Variability of the cone penetration resistance

In the WBI 2017 guideline (I&M, 2016) for slope stability the Appendices G, H and I describe the application of CPT’s and the approach to use CPT data to determine parameters for slope stability analyses. The variability of the shear strength within a dike section based on a number of CPT’s has been showed to be considerable. Within the WBI guidelines it is not specified yet how to deal with this variability of the soil properties in the assessment of a dike section. A site investigation is performed to investigate the variability of the cone penetration resistance. Literature research is performed in order to apply recent knowledge about interpretation and modelling spatial variability of soil properties. Based on this research it can be concluded that the characteristic lower bound of the cone penetration resistance for a dike section has to be derived from a series of CPT’s. This series of CPT’s represent the variability of the soil much more than one CPT. These series of CPT’s can belong to a dike section or a WBI-SOS segment for example. Averaging of variability along a slip surface can be taken into account by the variance reduction factor as described by TAW (2002). This variance reduction factor seems to be also very variable with dense datasets.