Condition Risk Assessment Of Underground Utilities With Sewreel Seismic Imaging

America has a major investment in underground utilities beneath its cities, principally sewers and<br>pipelines, and there is widespread concern that this urban infrastructure has not been adequately<br>maintained to meet needs. Managers of these utilities rely on condition assessments based on internal<br>inspection and limited geotechnical information. These assessments are inadequate as they fail to<br>effectively sample, test and account for external ground conditions. Unexpected catastrophic ground<br>collapse due to pipe collapse is a relatively common occurrence. Excessive expenditure on new<br>construction, rehabilitation and foreshortened repair life are also consequences of the failure fully<br>understand and evaluate the influence of ground conditions above and around these utilities.<br>Recently, a specially developed seismic imaging technology called SEWREEL has demonstrated<br>the ability to locate significant voids or weak ground around underground utilities and to prevent<br>collapses. SEWREEL is similar to crosshole seismic tomography and provides detailed information<br>between the pipe and the ground surface. This method represents a significant improvement over<br>surface seismic methods. Its use to prevent collapses around a gravity main is illustrated with a recent<br>field example from Orlando, Florida.<br>The application of SEWREEL within a condition assessment program provides the means for<br>establishing the subsurface condition of the soils around the pipe in a reproducible, timely, and efficient<br>manner. Any comprehensive program of condition risk assessments for underground utilities should<br>include seismic imaging as a key component in a preventive engineering and risk assessment and<br>reduction strategy.