Site Investigation In Urban Tunnelling Using Hr Seismic Reflection Survey: A Case Study

Tunnel planning and construction is a very complex and difficult task due to non homogeneous contacts between surface deposits and the bedrock, soil and rock properties, fractured zones and hydraulic conditions. Furthermore, the possibility of running into a thick filling material body, especially in urban areas, enhances dangers and further expenses. Subsoil geophysical exploration is a very useful tool to improve prognosis and to reduce risk and probability of damaging infrastructures and surface buildings. This note presents an application of a shallow reflection seismic survey aimed at a site investigation for an urban tunnelling program undertaken in a complex geotechnical environment. Time cross-sections and depth sections are discussed and compared with geognostic data. The opportunity of comparing the obtained results before and after a jet-grouting treatment, that was carried out due to the presence of poor lithological conditions, enabled to assess the effects of ground improvement on subsoil seismic imaging.