新永春隧道高壓湧水段處理過程之探討

新永春隧道決定改移至東側路線施工後,後續施工通過高壓湧水區段,仍存在諸多不確定之地工及地質災害特性。針對其可能的影響程度需加以釐清,並對後續施工可能發生災害加以評估後,作為突破策略與施工處理方案之建議及參考。而突破策略以遠排近灌、先撐後挖、随挖随襯之理念,依據新永春隧道災變段高壓、巨量湧水特性,採迂迴坑進行大口徑排水洩水降壓、阻水灌漿、補強岩體灌漿、施作管幕工法以防止斷層段或破碎岩盤崩坍、加強鋼支保、縮短輪進距離、將隧道斷面由馬蹄形改為正圓形、後績長期監測系統之建立,處理方案包括設置排水導坑、排水隧道、大口徑排水等措施降低水壓,導引水流,並在隧道開挖前進至湧水層之前,採熱瀝清灌漿予以先期灌漿阻水,阻斷地下水滲入隧道,提供較佳的開挖支撐環境等。俟開挖進行則搭配如管幕工法、錐體灌漿、微形樁、化學灌漿地質改良等適宜之輔助工法,加強支撐與補強岩體,以利順利開挖穿越突破。

STUDY ON TREATMENT OF HIGH-PRESSURE WATER GUSHING IN NEW YUNGCHUNG TUNNEL

In October 1998, during the excavation of New Yungchung Tunnel, massive and high-pressure water gushing occurred at the south portal workface. The project has been successfully completed and the measures adopted for this long-lasting water gushing problem are reviewed and discussed herein. During the treatment, the procedures or methodologies were modified based on the newly-obtained supplemental geologic data and the results of the previous treatment steps. The hot bitumen grouting was employed to reduce the hydraulic conductivity of the surrounding formations to advance the tunnel through the water bearing zone, which is the first application of hot bitumen grouting in Taiwan. The design was modified timely and properly according to the changes in site conditions, and information sharing and cooperation in construction teams helped the completion of the mission.