Dike Monitoring at Red River by Geophysical and Geotechnical Tools

Abstract

A dike monitoring system consisting of a permanent electrode array and geotechnical tools including tensiometers, frequency reflectometry sensors (FDR) and an observation well has been installed at a dike section of the Red River in Thai Binh province (Vietnam). Since the stability of the dike depends to a large extend on the seepage line the system is focused on data reflecting the water distribution inside the dike body caused by natural variations of the water level in the river and by precipitation. The conductivity data acquired during a two year period show significant temporal variations. Assuming that a conductivity increase is related to higher water content, the resulting 2D conductivity distribution can be transformed into a vertical cross-section displaying the water content in the dike body. The transformation of conductivity into water content requires reliable data from FDR sensors that are integrated in two multi-depth soil water monitoring probes “EnviroSCAN Plus”. Additionally, the water pressure or suction is determined by two tensiometers installed in the dike body close to the FDR sensors.