3D Effects on 2D Resistivity Monitoring in Embankment Dams

Abstract

Resistivity measurement is a potentially powerful method for monitoring the leakage zones developed in a dam or their expansion with time. Generally, two-dimensional (2D) resistivity data have been measured along the dam crest for the detection of leakage zones at embankment dams. However, the three-dimensional (3D) effects created by specific dam geometry and fluctuation in reservoir water level significantly distort the 2D resistivity data measured at the dam crest. The 3D modeling results demonstrated that the 3D effect from the dam geometry and variation in water level is significant. Especially, changes in 3D effects from water level fluctuation cause a spurious near-surface layer when time-lapse inversion using a cross-model constraint is applied. To overcome this problem, we introduced a combined reference model that was constructed from the independent inversion of both the time-lapse data and the original reference data. The combined reference model was able to effectively suppress the effect of the spurious near-surface layer and to clearly image the damaged zone when the change in water level is smaller than 0.5 m. However, the time-lapse inversion using the combined reference model also failed to identify the damaged zone when the change in water level became larger than 0.5 m.