- 學位論文
處置孔開挖順序對岩柱力學行為之研究
Effect of excavation sequence on the mechanical behaviour of rock pillars between deposition holes
摘要
高放核廢料深層地質處置屬於高應力作用問題，其破裂行為是由場址真實的現地主應力大小及母岩強度所控制。埋置核廢料桶的處置坑是在處置隧道向下鑽挖而成，坑與坑間所構成的岩柱極易因開挖所解除側向圍束壓力，致使發生坑壁剝落現象，長期可能因此形成地下水流及核種外釋的通道。 鑒於在處置坑開挖所構成的岩柱區顆粒之應力狀態，可能會因下一個處置坑開挖之應力重整所擾動。因此本文以PFC2D軟體為數值模擬分析工具，利用台灣離島潛在場址母岩實際力學特性與實測現地應力值，並針對台電所規劃之處置隧道與處置孔尺寸與配置距離為依據，探討開挖處置孔所構成之岩柱的力學微觀行為之改變。文中，分別探討於處置隧道段前端及中段，依順序開挖三個處置坑之開挖擾動行為。研究結果獲致以下主要結論： (1)處置孔的開挖對整體處置隧道開挖後岩體大範圍應力與位移分布行為影響不大，處置孔之開挖擾動僅發生在處置孔左右以及孔底之局部區域內。（2）於處置隧道之前段或中央段開挖處置孔之擾動行為很類似，惟中央段開挖造成的顆粒應力或變位分布行為較為左右對稱。(3)開挖處置孔所構成的岩柱兩側都會有一呈三角形狀主動土壓力解壓區，解壓區內顆粒間接觸力有減低現象、顆粒鍵結力趨於受張力狀態，岩柱內顆粒皆趨向處置孔移位，在岩柱上段的顆粒變位高於下段。(4)開挖岩柱區內顆粒的變位量，皆受旁邊下一個處置孔開挖擾動之影響而變位更大，但是開挖第三個處置孔之開挖擾動卻不足以跨越去影響到先前已形成的岩柱狀態。(5)處置孔開挖完受地震力影響後隧道口兩端與岩柱底部會均有剪力破壞與張力破壞現象發生，但主要以剪力破壞現象為主。
並列摘要
The stability of deep geological repository is controlled by the magnitude of the in-situ principal stresses and the uni-axial compression strength of intact rock. The canister deposition holes are vertically drilled holes from the floor of deposition tunnel. The stress and displacement behaviors of rock pillars between deposition holes will be altered by the stress redistributed during the next hole drilled. In this report, we use PFC 2D to model the effect of deposition holes excavation on the rock pillars. The aim is to study the distribution of grain contact stress and grain bonding stress within pillars after drilling deposition holes at the geological condition of site Taiwan. The main results are drawn as follows: (1) The disturbance of deposition hole excavation is limited around the holes and the rock pillars. (2) A tensile zone formed close to the deposition holes which the grain is taken the tension stress situation. (3) The grains of rock pillar displace toward to the deposition holes and the top end of rock pillar displacement is remarkable. (4) There is no difference on the stress distribution behavior after the hole excavation located at the end side or at the middle of deposition tunnel. (5) The mechanical behavior of rock pillar is affected by the next hole excavation, but the disturbance effect of the third hole does not cross to the first formed pillar.