A Seismic Investigation Of Fracturing Within An Earth Embankment

Granite Reef Aqueduct, Central Arizona Project, is a water-conveyance canal protected by four flood detention dikes which lie approximately 200 ft upslope of canal centerline. The dikes measure from 2 to 3.5 miles in length, for a total of 12.4 miles. The dikes are trapezoidal in crosssection with an approximate 50 ft height. Field observations in September, 1987 indicated the presence of numerous erosion gullies and piping tunnels on the upstream and downstream faces of dikes 1, 2, and 3. More recent observations indicate the presence of several longitudinal cracks and two transverse cracks along the crest of dikes 1 and 2. Such fracturing is of speculative origin (desiccation, subsidence, ?), but its potential effect on the dike’s ability to retain floodwaters could be significant. These fractures sometimes intersect the dike surface, but it is believed that a portion are either contained within the dike or have been rendered invisible to inspection by being filled with loose soils due to routine maintenance of or traffic on the dike road. In any case, it is believed that many of these fractured zones may be eluding detection by strictly visual means.