A procedure for the assessment of the undrained shear strength profile of soft clays

In the geotechnical research community, there is widespread agreement that the choice of the characteristic undrained shear strength (cuA) is very important and plays an essential role in the design and stability analysis of various geotechnical constructions placed in or on soft clay deposits. Thus, the choice of undrained shear strength, both conservative and non-conservative, could have major economic (and social) consequences in many projects. This paper summarizes the work carried out by engineers and scientists representing various institutions in Norway to provide a sound engineering method to determine characteristic shear strength of soft clays. This paper presents a recommendation on how to determine a characteristic cuA profile based on laboratory and in situ testing methods and discuss the impact of stress history, strain rates, Atterberg’s limits, and sample disturbance on the undrained shear strength of soft clays measured at a single borehole location. The discussion is supported by the results obtained from laboratory and field-testing. This paper highlights the key issues related to the extrapolation of undrained shear strength of soft clay from a given borehole location to a large soil volume.