Abstract
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.
Highlights
With the rapid development of urban transit planning and construction in China and around the world, an increasing number of cities have built underground tunnels to address the increased congestion of ground transportation during recent years
Many underground constructions need to be implemented in close proximity to existing tunnels [1,2,3,4,5,6]. e excavations of these underground constructions will unavoidably cause soil deformation either inside or outside of the excavation pit or even both, which may severely influence the stability of adjacent structures [7,8,9]
Huang et al [11] reported a field case in which an operating shield tunnel was disrupted by the unexpected extreme surcharge caused by adjacent constructions. e longitudinal joints between tunnel lining segments were severely disrupted and presented large openings
Summary
Previous engineering experiences and numerical studies have concluded that the deformation and stress of the existing tunnels and surrounding soils can be greatly impacted by adjacent constructions. Proper repair measures are proven to effectively mitigate these impacts Most of these studies focused more on the integrity of the tunnels rather than small tunnel components, which are crucial parts for preventing incidents and settlement problems. Is paper conducts a case study on the dense tunnel distresses caused by a large-area excavation close to an existing metro tunnel. E performance of connecting bolts, segmental cracking, and the stress of reinforcements and joint openings are discussed, which are further analysed numerically and theoretically to obtain the limitations of the tunnel deformation to prevent these tunnel distresses. Is paper conducts a case study on the dense tunnel distresses caused by a large-area excavation close to an existing metro tunnel. e induced tunnel distresses were first demonstrated and analysed in detail. e performance of connecting bolts, segmental cracking, and the stress of reinforcements and joint openings are discussed, which are further analysed numerically and theoretically to obtain the limitations of the tunnel deformation to prevent these tunnel distresses. e methods and experiences presented in this paper can be adopted for constructions adjacent to existing metro tunnels with greater applicability
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