| In recent years, non-destructive investigations and management of civil engineering
structures is increasingly improving, and assessments are now supported by national and
international standards. However, the literature on the applicability of different
geophysical techniques to the problem of levee and river embankment monitoring is
still limited. Accurate flood levee embankment stability assessment is critically
important because embankments and earth dams are subject to water infiltration and
internal erosion, which may lead to mechanical weakness and breaching. This study
includes a 2D analysis of the instability of an earthen levee, using multichannel
analysis of surface waves (MASW) and electrical resistivity imaging (ERI), along with
direct observations of the site engineering geology and geomorphology. Both the
modeled Vs and Ω indicate a horizontally-layered subsurface with rapid vertical
transitions in both stiffness and conductivity. This conclusion is supported by a
covariance analysis of Vs and Ω at varying depths and chainages along the levee.
Together with a geomorphic assessment, this indicates that the structure is being
destabilized by water infiltration, which is causing erosional-piping, leading to surface
subsidence. While the key reason for applying various types of geophysical methods
to embankment stability assessment is to undertake a safety examination of the
embankment, a secondary reason is to compare and contrast the efficacy of the geophysical
methods. To this end, it was found that the integration of covariance analysis of 2D
geophysical datasets, alongside sedimentary and topographic data, can help the rapid
location of anomalous zones in sub-levee soils between geotechnical boreholes. |