Disintegration Mechanism and Swelling–Consolidation Characteristics of Saturated Disintegrated Carbonaceous Mudstone

Highway constructions in southern China have revealed a massive distribution of carbonaceous mudstone. However, this mudstone is seldomly used as embankment fillers because of its significant disintegration upon wetting. Compared to bulk carbonaceous mudstone, small disintegrated carbonaceous mudstone (DCM) grains show less disintegration potential and may be applied to fill embankments in some regions. The purpose of this study is to reveal the mechanism behind the further disintegration of primarily DCM and investigate the swelling–consolidation characteristics of the DCM, scanning electron microscopy (SEM) was used to observe the difference for the compacted DCM specimens before and after wetting, and the microstructural change and the disintegration mechanism of the wetted DCM were analyzed accordingly. The saturated free swelling tests and saturated consolidation tests were conducted to elucidate the influences of dry density and grain size range on the swelling and consolidation characteristics of the DCM. The results show that the disintegration of the DCM is greatly affected by the swelling of hydrophilic clay minerals and softening and dissolving of inter-particle cementation. The free swelling deformation of the DCM increases with increasing dry density and decreasing grain size upon wetting. The DCM shows an increasing compression index as the consolidation pressure increases, which is related to its disintegrating nature. The settlement and compression index of the DCM reduce as an increase in dry density or the grain size. Therefore, relatively large grain sizes and compacted at a higher dry density for DCM is recommended in filling highway embankments.