Soil-rock mixtures (SRMs) are characterized by heterogeneous structural features that lead to multiscale mechanical evolution under varying cementation conditions. However, the shear failure mechanisms of cemented SRMs (CSRMs) remain insufficiently explored in existing studies. In this work, a heterogeneous threedimensional (3D) discrete element model (DEM) was developed for CSRMs, with parameters meticulously calibrated to examine the role of matrix-block interfaces under different volumetric block proportions (VBPs). At the macroscopic scale, significant influences of the interface state on the peak strength of CSRMs were observed, whereas the residual strength was found to be largely insensitive to the interface cementation properties. Pronounced dilatancy behaviour was identified in the postpeak and residual phases, with a positive correlation with both interface cementation and VBP. Quantitative particle-scale analyses revealed substantial heterogeneity and anisotropy in the contact force network of CSRMs across different components. A highly welded interface was shown to reduce the number of interface cracks at the peak strength state while increasing the proportion of tensile cracks within the interface zone. Furthermore, the welding degree of the interface was found to govern the formation and morphology of shear cracking surfaces at the peak strength state. Nevertheless, a reconstruction method for the shear slip surface was proposed to demonstrate that, at the same VBP, the primary roughness of the slip surfaces remained consistent and was independent of the interface properties. Based on the extended simulations, the peak strength of the weakly welded CSRMs progressively decreased with increasing VBP, whereas further exploration of the enhanced residual strength is needed.

This paper investigated the use of magnesium phosphate cement (MPC) for solidifying sludge with different humic acid (HA) content (ranging from 0 to 4.5%) and explored the solidification mechanism. Fluidity, setting time, unconfined compressive strength (UCS), the strength formation mechanism, and the spontaneous imbibition process of solidified sludge (SS) were studied. The results indicate that MPC can be used as a low-alkalinity curing agent. As the HA content increases, fluidity and setting time also increase, while hydration temperature and strength decrease. Additionally, the failure mode of SS transitions from brittleness to ductility. The strength of SS is composed of the cementation strength provided by MPC hydration products, matric suction, osmotic suction, and the structural strength of the sludge. MPC reduces the structural strength caused by the shrinkage of pure sludge under the action of matric suction, but the incorporation of MPC significantly improved the strength when the sludge is eroded by water. X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that the sludge and MPC can form a dense solid body, forming various hydration products, and synergistically improve the mechanical properties of the sludge. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

To broaden the sources of earthwork and the utilization of soda residue (SR) and fly ash (FA), SR, FA, and clay were mixed to form a soda-residue soil (SRS) by adding externally moderate content of lime or/and cement for further stabilization. Through the orthogonal scheme, 9 groups of proportions were designed. Subsequently, the unconfined compressive strength (UCS) at different curing ages was conducted. Afterward, the stress-strain pattern, the UCS and water absorption, the sensitivity of factors and levels to UCS, and the deformation modulus were analyzed. Finally, the enhancement mechanism of SRS from physicochemical reactions was explored by analyzing gradation and microstructure. The results show that the patterns of stress-strain curves on SRS at different curing ages are similar; all have obvious stress peaks, and the specimens of SRS present a brittle failure. With the extension of curing ages, the UCS of all proportions increased; the UCS of the G2 group increased the most, reaching 85.44%, and the G9 group increased the least, only 1.92%. However, the water absorption quality decreased, and G6 decreased the most (37.53%), G7 decreased the least (0.84%), and UCS and water absorption quality showed a negative correlation. The sensitivity of each factor to UCS was different; the SR was the most sensitive at 7 d, but the lime was the most sensitive at 28 d. The sensitivity of each factor level (content) to UCS remains unchanged at different curing ages. There is a linear relationship between the deformation modulus and UCS. The analysis demonstrates that the better strength properties of SRS are mainly determined by the superior gradation and the reaction of materials.