Effect of Compaction Effort and Initial Conditions on the Unsaturated Properties of Red Clay Soils

In geotechnical engineering, the principle of saturated soil mechanics is used in the construction of structures. However, defining the constitutive unsaturated soil model requires significant laboratory testing, and directly measuring the parameters of the soil–water characteristic curve (SWCC) by the pressure plate test is time‐consuming. To avoid overdesign and ensure cost‐effectiveness, it is essential to analyze how soil volume changes due to climate variations in tropical regions. The primary objective of this research is to develop a prediction model based on relationships with basic soil properties to simplify SWCC shape parameters. These parameters can usually be easily determined from basic soil characteristics through a simple and cost‐effective testing method. Pressure plate extractors were used in the laboratory to measure the SWCCs for 14 soil samples compacted using modified compaction effort, two compacted using standard compaction effort at optimum moisture content, and three that remained undisturbed. It was found that the compaction effort and initial soil conditions had an impact on the SWCC’s shape, resulting in variations in SWCC characteristics. The Fredlund and Xing model parameters, which are derived from least‐squares fits to the SWCC data, also reflect variations in the SWCC. The relationship between the SWCC shape parameters and basic soil characteristics was examined using regression models. The statistical software program SAS JMP Pro‐14 was used to perform regression analysis. A statistically simple regression model for air‐entry value (AEV) and residual water content was then developed and cross‐validated. Basic soil property test findings showed a strong correlation with the models.