Automated Airborne EM and borehole data integration for depth to bedrock extraction

Abstract

Airborne electromagnetic (AEM) was used to supplement a geotechnical investigation for a highway construction project in Norway. Variable bedrock threshold resistivity hindered efforts to track depth to bedrock, motivating us to develop an automated algorithm to extract depth to bedrock from both boreholes and AEM data. We developed two variations of this algorithm: one using simple Gaussian or inverse distance weighting interpolators, and another using ordinary kriging and combined parameter probability distribution functions. Evaluation shows that for preliminary surveys, significant savings in boreholes required can be made without sacrificing bedrock model accuracy. However, issues with AEM noise and data quality likely reduced the comparative advantage that including AEM provided. Moreover, AEM cannot supersede direct sampling where the model accuracy required exceed the resolution possible with the geophysical method. Nevertheless, using AEM in the way can still reduce the number of required boreholes and hence reduce site investigation costs because we can identify high probability zones for shallow bedrock, identify steep or anomalous bedrock topography, and estimate the spatial variability of depth