Comparison between DC ERT and moving multi-depth electrostatic arrays in an urban context

A series of experiments was undertaken in the province Scania in southern Sweden with the aim to acquire a better knowledge about the electrical resistivity of the soil surrounding heating and water distribution pipes, in order to assess the risk of corrosion. Electrical Resistivity Tomography (ERT) and moving multi-depth electrostatic arrays have been applied to determine the resistivity distribution in an urban context along selected pipes. Implimentation of the ERT was done by drilling holes, in the mostly paved surfaces, and inserting electrodes with a gel to decrease electrode contact resistance. The moving multi-depth electrostatic arrays was implimented in a “sliding” carpet dragged along the lines. Direct comparison between ERT and “sliding” carpet results show a good coherence. This confirms the high interest of the second solution for in-town measurements due to its easy implementation. The interpretation of the data proved to be complicated and was not simply explained as a pipe embedded in a homogeneous layer, which show that a careful attention must be paid to other external information about the underground work history. One practical application might be the mean resistivity values of the medium surrounding the pipe(s), to be used as a tool by the pipe owner.