| Although the shield method has been widely used in subway construction throughout the country and can draw on the design experience of similar projects in other cities in China,but we still lack of mature technology and experience suitable for the design and construction of shield engineering in the Changzhou area,especially lacking the law of settlement and deformation of the ground surface caused by the construction of parallel double-line(uplink and downlink)shield tunnels.Based on the engineering of Changzhou Metro Line 1 and Line 2,this paper analyzes the field data by using Peck curve,numerical simulation,and neural network model as mainly method,and studies the settlement law and structure of the parallel double-track shield tunnel of Changzhou Metro.The main research work and results are as follows:(1)Fitting the surface settlement monitoring data with Peck formula,the study found that the fitted surface settlement is basically consistent with the actual settlement.Among them,the impact of the excavation of the second line of the parallel tunnel on the ground surface is expanded by 5m ～ 10 m.The fitted maximum settlement is less than the actual settlement of 0.21 mm ～ 1.53 mm,and the loss rate of single line settlement is between 0.31% ～ 0.63%.Two parameters(the maximum surface settlement correction coefficient α and the settlement groove width correction coefficient β)are introduced to correct the traditional Peck formula;the corrected maximum settlement value error interval is between 0.13 mm and 0.74 mm,and the fitting result is better.(2)The shape law of the surface settlement trough is studied.The shape is mainly divided into "U" type and "W" type.The construction sequence is the main reason that affects the shape of the settlement channel.Simultaneous excavation of parallel tunnels is easy to form a "U" shape,and the excavation changes to a "W" shape.With the increase of the Ratio of tunnel depth to spacing the shape changes from "W" to "U".(3)The settlement changes caused by side-passing and under-passing buildings are analyzed through numerical simulation,.When the tunnel passes through the bridge sideways,the settlement rate in the middle of the bridge is greater than the settlement rate at both ends of the bridge;the horizontal displacement directions on both sides of the bridge are opposite,mainly caused by the overall deformation of the bridge.When the shield penetrates the building sideways,the closer the building measurement point is to the tunnel,the greater the maximum settlement value and accumulated deformation.When the shield passes under the building,the settlement caused by the advance line is greater,accounting for about 2/3 of the total settlement.Moreover,the settlement caused by the simultaneous excavation of parallel tunnels is greater than the settlement caused by successive excavations;the distribution of surface buildings will make the settlement caused by tunnel construction uneven,and the tunnel settlement with the main part biased is bigger.(4)Combined with the stratum conditions of Changzhou Metro Line 1 and Line 2 and the tunneling parameters,the factors affecting the ground settlement were analyzed.Among them,tunnel depth、grouting volume and soil pressure are the main factors affecting settlement.Combining the monitoring data and construction experience,we give the recommended values of shield tunneling parameters in Changzhou area and propose control measures for tunneling posture and segment waterproofing.(5)Based on neural network method to make prediction of ground settlement caused by tunnel construction.Research shows that the prediction effect is best when the number of neurons is 6.The maximum error between the prediction result and the actual settlement value of the surface does not exceed 0.25 mm.The neural network is improved by the two methods of momentum factor algorithm and adaptive learning rate,and the prediction period is shorten. |
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