Seismic refraction and electrical resistivity tomographies for geotechnical site characterization of two water reservoirs (El Hierro, Spain)

Abstract

On El Hierro (Canary Islands, Spain), the company Gorona del Viento El Hierro S.A. carried out the construction of a Wind-Pumped Hydro Power Station in order to achieve the energy autonomy on the island through 100% renewable energy. The station consists of two man-made water reservoirs, whose design was adapted to the island topography and emplaced in a valley and an inactive crater. In order to study the subsurface of both reservoirs, the characteristic heterogeneity of volcanic materials was taken into account. Therefore, a research campaign combining different methods was proposed; mechanical investigations traditionally applied in engineering (rotary boreholes, dynamic probing super heavy tests and pits) and geophysical methods (seismic refraction tomography and electrical resistivity tomography) were both utilized. The aims were to determine the geological structure of each site, detect possible anomalies or structures (i.e., faults, volcanic cavities, etc.), identify the different lithologies, determine the soil thickness and depth to bedrock, predict the excavatability of the materials, and obtain data about the physical properties and mechanical behaviour of the ground in an effort to carry out a geotechnical site characterization of both sites. At the site of the upper reservoir, electrical resistivity tomography recorded a high thickness of low resistivity soils, which were subsequently investigated by deep boreholes in order to sample and test them properly, since they could generate high settlements during the construction of the reservoir. At the site of the lower reservoir, the existing palaeorelief in the basaltic bedrock was detected by seismic refraction tomography, which allowed for the selection of the appropriate excavation machinery for the planned earthworks. The geological interpretation of the P-wave velocity models and electrical resistivity models are shown in this paper, as well as a correlation between geotechnical parameters and geophysical properties of volcanic materials and recent deposits, which will be useful for other civil projects which may be carried out in the future at sites with similar geological conditions.

Geotechnical Characterization for Territorial Planning of a Special Economic Zone at a University Campus in Ecuador

“…Drill holes 2, 3 and 4 corroborated the presence of lapilli tuff from 0.5 to 5 m deep, with Vp ranges of 557-702 m/s and electrical resistivity of 226-786 Ω• m. The values obtained are consistent with the values of Vp (500-1650 m/s) and electrical resistivities (576-25,000 Ω• m) of different types of lapilli tuffs determined by Paembonan et al [63] and Ferná ndez et al [64] with tuff resistivities ranging from 212 to 655 Ω• m and 200-1000 m/s in surveys developed in El Hierro, Spain. In this investigation, they carried out similar tests to obtain a geological correlation and a geotechnical characterization for a hydroelectric plant but using electrical tomography (not VESs).…”

An assessment of seismicity and near surface geophysical characteristics of potential solid waste landfill sites in the Eastern Black Sea Region of Türkiye

“…The main way to overcome this problem is to carry out geophysical investigations. Because geophysical methods help reduce the number of these traditional and more expensive mechanical investigations, they make a significant contribution to directly reducing project costs (Zhan et al 2018 ; Boudreault et al 2010 ; Fernández-Baniela et al 2021 ).…”

Theoretical Issues with Rayleigh Surface Waves and Geoelectrical Method Used for the Inversion of Near Surface Geophysical Structure

“…The gravity method combined with the seismic method can be used better to determine the density distribution within the Earth. Therefore, a combination of different geophysical methods may be useful to overcome the sensitivity problem, i.e., one geophysical method can help resolve ambiguities in another geophysical method [8][9]. In this respect, we consider the geoelectrical method alongside the Rayleigh surface waves in a joint manner to study the near surface Earth assembly.…”