Case history examples of estimating OCR in structured and structured organic cohesive soil with field vane tests using the SHANSEP-based method

Abstract

Accurate estimation of the preconsolidation stress and overconsolidation ratio, OCR, in uniform cohesive soils using the field vane test is influenced by the combined effects of soil type and plasticity, geologic history, soil structure, and the presence of organic matter. Published empirical correlations for cohesive soils consider the effects of soil type and plasticity, but significant variability can occur with changes in soil structure and the presence of organic matter content. The adaption of the “stress history and normalized soil engineering properties” (SHANSEP) format improves the characterization of overconsolidated soils using field vane tests by applying a proposed empirical approach to identify structured soils from unstructured soils and updating the SHANSEP-based approach to separately evaluate stress history in structured and unstructured soils. Validation of the correlation coefficients for individual projects is needed as the approach is applied to new geologic materials and with potentially different field vane equipment and laboratory testing procedures used to characterize the soils. This additional testing provides an opportunity to improve the correlations for specific conditions and reduce the variability in current OCR assessments.