GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 3.2 GNGTS 2024 were carried out with the Tx/Rx dipoles translated at variable distances, internally to the line, according to a "pseudo-gradient" geometry. In the second phase three-dimensional DERT survey was performed on the central part of the slope using the FullWaver system (Leite et al., 2017; Gance et al., 2021). The FullWaver devices (Iris Instruments) have been designed for the measurement of resistvity, Induced Polarizaton and Self Potental on large 3D surfaces with complex topography. Depending on the size of the area to investgate, many V-FullWaver devices can be located on the surface of investgaton, performing a contnuous measurement. In the meantme, the operator moves a transmiter and the I-FullWaver on the same surface, to perform diferent current injectons according to the survey geometry. In our case 27 V-FullWaver were used, with a current transmission system TIPIX 3000 capable of injectng current up to 13 A. The energizaton paterns were the following. A frst set of 29 transmissions consists of a fxed pole A (labelled as TX 1) and a second transmiter B moving from TX2 to TX29, where the dipole aperture reaches the maximum value of about 1100 m. This acquisiton sequence was followed by a backward energizaton scheme with the pole A fxed in TX29 and the pole B moving from TX28 to TX1. The combinaton of these dipole transmission paterns allowed to acquire diferent type of electrode arrays: dipole-dipole type, when the transmission dipole is very far from the receiving dipole; pole-dipole type, when the mobile transmiter B is close to the receiving dipole; gradient type, when both transmiters A and B are external and away from the receiving dipole. Data Processing and inversion ERT data processing and inversion were carried out by using the ERTLab Studio sofware (Fischanger et al., 2013), modifed to manage both MS and FW measurements. The applicaton of the two methodologies produced a robust dataset where the 2D MS data and the 3D FW data are in good agreement. The maximum investgaton depth, of about 110 - 120 m, has been reached by the FullWaver system under the village of Cazzaso. The inversion algorithm is based smoothness-constrained least squares approach under the Occam assumptons and consists in minimizing the diferences between calculated and measured diference of potentals (Fischanger et al., 2013). Data Interpretaton In agreement with the geological setng, the measured physical parameters of the subsoil have been interpreted by assuming the landslide body composed by four main formatons: inconsistent material; prevalence of sandstone, calcarenites; prevalence of shale and silt; dark stratfed limestone and dolomite. The interpretaton of the DERT sectons describes some important peculiarites, the most evident is the presence of a deep and large resistve body ascribable to the dolomite formaton that increases towards the south and consttutes a barrier to the more conductve materials of the western and more steep part of the slope (fg 2).