GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 3.2 GNGTS 2024 this way, the electrodes don’t need to be hammered between the boulders, but we can simply push them, and, compared to the sponges, we can use lower quantty of salt-water to wet them. To evaluate the performance of the conductve textle sachets, we compared the ERT measurements performed with this new electrode approach with the ERT measurements collected with the traditonal steel spikes and sponges, considering common investgaton lines. This comparatve test has been carried out in three sites, which present diferent lithologies and size of the debris/boulders on the surface, and using diferent electrodes spacing. The collected datasets have been compered in terms of contact resistances, injected electrical current, measured apparent resistvites, reciprocal error, and inverted resistvity values. 3. Sites descripton We tested the conductve textle sachets electrodes in three diferent envinroments that presents a debris and coarse-blocky surface: i) the Marocche di Drò landslide deposit, ii) the inactve rock glacier of Sadole, and iii) the actve rock glacier of Flüelapass. Marocche di Drò is a landslide deposit located in the lower part of Sarca Valley (Trento, Italy). Among the various landslide deposits in the area, we selected the Kas deposit, which is composed of calcareous debris, angular blocks, and limited vegetaton cover (Martn et al., 2014). The comparatve test was realized with 40 electrodes spaced 3 meters. Sadole inactve rock glacier is located in the Sadole Valley (Trento, Italy). Steep rock walls and sharp crests, composed of magmatc ignimbrites rocks, surround the rootng area of the rock glacier. The rock glacier surface is composed of large size boulders, and widespread vegetaton cover. The ERT survey line for the comparatve test was realized with 43 electrodes spaced 5 meters, in a positon with a coarse-blocky surface without vegetaton, and where a discontnuos frozen layer was found in previous ERT investgatons (Pavoni et al., 2023). The Flüelapass actve rock glacier is located in the eastern Swiss Alps (Engadin). The rootng area is surrounded by steep rock walls consistng of metamorphic amphibolite and paragneiss. Its surface is composed by a various granulometric size of debris and boulders, and isolated areas with fner sediment. The comparatve test was carried out with an array of 48 electrodes spaced 2 meters. 4. Conductve textle sachets electrodes Conductve textle sachets electrodes are realized with a commercial fabric (Holland Shielding Systems BV) made of polyester (65±5%) metallized with copper (20±2 %) and Nickel (15±2 %). Each sachet was realized with square pieces of 30 cm x 30 cm (the textle can be easily cut with sewing scissors), which were flled with 300 g of fne sand. The sachet is sealed with thin zip tes in such a way to leave a fake at the top where is possible to link the ERT cord clips. The cost to produce one conductve textle sachet electrode is about 15 euros, mainly due to the value of the metallic fabric, and the manufacturing of one sachet takes few minutes. 5. Data acquisiton In each test site, the ERT measurements have been collected with the same acquisiton parameters and georesistvimeter (Syscal Pro, Iris Instruments). The datasets have been acquired with a dipole- dipole acquisiton scheme with multple dipole length, a stacking range between 3-6 (standard deviaton threshold 5%), and with direct-reciprocal confguraton to obtain a reliable estmaton of the data error (Binley et al., 2015). Firstly, we collected the measurements with steel-spikes