裂隙岩體力學-水力耦合模式應用於豎井開挖滲流行為

Abstract

核廢料處置、地熱能源、碳封存等地下資源的開發與地下空間的使用為現代國際間大地工程領域致力發展重點之一，相關岩石力學之學術研究也因此正快速發展中。然而岩體通常伴隨許多裂隙，產生裂隙岩體，成為流體通過的主要通道。裂隙空間分布上的不確定性使岩體特性難以量化與評估，此外，裂隙之幾何對於正向應力加壓、解壓與剪應力剪動有顯著性影響，意味著應力將對岩體透水性造成顯著改變，因此，如何描述工程應力改變造成裂隙特性變化為本研究主要目的。 本研究使用草埔井場所蒐集裂隙資料作為離散裂隙網絡建模基礎，模擬草埔豎井開挖應力改變造成裂隙岩體透水性變化。為了簡化模型，本研究以離散裂隙網絡評估所得代表性單元體積與之對應代表性水力傳導係數張量，作為等值連續體水力特性，取代模型大部分區域裂隙岩體，只於靠近豎井開挖周圍建立離散裂隙網絡，呈現應力解壓造成透水性改變之行為。最後以根據草埔井場的調查資料建立等值連續體(EPM)-離散裂隙網絡(DFN)耦合模型模擬豎井開挖後水流分析，比較有無考慮應力狀態模型於水流分析結果差異，同時亦與現地觀測井隨開挖深度紀錄所得數據作為模擬結果比對。比較結果顯示，考慮岩覆壓力與豎井開挖解壓EPM-DFN耦合模型是最接近現地真實量測數據的模型。 本研究所整合一系列建模方法，可以利用現地調查、實驗裂隙參數，建立EPM-DFN耦合模型，使現地離散裂隙網絡之分布與裂隙參數視覺化，模擬岩盤工程開挖前後可能的水流情形，並呈現裂隙異質性與異向性，可以作為未來岩盤工程精細化工程設計研究方法之一。例如針對優勢水流路徑主導裂隙進行灌漿，設計最有效解決湧水問題方案。

Nuclear waste disposal, geothermal energy, and carbon capture and storage are among the key focuses of modern international geotechnical engineering in terms of the development of offshore resources and the utilization of underground space. As a result, academic research in rock mechanics is rapidly advancing. However, rock masses are often characterized by numerous fractures, which form fracture networks and serve as the main channels for fluid flow. The uncertainty in the distribution of fracture spaces makes it difficult to quantify and assess rock mass properties. Additionally, the geometry of fractures significantly affects the response of the rock mass to normal stress loading, stress relief, and shear stress, implying that stress will cause significant changes in the permeability of the rock mass. Therefore, the main objective of this study is to describe the changes in fracture characteristics caused by engineering stress variations. To achieve this goal, this research uses fracture data collected from the Tsaopu well site as the basis for modeling discrete fracture networks. It simulates how excavation-induced stress changes affect the permeability of fractured rock masses in the vicinity of the Tsaopu Shaft. To simplify the model, representative element volumes obtained through the evaluation of the discrete fracture network are used, along with corresponding representative hydraulic conductivity tensor values, as equivalent continuous medium hydraulic properties. These properties replace the majority of the fractured rock mass in the model, focusing only on establishing a discrete fracture network around the vicinity of the shaft to represent the behavior of permeability changes due to stress unloading. Finally, an Equivalent Porous Medium (EPM) - Discrete Fracture Network (DFN) coupled model is established based on the survey data from the Tsaopu well site. This model is used to simulate groundwater flow after shaft excavation and to compare the differences in the simulation results between models with and without considering stress conditions. The simulation results are also compared with data recorded from onsite observation wells at different depths. The comparison shows that the EPM-DFN coupled model that considers both overlying rock stress and stress-induced unloading is the model that best matches the real measured data from the site. By integrating a series of modeling methods, this research can use on-site surveys and experimental fracture parameters to establish an EPM-DFN coupled model. This model visualizes the distribution of discrete fracture networks and fracture parameters in the field and simulates potential water flow conditions before and after rock engineering excavation. It also represents fracture heterogeneity and anisotropy, making it a valuable approach for future detailed engineering design research in rock engineering. For example, it can be used to design the most effective solutions, such as grouting dominant water flow pathways in fractures, to address water inflow issues.