Carlo Piga

Measurement system for non-destructive testing using ultrasonic tomography spectral attenuation

This paper presents a measuring system and the automated measuring procedure for non-destructive diagnosis of stone masonry structures. The diagnosis is based on algorithms using the propagation times and the frequency centroid downshift of ultrasonic signals.

Integrated geophysical and aerial sensing methods for archaeology: A case history in the Punic site of Villamar (Sardinia, Italy)

In this paper, the authors present a recent integrated survey carried out on an archaeological urban site, generally free of buildings, except some temporary structures related to excavated areas where multi-chamber tombs were found. The two methods used to investigate this site were thermal infrared and ground penetrating radar (GPR). The thermography was carried out with the sensor mounted under a helium balloon simultaneously with a photographic camera. In order to have a synthetic view of the surface thermal behavior, a simplified version of the existing night thermal gradient algorithm was applied. By this approach, we have a wide extension of thermal maps due to the balloon oscillation, because we are able to compute the maps despite collecting few acquisition samples. By the integration of GPR and the thermal imaging, we can evaluate the depth of the thermal influence of possible archaeological targets, such as buried Punic tombs or walls belonging to the succeeding medieval buildings, which have been subsequently destroyed. The thermal anomalies present correspondences to the radar time slices obtained from 30 to 50 cm. Furthermore, by superimposing historical aerial pictures on the GPR and thermal imaging data, we can identify these anomalies as the foundations of the destroyed buildings.

Time-lapse electrical resistivity tomography to delineate mud structures in archaeological prospections

Archaeological sites in rural areas are often characterized by structural remains that are made of mud or raw brick, and that produce a very small contrast in physical characteristics, as the surrounding materials of both anthropogenic and natural origins have similar lithological and mineralogical properties. The main measurable differences are due to changes in compaction and porosity and, as a consequence, in permeability, which influence the hydrological behaviour of the subsurface materials. In this paper, we present some applications based on Electrical Resistivity Tomography (ERT) surveys that are routinely applied in archaeological prospection, carried out over two different weather conditions. Measurement of the changing resistivity, corresponding to different moisture conditions in the subsoil, allowed us to identify archaeological strata and structures surrounded by natural, undisturbed soil. A number of tests carried out on a physical model permitted a further definition of the acquisition parameters and methodologies to be used to secure the best results. The field surveys were carried out in the necropolis of “Pill’e Matta” (IV BC - V AD), located in the suburbs of the metropolitan area of Cagliari, in the southern part of Sardinia, and in a Punic and Roman site near the village of Terralba, located in the Campidano plane, in the western part of Sardinia. The results show that time-lapse prospecting can increase the resistivity contrast between archaeological structures and soil.

Synergical Use of Passive and Active Methods to Reconstruct the Subsoil in Urban Areas

In urban areas it is often difficult to carry out not only direct but also indirect investigations, such as geophysical surveys. In fact, because of traffic noise, power lines and pipelines it is not possible to obtain reliable and repetitive measures using seismic, magnetic, electrical and electromagnetic methods. In addition, the asphalt and the paving of the sidewalks don’t facilitate the placing of geophones and electrodes. So only a few methods can usefully be applied. The gravimetric method in particular makes it possible to reconstruct maps of vulnerability that can be a useful document for the planning of appraisal or the prevention of risk of collapse for buildings. Finally the gravimetric maps represent a basic document for municipal urban development plans. Recently a seismic passive method was also developed that uses a 3-component seismic system called Tromino, which enables us to measure over time for periods of several hours, the spatial components of acceleration and velocity produced by natural tremors and vehicular traffic. Recently seismic land streamer devices have also been produced, that allow us to make profiles of seismic refraction on unpierceable areas and also to drag the system along a profile increasing its length.

Non Invasive Acoustic Measurements for Faults Detecting in Building Materials and Structures

Over the past years both large and small restoration and conservation works on monuments, civil and industrial buildings have become of great interest. As indicators of the historical period in which they were built, all construction works have both their architectural style and the material used in their construction. Indeed, for thousands of years humans built using the same materials (wood, stone, brick, mortar and gypsum) up to the introduction of concrete at the beginning of the 19th century. Although concrete has replaced the old materials used in historical buildings, there still remains the problem of forestalling their deterioration and restoring them, also in the light of the importance of such works from the historical, cultural and economic viewpoints. Problems connected with the restoration of buildings, whether in reinforced concrete, masonry or wood, are quite complex and are essentially linked to the reuse, and thus the redesign, of the existing heritage of buildings. Indeed, cultural, social and economic reasons foster to the desire to lengthen the life of this heritage beyond normal physiological limits and thus its fruition far beyond its useful life. The problems to be addressed vary widely since there are noteworthy differences from one job to another; it is sufficient to consider just the social value of a building of great historical value, which is usually protected by severe restrictions aimed at conserving its artistic and cultural features, or an industrial building the use of which must be completely changed while at the same time maintaining its structural characteristics. It is evident that there is not one single answer to such widely differing situations: each job must be addressed from the cultural, technological and technical standpoints as a special case. The proper management of the rehabilitation of a building implies a knowledge of its real static conditions to be restored, the mechanical, physical and chemical characteristics of the materials of which it is built and the presence and characteristics of defects, anomalies and so on. Of fundamental importance is the diagnosis of materials and structures and many researchers, as well as companies that produce restoration materials, have carried out studies in this field. Methods for structural diagnosis and faults detecting are beginning to appear, albeit in an extremely divergent way, in tenders, rules, guidelines and so on. To exemplify, non-invasive diagnostic techniques are often used to determine whether or not materials compatible with the original structure have been used in restoration works: if not,