A Case Study of Undrained Shear Strength Evaluation from In Situ Tests in Soft Louisiana Soils

The undrained strength is one of the governing soil properties when evaluating stability issues associated with clays. The undrained shear strength is not a unique measure of soil strength; it may be obtained by conducting laboratory tests or by in-situ tests, or a combination of both. This paper presents a case study using piezocone penetration test (PCPT or CPTu) and flat dilatometer test (DMT) to ascertain undrained shear strengths at a site in New Orleans where soft clay deposits are predominant. This paper attempted to correlate the undrained shear strengths obtained from PCPT and DMT to those obtained from laboratory unconfined compression and triaxial unconsolidated undrained tests. A calibration study was performed and a set of site-specific values were suggested to best suit the soils at the exploration site. The suggested parameters or correlations may be valuable to practitioners to evaluate undrained shear strengths in New Orleans area using popular in-situ test methods.