Detection of shear zones in a natural clay slope using the cone penetration test and continuous dynamic sampling

Abstract

The detection of shear zones along which a mass of soil is moving is essential for understanding the state of stability of natural slopes. Weaker zones in clay soils can be identified from low values of cone penetration test (CPT) tip resistance measured during penetration. This paper presents a case history illustrating the identification of softened shear zones in clay soils using the CPT and the observation of shear surfaces using continuous dynamic sampling (CDS). The analysis and interpretation of the CPT data are discussed in relation to the detection of shear surfaces using the CDS at a site with a history of slope instability. Difficulties encountered in identifying shear zones and detecting shear surfaces are discussed.Key words: cone penetration testing, slope stability, in situ testing, case history, shear zone.