To improve the problem of collapsibility of loess, adding industrial materials such as cement is common engineering treatment, but this seriously damages the reclamation performance of soil. Calcium lignosulfonate (CLS) from paper plant waste fluids is a natural bio-based polymer with good application prospects as a soil improver. In this paper, the collapsibility and mechanical properties of CLS improved loess were investigated using a collapsibility test, gray correlation analysis, and an unconfined compressive strength test (UCS). In addition, the strengthening mechanism of CLS-improved loess was also explored based on scanning electron microscopy (SEM), microstructure parameters, and X-ray diffraction. The collapsibility coefficient decreased rapidly after CLS was admixed, and the single and double-oedometer methods showed the same change trend. The order of grey correlation degree of collapsibility on each index from large to small was: moisture content, pore ratio, dry density, and CLS content. The dosage of CLS greatly influenced the mechanical properties and collapsibility of stabilized loess. The optimum amount of CLS for Xi’an loess was 3%, at which the collapsibility coefficient was reduced by more than 95%, and the 28 d UCS increased by 180.01%. From the microstructure and mineral composition analysis perspective, CLS plays a role in filling pores and linking soil particles. After the protonation and ion exchange effect of CLS, the grain size and double electric layer thickness of mineral composition were reduced, and the structural compactness was increased. These research results are of great scientific significance for the ecological modification of soils.

Although cemented soil as a subgrade fill material can meet certain performance requirements, it is susceptible to capillary erosion caused by groundwater. In order to eliminate the hazards caused by capillary water rise and to summarize the relevant laws of water transport properties, graphene oxide (GO) was used to improve cemented soil. This paper conducted capillary water absorption tests, unconfined compressive strength (UCS) tests, softening coefficient tests, and scanning electron microscope (SEM) tests on cemented soil using various contents of GO. The results showed that the capillary water absorption capacity and capillary water absorption rate exhibited a decreasing and then increasing trend with increasing GO content, while the UCS demonstrated an increasing and then decreasing trend. The improvement effect is most obvious when the content is 0.09%. At this content, the capillary absorption and capillary water absorption rate were reduced by 25.8% and 33.9%, respectively, and the UCS at 7d, 14d, and 28d was increased by 70.32%, 57.94%, and 61.97%, respectively. SEM testing results demonstrated that GO reduces the apparent void ratio of cemented soil by stimulating cement hydration and promoting ion exchange, thereby optimizing the microstructure and improving water resistance and mechanical properties. This research serves as a foundation for further investigating water migration and the appropriate treatment of GO-modified cemented soil subgrade.

The potential application of lignin in modifying loess subgrades has attracted considerable attention due to its ability to significantly enhance the water-holding capacity and mechanical properties of loess. However, the impact of moisture content variations on the shear strength of lignin-modified unsaturated loess remains insufficiently explored. This study systematically examined the water-holding performance and shear strength characteristics of lignin-modified loess through soil-water characteristic tests and triaxial consolidation undrained tests. The experimental results demonstrated that the water-holding capacity of lignin-modified loess increased markedly with rising lignin content, peaking at 1.5% lignin content, followed by a slight decline with further increases in lignin content. Triaxial test results revealed that the cohesion and the internal friction angle of 1.5% lignin-modified loess decreased progressively with increasing moisture content; however, this degradation occurred at a significantly lower rate than in remolded loess. Analysis of the soil-water characteristic curves further indicated that both cohesion and the internal friction angle increased with increasing matric suction. On this basis, the evolution of cohesion and internal friction angle was expressed as a function of hydraulic state variables and then incorporated into the Mohr-Coulomb shear strength criterion, establishing a unified model for predicting shear strength under varying moisture contents, matric suctions, and normal stresses. The model's applicability was validated using experimental data from both remolded loess and lignin-modified loess. Compared with conventional unsaturated soil shear strength models, the proposed model exhibits a broader application scope and higher prediction accuracy, particularly under varying suction conditions and in modified soil scenarios. This study provides valuable theoretical support for the application of lignin modification technology in loess engineering and extends the practical applicability of unsaturated soil shear strength models.

Collapsibility is an inherent characteristic of loess, which is often treated by adding industrial materials such as cement and lime in engineering, it seriously damages the reclamation performance of soil. Degradable calcium lignosulfonate (CLS) has a good prospect in balancing soil stabilization and environmental protection. Therefore, this paper evaluates the collapsibility and mechanical characteristics of CLS improved loess based on the collapsibility test, grey correlation analysis, and unconfined compressive strength test. The results show that when the content is 3%, the stabilization effect is most obvious, and the collapsibility coefficient can be reduced by more than 95%. The order of grey correlation degree of collapsibility on each index is moisture content, void ratio, dry density, and CLS content from large to small. The unconfined compressive strength increases rapidly in the first 14 days and then decreases with the content. When the content is too high, the strength of improved loess is lower than that of plain loess. Combined with SEM, microstructure parameters, and X-ray diffraction analysis, the carbonate minerals can play the role of filling pores and connecting soil particles, which reduces the grain size of mineral composition and the thickness of the electric double layer and makes the structure more compact. The research results have scientific significance and application value for the ecological modification research and engineering application of soil.