The penetrometer and soil exploration. Interpretation of penetration diagrams — Theory and practice

Many flexible pavements in western Palm Beach County, Florida, are underlain at shallow depths by thick deposits of organic soils and peats. These soils undergo long-term secondary compression as a result of sustained overburden pressure of the pavement and thereby cause excessive premature structural distress in the form of cracking, rutting, and differential settlement. Although cementitious materials have been successfully used to stabilize soft, expansive, and inorganic soils, research and experience regarding the stabilization of highly organic soils are limited. The authors' main motivation for doing this research was to investigate the effects of cement stabilization on the compressibility of soils consisting of organic content in the range of 67% to 90%. The undisturbed soil samples were collected from the subsurface of the SR-15 (US-98) roadway, which had experienced severe distress attributable to organic layers and had undergone frequent and costly rehabilitation in recent years. It was found t...

Cement Stabilization of Highly Organic Subgrade Soils to Control Secondary Compression Settlement

Many existing roadways in Florida are built over thick organic and peat layers that cause excessive pavement distress in the form of cracking, distortion, rutting, and differential settlement. A case study shows the use of a variety of geosynthetic and steel mesh reinforcing products embedded in the asphalt overlay placed in SR-15 and US-98 in southeast Florida in an effort to extend the useful life of the pavement structure. Twenty-four test sections, each 152 m (500 ft) long, were constructed, which included eight control sections and 16 reinforced asphalt sections containing GlassGrid, PetroGrid, PaveTrac, and asphalt rubber membrane interlayer at two different test locations with different subsoil characteristics. Before the rehabilitation project, a series of falling weight deflectometer (FWD) tests was conducted at every 15.2 m (50 ft) along the proposed test section alignment for evaluating the existing pavement capacity, statistically determining the site variability among the test sections. Six m...

Stiffness Characterization of Reinforced Asphalt Pavement Structures Built over Soft Organic Soils

Geotechnical characteristics of subsoils should be adequately incorporated in the rehabilitation strategies of existing pavements which have performed poorly due to problematic subsurface conditions. However, there appears to be a disconnect between the advances in our understanding of the mechanics of soft or problematic soils and the rehabilitation design of the overlying pavement structure, leading to repeated cycles of premature distresses, underperformance, and failures. A case study is presented for the rehabilitation of a flexible pavement built over soft organic soils in Southeastern Florida, USA. The study incorporates forensic investigation of the deteriorated pavement structure, subsurface investigations with cone penetration testing, design and construction of reinforced overlays in field test sections, and long-term performance monitoring with non-destructive dynamic tests. Efforts are made to correlate site characteristics with pavement performance. Based on the secondary compression behavior of the organic soils, cement deep mixing criteria are proposed for a more durable and sustainable solution.

Challenges due to problematic soils: a case study at the crossroads of geotechnology and sustainable pavement solutions

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Ground and Groundwater Responses Due to Shaft Excavation in Organic Soils

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 α /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 fro...

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 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

Hieu Huynh

Papers

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

Field and Laboratory Compressibility Characteristics of Soft Organic Soils in Florida