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Radio detection to prospection in urban area


The sustainable development of the cities demands a great interaction between the underground and the superficial urban systems. For example, some subway stations connect different types of transport systems (bus, railway, taxis). Other structures, specially constructed to support pipelines, nets, sewage systems, etc. are also installed in the underground.Years ago, the underground was used to place pipes used to send water to houses and to carry sewage away from them. Today, the underground is used for public transport (subway), parking, tunnels for cars, gas pipelines, TV cables, water reservoirs, etc.To repair these nets or to excavate soils or rocks for civil constructions, it's necessary to make an appropriate geological and geotechnical investigation which can prevent accidents and negative environmental impacts. Nowadays, there are a great number of techniques available for locating unknown lines in underground, like Ground Penetrating Radar (GPR), vertical electric sounding, seismic method, radiodetection and others. The application of these techniques are particularly important before digging in order to avoid damage to buried lines.The use of GPR has increased in soil investigations, especially in urban areas. The systematic application of this technique, sometimes in an indiscriminate way and without technical criteria, brought problems as much in the acquisition of the data as in its interpretation. Some professionals don’t consider this method as being a good tool for soil investigations.However, in experimental surveys when tests were carried out with technical criteria, the GPR presented some problems to identify ducts or other structures, like aqueducts, pipelines, etc. Situations are not rare when the GPR is located on top of the ducts or aqueducts: it’s possible that the registers from the equipment might not indicate these structures. This problem motivated the development of a study with proposing to evaluate the potential of GPR techniques as an investigation tool of subterranean places to find ducts or micro tunnels and also to understand its field limitations. Due to this, studies were performed in the laboratory, in a test field and in an area near the Pinheiros River. It was concluded that the GPR presents limitations for physical principles and its results depend on the characteristics of the ground soil, as the electrical resistivity, that can attenuate the signal emitted by the equipment, decreasing or even hindering the penetration of the radar wave in the terrain, independent of the signal frequency. Such facts can hide some ducts during the investigation work and can bring serious accidents in a construction.Considering the comments above, this project intends to develop a new study using other equipment (Radiodetection) to identify pipelines, water and sewage nets, TV cables, etc. The Radiodetection locator (comprising a Transmitter and a Receiver equipment) is designed for locating buried lines. In the field, it's so easy to deal with this equipment and it can bring lots of information in complex problems of engineering. Obtaining site plans or identifying the local utilities before locating is mandatory in some areas. Although the information obtained may not be accurate or complete, it usually warns of what to expect. A large number of optional accessories are available for Radiodetection locators which can increase their usefulness and widen their scope. A knowledge of the theory of electromagnetic principles with some experience in the fields will be necessary to recognize the advantages and its limitations. (AU)

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