Comparison of geological profiles from borehole data based 3D geological model and geophysical testing

Three-dimensional (3D) geological modeling has been used for design and construction works to overcome the complex nature of underground geological conditions. The accuracy and reliability of geological information reflected by the 3D model are critical for engineers to make sound judgement. The 3D model is usually established using borehole data. The data gaps between boreholes affect the accuracy of the 3D geological model. Instead of getting additional borehole data, geophysical survey is a promisingly cost-effective method to fill the data gaps and improve the assessment of the underground uncertainties. In this study, a case of using the seismic surface wave methods to determine the engineering rockhead and thus fill the data gap in the 3D geological model is presented. In relation to a subway project in Singapore, the combination of geophysical methods and 3D geological model for rockhead detection at this site was explored. Seismic geophysical survey was carried out to map the rockhead which was calibrated and verified using borehole data. This improves the accuracy of the rockhead obtained from 3D geological model. Through this study, a procedure of using geophysical methods to obtain additional data to verify and update the existing 3D geological model has been established.