| Due to the continuous construction and development of urban rail transit in China,there are more and more deep foundation pit projects in the subway protection area,and the excavation and unloading of foundation pit will break the initial stress balance state of surrounding soil,and generate new stress and displacement fields in the interior,which will lead to excessive additional deformation of the tunnel between the shield areas of the side subway,and may lead to cracks,seepage and other diseases of the tunnel structure It threatens the safety of the tunnel structure and the safe operation of the line.The problem of longitudinal deformation and control caused by excavation of foundation pit around metro shield tunnel has become an important problem to be solved urgently in the field of geotechnical engineering in China.Based on the project of Zhongshan International Foundation Pit in Xuzhou,this paper analyzes and studies this problem by using mathematical statistics analysis,theoretical calculation,numerical simulation and comparative analysis.The main achievements of this paper are as follows:(1)This paper collects and arranges 20 foundation pit projects of adjacent metro tunnels with actual monitoring data in China,classifies and arranges relevant data,and makes statistics on the distribution range of vertical and horizontal additional displacement values of metro tunnels.The results show that most of the vertical and horizontal additional displacement of tunnels are concentrated in the range of 0 ~ 8mm.Then,according to the horizontal distance between the retaining structure of the foundation pit and the tunnel,the height difference between the pit bottom and the vault,the space-time effect,the soil reinforcement inside and outside the pit and other factors that affect the additional deformation of the subway tunnel,the deformation mechanism and the basic characteristics of the additional deformation of the subway tunnel under the influence of the excavation of the surrounding foundation pit are summarized.(2)Based on the longitudinal equivalent stiffness model of the tunnel and the theory of double-sided elastic foundation beam considering the influence of the soil overlying the tunnel,a two-stage analysis method suitable for the calculation of the additional deformation of the metro shield tunnel in Xuzhou area is proposed: firstly,the additional load caused by the unloading of the foundation pit bottom and three side walls on the adjacent shield tunnel structure is calculated by using Mindlin elastic solution;secondly,the additional load caused by the unloading of the foundation pit bottom and three side walls is transported Based on the two-sided elastic foundation beam model,the subway tunnel is regarded as an infinite elastic beam,and its longitudinal additional deformation differential equation is established.Then,the finite element model of Xuzhou clay mechanical parameters is established,and the results of this method are compared with the results of the traditional winker model,the results show that the results of this method are more accurate.(3)Through changing the parameters such as the horizontal distance between the foundation pit and the tunnel,the excavation depth of the foundation pit and the coefficient of the foundation bed in the mechanical model of the metro shield tunnel in Xuzhou area,the parameter sensitivity analysis is carried out.The theoretical calculation results show that: the maximum vertical and horizontal displacement deformation of the subway tunnel structure occurs at the corresponding position of the foundation pit center,with the increase of the horizontal distance between the two,the vertical and horizontal deformation of the tunnel decreases rapidly,and finally tends to be gentle;the tunnel uplift deformation increases gradually with the increase of the excavation depth of the foundation pit,and reaches the maximum when the excavation surface is close to the tunnel buried depth,Then it becomes settlement deformation.The horizontal displacement and deformation of the tunnel increase with the increase of the excavation depth;the longitudinal deformation of the tunnel is greatly affected by the coefficient K of the foundation bed,and with the increase of the value K,the horizontal displacement and deformation of the tunnel increase with the increase of the excavation depth The sensitivity of the vertical and horizontal deformation of the tunnel to the above three parameters is: excavation depth > horizontal spacing > foundation bed coefficient,horizontal spacing > foundation bed coefficient > foundation pit excavation depth.There are 66 figures,11 tables and 105 references in this paper.(4)The numerical simulation method is used to study the influence of the excavation of Zhongshan International Foundation Pit on the deformation of the tunnel adjacent to line 2 under the condition of conventional layered excavation.The results show that the vertical and horizontal deformation of the right line tunnel are greater than that of the left line tunnel,and the size effect of the foundation pit has more obvious influence on the vertical and horizontal deformation of the right line tunnel,and the maximum vertical displacement of the right line tunnel exceeds the specification Early warning standard.Then combined with the soil quality of Xuzhou area,the control and reinforcement measures of excavation and unloading of foundation pit,soil reinforcement in pit and structural reinforcement of tunnel are studied and analyzed to control the vertical deformation of the right line tunnel.Finally,considering the principle of economic and convenient construction,a set of control schemes with multiple measures are put forward.The results show that the control effect is significant,and the vertical deformation of the tunnel is obvious Slight change.The research results can provide some experience of similar projects in Xuzhou area. |
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