Integrated Geophysical Investigation For The Vulnerability Assessment Of Earthen Levee

Abstract

Integrated geophysical investigation was undertaken to assess the vulnerability of earthen levees to flooding and earthquake. The tested geophysical methods involved multi-channel surface wave dispersion measurement (MASW), capacitively coupled (CC) resistivity measurement, multi-frequency electromagnetic (EM) survey, and high-resolution seismic reflection survey using S-wave type Land Streamer. Because these methods required no fixing of sensors on the levee surface, high performance on field measurement work could be accomplished. The CC resistivity as well as EM survey successfully reconstructed resistivity profiles along levees, and delineated anomalously high or low resistivity zones within or beneath the levee body. The MASW method mapped shear wave velocity structures along levees, and clearly imaged relatively high or low velocity zones in the levee body. High-resolution seismic reflection surveying delineated the layered structure in the levee and in the underlying foundation sediments. Integrated investigations of resistivity and shear wave velocity structure remarkably highlighted the potentially permeable zones in the levee body as high resistivities and intermediate to low S-wave velocity areas. As a result, the geophysical methods effectively delineated the unexpectedly heterogeneous structure in the body of the levee, and the comprehensive investigation approach is shown to be helpful for the vulnerability assessment of levees through interpreting geophysical anomaly identified by means of integrated surveying.