Total engineering geology approach applied to motorway construction and widening in the Netherlands: Part I: A pragmatic approach

The current practice of site investigation for motorways in soft soil areas like the Western Netherlands can be described as an ‘engineering approach’ rather than an ‘engineering geology approach’. After a highlight of the engineering geological concerns related to building line infrastructures on soft soils, the Dutch practice of site investigation is critically reviewed. Then, a new pragmatic methodology is suggested. It combines 1:50 000 lithostratigraphical models of the subsurface, archived geological and geotechnical data, airborne laser surface altimetry data, walk-over survey observations, and low cost geoelectric and electromagnetic data, in that order. A conceptual model is produced that breaks down the subsurface into terrain units, formations, members, and types and highlights expected heterogeneities. Ground heterogeneities are then classified based on their mapped geology and geomorphology, surface altimetry and, geophysical signatures. Cone Penetration Tests are ordered to map a limited set of representative heterogeneities. The complete profile of all heterogenieties is obtained by matching geological, geophysical and, altimetry signatures with the reference set. In a companion paper, this new methodology is applied to motorway widening on the tidal deposits of the Western Netherlands.