傳統的隧道理論多侷限於地質均勻、圓形斷面、應力應變關係為彈性假設等理想情況，電腦數值分析亦多偏向二維的探討，但隧道隨著開挖面的推進，其力學機制本質上應屬於三維問題，以往的二維理論難以完整描述隧道的力學行為，尤其隧道的應力狀況因為隧道尺寸及深度的關係，受大地應力影響甚鉅，加上現地應力量測不易，因此常藉量測變形再回饋反推其受力行為，或作簡化性的假設，來建立其力學分析理論，但是在三維的問題上，關於隧道掘進過程的受力狀況，地拱作用的發展過程，均仍有待了解。此外，由於傳統的單孔隧道設計已無法負荷快速膨脹的交通量，近代隧道多採用雙孔甚至三孔來設計，使得隧道的力學行為更為複雜。
本研究利用有限差分之FLAC3D程式以三維數值模擬，探討隧道工作面掘進過程中之應力調整行為，並分別就不同覆蓋深度及不同側向壓力係數等地質條件下的應力調整狀況加以分析，評估隧道掘進過程的安全性，並建立預估公式。此外，由於地拱發展的機制影響隧道的支撐時機，本研究除對掘進過程中的地拱發展加以探討外，對不同覆蓋深度及不同側向壓力係數的地拱行為也加以比較。雙孔隧道部分，則藉由平行隧道的應力調整、變形行為、安全性評估加以分析，並就不同間距下的應力調整狀況，提出較適間距的評估。本研究希望藉由三維的數值分析，進一步了解隧道掘進的力學行為，以提供隧道工程規劃、設計、施工及監測的參考。

Most theories of tunneling are limited to ideal assumptions under plane-strain condition, such as tunneling into uniform geology, circular cross-section, and elastic stress-strain behavior. Most numerical analyses are also deflected to two-dimensional discussions. However, the drilling characterizations of tunneling and excavation mechanisms should be three-dimensional. The two-dimensional theories are not enough to characterize the excavation behavior completely, especially in understanding the mechanisms and predicting the stress redistribution of tunneling. The shape, size, overburden depth of the tunnel and later earth pressure coefficient of surrounding rock should have significant influence on tunneling mechanisms. Traditionally engineers prefer monitoring displacements to monitoring stress during tunneling due to easy performance consideration. However, the stress redistribution plays a very important role for excavation and support design. The stress redistribution of and ground arch development process of single tunnel excavation are still not clearly. Two parallel, tunnels will be more complicated than single tunnel. These are the study subjects of the paper.
The program FLAC3D was used in this study that simulated the three-dimensional tunneling conditions. The three-dimensional stress adjustments of working surface are analyzed into different geological condition with various depths and lateral pressure coefficients. the safety assessment of tunneling based on stress redistribution are also analyzed. Furthermore, the ground arching development process are also investigated and discussed. The interaction between two parallel tunnels are analyzed from stress adjustment, deformation, safety assessment. Finally some suggestions that help to planning, design, construction, and monitoring of tunneling are proposed.

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