岩體裂隙之完整水力傳導係數張量評估與應用

Abstract

近年能源工程議題火熱，諸如地熱能源探勘、核廢料處置等地底工程，皆須慎重評估現地場址之岩體水力傳導特性。然而岩體內存在許多規模不一之葉理、節理等不連續面(或稱--裂隙)，其對岩體之力學、水力性質影響甚鉅，導致咫尺範圍內的岩體水流特性差異甚大。而實務上評估場址尺度之岩體水力傳導特性時，經常採用有限範圍的現地試驗與鑽孔岩心的室內試驗成果，其試驗尺度與場址尺度差異甚大，導致岩體水力傳導特性存在因岩體規模效應引致的變異性與不確定性。因此本研究之目的欲釐清實驗室尺度單一裂隙水流特性及規模效應所導致水力傳導特性之變異，並發展具應用性的實驗方法、務實驗證與修正程序。 為了探求單一裂隙之完整水力傳導係數張量，首先推導單一裂隙滲流數值解析方程式，並規劃設計應用於單一裂隙滲流試驗與滲流模擬之邊界條件。透過量測試驗中各種水流方向之滲流試驗參數，求得完整水力傳導係數張量中各元值，藉以評估單一裂隙等值代表性的完整水力傳導係數張量。本研究同時發展單一裂隙滲流模擬驗證程序，，以快速評估單一裂隙水力特性並將其應用於探討裂隙水力傳導特性之規模效應。 本研究最後將已知水力傳導特性之單一裂隙以反覆鏡像的方式，擴展原有裂隙為更大尺度的裂隙表面，運用裂隙滲流模擬探討單一裂隙水流特性與完整水力傳導係數張量受規模效應的影響。

Energy engineering topics such as geothermal energy exploration and nuclear waste disposal have gone viral in recent years. These underground engineering projects require careful evaluation of the hydraulic conductivity characteristics of the rock mass at the site. However, various scales of discontinuities, such as foliations and joints (so-called fractures), significantly impact the mechanical and hydraulic properties of the rock mass, leading to considerable variability in the hydraulic characteristics of the rock mass even within a short distance. In practice, when assessing the hydraulic conductivity characteristics of rock masses at the in-situ scale, the in-situ tests and laboratory tests on core samples are often used. The discrepancy in scales between these tests and the in-situ scale results in variability and uncertainty in the hydraulic conductivity characteristics due to the rock mass scale effect. Therefore, the purpose of this study is to clarify the variation in hydraulic conductivity characteristics caused by the flow behavior of a single fracture at the laboratory scale and the scale effect and to develop applicable experimental methods and practical verification and correction procedures. To determine the completely hydraulic conductivity tensor of a single fracture, we first derive the analytical equation for the seepage flows through a single fracture and accordingly, plan the boundary conditions applied to the single fracture seepage test and seepage simulation. By measuring the seepage characteristics in various flow directions during the test, we obtain the values of each entry in the hydraulic conductivity tensor, thereby evaluating the complete representative hydraulic conductivity tensor of a single fracture.This study also develops a verification procedure for single fracture seepage simulation to quickly assess the hydraulic characteristics of a single fracture and applies it to investigate the scale effect on the hydraulic conductivity characteristics of fractures. Finally, this study extends a known single fracture with hydraulic conductivity characteristics into a larger-scale fracture surface through repeated mirroring. Using fracture seepage simulation, we explore the application of the complete hydraulic conductivity tensor of a single fracture, emphasizing the concentration of seepage flow paths and the significant impact of scale effects on hydraulic characteristics.