Evaluating the compressibility behavior of organic soils using laboratory characterization and rapid on-site piezocone penetration testing

A coordinated field and laboratory investigation was conducted to evaluate the compressibility behavior of organic soils and peat existing under SR 15/US 98 in Palm Beach County, Florida. Historically, the existence of soft compressible layers under these highways had been the root cause for premature failure leading to costly and frequent repair/reconstruction projects. The objectives of this study were: (i) to conduct Piezocone Penetration Tests (CPTu) along with Porewater Dissipation Experiments (PDE) for in-situ determination of the Coefficient of Consolidation (C-v); (ii) to perform concurrent laboratory consolidation and secondary compression tests to validate the CPTu predicted properties; and (iii) to establish the (C-alpha/C-c) ratios for Florida organic soils following the well-known Time-Stress-Compressibility concepts. The horizontal Coefficient of Consolidation, C-h (and subsequently the C-v) was predicted from PDE data using several theoretical interpretation models. It was found that a unique relationship exists between Cc and Ca at any stress level, with C-alpha/C-c ratio ranging between 0.03 and 0.05. Considering the inherent difficulty in sampling and laboratory testing of undisturbed soft organic soils, CPTu holds promise as an effective tool for rapid in-situ characterization of the compressibility parameters, which may be useful for forensic interpretations of rutting-induced failures, and the validation of pavement performance models.