Study On The Calculation Model Of Surface Settlement Caused By Shield Tunneling And Its Engineering Verification

The continuous development of underground rail transit has effectively alleviated the current shortage of urban public land resources,which is mainly reflected in providing another favorable condition for urban residents to travel smoothly.Along with the accelerated pace of economic development in cities and towns around the country and the urgent need of people for high-quality life,the effective and rational development and utilization of underground space has gradually become the focus of attention.But it is not only expensive,but also will inevitably affect the soil environment of the construction section to a certain extent.Soil disturbance will cause uneven settlement of the ground surface,which will endanger the safety of ground buildings,structures and underground embedded pipelines within the construction section.Uneven subsidence effect caused by disturbance of surrounding soil during underground construction has always been the main problem in the process of tunnel excavation.In this paper,the trend of vertical displacement(settlement or uplift)of a key point on the surface caused by shield tunneling is analyzed and studied by applying the way of theoretical deduction.The stress state of the soil in the face and the change of the corresponding position of the soil around the tunnel and the surface during the construction of the target point,such as the head moving from far to near,the shield head reaching the target point,the shield head passing through the target point and the segment assembling and grouting reinforcement at the corresponding position,etc.Based on the analysis of shape displacement,a calculation and analysis model of "stress diffusion-stratified consolidation" is put forward.It is considered that the soil around the tunnel will be in the stress concentration area after excavation,and it will be carried out under the action of vertical component of concentrated stress and the restraint of segment(because the stiffness of segment is far greater than that of part of soil).One-dimensional vertical consolidation settlement calculation of soils(the development rule of traditional consolidation settlement has been slightly revised in this paper)is the deformation of soils in the first concentrated stress ring.When the consolidation of soils in the first concentrated stress ring is completed,a new "bare hole" will be formed,and the soil in the second concentrated stress ring should be carried out again.Force concentration deformation and consolidation settlement change,transfer upward layerby layer until the surface,the sum of the settlement of the surrounding soil is the total vertical deformation at a certain point in the process of subway tunnel excavation.Taking the shield construction section of Erdaoqiao-Xinjiang University Station in the03 section of Urumqi Metro Line 1 as an example,this paper establishes the correlation function between the shield construction process(time)and the vertical deformation at the target measuring point,and summarizes the analysis results and numerical simulation scores with the field measured data.Compared with the analytical results,the rationality and feasibility of the stress diffusion-stratified consolidation model proposed in this paper are verified.In this paper,different from the traditional Peck formula,a new theoretical model is used to analyze and calculate the change of vertical displacement of the target point in the whole process of shield tunnel excavation.The parameters required by the calculation results are related to the stratum and soil properties of the proposed excavation section.For the existing and planned construction,this paper presents a new theoretical model.The development of ground settlement analysis and prediction of subway tunnels has certain reference significance.