Deformation Characterisation and Distress Diagnosis of a Metro Shield Tunnel by Adjacent Constructions

Abstract

<jats:p>This paper presents a case history of the developmental effect of a large-area excavation, 8 high-rise main buildings, a series of annex constructions, and ground overloaded building demolition on the deformation characteristics of an existing shield tunnel within Guangzhou Metro Line No. 1 in close proximity to the development. The shield tunnel lies in a sandy layer of the typical upper-soft and lower-hard strata in Guangzhou district, and the deformation of the tunnel has been monitored since the tunnel was put into operation. The monitoring results reveal that the adjacent construction induces an excessive tunnel settlement with a maximum of 14.4 mm and an excess tunnel displacement with a maximum of 5.2 mm, which are within the corresponding limitations of the codes for the safe operation of urban rail transit tunnels. While the station expansion project is being conducted beside the tunnels, a series of tunnel distresses, including large-area water seepage, spalling concrete blocks, and segmental cracks, are recorded. Our field monitoring data indicate that the tunnel is subjected to further vertical contraction and horizontal expansion due to the station expansion project, and a maximum tunnel flattening rate of 36.78% is detected. Furthermore, the tunnel linings are studied numerically and theoretically to obtain the limitations of tunnel deformation and discuss why tunnel distresses of water seepage, concrete spalling, and segmental cracking occur. Finally, on the basis of the analyses and discussions above, counteracting corrective measures, including compensation grouting soil strengthening and bonded steel plates, are adopted as exterior and interior strengthening methods, respectively, to eliminate further tunnel distresses and ensure safe operation. The lessons learned and summarized in this study may help prevent similar tunnel distresses from reoccurring in the future.</jats:p>

Research on Lateral Deformation Control Criteria of Metro Shield Tunnels with Excessive Ellipticity

“…Excessive elliptical deformation in shield tunnels irreparably damages concrete structures. Large lateral deformations from external loading, even if promptly unloaded, make it challenging to rectify the tunnel segment's lateral deformation [25]. This directly affects the safety margin for enduring structures like shield tunnel structures.…”

Experimental Study on the Transverse Effective Bending Rigidity of Segmental Lining Structures

“…e tensile result shows that the elastic modulus of the aluminium welding wire (type 1060) is 2.45 × 10 4 MPa, and it is suitable to be bent into the needed shape for its flexibility. us, we decided to select aluminium welding wire to simulate bolts and calculate the diameter and length of aluminium welding wire using equation (3). e geometric and mechanical properties of longitudinal bolts of model and prototype segmental lining are shown in Table 2.…”

“…As a result, the effect of the joints on internal forces and deformation characteristic should be taken into consideration in the design or safety evaluation of the tunnel lining. In the engineering and numerical analyses related to the underground shield-driven tunnel problems, figuring out accurately the mechanism performance of segmental linings has always been one of the major foci [1][2][3].…”

Characterization of Underlying Twin Shield Tunnels Due to Foundation-Excavation Unloading in Soft Soils: An Experimental and Numerical Study

“…Moreover, when the basement was built on the side of the existing tunnel, the diaphragm wall was more effective than the sheet pile wall in terms of controlling settlement and tensile strains of tunnels. Liu et al [24] reported that a series of hazards such as water seepage, concrete spalling, and segment cracks occurred when a station-expansion project was conducted beside the tunnels. Additionally, they further discussed the causes responsible for these hazards based on the performed numerical and theoretical investigations.…”