Intralayer Variability and Compressibility of Hawthorn Group Soils

This paper examines the intralayer variability and its effects on the compressibility response of Hawthorn Group (HG) soils in Central Florida. Field and laboratory testing programs were conducted at the deep foundation test site (DFTS) located at the University of Central Florida (UCF). Soil characterization methods included index, X-ray diffraction, and scanning electron microscopy tests to evaluate soil properties associated with the composition and structure of HG soils. The compressibility characteristics of the soils were studied via incremental loading, constant rate of strain, and triaxial K 0 -reconsolidation (pseudo K 0 -TX) tests conducted on thin-walled Shelby tube samples. Effects of sample disturbance, strain rate, and creep were considered when evaluating compressibility response, and the evolution of the at-rest earth pressure coefficient, K 0 , and the small-strain elastic shear modulus, G 0 , obtained by reproducing the stress history of the material in pseudo K 0 -TX testing were presented. The results were evaluated in terms of soil composition and structure, axial stress–strain response, and overall compressibility properties. It was found that the intralayer variability of HG soils abruptly changes within a few meters along the DFTS and triggers a wide range of compressibility responses. Less sample disturbance effects and consequently more representative mechanical parameters of the in situ conditions were obtained via pseudo K 0 -TX testing. HG soils were found to be insensitive to variations in the tested strain rates. Creep effects were found because of the clay content and tested strain rates. Measured K 0 and G 0 responses depended on the stress history of the material. Geotechnical designs in these soils must account for intralayer variability to properly predict ground deformations.