. School of Resources and Civil Engineering, Northeastern University, Shenyang 110819, China . School of Rail Transportation, Soochow University, Suzhou 215131, China . School of Civil Engineering, Sun Yat-sen University, Zhuhai 519082, China . South China Engineering Co., Ltd., China Railway No.5 Engineering Group Co., Ltd., Dongguan 523160, China
Though a comprehensive in situ measurement project, the performance of a deep pit-in-pit excavation constructed by the top-down method in seasonal frozen soil area in Shenyang was extensively examined. The measured excavation responses included the displacement of capping beam and retaining pile, settlement of ground surface, and deformation of metro lines. Based on the analyses of field data, some major findings were obtained: 1) the deformations of retaining structures fluctuated along with the increase of temperature, 2) the deformation variation of retaining structures after the occurrence of thawing of seasonal frozen soil was greater than that in winter, although the excavation depth was smaller than before, 3) the influence area of ground settlement was much smaller because of the features of seasonal frozen sandy soil, 4) the displacement of metro line showed a significant spatial effect, and the tunnel lining had an obviously hogging displacement pattern, and 5) earth pressure redistribution occurred due to the combined effects of freezing-thawing of seasonal frozen soil and excavation, leading to the deformation of metro line. The influence area of ground settlement was obviously smaller than that of Shanghai soft clay or other cases reported in literatures because of special geological conditions of Shenyang. However, the deformation of metro lines was significantly lager after the thawing of the frozen soil, the stress in deep soil was redistributed, and the metro lines were forced to deform to meet a new state of equilibrium.
Just Accepted Date: 03 September 2024Online First Date: 05 November 2024Issue Date: 28 November 2024
Cite this article:
Wenxin CAO,Pengjiao JIA,Pengpeng NI, et al. Performance of a deep top-down zoned pit-in-pit excavation close to existing metro lines through winter[J]. Front. Struct. Civ. Eng.,
2024, 18(11): 1680-1697.
Fig.1 3D illustration of deep excavation with actual photographs.
Fig.2 Properties of different soil layers.
Fig.3 Typical cross section of pit-in-pit excavation.
Fig.4 Schedule of zoned excavation. (Notes: S-1––Construction of supporting structures; S-2––Excavated to 7 m BGS; S-3––Zone N-2 excavated to 14 m BGS, other zones excavated to 8 m BGS; S-4––The Winter Break; S-5––Zone N excavated to 17.5 m BGS, zone E-1 excavated to 13.5 m BGS, zone E-2 and zone W-2 excavated to 17 m BGS, zone W-1 excavated to 13.5 m BGS; S-6––Zone N-1 excavated to 18.7 m BGS, zone N-2 excavated to 21.7 m BGS, zone S excavated to 12 m BGS, zone E excavated to 18.7 m BGS, zone W-2 excavated to 18.7 m BGS; S-7––Zone N-1, zone S, zone E-1, and zone W-1 excavated to 19.65 m BGS, zone N-2, zone E-2, and zone W-2 excavated to 22.15 m BGS.)
Fig.5 Plan view of instrumentation layout (unit: m).
Fig.6 Horizontal displacements of capping beams at different excavation stages: (a) west zone; (b) north zone; (c) east zone.
Fig.7 The maximum horizontal displacement of capping beams upon the completion of excavation.
Fig.8 Typical retaining pile deflections at different construction stages in 2015: (a) west zone; (b) north zone; (c) east zone.
Fig.9 Relationship between excavation depth and maximum lateral pile deflection.
Fig.10 Vertical displacements of retaining piles at different construction stages.
Fig.11 Development of ground settlements during excavation.
Fig.12 Influence zones of ground settlements.
Fig.13 Relationship between maximum ground settlement and maximum pile deflection.
Fig.14 Maximum ground settlement at different excavation depths.
Fig.15 Vertical track displacements of the adjacent metro line during excavation.
Fig.16 Displacement of metro line after each excavation stage: (a) vertical displacement; (b) horizontal displacement.
Fig.17 Tunnel convergences during excavation.
Fig.18 Relationship of displacements between retaining pile and tunnel section: (a) J112 and R5; (b) J144 and R7; (c) J185 and R12.
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