Monday, November 13, 2006 - 2:30 PM

Organic Soils and Geotechnical Research: Challenges and Perspectives.

Marika Santagata, Purdue Univ, Civil Engineering, 550 Stadium Mall Dr, West Lafayette, IN 47907-2051

From a geotechnical perspective, organic soils are generally viewed as “problem” soils indicating that their engineering properties are inferior to those of other soft soils, thus increasing risks of foundation failure and/or of inadmissible settlements, and that their behavior may deviate significantly from traditional rules of soil behavior. The presence of organics in soils is generally associated with: high compressibility (with values of the compression index Cc which can exceed by more than one order of magnitude those of other soft soils); high values of both the in situ hydraulic conductivity (k) and the coefficient of consolidation (Cv) (greater by 1-3 orders of magnitude compared to inorganic soils with the same void ratio); a marked decrease in both k and Cv with a reduction in void ratio; very high creep rates, greater than in any other geomaterial, which typically control the deformation behavior in the field. The strength characteristics of organic soils vary greatly depending on organic content, void ratio, degree of decomposition and presence and percentage of fibers, and are significantly anisotropic. In addition to providing an overview of the geotechnical properties of organic soils, the presentation will discuss design challenges associated with construction on these soils, through examples taken from recent projects in the US and abroad.