摘   要

近年來 由於施工技術之進步及地下深處空間需求之增加，超過千米以上之高岩覆隧道或洞室開挖有逐漸增加之趨勢。而地下深處之岩體具有高地應力、高地溫及高水壓等三高環境，在此三高環境中施工，所遭遇之問題與困難度均將大幅提升。本研究著重於高地應力對隧道設計與施工影響，整體研究構思為透過工程案例資料蒐集、深部岩石材料力學特性探討、脆性破壞數值分析方法研擬、數值案例庫建立、開挖工法與支撐材料研究等，彙整探討高岩覆隧道施工圍岩行為與可能面對之關鍵問題，並進一步嘗試對高岩覆隧道設計理念與挖撐工法提出建議與檢討，以提升臺灣地下開挖及隧道工程水準。

本報告為第一期研究成果報告，重點工作為工程案例與文獻資料蒐集、高地應力對岩石材料力學性質影響探討、深部岩體工程問題彙整與破壞機制初探、數值分析方法研擬等。研究結果顯示，由於臺灣目前缺乏足夠之高岩覆隧道案例可供參考，而國外之工程案例，則因地質及施工條件之差異，在臺灣之適用性有待檢討，故設計常用之案例類比法及經驗設計法，可能無法直接採用，需輔以數值分析法進行檢核。國內隧道工程界熟悉常用之彈塑性力學模式，在高岩覆時僅適用於斷層剪裂帶或軟弱岩層材料，對於深部完整硬岩，則需考慮其破壞峰後強度弱化特性。本研究以臺灣東部大理岩進行試驗，並研提考慮圍壓因子之強度弱化分析模式，可提供臺灣高岩覆隧道數值分析設計參考。

惟本報告為第一期之研究成果，針對高岩覆對隧道設計與施工影響仍有許多待研究之課題，包括臺灣代表性硬岩材料力學性質、適用節理岩體之強度弱化分析模式、臺灣高岩覆案例資料、擴挖預留變形空間及被動式支撐工材料等輔助工法、高岩覆隧道數值案例庫等，將於後續階段繼續進行研究探討，以期提升臺灣高岩覆地下開挖技術水準。

Influence of High Overburden on Tunnel
Design and Construction (I)

ABSTRACT

Due to the improvement of construction technology and the requirement of deep underground opening, the trend of tunnel overburden exceeding 1000 meters has increased recently. Rock mass in the depths has the three “high” characteristics – high ground stress, high earth temperature, and high groundwater pressure. Within environment of the three ‘high” characteristics, tunneling difficulty drastically increases. This research aims at the impact of high ground stress on tunnel design and construction. The conception of this research is to understand the mechanical behaviors of rock mass around the deep excavation and the possible significant construction problems by using the collection of deep tunnel cases, the investigation of hard rock’s properties, the development of brittleness numerical simulation, the installation of numerical database, the discussion of excavation method, and the examination of supporting work, etc. Furthermore, the design philosophies and the construction recommendations for deep tunneling are proposed in the research to improve the technology of tunnel engineering in Taiwan.

This is the first stage of the research. The data collection of literature and tunneling cases, the property studies of hard rock under high stress condition, the problem survey of deep excavation, the method development of brittleness numerical simulation, and the preliminary consultation of rock support were carried out in the stage. Basically, the actual deep tunneling cases are extremely insufficient in Taiwan. The foreign cases are not entirely suitable in Taiwan due to the different geological condition and construction technique. Therefore, both the case-based reasoning and the empirical design method may be used only to preliminary design in deep tunneling in Taiwan. It is advised to re-examine the preliminary design by using the numerical analysis. In high rock cover environment, the well-known mechanical model of elastic-plastic behavior is only applicable to the fault zone and shear materials. The characteristic of post-peak strength degradation is needed for the intact hard rock. The analysis method of strength degradation linked the confining pressure as proposed in this research may offer a feasible method to simulate the intact hard rock excavation.

Although many attempts have been made in this research stage, there are many issues needing to be further investigated, including the mechanical properties of typical brittle rocks in Taiwan, the numerical modeling of strength degradation accepted in jointed hard rocks, data collection of local deep tunnel cases, the reasonable enlargement design of tunnel excavation, the knowledge of yielding support work, and the installation of numerical database for deep tunnels, etc. In order to improve the technology of deep underground excavation in Taiwan, subsequent research projects are needed.