Earth anchor like a steel cables in construction of retaining wall

Earth anchors are steel cables used in the construction of earth-retaining walls to transmit load to earth or rock at greater depth away from the structure. In the construction of large multi-storey buildings it is common for percussion drilling to be conducted in close proximity to buried anchors. If an anchor is intercepted, there is a significant risk that the retaining wall and supported site offices would collapse. The detection of earth anchors beneath pavement in an urban environment is a difficult geophysical problem because the target has a dimension of about 0.01 m at a depth of about 10 m. Since one end of the anchor is exposed, the detectability of the target can be enhanced by injecting electrical current into it. Modelling of a buried inclined source has shown that the electric potential at ground surface is diagnostic of the anchor, and that the half-width of the anomaly is proportional to depth.