港珠澳大桥拱北隧道施工变形规律分析
Observed deformation behavior of Gongbei Tunnel of Hong Kong-Zhuhai-Macao Bridge during construction
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摘要: 在地质条件复杂的沿海富水地层开挖浅埋超大断面隧道,面临诸多风险,暗挖施工易对围岩进行扰动,引起地层变形。新型“管幕冻结”支护可以有效控制暗挖施工引起的地表沉降过大问题,该工法下隧道开挖过程中地表位移变化主要受暗挖产生的地层损失和土体冻结膨胀以及隧道开挖卸荷后的上浮效应等因素影响。基于现场实测数据,对洞内拱顶位移、水平收敛和地表变形规律进行分析发现,拱顶位移与对应地表处的位移变化具有较强的一致性,纵向上在隧道中部段出现上浮,两侧洞口段出现下沉。受分层开挖扰动影响,隧道两侧土体向内变形导致洞内水平收敛增大,最大水平收敛为15.72 mm,约为隧道横向跨度的0.8%。新型管幕冻结暗挖施工工法可以很好地控制富水地层渗漏水问题,且极大地减小了隧道内部的位移变形,但其冻结膨胀引起地表隆起及解冻后的地表融沉问题仍需密切关注。Abstract: The excavation of shallow buried tunnels with super-large section in coastal water-rich strata with complex geological conditions faces a lot of risks. The surrounding soil is easy to be disturbed during excavation, causing the ground deformation. The new method of "freezing-sealing pipe-roof for pre-support" can effectively control the surface settlement caused by the excavation construction. The change of surface displacement during tunnel excavation using this method is mainly affected by the factors such as the ground loss caused by tunnel excavation, expansion of frozen soil and floating effect after tunnel excavation unloading. The rules of tunnel crown displacement, horizontal convergence and ground deformation are investigated based on the in-situ observation. The displacements of the tunnel crown and the corresponding surface are consistent. In the longitudinal direction, the crown and ground surface move up in the middle section and move down in the sections at both sides near the working shafts. Under the influence of layered excavation disturbance, the inward deformation of the soil at both sides of the tunnel leads to the increase of horizontal convergence, and the maximum horizontal convergence is 15.72 mm, which is about 0.8% of the transverse span of the tunnel. The new freezing-sealing pipe-roof method can solve the problem of water leakage in the water-rich strata, and greatly reduce the internal deformation of the tunnel. However, the problem of surface heaving caused by soil freezing and the surface settlement after soil thawing still require great attention.