Image-based measurement of one-dimensional compressibility in cement-treated soils

This paper reports an attempt to accurately quantify one-dimensional compressibility of stiff, cement-treated high-water-content clays by using a constant-rate-of-strain (CRS) oedometer equipped with an image-based strain measurement system. The errors in stiffness measurements due to imperfect specimen–platen bedding and apparatus compliances, significant factors when stiff soils are tested, were avoided by directly observing movements of the specimen's lateral surface over a transparent confining ring. The proposed system is meant to be practical, requiring only minimum alterations to existing CRS oedometers and a generally available mid-market digital camera. The effectiveness of the method is demonstrated by testing six cement-treated clay specimens with or without air-foam inclusions in one-dimensional compression and by comparing the obtained compression curves with those obtained by more conventional measuring systems. The image analysis always revealed significantly stiffer responses than observed by the conventional methods. Validity of the image-based stiffness determination at small strains was confirmed by generally good agreements of its derived stiffness values with those obtained from highly precise triaxial probes, which provided a full set of cross-anisotropic elastic parameters. Implications for field problems are discussed in relation to an offshore reclamation project, in which similar cement-treated high-water-content clays were extensively used for upper layers.