Field and Laboratory Compressibility Characteristics of Soft Organic Soils in Florida

Abstract

A coordinated field and laboratory investigation was conducted to evaluate the primary and long-term secondary compression characteristics of organic soils and peat existing under SR 15 / US 98 in northwest Palm Beach County, Florida. The specific objectives were: (i) to conduct Piezocone Penetration Tests (CPTu) accompanied with porewater dissipation experiments for predicting the Coefficient of Consolidation (Cv); (ii) to perform consolidation testing on organic silts and peat collected from various depths at each CPTu location; (iii) to conduct secondary compression tests at constant effective stress representing the in-situ conditions; and (iv) to establish the (Cα / Cc) ratios for Florida organic soils following the well-known Time-Stress-Compressibility concepts. The horizontal coefficient of consolidation (Ch) was predicted from porewater dissipation data, which was subsequently used to calculate the vertical coefficient of consolidation (Cv), and compared with laboratoryderived properties. It was found that the primary consolidation process in laboratory specimens is quite rapid, leading to the secondary compression phase. The Secondary Compression Index, Cα was calculated during the first log cycle after the End-ofPrimary (EOP) consolidation, and a unique relationship between Cc and Cα was established. Results indicated that for all practical purposes, the (Cα / Cc) ratio had constant values ranging from 0.03 to 0.05, which were consistent with the values reported in the literature for similar soils. BACKGROUND AND OBJECTIVES The western and northern parts Palm Beach County, Florida have shallow layers of organic silts and peat under existing roads, which often exhibit large amount of cracking, distortion and settlement in a short period of time after reconstruction work. Generally, the primary consolidation process in organic layers is quite rapid, followed by significant secondary compression stages under sustained effective overburden