Creep behavior and particle breakage of carbonaceous mudstone coarse-grained soil: experimental study and discrete element modeling

Carbonaceous mudstone coarse-grained soil is commonly used as embankment fill in southwestern China. It exhibits significant creep characteristics, and its long-term deformation is closely related to particle breakage. In this paper, large-scale confined creep tests, sieving tests, and single-particle compression tests were carried out, combined with a discrete element model considering stress corrosion effects, to investigate the creep characteristics, particle strength evolution, and mesoscopic breakage mechanisms of carbonaceous mudstone subgrade fill under different gradations. The results show that carbonaceous mudstone exhibits strain-hardening behavior. At low stress levels, the total strain is positively correlated with the gradation fractal dimension, while the opposite is true at high stress levels. The creep critical stress increases with increasing fractal dimension, whereas the creep rate shows the opposite trend. The single-particle crushing strength follows a Weibull distribution, and the characteristic crushing strength decreases with increasing particle size and applied stress, with particle size having a more significant effect. A time factor was introduced into the traditional stress corrosion model to establish a bond strength degradation model that accounts for the effect of loading time. The improved model can more accurately describe the progressive creep failure under high-stress and long-term conditions. Mesoscopic analysis indicates that during creep, the direction of strong contact loads gradually deflects from vertical to more dispersed orientations. Strong contact failure is concentrated on the particle surfaces. For specimens with a smaller fractal dimension, the force chain pattern is a "few but strong" sparse mode, which is sensitive to applied stress and loading time. For specimens with a larger fractal dimension, the force chain pattern transforms into a "many but weak" dense network mode. The research findings can provide a theoretical basis for the long-term stability evaluation of pre-disintegrated carbonaceous mudstone embankments.