A simple approach to probabilistic CPTu-based geotechnical stratigraphic profiling

Abstract

Geotechnical profile delineation is an important aspect of the geotechnical engineering design process. The Cone Penetration Test (CPTu) is widely used for this purpose, as it is simple to classify soils based on their different responses to the cone. However, CPTu-based delineations typically involve engineering interpretation, as they are affected by the classification scheme applied, by inherent soil variability and by measurements error. A semi-automated CPTu data treatment tool is here presented aiming to simplify the soil delineation task, adding consistency and transparency to the involved engineering interpretation process and facilitating the transference of information between the different parties involved in design. The tool fits bivariate normal distributions to interpreted CPTu data according to some user specified criteria that quantify estimated classification and measurement uncertainties. Classification makes use of conventional class boundaries –here taken from Robertson, 1990 chart-, which are applied with user-specified refinement. Thin layers are consolidated into adjacent ones to further simplify the resulting profile. The operation of the proposed algorithm is illustrated by interpreting CPTu records from a deltaic sedimentary environment. The outputs of this simple method may be used as input for more advanced probabilistic methodologies, helping thus to bridge the gap between qualitative practice and quantitative research methods.