Due to the significant hydrophilicity and cracking properties of expansive soils, expansive soil slopes are prone to destabilization and landslides after rainfall, seriously threatening the safety of buildings, highways, and railroads. Substantial economic losses often accompany the occurrence of expansive soil slope disasters; thus, it is of great significance to understand the slope failure mechanisms experienced by expansive soil slopes and to prevent expansive soil slope disasters. In this paper, the current research status of the landslide failure mechanism of expansive soil slopes is systematically reviewed based on three research methods: field test, model test, and numerical simulation. The failure mechanisms of expansive soil slopes and the main influencing factors are summarized. Based on the failure mechanisms, three protection principles (waterproofing and water blocking, swelling–shrinkage deformation limitation, and crack inhibition and strength enhancement) that can be followed for disaster prevention of expansive soil slopes are proposed. The research status and advantages and disadvantages of these protection methods are reviewed, and future researchable directions of the stability of expansive soil slopes and slope protection methods are explored. Based on the previous work, a new flexible ecological slope protection system with a double waterproof layer is proposed for expansive soil slopes to realize ecological, efficient, and long-term protection. This paper thus aims to provide technical reference for the prevention and control of slope engineering disasters in expansive soil areas.

The characteristics of expansive soil, including over consolidation, swelling-shrinkage, fissures, and strength attenuation, can cause potential hazards in road construction, which are mainly manifested as subgrade swelling-shrinkage deformation and slope collapse. Effective treatment can not only ensure long-term subgrade stability but also reduce investment costs and environmental impact. In this review, the current development status of embankment filling and cutting slope treatment technology in expansive soil areas were summarized, and the classification standards of expansive soil filler, moisture retention, and antiseepage technology were described. Then, the utility of chemical, physical, biological, and solid waste modification materials in improving the engineering characteristics of core-filled expansive soil was discussed, and the cost and technical characteristics of these modification technologies were compared and analysed. Next, the application of rigid and flexible support technology in the treatment of cutting slope collapse was analysed, and the advantages and disadvantages of rigid and flexible supports were summarized. Finally, the development direction of expansive soil subgrade treatment technology was discussed. This review includes a summary of the treatment methods of highway subgrade in expansive soil areas and can provide a technical reference for treatment methods of expansive soil subgrade.

To investigate the effect of oyster shell powder (OSP) on the static and dynamic properties of expansive soil, the mechanical properties of modified soil were obtained. Taking Ningming expansive soil as the research object, triaxial shear test, dynamic triaxial test and scanning electron microscope test were carried out on plain soil and 9 % expansive soil modified by oyster shell powder (ESMO). The results show that compared with plain soil, the effective cohesion of modified expansive soil with d_osp < 1 mm (ESMO (d_osp < 1 mm)) and d_osp < 0.075 mm (ESMO (d_osp < 0.075 mm)) is increased by 15.4 % and 32.8 %, respectively. Under cyclic loading, compared with plain soil, the plastic strain stability value of ESMO (d_osp<0.075 mm) is reduced by 40.2 %, the pore water pressure stability value is reduced, and the stiffness is increased. The dynamic mechanical properties of ESMO (d_osp<1 mm) showed the opposite trend. Through microscopic experimental analysis, the main reasons for this phenomenon are the particle size distribution, bonding form, and cementation of the two. The results can provide a theoretical basis for the practical application of ESMO and the establishment of constitutive model.