ABSTRACT
A case study of reliable 3-D geotechnical modelling based on drilling and geophysical survey data is presented. In this study, the distribution of a soft alluvial clay deposit having the risk of consolidation/deformation/subsidence was required for a new road planning. It was first estimated based only on drilling data. Then, a 2-D microtremor survey was conducted for more detailed modelling and resulted in the detection of a deeply buried valley filled with soft sediments, which have potential risks. The buried valley was confirmed by the additional drilling. The scale and direction were detected using a 3-D microtremor array measurement. The direction of the buried structure was oblique to the planning line of the road. It means that only drilling and a geophysical survey in 2-D were insufficient, and a 3-D survey was necessary to capture the geometry of the buried structure. These investigation results have been reflected in the 3-D geotechnical model. This study demonstrated the effectiveness of the geophysical survey for geotechnical modelling. The updated model, including the risk information, can be handed over to the owner and designers and planned to be used as a BIM model.
