Electrical imaging of engineered hydraulic barriers

Electrical resistance tomography (ERT) was used to image the full-scale test emplacement of a thin-wall grout barrier installed by high-pressure jetting and a thick-wall polymer barrier installed by low-pressure permeation injection. Both case studies compared images of electrical resistivity before and after barrier installation. Barrier materials were imaged as anomalies which were more electrically conducting than the native sandy soils at the test sites. Although the spatial resolution of the ERT was insufficient to resolve flaws smaller than a reconstruction voxel (50 cm on a side), the images did show the spatial extent of the barrier materials and therefore the general shape of the structures. To verify barrier performance, ERT was also used to monitor a flood test of a thin-wall grout barrier. Electrical resistivity changes were imaged as a saltwater tracer moved through the barrier at locations which were later found to be defects in a wall or the joining of two walls.