Assessment of channel side-walls with GPR techniques

A Ground Penetrating Radar (G.P.R.) survey was recently carried out in the Murano island near Venice. The aim of the survey was two fold: outline the potential capabilities of this geophysical technique as related to assessing physical properties of channel side walls before and after cement infiltration; achieve an initial understanding of electro-magnetic wave propagation in fairly conductive layers and estimating the depth of buildings' foundations to optimize ground consolidation activities. The attention to this matter has grown up in the last years in relation to the necessity of excavating the bottom of some channels to remove natural and artificial sediments for boat traffic resto ring and to re-design the channel profile to improve the side-wall stability. The water. pumping and the mud excavation, prior to the maintenance intervention, dramatically increase the stress on the channel-side walls and could cause, especially in presence of fractures and cavities, a collapse of the wall structure with serious damages to the near buildings' foundations. In order to address all these issues the problem was structured in some different steps: c1early imaging the sub surf ace of the "fondamenta" (passagewalk on the side of the building facing the channel) inc1uding a rough estimation of buildings' foundations and technical utilities location, detecting weak zones, such as cavities and fractures in the wall, and estimating the efficiency of cement mixture infiltration.