Giovanni Leucci

GPR and sonic tomography for structural restoration: the case of the cathedral of Tricarico

In this paper, we present the results of a diagnostics survey, based on the exploitation of ground penetrating radar (GPR) and sonic prospecting, to characterize the deterioration status of the pillars of the cathedral of Tricarico, in the Basilicata region (Southern Italy). The prospecting falls within the more general framework of investigating the structural conditions of this monument, which is affected by heavy instability problems. This study case points out the great effectiveness of the two employed diagnostic methods, when used in an integrated way, for detecting cracks and inhomogeneities in the inner structure of masonry building elements. With regard to GPR prospecting, a comparison is made between the results obtained by a standard processing and those obtained by means of an inverse scattering algorithm. For one of the investigated pillars, the results obtained from non-invasive tests are compared with those of direct inspection. This is performed by coring the pillar and examining both the core and the hole (the latter by means of an endoscope). The seismic investigation allowed us to prove the mediocre or bad state of conservation of the pillars.

Geophysical and Geological Investigations in a Karstic Environment (Salice Salentino, Lecce, Italy)

Karstic forms (dolines and sinkholes) are notoriously difficult geophysical targets, and selecting an appropriate geophysical solution is not straightforward. The fundamental objective in the application of geophysical techniques to environmental studies is to assess and use the correct techniques for the investigation being undertaken. Electrical Resistivity Tomography (ERT) and Ground-Penetrating Radar (GPR) investigations were carried out, primarily to assess the feasibility of geophysical investigations to map the underground stratigraphy of shallow karstic aquifers, in order to help in the prevention of both groundwater pollution from agricultural activities and risk of ground surface collapse. This preliminary study was carried out at-two test areas (labelled area A and area B respectively) near Salice Salentino village, located few kilometers north-west of Lecce (Italy). The main characteristics of these areas are the high density of superficial karstic formation (dolines and sinkholes), the presen...

Use of Ground Penetrating Radar to Map Subsurface Moisture Variations in an Urban Area

The range of Ground Penetrating Radar (GPR) applications is very wide and diverse. GPR provides high-resolution continuos profiles, and has been used in various fields (environmental problems, geology, geotechnical engineering, archaeology etc.). This paper describes a test application of GPR in an urban area (Mesagne, Apulia, Italy) for the detection of underground water pipes and to obtain a map of the moisture in the ground around them. Some authors have proven that GPR can be used effectively, although only as a reconnaissance tool, for studies of moisture in the subsurface. Electromagnetic wave velocity in the subsurface depends on moisture via the dielectric properties of the wet material. The free volumetric water content can be determined from the dielectric constant of subsurface terrain by an empirical relation proposed by Topp et al. (1980). GPR wave velocity determination can be carried out by means of several methods. In this paper the hyperbolic anomalies caused by small inhomogeneities and ...

Microgravimetric and ground penetrating radar geophysical methods to map the shallow karstic cavities network in a coastal area (Marina Di Capilungo, Lecce, Italy)

The coastal area Marina di Capilungo located ~50 km south-west of Lecce (Italy) is one of the sites at greatest geological risk in the Salento peninsula. In the past few decades, Marina di Capilungo has been affected by a series of subsidence events, which have led in some cases to the partial collapse of buildings and road surfaces. These events had both social repercussions, causing alarm and emergency situations, and economic ones in terms of the funds for restoration. With the aim of mapping the subsurface karstic features, and so to assess the dimensions of the phenomena in order to prevent and/or limit the ground subsidence events, integrated geophysical surveys were undertaken in an area of ~70 000 m2 at Marina di Capilungo. Large volume voids such as karstic cavities are excellent targets for microgravity surveys. The absent mass of the void creates a quantifiable disturbance in the earth’s gravitational field, with the magnitude of the disturbance directly proportional to the volume of the void. Smaller shallow voids can be detected using ground-penetrating radar (GPR). Microgravimetric and GPR geophysical methods were therefore used. An accurate interpretation was obtained using small station spacing and accurate geophysical data processing. The interpretation was facilitated by combining the modelling of the data with the geological and topographic information for explored caves. The GPR method can complement the microgravimetric technique in determining cavity depths and in verifying the presence of off-line features and numerous areas of small cavities, which may be difficult to be resolved with only microgravimetric data. However, the microgravimetric can complement GPR in delineating with accuracy the shallow cavities in a wide area where GPR measurements are difficult. Furthermore, microgravity surveys in an urban environment require effective and accurate consideration of the effects given by infrastructures, such as buildings, as well as those given by topography, near a gravity station. The acquired negative anomaly in the residual Bouguer anomalies field suggested the presence of possible void features. GPR and modelling data were used to estimate the depth and shape of the anomalous source.

