Spatiotemporal Deformation of Existing Pipeline Due to New Shield Tunnelling Parallel Beneath Considering Construction Process

In this paper, we study the effects of the shield tunnel construction on the deformation of an existing pipeline parallel to and above the new shield tunnel. We propose an analytical solution to predict the spatiotemporal deformation of the existing pipeline and consider different force patterns of the shield tunnelling, i.e., ground volume loss, support pressure, frictional force, and torsional force. The proposed method is validated by the monitoring data of Subway Line 3 of Nanchang and provides a reasonable estimation of the pipeline’s deformation. The parametric analyses are performed to study the influences on the pipeline’s deformation. The main advantage of our paper is that the spatiotemporal characteristics of the existing pipeline’s deformation are analysed, providing longitudinal deformation curve (LDC), deformation development curve (DDC), and grouting reinforcement curve (GRC). Compared with the perpendicular undercrossing project, both LDC and DDC have the same profiles and maximum values and move forward as a whole with the shield tunnel advance. Thus, the spatiotemporal deformation of the overall pipeline can be extrapolated from the deformation of two known points on the pipeline. The spatiotemporal characteristic curves combined with LDC, DDC, and GRC can suggest feasible, effective, and economical construction and grouting schemes to control the pipeline’s deformation after the deformation control standards have been determined.

Compound Karst Cave Treatment and Waterproofing Strategy for EPB Shield Tunnelling in Karst Areas: A Case Study

There is high risk of water inrush and ground collapse accidents when tunnelling in karst areas. Based on the case study of an urban metro tunnel, this paper focuses on karst cave treatment and waterproofing strategies for earth pressure balancing (EPB) shield tunnelling in karst areas containing large amounts of karst caves and fissures. When the shield machine enters the karst area, water gush easily occurs, posing serious threats to tunnelling safety. The distribution characteristic of limestone fractures, karst caves, and fissures in the karst area were analyzed according to the geological survey results. Further, water inrush risk and engineering difficulties were analyzed. Subsequently, a compound karst cave treatment and waterproofing strategy for EPB shield tunnelling was proposed and implemented. Water inflow is successfully reduced and ground collapse accident is avoided using the compound karst cave treatment and waterproofing strategy.

Deformation Characteristics of Existing Twin Tunnels Induced by Double Shield Undercrossing with Prereinforcement: A Case Study in Hangzhou

This paper is based on the case of the earth pressure balance (EPB) shield tunnelling project of the new Metro Line 2 undercrossing the existing Metro Line 1 in the soft soil urban area of Hangzhou. Because the EPB shield must break through a plain concrete wall before undercrossing the existing tunnels, the pipe roof prereinforcement was adopted to stabilize the soil between the existing tunnels and the new shield tunnel. The deformation characteristics of the existing tunnels in the process of double shield undercrossing were discussed. According to the variation of shield position, the settlement development could be divided into three stages: shield approaching subsidence, shield crossing heave, and shield leaving subsidence. The horizontal displacement shows a back and forth variation characteristic consistent with the direction of shield tunnelling. At the junction of tunnel and station, the shield undercrossing caused considerable differential settlement between the existing tunnel and the station. The construction of pipe roof prereinforcement will lead to the presettlement of the existing tunnels. The settlement of the existing tunnels caused by the attitude deviation of pipe roof and grouting disturbance should be reduced in reasonable ranges. In addition, the maximum longitudinal settlement of the existing tunnel during the shield second undercrossing was also discussed. It was considered that the influence of wall breaking is greater than the sequence of shield undercrossing. The driving parameters of shield tunnelling should be optimized before the second crossing.