Use of parallel-seismic and induction -logging tests for foundation depth evaluation under difficult conditions, a root-pile foundation embedded in rock

A case study on the application of the parallel-seismic (PS) and induction-logging (IL) tests combined to evaluate the depth of a 25-cm diameter root-pile belonging to the foundations of a telecommunication tower located in Santana de Parnaíba, São Paulo, Brazil, is presented. The foundation element is embedded in a friable and altered meta-sandstone rock. The relatively small diameter of the pile and the presence of rock as surrounding material tend to limit the interpretation of the PS test. Nevertheless, the technique applied in this study showed satisfactory results. On the other hand, the existence of electromagnetic interference from the antenna itself limited the interpretation of the IL test in this case. The estimated depth of the foundation element was evaluated from the PS test as ranging from 6.5 to 7.5 m, which was later verified to be in agreement with the pile as-built documentation. When the possibility to drill boreholes at a site under investigation exists, the methods presented in this paper may become good options for the determination of the unknown depth of foundation elements in altered rock.