Mechanism of Influence of Fine-Grained Content and Mineral Characteristics in Compressive Fault Fracture Zone on Evolution of Seepage Characteristics

The evolution of seepage characteristics in compressive fault fracture zones at dam foundations and abutments is influenced by fine-grained content and its mineral characteristics, which is crucial for the prevention and control of seepage disasters in reservoir and dam projects. Taking the F2 compressive fault on the right bank of the Yulong Kashi Water Control Project as the research object, this study prepared remolded fault specimens based on fine-grained content (fine particles with a particle size < 0.075 mm) and its mineral fabric (kaolinite, chlorite, and their mixture). The specimens included three types: those with fine grains entirely composed of kaolinite, those with fine grains entirely composed of chlorite, and those with fine grains as a mixture of the two. Confined seepage tests were conducted to reveal the influence mechanism of the evolution of seepage characteristics of the compressive fault specimens. The test results show that: 1) With the increase of fine-grained content, the specimens exhibit three states: "under-filled", "fully filled", and "over-filled". The transition of filling states dominates the nonlinear evolution process of the specimens' seepage behavior through pore reconstruction; 2) The mineral characteristics of fine grains affect the threshold pressure gradient of the specimens. Kaolinite is prone to migration and clogging, while chlorite has a stable structure, resulting in a significantly higher threshold gradient of specimens with kaolinite fabric than those with chlorite fabric. However, the specimens with mixed fabric form a porous agglomerate structure through electrical neutralization and heterogeneous flocculation, leading to a significant reduction in the threshold pressure gradient; 3) The mineral fabric of fine grains leads to obvious differences in the evolution of seepage characteristics of the specimens. The permeability coefficient of specimens with chlorite fabric gradually increases without abrupt changes during the seepage deformation process, while specimens with kaolinite fabric exhibit abrupt changes. This study clarifies the influence mechanism of fine-grained content and its mineral characteristics in compressive fault fracture zones on the evolution of seepage characteristics, and provides a theoretical reference for the prevention and control of seepage disasters in water conservancy and hydropower projects.