Permeability evolution of carbonaceous mudstone fill material induced by particle breakage under dynamic loading and seepage conditions

Highway embankments with carbonaceous mudstone fill material are prone to deformation and instability under traffic loading and rainfall due to particle breakage-induced stiffness and strength degradation. This study aims to investigate the particle breakage characteristics of carbonaceous mudstone fill material under dynamic loading with prior seepage conditioning, and to establish a permeability model considering breakage behavior. To this end, a custom-designed testing apparatus was employed to conduct dynamic loading and permeability tests on specimens with varying coarse particle contents (CPC) under different dynamic loads and seepage durations. Changes in particle size distribution, average saturated permeability coefficient, and relative breakage ratio were analyzed, and a permeability model relating the coefficient to the breakage ratio was proposed. The results indicate that the dynamic loading-affected range in the upper part of the specimens increases with higher CPC and greater loading levels. When CPC is below 40%, permeability changes little, whereas significant local variation occurs at higher CPC. A threshold dynamic load of 40 kPa, particularly at a CPC of 40%, was identified as the condition that triggers particle breakage and induces abrupt changes in seepage behavior. The developed model effectively captures the nonlinear relationship between permeability and relative breakage ratio.