Radar de subsuelo.Evaluación para aplicaciones en arqueología y en patrimonio histórico-artístico

Laburpena

The Ground-Penetrating Radar (GPR) is a tool more and more used in different geological, Environmental Engineering and Civil Engineering research, as well as in studies of characterisation of archaeological locations and in the diagnosis of the damages in buildings of the historical and cultural heritage. In this thesis, methodological aspects of calibration of the instrumentation are performed. Also, methodological aspects of the soils characterisation by using its electromagnetic properties are analysed. These properties govern the propagation and attenuation of electromagnetic waves in the soils. On the other hand, several applications to the study of historical monuments, archaeological locations and diagnosis of damages are investigated. Particularly, in this thesis four antennae are gauged. These antennae are characterised by their central frequency of emission: 200, 500, 900 and 1000 MHz. For each case, the internal noise of the antenna (radar record without reflections) is obtained;the highest noise is the initial signal (usually the direct wave); its longitude determines the minimum distance between the antenna and the first reflective surface to obtain a radar data where the two events (direct wave and reflected wave) are clearly separated. It is also analysed the time origin of the traces for each antenna (zero of the antenna). The attenuation of the traces during the wave propagation in the air (non-absorbent medium) is also studied. Therefore, in that case, the attenuation is caused by the geometric spreading, and the wave amplitude is inversely proportional to the distance. A procedure is tested to characterise media using its electromagnetic properties: the conductivity, the permitivity and the frequency, relating them with its physical properties: grain size, specific weight, porosity and saturation. Three different media are analysed, formed by the same solid material and modifying three physical properties: the apparent specific weight, the compactation (and, therefore, the porosity) and the saturation. In each case, the wave propagation velocity, the dielectric permitivity, the spectrum of frequencies and the attenuation are obtained. When the saturation increases, the velocity decreases, a displacement takes place toward the low frequencies, the band width is narrowed and the attenuation caused by absorption increases. In addition, different methods to obtain the wave velocity are analysed and discussed: times and well-known thickness, analysis of hyperbolas, comparison of amplitude, radar records obtained in a CMP, geotechnical models, contrast of capacitancy and profiles of well-known stratigraphy. The best results are obtained from the laboratory measurements using samples of well-known thickness and from the analysis of hyperbolic reflections. Comparison of these results and the values provide by the literature is performed. This comparison shows the convenience of carrying out a characterisation of the medium in laboratory in the cases when a fine resolution of the superficial anomalies or of intermediate depth is required. Related with these investigations (characterisation of means and calibration of antennas), several applications to real cases have been performed and studied. These applications have allowed to solve practical problems and, at the same time, to observe the advantages of applying the advances of the investigation, as well as to make progress in the identification techniques and suppression of noise introduced by external or multiple reflections. The main cases resolved make reference to: control of restoration, interventions and rehabilitation in monuments or in historical buildings (cases of the Roman theatre of Sagunto and the Gothic bridges on the river Turia), study of damages in buildings of the cultural heritage (cases of the Cathedral of Valencia and the Church of San Jorge, in Paiporta), characterisation of archaeological locations (cases of the underground of the Cathedral of Valencia, Church of San Jorge and the Roman fortress and the convent in Alcántara). Some results and the best cases cases are synthesised in monographic cards. These cards present, in schematic form, all the information about the studied problem, the emplacement and the used tool. These cards will be very useful in the study of similar cases, and it is expected that they constitute the beginning of a catalogue of cases and solutions.