本研究利用UDEC軟體探討覆岩深度為300公尺之處置隧道開挖於良好之岩盤(花崗岩)中，進行全斷面開挖且無支撐打設。處置隧道為馬蹄形隧道與下方處置槽所組成，隧道共分為三階段開挖，分別為第一階段的馬蹄形隧道開挖，與下方處置槽的第二、三階段的分階降挖。首先分析馬蹄形隧道開挖於無節理岩盤之情況，接著引入一條傾角45°之節理，且通過隧道之右側角隅，就開挖伴隨之應力再分配、位移分佈與安全性評估，並延伸至三種不同初始應力(K=0.5、1、2)進行綜合對比。
本研究結果顯示當一條 45° 節理通過隧道右側角隅時，馬蹄形隧道角隅周遭在不同初始應力情況(K=0.5、1、2)與不同開挖階段均會產生張力破壞。而馬蹄形隧道在開挖穩定後，最需要注意(危險)的測點為單一節理分佈且初始應力K=2時之頂拱處，此測點於處置隧道三階段開挖中，均為安全係數最小之測點(FS=3)。

In this paper, the UDEC code was used to explore the tunnel with a depth of 300 meters. The tunnel was excavated in a hard rock (granite), and the whole section was excavated without support. Disposal tunnel composed of a horseshoe and the lower deposition hole. The tunnel is divided into three stages of excavation, a first stage is excavated for horseshoe tunnel, and a second and third stage is excavated for deposition hole. First, analyzed the tunneling of rock mass without joint, and then to discuss a 45 ° angle of the joint is through the tunnel on the right corner. The tunneling stress redistribution, displacement distribution and safety assessment of excavation and surrounding rock were investigated under K=1, and extended under three initial stresses(K=0.5,1,2)for comprehensive comparison.
The results of this paper show that when a 45 ° joint passes through the right corner of the horseshoe tunnel, the horseshoe tunnel corner around at different initial stress conditions(K=0.5,1,2)and different excavation stages will produce tension failure. And the horseshoe tunnel in the excavation steady state, the most need to pay attention to ( dangerous ) the monitoring position for a single joint distribution and the initial stress is K=2 at the top of the arch, the monitoring position in the three-stage tunnel excavation, has the minimum factor of safety(FS=3).

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