軟弱地盤內之新奧工法隧道施工

Abstract

本論文介紹於都會區軟弱土層內以新奧工法（NATM）構築隧道之設計及施工方法。本文首 先探討新奧工法的設計理念，其在軟弱地盤施工應注意之問題及常用的施工方法，接著介 紹近年在德國波昂、慕尼黑及奧地利薩爾斯堡之軟弱地盤內以新奧工法開挖隧道之成功施 工案例。論文接著介紹與台北捷運系統新店線CH221標NATM隧道開挖相關之地質狀況、設 計理念及施工步驟。施工中所採用的水泥皂土截水牆、預先支撐法、台階式開挖、噴泥土 支撐以及壓氣工法等施工技術都在本論文中加以介紹。文章內也敘述CH221標NATM 隧道開 挖所造成之各項意外事件。本研究發現： 1.CH221標NATM施工造成之沉陷觀測資料皆落在以Peck-Fujita方法（ Fang , et al. , 1994）預測開放式潛盾機施工造成沉陷槽之上限曲線與下限曲線之間。 2.依據CH221標NATM的地表沉陷觀測資料可知，地表沉陷與時間之關係可以用Fang et al. (1993)所建議之雙曲線模式(Hyperbolic model）加以預估，但是雙曲線模式並不適合用 來預估開挖面通過該點前後若干天的地表沉陷行為。 3.CH221標NATM的地表沉陷縱斷面資料顯示，隧道開挖對前方地盤的擾動範圍達17m至23m。 根據國內外NATM在軟弱地盤內24個施工案例，本論文對噴凝土厚度、混凝土內襯砌厚度 、鋼矢板及鋼管預先支撐長度、及 開挖方式歸納出數項經驗法則，供NATM隧道初步設計 之參考。 The design and construction of soft ground tunnels with the New Austrian Tunnelling Method (NATM) is studied in this article. The general principles, and construction techniques of NATM are introduced. Case histories associated with the construction of soft ground tunnels at Bonn, and Munich of Germany and Salzburg, Austria are discussed. In the latter part of this paper, geological condition6s, design concepts and construction procedures related to the tunnelling of Hsintien Line lot CH221 of the Taipei MRT systems are investigated .Tunnelling techniques such as cement-bentonite cutoff walling,pre-support method,bench excavation, shotcrete support and compressed-airmethods are introduced in this paper. A few accidents associated with NATM tunnel excavation are discussed.Based on the study regarding lot CH221 of Taipei Rapid Transit systems,it is conclude that : 1.Field settlement data1.Field settlement data due to NATM construction fall between the upper and lower settlement curves predicted bytruction Peck-Fujta Method (Fang,et al. 1994) for open shield. 2.Observed surface settlement data indicate that, the settlement versus time relationship can be properly approximated with the hyperbolic model suggestedby Fang et al (1993). However,the hyperbolic model can not be used to estimatethe settlement behavior a few days before and after the face pass through the monitoring point. 3.Longitude settlement profile indicate that the disturbed range in theground ahead of the face is approximately 17 m to 23 m long. Based on the 24 cases of soft ground tunnelling with NATM in different countries, several design recommendations regarding thickness of shotcrete, thickness of concrete lining, length of pre-support,and methods of excavation are proposed.