Calculation of Soil Deformation Caused by Shield Tunneling through the Sludge Layer with Plastic Drainage Plates

Due to a lack of engineering experience, research on ground deformation during shield machine tunneling in sludge layers is limited, especially in areas with plastic drainage plates installed for ground stabilization. When the shield passes through this area, the shield cutterhead may be jammed by the drainage plates, resulting in excavation surface instability, excess ground deformation, and schedule delay. In this work, a Mindlin solution for ground deformation in such a layer is obtained, considering four factors: the frontal additional pressure generated by the shield cutterhead due to the soil squeezing effect, the uneven lateral friction between the shield shell and the soil, the frontal friction generated by the shield cutterhead when cutting through the drainage plate, and the shield machine restart after shutdown. The results show that the theoretical curve is in good agreement with the measured values. The maximum settlement was approximately 10 m behind the excavation surface, and the maximum uplift was approximately 5 m in front of the excavation surface. The most influential factor among all the studied factors was the additional pressure on the shield cutter, which accounted for approximately 56% of the maximum settlement and 60% of the maximum uplift. The soil settlement mainly occurred within 12 m on both sides of the tunnel axis. The maximum settlements at the different soil depths tested were all directly below the tunnel axis.

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