Integrated geophysical techniques in detecting hidden dangers in river embankments

Noninvasive geophysical technologies are often used for detecting hidden defects and monitoring seepage in dams. In 2003 a series of experiments were conducted to detect and discover hidden defects in the embankment of the Yangtze River, Songzi County, Hubei Province, China. High-resolution reflection and surface-wave seismic methods with non-explosive sources were used to investigate the structure of the embankment and to obtain the shear (S)-wave velocity profile of different materials. As an effective approach for investigating groundwater, a DC multi-channel resistivity survey was also used to evaluate the moisture content of material inside and under the embankment. This paper discusses the exploration strategy and preliminary results for several sections of the embankment. Based on the experimental data, seismic reflection images and S-wave velocity contours are used to describe embankments geometrically and qualitatively. Known anomalies are identified on seismic profiles. A practical approach, which combines seismic and electric resistivity data, is proposed to locate potential seepage sites in the embankment. The new method is used to evaluate seepage potential and the presence of anomalies using the S-wave velocity and the resistivity of the medium. An anomaly detected in a section of the embankment was verified where piping occurred during 1998 flooding.