The study examines the effects of pressmud (PM), an innovative, sustainable, and beneficial alternative for soil treatment, on the hydromechanical behaviors of sand-bentonite (SB) through a series of laboratory tests, including unconfined compressive strength (UCS), free swelling, and 1D consolidation. SB mixtures with 10 and 15% bentonite (by sand weight) and PM at 4, 8, and 12% (by SB weight) were evaluated. Additionally, microstructural analyses using X-ray diffraction (XRD) and scanning electron microscopy (SEM) were performed to elucidate the mechanisms of soil improvement. The results indicate that PM incorporation reduces the maximum dry unit weight while significantly enhancing the UCS of SB mixtures, with maximum strength increases of 111.5 and 65.5% observed in mixtures containing 10 and 15% bentonite, respectively, after 28 days of curing. These changes help not only enhance the strength properties but also decrease the self-loading on the landfill liner. Moreover, higher PM contents exhibit a dual impact of reducing swelling strain while slightly increasing both compressibility and permeability. Despite the marginal increase in permeability, it still meets the necessary criteria for serving as a landfill liner (< 10(-7) cm s(-1)). The observed effects of PM on SB behavior can be ascribed to the synergistic effects of natural fibers and cementitious gels, as confirmed by microstructural analyses. The natural fibers mainly contribute to the shear resistance of the interface, while the cementitious gels bridge and interlock the solid particles, thereby enhancing the hydromechanical performance of SB. It is concluded that the reuse of PM in soil stabilization not only enhances the hydromechanical performance of SB but also results in better PM management.

The road network in Colombia, as reported by the National Roads Institute of Colombia (INVIAS), comprises a total of 206,708 kilometers, with 142,284 kilometers falling under the rural roads with low traffic volume network category. Sadly, an estimated of 96% of these roads are in poor condition. The primary reason behind this issue is the presence of subgrades that exhibit inadequate mechanical performance, largely due to the lack of proper stabilization methods. Moreover, these roads often serve as the sole access and exit routes for rural communities, significantly impacting their connectivity with nearby urban centers. Recognizing this critical issue, this article proposes the use of coal ash for subgrade stabilization during the construction of low-traffic-volume roads. The study conducted demonstrates that coal ash can enhance the mechanical properties of subgrades, leading to an increase in strength and load-bearing capacity. The improved mechanical properties are attributed to the binding and reactive characteristics displayed by the coal ashes, which greatly contribute to soil stabilization. To verify these claims, a series of physical, mechanical, and strength characterization tests were conducted on both natural and treated clayey sand samples obtained from a rural population in Colombia. The detailed analysis of the results shows an improvement in the mechanical properties of the soil due to the use of coal ash as a stabilizing agent.