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  • 學位論文

以FLAC探討現地應力對處置坑道開挖穩定性之影響

Study on the stability of deposition tunnel excavation under various in-situ stresses using FLAC

指導教授 : 楊長義

摘要


在國際處置高放射性廢棄物的方式,是將核廢料罐深埋在300~1000m高應力環境的地下坑道中,藉由障壁組成有效圍阻遲滯核種的外釋,使輻射強度到達生物圈之前已衰減至可忽略的程度。目前國內台電公司預擬的深層處置場坑道配置與尺寸之設計,採用KBS-3V設計,其處置設計概念係先開挖處置隧道(deposition tunnel),再在其隧道地面上垂直向下逐一鑽挖深度8m的一系列處置孔(deposition hole)。而深層地質處置設施的力學穩定安全性是由應力在主控(stress-dominated),其穩定性或破壞與否之關鍵因子是在現地應力(in-situ stress)之大小與方位以及岩石之破壞強度。受高應力作用下,所造成應力釋放與應力調整係屬相互影響,故本研究目的為擬以FLAC2D程式模擬,探討其應力分佈之變化與破裂損傷程度,並針對台灣本土現地應力條件作進一步研究。 本文主要獲致結論如下: (1)以FLAC分析處置坑道周圍岩體應力分布行為,獲知其關鍵因子為現地應力比K與深度Z,隨著參數K及Z值愈大其應力變化愈顯著。K值主控處置坑道周圍應力等高線分布區之形狀,深度Z則主控開挖平衡後岩體整體應力值之範圍。其中K值主要控制處置坑道發生破壞處,深度Z則控制處置坑道是否破壞以及其破壞範圍;(2)處置坑道開挖分為兩階段開挖,第一階段先挖處置隧道後,在較大現地應力方向之開挖面處附近會呈現低壓力區或張力區,因此當圍岩承受之環境壓力愈大時,愈容易在此處形成損傷破壞區;開挖處置孔後,會因應力重新分配轉移過程,釋放原來應力集中於處置隧道底部之現象,且第一階段開挖時原本在仰拱的破壞會因為第二階段開挖的解壓以及網格移除而消失;(3)坑道破壞型態分為兩種:張力破壞與剪切破壞,張力破壞由張力強度主控,多發生於處置隧道、處置孔的側壁與底面;剪切破壞主要發生在高壓應力集中區,如處置隧道轉角處;(4)影響變形量的最大因素為母岩之楊氏模數E,第一階段處置隧道開挖,最大變形量位置常發生在隧道頂拱處沉陷;第二階段處置孔開挖,最大變形發生在處置孔上段2公尺處,由其詳細數值結果可得,最大位移量與E值呈現反比關係;(5)在較淺的低應力條件下,岩體為彈性的穩定狀態,處置隧道形狀對處置孔影響甚微。但在較深的高應力條件下,可由坑道之破壞判別各形狀之優劣:(a)在方形處置隧道下的處置孔之張力破壞範圍分布最廣,坑道轉角處容易發生剪切破壞 (b)在棚形或拱形處置隧道下的處置孔之張力破壞區域相似,然因棚形之坑道轉角亦易形成剪切破壞,由此判斷拱形處置隧道為處置坑道最佳的選擇。

並列摘要


The international method of disposing of high-level radioactive waste is to bury nuclear waste tanks deep in an underground tunnel with a high stress environment of 300~1000m. The barrier is formed to effectively block and delay the external release of nuclear species, so that the radiation intensity is attenuated before reaching the biosphere To the extent that it can be ignored. At present, the design of the tunnel configuration and size of the deep disposal site pre-planned by the domestic Taiwan Power Company adopts the KBS-3V design. The disposal design concept is to first excavate the disposal tunnel (deposition tunnel), and then drill vertically downwards one by one on the ground of the tunnel A series of deposition holes with a depth of 8m. The mechanical stability and safety of deep geological disposal facilities are controlled by stress (stress-dominated), and the key factors for its stability or failure are the magnitude and orientation of in-situ stress and the destruction of rocks. strength. Under the action of high stress, the resulting stress release and stress adjustment are mutually affected. Therefore, the purpose of this research is to simulate the change of stress distribution and the degree of rupture damage with the FLAC2D program, and to conduct further research on the local in-situ stress conditions in Taiwan. The main conclusions obtained in this paper are as follows: (1) Using FLAC to analyze the stress distribution behavior of the rock mass around the disposal tunnel, it is known that the key factors are the in-situ stress ratio K and the depth Z. The greater the value of the parameters K and Z, the more significant the stress changes. The K value mainly controls the shape of the stress contour distribution area around the tunnel, and the depth Z mainly controls the range of the overall stress value of the rock mass after the excavation is balanced. Among them, the K value mainly controls the destruction of the disposal tunnel, and the depth Z controls whether the disposal tunnel is destroyed and its destruction range; (2) The excavation of the disposal tunnel is divided into two stages of excavation. There will be a low pressure zone or a tension zone near the excavation face in the direction of the current in-situ stress. Therefore, when the surrounding rock is subjected to greater environmental pressure, it is easier to form a damage zone here; after the excavation and disposal of the hole, the stress will be renewed. The distribution and transfer process releases the phenomenon that the original stress is concentrated on the bottom of the treatment tunnel, and the damage that was originally in the invert during the first stage of excavation will disappear due to the decompression of the second stage of excavation and removal of the mesh; (3) tunnel damage There are two types: tension failure and shear failure. Tension failure is dominated by tensile strength, which mostly occurs on the sidewall and bottom of the disposal tunnel and disposal hole; shear failure mainly occurs in the high-pressure stress concentration area, such as the corner of the disposal tunnel (4) The largest factor affecting the deformation is the Young's modulus E of the parent rock. The tunnel excavation is dealt with in the first stage, and the position of the largest deformation often occurs at the top of the tunnel. The second stage is the excavation of the disposal hole. The maximum deformation occurs at 2 meters in the upper section of the disposal hole. According to the detailed numerical results, the maximum displacement is inversely proportional to the E value; (5) Under shallow and low stress conditions, the rock mass is in an elastic and stable state. The shape of the disposal tunnel has little effect on the disposal hole. However, under deep and high stress conditions, the advantages and disadvantages of each shape can be judged by the destruction of the tunnel: (a) The tensile damage range of the disposal hole under the square disposal tunnel is the widest, and the corners of the tunnel are prone to shear failure (b) The tension failure area of the disposal hole under the shed-shaped or arch-shaped disposal tunnel is similar, but the corner of the shed-shaped tunnel is also prone to shear failure. Therefore, it is judged that the arch-shaped disposal tunnel is the best choice for the disposal tunnel.

參考文獻


1. 台灣電力公司(2017),我國用過核子燃料最終處置可行性評估報告SNFD 2017。
2. 吳勁頤(2017),以PFC模擬離島花崗岩處置坑道之破裂行為,私立淡江大學土木工程研究所碩士論文。
3. 楊長義(2017),台灣潛在母岩破壞強度特性與處置坑到破裂關係之研析,科技部補助專題研究計畫案,淡江大學土木系。
4. 楊長義(2018,2),研析瑞典SR-site 處置坑道岩力設計前提之訂定原則,科技部專題計畫成果報告,MOST 106-2623-E-032-002-NU,淡江大學土木系。
5. 楊長義(2021),處置隧道形狀對處置孔開挖損傷影響之模擬研究,科技部專題研究計畫案,淡江大學土木系。

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