Settlement behaviors of existing tunnel caused by obliquely under-crossing shield tunneling in close proximity with small intersection angle

Taking a super large deep foundation pit project as an example, the horizontal displacement of crown beam and driveway, surface settlement, axial force of anchor cable, and underground water level in the construction process of the foundation pit are dynamically monitored and analyzed. The excavation deformation rule of the deep foundation pit and the influence of excavation on surrounding buildings are analyzed. The results show that, with the excavation of the foundation pit, the crown beam and driveway of the foundation pit incline towards the direction of the pit and eventually tend to be stable. The variation of axial force of the prestressed anchor cable in the first layer of the foundation pit is basically consistent with the variation of horizontal displacement time history. The variation trend of the groundwater level at each side of the foundation pit is different but tends to be stable in a short time. In the whole monitoring period, the cumulative settlement value of each area of the foundation pit is within the controllable range, but the surface settlement of the north side of the foundation pit and a surrounding building has not reached stability, so it is suggested to extend the monitoring time of settlement in the relevant area.

Section: Introductionmentioning

confidence: 99%

Displacement Monitoring during the Excavation and Support of Deep Foundation Pit in Complex Environment

Li¹

2021

“…Newly built metro tunnels underpassing through the upper existing buildings (structures) and traffic lines are common engineering problems in urban infrastructure construction [1][2][3]. During the construction of metro tunnels, it is very easy to cause large surface settlement, which will threaten the safety of existing buildings (structures) and traffic lines on the upper part [4][5][6]. erefore, it is necessary to study the impact of metro tunnel construction on the existing buildings (structures) and traffic lines and the corresponding construction control countermeasures [7][8][9].…”

Section: Introductionmentioning

confidence: 99%

“…Castaldo et al [22] used the results of the numerical model of the boundary value problem and proposed a simplified probabilistic method to evaluate the impact of the new tunnel excavation on the adjacent existing buildings. Lai et al [6] studied the influence of shield tunnel construction on the settlement characteristics of existing tunnels based on on-site monitoring data and numerical simulation software, and the results showed that the deformation of existing tunnels caused by shield tunneling was mainly the vertical settlement, accompanied by the torsion deformation. At present, most of the two-line or three-line metro tunnels under construction and already built are in parallel in a straight line, while the triangulardistributed three-line tunnel section is still rare in metro construction [23][24][25][26].…”

Section: Introductionmentioning

confidence: 99%

Construction Sequence Optimization and Settlement Control Countermeasures of Metro Tunnels Underpassing Expressway

Zhang

Pei

et al. 2021

The Chongqing metro line 6 underpass expressway around the city is taken as an engineering background, and the optimal excavation sequence and corresponding control countermeasures for the triangular-distributed three-line metro tunnel underpass expressway are studied. The influences of excavation sequence on the tunnel surrounding rock deformation, surrounding rock stress, supporting structure stress, plastic zone, and surface settlement are analyzed by using MIDAS/GTS NX finite element software. The numerical simulation results showed that Case 1 is the optimal excavation sequence of the metro tunnel. However, the surface settlement under the optimal excavation sequence exceeds the limit value of 30 mm, which cannot guarantee the safety of expressway traffic. On this basis, the control measure for strengthening the three-line tunnels with advanced small pipe grouting and reinforcing the middle tunnel with concrete-filled steel tube piles are proposed. Moreover, the excavation process of the metro tunnel with and without reinforcement schemes is numerically simulated. The results show that the reinforcement scheme can effectively control the surface settlement value within the limited value (16.47 mm), which is close to the maximum surface settlement of 18.31 mm after the metro tunnel excavation is completed, indicating that the proposed reinforcement scheme is beneficial to ensure the safety of metro tunnel construction and the driving safety of the expressway.

“…With the continuous advancement of urbanization, the metro system in Chinese major cities is developing rapidly, and the new shield tunnel crossing the existing metro tunnel is increasing frequently [1][2][3][4]. Especially in the city, underground space is increasingly complex nowadays, and the dangerous conditions such as small clearance, narrow space, and multiline staggered bring new challenges to shield crossing construction [5][6][7]. e disturbance of the shield tunnelling changes the stress and pore pressure of the surrounding soil, resulting in the soil deformation.…”

Section: Introductionmentioning

confidence: 99%

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

Wei

Zhang

et al. 2021

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.