Voxel modeling of geotechnical characteristics in an urban area by natural neighbor interpolation using a large number of borehole logs

Borehole logs are important geospatial data for understanding subsurface geological and geotechnical conditions. Recently, many borehole logs in urban areas have been open to the public on the Internet in machine-readable file format. However, a few simple methods allow us to construct a voxel model of geological and geotechnical characteristics with high objectivity of the modeling process. Our work aims to develop a simple method that facilitates the use of open borehole logs in geological and geotechnical investigations in urban areas. In this paper, we propose a voxel modeling method of geotechnical data using the machine-readable open borehole logs. The method is designed to construct voxel models of lithofacies and standard penetration test results by stacking a series of horizontal two-dimensional grid data that are created by natural neighbor interpolation using geotechnical data stored in borehole logs at regular elevation intervals. A test calculation to evaluate the proposed method was performed using a large number of borehole logs in the Tokyo metropolitan area, Japan. Results confirmed that the proposed method not only allows us to ensure the objectivity of the modeling process but also provides a good overview of the three-dimensional distribution pattern of the subsurface geotechnical characteristics without any setting of complicated calculation parameters. In conclusion, the proposed method improves the efficiency of geological analyses, such as stratigraphic correlation using borehole logs, and facilitates the use of open borehole logs in urban areas.