GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 3.2 547 Geophysical investigations in humid subsoil and shallow water environment L. Capozzoli, G. De Martino, V. Giampaolo, F. Perciante, E. Rizzo Istituto di Metodologie per le Analisi Ambientali, Consiglio Nazionale delle Ricerche, Tito (PZ), Italy Introduction. Geophysical techniques are frequently used to investigate the subsoil to identify buried structures placed at different depth non invasively saving time and money. Among all geophysical techniques, ground penetrating radar (GPR) and electrical resistivity tomographies (ERTs) are themost used, often in tandemwithmagnetometric and electromagnetic surveys. During last years there has been an increasing interest for geophysical acquisition in lacustrine and marine context; in particular for resistivity acquisitions due their capability to investigate very conductive scenarios without problem of attenuation as unlucky happens for GPR signal. The advantages of the geophysical approach are constituted in provide good information to detect buried target without necessity of excavations; however the methods often suffers of great limitations in resolution and depth of investigation caused by signal attenuation phenomenon and low physical contrasts occurring between existing structures and surrounding environment. Non-conventional ERTs are made for off-shore application in many fields of the research to achieve different objectives as characterization of geological formations (Rucker et al. , 2011), characterization of geological stratigraphy (Colombero et al. , 2014), analysis of submarine archaeological sites (Passaro, 2010; Simyrdanis et al. , 2015). GPR and ERTs are less effective when are applied in humid or water saturated scenarios and for these reasons an experimental activity has been performed at the Hydrogeosite laboratory. The test has been performed with GPR acquisitions con water in tandemwith ERTs realized with different electrodes arrays. In particular ERTs are carried out with 3D-loop shaped acquisitions and 2D surveys made both directly on the water surface both under water. This paper presents the preliminary results obtained with GPR and ERT surveys at an archaeological test site to detect subsurface anomalous bodies. Experimental set-up. The experiments are realized at the Hydrogeosite CNR-IMAA laboratory in Marsico Nuovo (PZ) in a concrete pool of 252 m 3 (12 x 7 x 3 m) filled with silica sand (average diameter equal to 0.09 mm, very fine sand), a porosity of about 45 ÷ 50% and hydraulic conductivity in the order of 10 -5 m/s. The pool is equipped with seventeen wells and a hydraulic system to simulate variation of variation of groundwater level. In an limited area of the pool with size of 6 x 4 m was reproduced an archaeological roman site with structures placed at a depth reaching about 1-1.50 m from the ground surface. An accurate reconstruction of a roman archaeological site buried site was simulated with ancient burials, paved road and stone wall as showed in Fig. 1. Several papers are yet published for this study cases where traditional Fig. 1 – Plan of the test site at “Hydrogeosite” laboratory in Marsico Nuovo (PZ-Basilicata) with indication of the buried structures.