Integrating Geophysical and Geotechnical Engineering Methods for Assessment of Pipeline Geohazards

Because pipelines can cover extensive distances through diverse terrain, they are subject to various geohazards, including slope failure and earthquake damage, which can have costly environmental and monetary impacts over their designed operational lifetime. Here, we show how geophysical investigative techniques can be used to complement other geotechnical investigation methods to provide a detailed understanding of site geology to best inform geohazard assessments. We pay particular attention to how multiple geophysical methods can be used to obtain spatially continuous measurements of subsurface physical properties, and layer and structural geometries. The geophysical data can then be used to either interpolate or extrapolate geotechnical engineering properties between and away from boreholes and excavations, or optimize the locations of subsequent boreholes or excavations. To demonstrate the utility of our integrated approach of incorporating geophysical methods to geohazard assessments, two case studies are presented. The first case study shows how electrical resistivity tomography (ERT), seismic refraction tomography (SRT) and multichannel analysis of surface wave (MASW) datasets are used to constrain the thickness and extent of potentially sensitive glaciomarine clay layers that are subject to slope instability and structural failure along a proposed pipeline route near Kitimat, British Columbia (BC). A second case study describes how high-resolution ground-penetrating radar (GPR) and seismic reflection surveys are used to locate and characterize fault strands that may cause future ground deformation at a proposed pipeline crossing of the Tintina/Rocky Mountain Trench fault in northeastern BC.