole grouting was put forward.The law of grouting efficiency and effective range under different grouting parameters was obtained.According to the test results and the finite element calculation results,it is suggested that the method of "closer distance,more grouting holes and less quantity” should be adopted in the active control of grouting.(4)Based on a foundation pit project,the displacement of adjacent tunnel during the whole process of foundation pit construction was analyzed.The relationship between the displacement of the subway tunnel and the horizontal displacement of the retaining structure and the vertical displacement of the ground surface was analyzed,and the law of the tunnel displacement was analyzed.The measures of blocked excavation,raising support stiffness and optimization of dismantling support scheme can reduce the influence on the adjacent tunnel,but it has limitations such as high cost and limited control effect.In this project,the application of compensating grouting for correcting horizontal displacement of tunnel were carried out.Compared with the measures of reducing the deformation of foundation pit,the active control of grouting shows its superiority.