Zhigao Xie

To improve the engineering properties of red clay, sodium polyacrylate (PAAS) and locust bean gum (LBG) were used as modifiers, either singly or in combination. The modified soils were subjected to variable head permeability tests, triaxial compression tests, and scanning electron microscopy (SEM) tests to analyze the effects of different modifiers on the permeability and shear strength of the red clay and systematically explore the modification mechanism. The results showed that both PAAS and LBG significantly reduced the permeability of the red clay, with PAAS having a more pronounced effect. This mechanism is attributed to PAAS swelling upon water absorption, forming a hydrogel network that fills micropores and forms ionic bonds with clay particles. LBG, on the other hand, encapsulates the particles in a highly viscous colloid, enhancing their aggregation. Regarding shear strength, both PAAS and LBG improved soil cohesion, with PAAS exhibiting a superior combined improvement in cohesion and internal friction angle compared to LBG. The PAAS-LBG composite modification exhibits a significant synergistic effect: PAAS forms a continuous hydrogel network as the primary skeletal structure of the soil, while LBG supplements the pores and increases bonding, resulting in a denser soil structure. Microscopic analysis further confirms that the PAAS-LBG composite modification significantly reduces porosity and enhances interparticle interlocking, thereby simultaneously improving both the impermeability and shear strength of the red clay. This research can provide a reference for sustainable development and red clay modification in red clay regions.

To address the engineering challenges associated with Guilin red clay, such as its potentially low strength and unfavorable mechanical behavior, this study investigated the effectiveness of lignin and lime as modifiers. Consolidation undrained triaxial tests and scanning electron microscopy (SEM) were employed to evaluate the strength characteristics and microstructural changes in modified clay specimens with varying dosages. The results demonstrate distinct strengthening mechanisms: Lignin exhibits an optimal dosage (6%), significantly increasing cohesion and internal friction angle through physical reinforcement (“soil fiber” formation), but higher dosages (8%) lead to particle separation and strength reduction. In contrast, lime provides continuous and substantial strength enhancement with increasing dosage (up to 8%), primarily through chemical reactions producing cementitious compounds (e.g., C-S-H, C-A-H) that densify the structure. Consequently, lime-modified clay shows significantly higher cohesion and internal friction angle compared to lignin-modified clay at equivalent or higher dosages, with corresponding stress–strain curves shifting from enhanced (strain-hardening) to softening behavior. These findings provide practical insights into red clay improvement in geotechnical engineering applications.

In order to study the strength characteristics of organic-matter-contaminated red soil and the improvement effects of different modifiers, the red soil in the Yulin area was taken as the research object, and triaxial compression tests were carried out to study the effects of different mass fractions (0%, 2%, 4%, 6%, 8%) of organic matter (sodium humate) on the strength characteristics of red soil. Unconfined compressive strength (UCS) tests and scanning electron microscopy (SEM) tests were carried out to study the improvement effects of different amounts of lignin, fly ash, and xanthan gum on organic-matter-contaminated red soil (organic matter content of 8%). The results of the tests showed that the cohesion and internal friction angle of red soil both tended to decrease with the increase in organic matter content. When the organic matter content increased from 0% to 8%, the cohesion of the red soil decreased from 60.98 kPa to 40.07 kPa, a decrease of 34.29%; and the internal friction angle decreased from 17.42° to 7.28°, a decrease of 58.21%. The stress–strain relationship curves of organic-matter-contaminated red soil all show a hardening type. Under different confining pressures, as the organic matter content increased, the shear strength of the red soil decreased continuously. The unconfined compressive strength of organic-matter-contaminated red soil increased with the increase in lignin content, and increased first and then decreased with the increase in fly ash content and xanthan gum content. Through comparative analysis, it was found that the fly ash with a content of 15% had the best improvement effect. The lignin-amended red soil enhanced the connection of soil particles through reinforcement, reduced pores, and improved soil strength. Fly ash improved the acidification reaction, and the hydrates filled the pores and enhanced the soil strength. Xanthan gum improved the red soil by absorbing water and promoting microbial growth, further enhancing the bonding force between soil particles. This study can provide a reference for engineering construction and red soil improvement in red soil areas.