Geophysical monitoring for inspecting the stability of the sea dike in South Korea

Abstract

Geophysical methods including electrical resistivity and MASW are used for delineating seawater inflow through sea dike and detecting the abnormal compactness region that could affect the structure of dike. To identify the part of anomalous seawater inflow through the sea dike, we periodically carried out 3D resistivity survey along the dike including anomalous regions. 3D resistivity survey and monitoring for the dike can define effectively the low resistivity zones lower than 1 ohm-m, which may indicate seawater inflow through the dike. For detailed analysis of 3D resistivity monitoring data, time-lapse inversion method was adopted in this study. Time-lapse inversion is effective for identifying the subtle changes over time and for suppressing inversion artifact. The results of time-lapse inversion method show no significant changes in the sea dike with time. Shear wave velocity profiles obtained by MASW periodically indicate less compacted layer that could be originated by the loss of dredge sand or the bad compactness condition during the construction and would be predicted the possibilities of subsidence. From this study, 3D electrical resistivity surveys using time-lapse inversion approach and periodic MASW surveys are revealed to be effective for identifying seawater inflow pathway through the sea dike and investigating its safety, respectively.