Abstract:

Compressive fault fracture zones are characterized by their dense structures, weak cementation, and low permeability. Within these zones, fine clay particle constituents, which contain a high proportion of clay minerals, are susceptible to softening and argillization upon contact with water, thereby playing a crucial role in the permeability-deformation failure mechanism of the entire structure and long-term seepage stability of reservoir areas. This study takes stone content ratio S and Talbot index n as key parameters, and reveals the dominant role of fine clay particle content (p) in the permeability evolution characteristics of fault fracture zones through systematic laboratory permeability tests. Experimental results indicate that: 1) The initial permeability coefficient k₀ exhibits a negative exponential relationship with fine clay particle content, where increased fine clay particle content can effectively reduce permeability.2) Fine clay particle content significantly controls the formation and evolution of threshold pressure gradient: at low content levels, it conforms to Darcy’s law (approximately non-viscous), and as p increases, it shows a linear growth (2.5%＜p＜20%) and an exponential growth (p≥20%) in turn. 3) Critical and failure hydraulic gradients are regulated by the coupling of p and S, with sensitivity of gradient to p changes diminishing at high stone content ratios (S=60%). 4) Seepage failure modes undergo systematic transformation with increasing p: it shifts progressively from piping type (p≤2.5%) to transitional type (2.5%＜p＜20%), and ultimately evolves into soil flow type (p≥20%); concurrently, post-failure phenomena manifest as three modes: progressive penetration, central cavity formation, and concentrated failure. This study quantitatively elucidates the evolution law of the entire permeability-deformation process dominated by fine clay particle content, providing important theoretical basis for engineering disaster prevention and control in compressive dense fault fracture zones.

Key words: fine clay particle content, permeability, threshold pressure gradient, failure mode, particle loss amount