Research On Non-uniform Settlement Of Operation Period Tunnel Shield Under Stack Load

In recent years,with the rapid development of economy,urban subway has become one of the important means to solve traffic congestion.With more and more urban subway put into operation,the settlement of shield tunnel is prominent,especially uneven settlement.In this paper,the uneven settlement of shield tunnel is studied from two aspects: ground surcharge and longitudinal soft and abrupt soil layer.The main elements include:The main contents are as follows:(1)the settlement of shield tunnel under ground surcharge is calculated with Boussinesq solution and Winkler elastic foundation beam model in elastic mechanics,and the settlement of shield tunnel is solved by difference method,and the size,size and offset distance of surcharge are analyzed.The influence of the buried depth and the bed coefficient on the tunnel structure shows that the settlement curve of the tunnel is positively distributed in the form of curve and the larger the center of the surcharge the greater the settlement value of the tunnel.The displacement position of heapload,the size of heaped load,the width of heap-load and the coefficient of soil foundation have little influence on the settlement range of tunnel,while the length of heaped load and the depth of burying have little effect on the settlement range of tunnel.With the increase of the length of heaped load and the depth of burying,the influence range of tunnel will be enlarged accordingly.The heap-load offset position,buried depth,heap-load dimension and the coefficient of soil base and the maximum settlement value of the tunnel are distributed exponentially,and the heaped load and the maximum settlement value of the tunnel are distributed linearly.(2)the formula of elastic foundation beam of longitudinal soft and hard abrupt soil layer is deduced,and the settlement value of tunnel in soft and hard abrupt soil layer under surcharge is calculated,and the size,size and offset distance of pile load are analyzed.The influence of the buried depth and the difference degree of the bed coefficient on the settlement of the tunnel is obtained.The results show that the maximum settlement of the tunnel occurs in the center of the surcharge,but on the side of the soft soil,because of the uneven soft and hard soil in the longitudinal layer of the tunnel,and the maximum settlement of the tunnel occurs in the center of the surcharge.Soft soil increases the overall settlement of the tunnel and expands the range of uneven settlement.Position shadow of maximum settlement value of tunnel by changing heapload offset distance,heaped load size and surcharge width The depth of burying,the length of pile load and the degree of soft and hard soil have great influence on the position of the maximum settlement of tunnel,so we should pay more attention to the monitoring and measurement.(3)using MIDAS-GTS software to establish the tunnel model in the soft and hard abrupt soil layer under the condition of surcharge,and to study the settlement of the tunnel by changing the parameters such as the size,offset distance,buried depth and elastic modulus of the soft soil,etc.The results show that the conclusions obtained are similar to those obtained from the calculation of the beam formula of the elastic foundation in the longitudinal soft and hard abrupt soil layers,which proves the correctness of the derived formula.(4)The common diseases of shield tunnels during operation are summarized,which are divided into four categories: segment diseases,seepage diseases,ballast diseases and longitudinal uneven settlement diseases of tunnels.According to different tunnel diseases,the paper summarizes their causes and corresponding treatment measures,which provides experience for the prevention and treatment of shield tunnel diseases.