本研究利用UDEC軟體探討不同節理分佈對馬蹄形隧道開挖之應力與變形影響，首先分析無節理情況之馬蹄形隧道開挖，接著引入三種不同節理分佈，包含一條節理之傾角分別為45°及135°，以及合併成兩條節理，三種分佈情況之節理皆通過隧道之右角隅，就開挖伴隨之應力再分配與位移分佈進行探討，並延伸至四種不同初始應力 (K=0.5、1、2、3) 進行綜合對比。隧道之開挖係穿越良好之岩盤，採用全斷面開挖及無支撐打設，隧道覆蓋深度設定為300公尺。
本研究結果顯示當一條 45° 節理通過隧道右角隅，節理有產生類似應力遮蔽效應，在節理與馬蹄形隧道區域之另側區域應力，幾乎不受隧道開挖影響；而當一條135°節理通過時，節理周圍等壓線分佈大致在單一節理兩側呈對稱形狀；在兩條節理分佈之情況時，應力再分配與位移分佈大致為一條 45° 節理及一條135°節理分佈之影響趨勢的疊加。在本研究的分析範圍內，最需要關注的情況為兩條節理分佈且K = 3。

This study investigates the effect of stress and deformation redistribution of a horse-shoe tunnel excavation under three different joint distributions using the UDEC code. First, analyzed the tunneling of rock mass without joint, and then extended the rock masses contain three different joint distributions as follows: single joint with dip angle 45°, 135° and the combination of these two joints. All joints are set to pass the right corner. The tunneling stress redistribution and displacement distribution at the excavation and surrounding rock were investigated under K=1, and extended under four initial stresses(K=0.5、1、2、3). The tunnel excavated through hard rock under full-face excavation, no support installation and at overburden depth of 300 meters.
This study found that single joint with dip angle 45° produce a shaded effect of equal stress contour, and the tunnel excavation does not significant affect in the opposite side of the single joint. Single joint with dip angle135°forms an approximately symmetrical shape and equal stresses contour after excavation is also roughly symmetrical. As for two joints combination, the stress redistribution and displacement distribution are roughly the combination of single joint with dip angle 45° and single joint with dip angle135°. Within the study scope, the most critical condition happens at two joints combination under K = 3.

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