Influence of Soil Water Content and Bulk Density on Precompression Stress of Shajiang Black Soil and Establishment of Pedo-transfer Function

Objective The Shajiang black soil (Vertisol) is characterized by high bulk density and high clay content, which often leads to problems such as swelling and shrinkage, limited infiltration and increased strength. At the same time, agricultural machinery is often used for field work in the district. Precompression stress is often used to evaluate the compressive properties and bearing capacity of soils. An in-depth study of soil compression characteristics of Shajiang black soil is of great significance for the protection of soil structure and the uptime of agricultural machinery.

Method Repacked Shajiang black soil was chosen to examine the effects of initial water content and bulk density on precompression stress and to establish a Pedo-transfer function. The soil bulk densityies(ρ) were established at 1.2, 1.4, or 1.6 g·cm⁻³, while the soil water contents (θ) were set at 100%, 85%, 70%, 55%, and 40% of field capacity. Uniaxial compression tests were conducted using a consolidator to obtain soil compression curves, and the precompression stress was calculated using the Casagrande method.

Result The van Genuchten equation provided a good fit for the soil compression curve, while the initial void ratio, soil water content, and bulk density significantly influenced the soil compression characteristics (P < 0.05). The precompression stress of Shajiang black soil varied between 15.2 kPa and 150.6 kPa and showed a significant negative exponential correlation with soil water content and a significant positive correlation with bulk density. (P < 0.05). A Pedo-transfer function (σ_p=aexp(bθ + cρ), R² = 0.832, P < 0.01) was established among water content (θ), bulk density (ρ), and precompression stress (σ_p), considering the swelling and shrinkage characteristics of Shajiang black soil.

Conclusion The soil water content and bulk density are the two core elements these regulate the compressive strength of Shajiang black soil. The results of this study can serve as a reference for assessing the risk of compaction and determining a suitable time for trafficability.