E. Martinho

Main geophysical techniques used for non-destructive evaluation in cultural built heritage: a review

Geophysical methodologies have been implemented, tested and validated as diagnostic and / or monitoring tools in artworks or historical monuments. They are non-destructive and can give an image of internal structure of investigated medium. This paper is a review about the main geophysical techniques applied to the study of cultural built heritage (excluding the archaeology field). A brief description of the used methodologies is presented, the main investigations done in this field are showed, the method or methods most appropriate to answer each problem (moisture detection, characterization of the materials, study of the structural continuity of the material, assessment of intervention’s effectiveness) are indicated and the main advances and gaps and future developments are also pointed out.

An investigation into the use of geophysical methods in the study of aquifer contamination by graveyards

Graveyards are the traditional way of dealing with the deceased and often their location is unsuitable so that there is a potential contamination danger for local aquifers and soils. Such a contamination is complex as organic, inorganic and biological pollutants will be present. This problem has been studied by direct methods, i.e. boreholes. However borehole location can be difficult and so it is proposed here to use geophysical multiparameter surveys, as well as hydrochemistry studies, to investigate the contamination in the vicinity of two graveyards located in very porous and permeable formations. Based on the geophysical interpretation, two shallow boreholes were drilled and groundwater sampling confirmed local aquifer contamination. The geophysical response is shownto depend on the water table depth, and when this is close to the ground surface, it is demonstrated that geophysical methods can be used to map contamination plumes originated in the graveyards and, therefore, assist borehole location.

Examples of the Use of Non-Invasive Techniques for the Evaluation of Stone Decay in Portugal

Today experts agree that precise damage diagnosis is the key to comprehensive characterization, interpretation, rating and prediction of stone damage. It provides vital information for monument conservation and sustainable preservation. Better understanding of the stones used in monuments and the factors, processes and characteristics involved in stone decay is therefore essential to the sustainable preservation of cultural heritage. A frequent and major obstacle to studying stone decay in monuments is the impossibility of touching or obtaining samples for study in the laboratory or even in-situ. The aim of this paper is to present the results of three non-invasive geophysical (3-D electrical resistivity and seismic refraction) and geochemical (soluble salts typology and distribution) techniques, that were used to diagnose stone damage in case studies involving Portuguese cultural heritage. Different techniques were applied based on decay typology or observed phenomena.

Detecting oil-contaminants by time domain induced polarisation

Oil products constitute one of the main types of organic contaminants in the soil. In order to understand the effects caused by oil contamination the polarization mechanisms in soillorganic mixtures must be understood.

Time domain induced polarisation experiments on gasoline contaminated samples

Recently environmental studies have used geophysical methods to delineate oil contaminated sites (Vanhala, 1997). Organic liquids have a high resistivity and thus induction methods are not weil adapted to fine contaminated areas. On the other hand Induction Polarisation has been widely recognised as a useful method for the detecting organic electrical response In field ( Vanhala et al, 1992) and in laboratory (Vanhala et Soininen. 1995) experiments. The later author had a frequency domain approach (SIP) to the problem. On the other hand our initial work carried out in the time domain (Sumner, 1976) and is still in a laboratory phase. In order to study the induced polarisation effect in gasoline contaminated soil samples a GPIB controlled system was developed to carry out electrical measurements as it is shown in Fig.l. This System is able 10 obtain measurements at a rate of ten samples per second. Specially developed porous ceramic electrodes were built to obtain suitable electrical current contacts. Non polarizable electrodes SilverlSilver Chloride were used to measure potential.