3D Cross-hole Electrical Resistivity Tomography to Control the Injection of Expanding Resins: A Case History in Venice

Injection of expanding polyurethane resins has recently become a widespread technique to improve the geotechnical characteristics of shallow soils for consolidation purposes. Although resins injection practice has revealed to be a satisfactory solution for the above mentioned problems, a continuous monitoring of the process is needed to achieve optimal results. In order to control the injection of expanding resins a field procedure has been developed, based on the use of three dimensional Electrical Resistivity Tomography. The choice of electrical resistivity, as a parameter for designing, monitoring and validating the homogenisation task, is based on the basic assumption that such a property is the most sensitive to water content. During the injection stage, repeated ERT acquisitions allow to control the process and to modify the injection program/parameters, whenever necessary. In this paper the procedure and its results are illustrated, through a case history in Venice (Italy), where environmental problems, due to the presence of salt water bearing soils, had to be taken into account. Therefore a specific, careful analysis of arrays of electrodes and selection of the main parameters affecting ERT resolution had to be performed in advance.