摘要
This study employs microstructural and mineralogical characterization to analyze deformation within the Chungliao Tunnel (Formosan Freeway, Taiwan) caused by the movement along the Chishan Fault, as well as its effect on accelerated creep along the fault. The results reveal pyrite-filled fissures and a large amount of wavy extinction quartz and bent muscovite. The mineral particles are fragmented and finely granulated. Additionally, slippage between grains and dislocation creep are observed within Chishan Fault. Therefore, the primary deformation mechanisms of this fault are cracking/frictional sliding, dislocation creep, and grain-boundary sliding. The presence of calcite, clay minerals, physically absorbed water, and crystalline water in the rock enhances fault movement and significantly weakens the strength of rock layers. As a result, the Chungliao Tunnel over the past 18 years has risen at an average annual rate of 8 cm, and is now 130 cm higher than at the time of construction. This study is expected to contribute to future infrastructure planning along the fault. For example, mineral grains in the rock layer tend to align themselves along the fracture orientation, implying the possible stress direction. Moreover, the content of index minerals (e.g. calcite, pyrite, and clay minerals) in the rock layer can be utilized to predict the scale of rock-layer sliding and the severity of potential fault-related disasters.