Revised Soil Classification System: Implementation and Engineering Implications

Soil classification systems help geotechnical engineers anticipate soil properties and provide early guidance for engineering analyses. Current soil classification systems recognize the central role of particle size and inherent differences between coarse- and fine-grained fractions. However, they adopt fixed classification boundaries irrespective of a broad range of fines plasticity and particle shape, disregard the distinct fines thresholds for mechanical and hydraulic properties, and overlook pore-fluid chemistry effects on fines behavior. The Revised Soil Classification System (RSCS) addresses these limitations and benefits from published data and physical insights gained during the last century. By comparison, the classification boundaries in the prevailing Unified Soil Classification System (USCS) resemble those in the RSCS only for the case of angular sands and gravels mixed with low-plasticity fines; in all other cases, extensive data sets corroborate the transition thresholds adopted in the RSCS. The complete logic tree for the RSCS facilitates its implementation; it is available as user-friendly Excel macro and a mobile application that automatically produce the soil-specific classification charts and show the soil classification in terms of the controlling fraction for both mechanical and hydraulic properties. Multiple studies have demonstrated the predictive power of the RSCS in terms of soil properties (e.g., compressibility, strength, hydraulic conductivity, and capillarity), soil phenomena (e.g., fines migration and bioactivity), and the preliminary selection of geotechnical solutions (e.g., soil improvement).