Engineering properties and microscopic mechanisms of carbonaceous mudstone modified by hydrophobic sodium methylsilicate

Carbonaceous mudstone slopes are prone to rapid disintegration and softening under repeated dry-wet cycles, forming loose and fragile disintegrated soil layers that can easily cause shallow landslides, slope erosion, and debris flows. In this study, sodium metasilicate (SMS), a hydrophobic material, was used to enhance the surface soil properties of carbonaceous mudstone slopes, thereby increasing their strength and preventing disintegration, which reduces the risk of shallow landslides. Unconfined compressive strength (UCS), disintegration, permeability, and physicochemical tests were conducted on SMS-modified carbonaceous mudstone (SMSCM) to evaluate the effects of dry-wet cycles. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to elucidate the modification mechanism and microstructural degradation of SMSCM. The results show that the UCS of SMSCM increases with the increase in SMS content and curing time. Under the same dry-wet cycle conditions, the higher SMS content reduces the decrease in UCS. Furthermore, the addition of SMS causes the particles in SMSCM to form large aggregates, effectively suppressing the disintegration and reducing the permeability coefficient of SMSCM. The disintegration resistance index decreases with increasing number of cycles, while the permeability coefficient, pH value, and total dissolved solids (TDS) exhibit an opposite trend. SMS inhibits the disintegration of carbonaceous mudstone mainly through four mechanisms: cementation, filling, encapsulation, and bonding. This reduces the deterioration caused by dry-wet cycles on SMSCM and helps ensure the long-term stability of the carbonaceous mudstone slope surface.