A study of the Mechanical Behavior of EDZ in Rock Masses around Tunnel using Finite Difference Method

[[abstract]]隨著地球人口的劇增，能源的需求也與日的增加，然而地球的資源畢竟有限，尤其在台灣目前除了取自石化燃料之外，核能也是主要取得能源的選項之一。然而，核能的發電，會伴隨著放射性廢棄物的產生，對人類的生活環境造成潛在而且長期性的威脅。所以，為了讓放射性廢棄物完全阻隔於人類的生活圈之外，國際上核能先進國家長期以來即從事相關的研究，目前的共識則一致認為深層地質處置法(Deep Geological Disposal Method)為永久處置該廢棄物最可行的方法。 本研究採用深層地質處置方法永久處置高放射性廢棄物的概念，進行了具開挖擾動帶(Excavation Disturbed Zone EDZ)之隧道開挖的三維力學行為有限差分法(Finite difference Method)的數值模擬分析，使用之程式為美國ITASCA公司在1997年所開發之FLAC3D(Fast Lagrangian Analysis of Continua in 3 Dimensions)程式。分析中所使採用之岩體為完全彈塑性材料(perfectly elasto-plastic material)且符合Mohr-Coulomb破壞準則，並假設岩盤的地質條件為RMR=70，岩盤之現地應力則藉由500m的岩體覆蓋進行推算，而側向壓力係數K則因深地層的關係而取為1。本研究結果分成兩個部分，一為不考慮隧道開挖後所造成之EDZ，二為考慮隧道開挖後所造成之EDZ，其厚度取2m，其岩體評分RMR降至30，最後進行分析結果之相互之比對，以獲取EDZ對隧道穩定性所造成之影響程度。數值分析結果顯示：(1)隧道開挖後產生之EDZ會明顯的造成處置場之變形。(2)主隧道開挖面之應力受到EDZ的影響而大幅地減少，也產生大量的變形，應力安全係數劇降至接近1左右，因而需施加支撐，以策安全。[[abstract]]The energy requirement for human beings has been dramatically increased due to the fast growing population on earth recently However the energy resource on earth is limited especially in Taiwan which results in the nuclear energy has been a major resource for the island However the nuclear waste has been produced in the process of nuclear power generation and that potentially and probably permanently jeopardizes the human being’s living environment Therefore in order to completely isolate the waste from the living circle of human beings the related researches has been conducted by the advanced nuclear power consuming countries The conclusion indicates that the deep geological disposal method has been unanimously treated as a most reliable one The deep geological disposal method is adopted in this research for the permanent disposal of nuclear waste The effect of excavation disturbed zone (EDZ) induced during the main tunnel excavation is numerically simulated by using the FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions) program which was originally developed by ITASCA in US in 1997 by using 3-D Finite Difference Method Rock mass in the analysis is assumed to be a perfectly elasto-plastic material and obeys the Mohr-Coulomb failure criterion The magnitude of RMR is 70 adopted to represent the geological condition of rocks The in-situ stress of rocks is obtained from the calculation of the 500 m overburden of rocks induced by its self-weight The magnitude of the horizontal coefficient of in-situ stress K is one due to the consideration of deep underground excavation in this research This research is composed of two parts The EDZ effect is not considered in the first part but is included in the second part The thickness of EDZ is 2 meters adopted in this research and its RMR value is dropped to 30 Finally both numerical results are compared in order to capture the effect of the existence of EDZ to the stability of tunneling excavation The numerical results show that (1) the deformation of disposal site is obviously affected by the existence of EDZ and (2) at the excavation face the state of stresses is dramatically reduced deformation is also largely increased and the factor of safety of stresses is abruptly down to almost 1 resulting in the requirement of extra tunnel support for the safety of excavatio