On Georeferenced Soil Engineering Properties and Interpolations

Due to the inherent variability of soil properties, geotechnical engineers often leverage multiple tools to estimate site subsurface conditions, including historical records, in situ measurements, and laboratory testing data. A comprehensive site investigation may be uneconomical for certain projects; thus engineers typically perform site characterization, which potentially could balance project costs and the extent of site investigation. To aid in preliminary analyses of site conditions, we have created a web-GIS database to compile soil engineering properties across the state of Oregon. The database, Georeferenced Oregon Soil Engineering Properties (GOSEP), is populated by existing data across projects from all over the state, including monotonic strength, laboratory characterization data, borehole logs, and in situ test results. In this paper, a detailed procedure showing kriging was used to generate three-dimensionally interpolated standard-penetration-test (SPT) data through the GOSEP interface. In addition, this study reveals the use of oblate spheroid as a kriging search geometry and the approach to dealing with modeling variograms with few data points. Ultimately, a crossvalidation analysis was performed to study the accuracy of predicted values, and the limitations were discussed regarding the estimation.