潛盾隧道施工引致之地表及深層沉陷

Abstract

本研究之第一部份探討在台北盆地粘土層內，平行潛盾隧道施工所引致的 地表沉陷、土層水平位移及地表沉陷隨時間變化之關係。本研究在台北捷 運系統南港線CN254標設置了包含傾斜儀及地表沉陷釘之測陣，長期進行 監測以獲得土層變位的資料。本研究發現第一條隧道施工後，引致之單位 長度地表沉陷槽約為隧道開挖體積之2.6%~3.2%。地表沉陷釘的資料顯示 ，潛盾機盾首通過測陣二星期內，主要沉陷即已完成。第一條隧道施工後 所引致之次要沉陷量明顯大於第二條隧道施工後引致之值，這可能是由於 在第一條隧道施工後，已對鄰近土層造成壓密及擾動之故。關於地表沉陷 與時間之關係，本研究將監測值與雙曲線模式之預測曲線相互比較，發現 雙曲線模式除了可預測隧道中心沉陷行為外，亦可對隧道中心兩側測點之 地表沉陷與時間的關係加以描述。潛盾機通過測陣542天之地表沉陷值與 依 Peck-Fujita經驗方法求得之預測範圍符合。顯示Peck-Fujita經驗方 法亦適用於預測台北粘土層平行隧道施工所造成之沉陷。而在研究的第二 部份探討潛盾隧道施工所引致之深層沉陷。本研究分析國內外已發表的深 層沉陷監測資料，提出了一簡易的經驗方法去估算深層沉陷的範圍。將所 蒐集的國內外10組監測資料與所建議經驗法預測範圍比較後發現，各深度 之監測值大都位於預測範圍之內，顯示所倡議經驗方法具有高度之可行性 。 The first part of this paper presents the field data monitored during the construction of parallel shield tunnels of contract CN254 for the Taipei MRT system.To measure the soil displacements above the tunnels, Surface settlement points and inclinometer casings were installed.The volume of settlement trough measured after the construction of the first tube is about 2.7% to 3.2% of the tunnel volume. Primary settlement was completed about two weeks after shield's passage. The secondary settlement caused by the first tunnel is larger than that caused by the second tunnel. This is because a large part of consolidation of soil was comple- ted during the construction of the first tunnel. Basn on the field data,it is found that settlement-time relationship can be properly described by the hyperbolic model.Five hundred and forty two days after the passed of shield,the settlement trough obser- ved was in good agreement with the range predicted by Peck-Fujita method. The second part of this study suggests an empirical method to estimate the subsurface settlement due to shield tunnelling. It is suggested that the subsurface settlement trough can also be described with the error function. Relationship between surface and subsurface settlement trough width and maximum settlement have been established.An illustrative example is given indicating how to evaluate the range of subsurface settlement with the method proposed. The comparison between the field data and estimated subsidence range indicates that the suggest method can properly evaluate the subsurface settlement due to