Towards an integrated approach for characterization of sinkhole hazards in urban environments: the unstable coastal site of Casalabate, Lecce, Italy

Sinkholes occur in many areas of the world, especially where carbonate rocks crop out. They are formed due to natural processes or caused by mans activities. In both cases, severe consequences have to be registered on the anthropogenic environment and related infrastructures. Knowledge of both the mechanism of the sinkhole formation and the localization of this subtle geohazard is therefore necessary for planners and decision makers to perform the most appropriate and suitable programs of land use and development. The Apulia region of southern Italy is characterized for most of its extension by carbonate rocks, which makes it one of the most remarkable examples of karst in the Mediterranean basin. The sinkhole formation in Apulia urban areas has recently produced severe damages, especially along its coastal planes, where different types of sinkholes occur. The detection of cavities, that could collapse and create a sinkhole, in an urban environment presents numerous difficulties (buried networks, reworked soils, etc). A methodology has been developed to respond to this need based on the integration of four complementary methods: geological analysis of outcrops and existing borehole descriptions, aerophotogrammetric interpretation of aerial photos, electrical resistivity tomography (ERT) and ground penetrating radar (GPR). The combination of these methods, applied to a test sector in the city of Casalabate, made it possible to locate the principal karstic conduits beneath the study area and identify a zone of high sinkhole geohazard associated with one such feature.

The use of three geophysical methods for 3D images of total root volume of soil in urban environments

How does the tree root system develop in the subsoil? This question is important to the development and urban planning disciplines, especially when the trees occur near building foundations and underground utilities. This interest is based on the potential for buildings to suffer subsidence or structural damage from nearby trees. The inspection of both the extension of the tree roots and the degree of decay in wood are still undertaken using classical single-point and destructive methods. However, as pointed out by several authors, geophysical methods provide an alternative method of studying root architecture in a non-invasive fashion. In this paper, three geophysical methods were applied to produce 3D images of total root volume in the soil in an urban environment. The three geophysical methods used were ground-penetrating radar, electrical-resistivity tomography, and seismic refraction tomography. Each of the geophysical methods alone is able to isolate root system but cannot resolve the ring structures.

Effect of the height of the observation line on the the diffraction curve in GPR prospecting

This paper deals with the shape of the GPR diffraction curve in dependence of the distance of the measurement line from to the air/soil interface. It will be shown that the diffraction curve changes with respect to the case of data gathered at the air-soil interface, and the calculation of the diffraction curve requires the solution of a fourth degree algebraic equation. The solution in closed form of this equation will be presented, and a physical discussion of the effects of the non-null height of the observation line will be provided.

Diagnostic of the conservation state in the crypt of the Abbey of Montecorona: biological, microclimatic and geophysical evaluations

The Abbey S Salvatore of Montecorona, an important Benedictine monastary of the eleventh century, is placed at Umbertide, on the Northwest of Perugia (Italy). The site is in the Umbria region, characterized by a well-documented historical and instrumental seismicity, which periodically exposes this area to hazards with widespread damage for the population and the built-up environment. This paper focused on the study of the conservation state of the crypt of the Abbey. A multidisciplinary approach, using biological and physical non-destructive methods, is proposed. First, we investigated the microbial biodiversity of the crypt, analysing the presence of microorganisms by microscopic and cultivation methods. The second step was the study of the influence of the environment on the colonization and growth of these microorganisms, with a continuous monitoring of the microclimate inside the crypt, especially the thermo-hygrometric conditions. Moreover, with the aims of localizing the structures involved in the deterioration process, such as fractures, moisture, etc, ground penetrating radar (GPR) surveys, with different methodologies, were carried out in the crypt: reflection mode on the floor and traveltime tomography on the ceiling. From GPR data, a structure of archaeological interest was evidenced and, by means of a frequency signal analysis, the underground water content of the stone was also evaluated, assessing the correlation between the spectral content and moisture degree. The integration of information from these different methods provided some interesting results, also addressing possible interventions for protection and conservation of the crypt.

Non-destructive prospecting and virtual reconstruction of the chapel of the Holy Spirit in Lecce, Italy

In this contribution, we show the results of a GPR measurement campaign, combined with temperature and humidity measurements, gathered in a Renaissance monument of the 16th century in Lecce, Southern Italy. The data are processed by means of standard processing and the results interpreted with the aid of an archive research. Moreover, the reconstruction is inserted into a 3D virtual reconstruction of the monument, achieved by means of a laser scanner.

Time–frequency analysis of GPR data to investigate the damage of monumental buildings

The presence of particular microclimatic conditions inside monumental buildings is responsible for bio-deterioration processes. In many cases, efflorescence and moulds are visible on the facades of several monuments of historical importance. In many other cases, the effects of decay processes are not visible, thus making difficult the diagnosis and the consequent setup of effective rehabilitation and preservation interventions, especially in the presence of a complex geometry and/or a large variability of construction materials. In such cases, a valuable contribution could be provided by geophysical methods (such as electrical resistivity, electromagnetic conductivity, ground-penetrating radar (GPR), etc), which have been proved to be successful tools for sub-surface investigation and characterization of historical buildings. In old monumental buildings, the masonry structures frequently exhibit cracks, voids, detachments and high moisture contrasts that can give rise to reflection events in radar signals. However, the complexity of the geometry and the structural heterogeneity that characterize these old structures often make the GPR results difficult to analyse and interpret. In particular, the spatial variation in GPR signal attenuation can provide important information about the electrical properties of the investigated materials that, in turn, can be used to assess the physical parameters associated with damage. In this paper, we propose an approach that analyses the data in the form of ?frequency maps? to evidence absorption losses probably linked to higher moisture content. Two real case histories back up the proposed method.