Performance of hydroxy-aluminum-stabilized expansive soil as a covering layer

Expansive soil, a problematic clay soil susceptible to significant volume changes with moisture variation, is typically mitigated using cohesive non-swelling soil (CNS) covering technology. This study evaluates the comprehensive performance and feasibility of using chemically stabilized expansive soil (CSS) treated with hydroxy-aluminum solution as a replacement for natural CNS as a covering layer for expansive soil (ES). Through a series of physical-mechanical tests, chemical analyses, and laboratory model tests, the inhibition effect of different covering layers (CSS, CNS, and gravel) on expansive soil was investigated, along with the relationship between electrical resistivity and swelling deformation. The results indicate that: (1) After modification with hydroxy-aluminum solution, the engineering properties of expansive soil were substantially improved, with shear strength enhanced and swelling percentage significantly reduced. Overall, CSS exhibited performance comparable to that of CNS. (2) The CSS layer provided the most effective inhibition of expansive soil, reducing swelling deformation by approximately 67%--a clear improvement over both gravel and CNS layers, thereby confirming the viability of CSS as an alternative covering material. (3) A strong correlation was observed between the resistivity ratio and the swelling rate of the expansive soil layer. Specifically, this relationship followed a linear function under the gravel and CNS layers, whereas it exhibited a power function under the CSS layer. These findings offer valuable insights for the engineering application of CSS covering technology and for the use of electrical resistivity as a practical evaluation method.