TITLE:
A Novel Approach to the Classification of Soil Swelling Potential Using the Weighted Plasticity Index (wPI)
AUTHORS:
Damian V. A. Alexander, Anton N. Ali
KEYWORDS:
Cation Exchange Capacity (CEC), Expansive Soils, Geotechnical Site Investigation, Swelling Potential, Weighted Plasticity Index (wPI)
JOURNAL NAME:
Journal of Geoscience and Environment Protection,
Vol.13 No.11,
November
24,
2025
ABSTRACT: Expansive soils present a significant geohazard to light infrastructure worldwide, causing costly damage through swelling and shrinkage cycles driven by moisture content changes. One key property controlling this behavior, the Cation Exchange Capacity (CEC), is complex and expensive to measure directly, making it necessary to find reliable and affordable proxies for initial site assessments. This study introduces and validates a novel parameter, the weighted plasticity index (wPI), for classifying the swelling potential of expansive clays. Twenty-six soil samples, representing a range from low to high plasticity clays from Trinidad, underwent standard geotechnical laboratory tests, including Atterberg limits and grain size analysis. The wPI was calculated for each sample as the product of its Plasticity Index (PI) and the percentage of fine particles (percent passing the 425-µm sieve). A strong linear relationship (R2 = 0.94) was found between the wPI and the Liquid Limit (LL). Using a previously established relationship between LL and CEC, a robust mathematical model connecting wPI directly to CEC was derived. This model formed the basis for a new four-tiered swelling potential classification system (Low, Medium, High, and Very High) based on the calculated wPI values. The wPI method provides a reliable, quick, and cost-effective tool for geotechnical engineers to evaluate swelling potential, promoting the design of more resilient and sustainable infrastructure in areas prone to expansive soils.