Research On Ground Settlement Of Embankment In Construction Of Shield Tunnels

Shield tunneling method is an important construction method of tunnel construction,which is different from the new Austrian law,mining law and other tunnel construction methods.Shield tunneling method has the advantages of high efficiency,safety,reliability and small impact on the surrounding environment.Nevertheless,shield construction method will still inevitably disturb the surrounding soil,and then directly affect the tunnel construction and the safety of surrounding environment.Therefore,the diminution of the disturbance of surrounding ground surface which caused by shield tunneling construction.The analysis of ground settlement principles and the influencing factors of subsidence are important to tunnel construction.The levee section of cross-river tunnel which on the Weisan road in Nanjing City is the background of this article.The finite element software ABAQUS is used to establish the three-dimensional finite element model.The dynamic construction process of shield crossing high embankment is researched by numerical simulation,and then obtain predicted settlement values of surrounding ground surface.Meanwhile,the article monitors the ground settlement of horizontal and vertical monitoring sections in the process of shield crossing the embankment,and then compares simulation calculation values with monitoring results The comparison between measured data and prediction values shows that the calculated values are in good agreement with the measured data.In order to further guide the tunnel excavation.Based on the three-dimensional model of shield excavation,the article study the ground settlement under the influence of the shield tunneling pressure,grouting conditions,covering soil condition and surrounding rock stress relief respectively,and put forward the corresponding control measures,which provides references for shield construction.The main works and research results are as follows(1)Shield tunneling pressure has great influence on the vertical ground settlement ground settlement,and the driving pressure should be controlled in the vicinity of the water and soil pressure in the excavation face.The driving pressure crossing the embankment of Jiangxinzhou should be controlled around 500 kPa.(2)The equivalent circle zone is used to simulate the synchronous grouting,it found that the modulus change of the equivalent circle zone has little influence on the ground settlement,while the thickness change of the equivalent circle zone has a great influence on the ground settlement.(3)The result shows that the secondary grouting pressure has great influence on the ground settlement.As the grouting pressure greater,so the ground settlement smaller.What's more,the secondary grouting can cause the vertical surface to appear uneven settlement.(4)Under normal stratum loss,covering soil modulus has great influence on the final vertical ground settlement,but has little effect on the horizontal ground settlement.If the covering soil conditions are the same,the more close to the tunnel,the more obvious the disturbance of the soil layer is,and then the deformation of the stratum becomes greater.(5)Under the same condition of geological condition and shield construction parameters,the settlement of ground surface increases with the increase of the stress relief rate of surrounding rock.But it varies slightly.