潛盾隧道於混合地盤開挖之案例研究

Abstract

摘要 本研究廣泛地收集於含礫石地層潛盾開挖之國內外案例，提出於混合地盤內隧道施工所可能遭遇之問題，並建議解決方法。本論文並介紹台北捷運南港線CN259C標、新店線CH222、CH223及CH224標潛盾隧道工程遭遇卵礫石混合地盤之施工經驗，獲得以下結論。 1. 開放式潛盾機亦適用於卵礫石地層，其優點為較容易將卵礫石自地層中開挖並運至地表。但開放式潛盾機施工常需配合輔助工法，如降水工法、壓氣工法、灌漿工法、冰凍工法等，以穩定開挖面及控制地下水滲入隧道造成開挖面不穩定之問題。 2. 封閉式潛盾機通過卵礫石地層，需要用切刃盤上的切削輪以及切削齒將卵礫石破除並磨碎成較小粒徑的碎屑，以便通過螺運管。 3. 台北捷運南港線CN259C標隧道通過地層包括軟硬程度不同之黏土層、砂土層、卵礫石層、及岩層。在此混合地盤內，施工單位採取JSG噴射灌漿工法改良開挖面上部軟弱黏土之強度，使改良土體和開挖面下部之卵礫石層形成一完整的土體，有效控制潛盾機掘進方向。 4. 就同一深徑比（Z/D）而言，開放式潛盾機所造成之最大地表沉陷量Smax顯然大於密閉式潛盾機所造成的沉陷量。 5. 隧道中心線深度Z越大，地表沉陷槽越寬。若以O’Reilly and New（1982）建議之經驗公式(i=kZ)評估所收集到之沉陷槽寬度監測值可知，k介於0.2至0.7間。

ABSTRACT This paper investigates the problems encountered during the construction of shield tunnels through gravelly soils. Case histories reported in the literature are studied and recommendations are made regarding how to solve the tunneling difficulties. The tunneling experience obtained for the construction of lot CN259C, CH222, CH223 and CH224 of the Taipei Rapid Transit Systems (TRTS) have been collected, and the following conclusions are drawn. 1. Open shields could be used to tunnel through gravelly soils. It would be easier to excavate large particles at the face, and to transport the particles to the ground surface. However, auxiliary methods, such as dewatering, compressed air, grouting, and ground freezing methods, are commonly employed to stabilize the face, and to resist the seepage of ground water into the tunnel. 2. When tunneling through gravelly soils with a closed shield, it would be necessary to break large particles at the face with cutter bits and roller bits mounted on the cutter disc. The smaller particles could then be transported through the screw conveyor or slurry discharge pipe. 3. The shield machine for lot CN 259C of TRTS had to tunnel through soils with different stiffness, such as clayey, sandy, gravelly, and rock layers. To effectively control the direction of excavation, the soft clay encountered at the upper part of the face was modified with JSG method. So that its stiffness becomes consistent with the gravelly soil encountered at the lower part of the face. 4. At the same depth/diameter ratio Z/D, the maximum surface settlement Smax due to an open shield is obviously greater than that due to a closed shield. 5. The deeper the tunnel centerline would result in a wider surface settlement trough. By comparing the monitored data with the empirical equation(i=kZ) suggested by O’Reilly and New (1982), it is found that the k value varies from 0.2 to 0.7 for tunneling through gravelly soils with shield machines.