126 research outputs found
Geophysical characterization of an unstable rock mass
No full textA pre-requisite in rock mass stability analysis is to obtain the internal structure and the mechanical
properties of the investigated rock mass with a reasonable degree of uncertainty. In this respect, geophysical
methods can be profitably used as an imaging and characterization tool. Seismic methods are often more suitable
because the measurements depend on the mechanical properties of the rock mass. The present paper presents
the use of cross-hole seismic tomography in a site (Madonna del Sasso – NW Italy) affected by a rock instability
phenomenon, highlighted by episodes of slow deformation recorded by standard measurement devices.
Geophysical tests have been fundamental in imaging the fracturing state and the relative variation of seismic
velocities between intact an altered rock and in defining the seismic velocity field of the rock mass, a basic
prerequisite for the future planned microseismic monitoring step
Detecting Near-Surface Cavities and Shallow Heterogeneities through Surface Wave Attributes: Methods and Applications
No full textDetecting cavities, fault zones, and low-velocity anomalies is a primary objective for geotechnical characterization and urban planning, as well as for geohazard studies and mineral exploration. Surface wave attributes based on energy and attenuation of the raw seismic data can provide a major contribution in the identification and location of these near-surface heterogeneities. The attribute computation is fast and straightforward, making them ideal tools for automatic site screening in near real time. Their effectiveness has been tested on a wide variety of numerical models and real data
Continuous vertical electrical soundings (CVES) for the geological investigation of underwater deposits beneath the lake of Candia (Turin NW Italy)
No full textWe discuss below the results of a survey conducted with the CVES method on the Lake of Candia, near the city of Turin, in north-western Italy. The main objective of the study was the characterization of the sediments of the basin, in order to define the nature, the composition, the geometry and the spatial relationships of detected geological bodies. Another aim of the survey was to try to understand the hydrogeological dynamics that govern the lake basin, in order to determine, at least qualitatively, the presence of interconnecting paths with groundwater and to locate areas in which recharge or seepage flows are concentrated. Using a Laterally Constrained Inversion (LCI) approach for the data inversion, we managed to obtain fifteen resistivity sections that cover almost the entire area of the lake. By joining and interpolating the profiles it was possible to produce a three-dimensional model of the electrical resistivity distribution below the water basin. Thanks to the study, we found the presence of coarse glacial deposits, with high resistivity values, along the southern shore of the lake. These coarse deposits, primarily consisting of gravel and pebbles mixed with a sandy matrix, could be considered as the main hydrogeological window connecting surface and underground wate
Machine Learning-Based Event Classification of Passive Seismic Data for the Early Warning of Landslides
No full textSpecial Issue “Remote Sensing in Applied Geophysics”
No full textThe Special Issue "Remote Sensing in Applied Geophysics" is focused on recent and upcoming advances in the combined application of remote sensing and applied geophysics techniques, sharing the advantages of being non-invasive research methods, suitable for surface and near-surface high-resolution investigations of even wide and remote areas. Applied geophysics analyzes the distribution of physical properties in the subsurface for a wide range of geological, engineering and environmental applications at different scales. Geophysical surveys are usually carried out deploying or moving the appropriate instrumentation directly on the ground surface. However, recent technological advances have brought to the development of innovative acquisition systems more typical of the remote sensing community (e.g., airborne surveys and unmanned aerial vehicle systems). At the same time, while applied geophysics mainly focuses on the subsurface, typical remote sensing techniques have the ability to accurately image the Earth's surface with high-resolution investigations carried out by means of terrestrial, airborne, or satellite-based platforms. The integration of surface and subsurface information is often crucial for several purposes, including the georeferencing and processing of geophysical data, the characterization and time-lapse monitoring of surface and near-surface targets, and the reconstruction of highly detailed and comprehensive 3D models of the investigated areas. Contributions to the issue showing the added value of surface reconstruction and/or monitoring in the processing and interpretation of geophysical data, integration and cross-comparison of geophysical and remote sensing techniques were required to the research community. Contributions discussing the results of pioneering geophysical acquisitions by means of innovative remote systems were also addressed as interesting topics. The Special Issue received great attention in the combined community of applied geophysicists and remote sensing researchers. A total of 15 papers are included in the Special Issue, covering a wide range of applications. This is one of the highest number of papers among the Remote Sensing Special Issues, showing great interest in the proposed topic. The relevant number of contributions also highlights the relevance and increasing need for integration between remote sensing and ground-based geophysical exploration or monitoring methods. In particular, one of the main fields of research showing the potential integration of the geophysical and remote sensing techniques is archaeological exploration
Waterborne Continuous Vertical Electric Soundings for geological characterization in shallow water environments: some field applications
No full textMechanical properties of microcrystalline branching selenite gypsum samples and influence of constituting factors
No full textThe high sedimentological variability of gypsum rocks has the effect that a univocal characterization of this material is not easy to establish. This is particularly true from the geomechanical point of view: when the mechanical properties of gypsum rocks are requested, it is therefore necessary to undertake detailed characterization analyses. Common facies of gypsum was observed in the Upper Miocene evaporitic succession (Messinian Salinity Crisis) within the whole Mediterranean Basin. In this work, mechanical tests were conducted on a site-specific facies, represented by the microcrystalline branching selenite. The tested samples came from the Monferrato area (northwestern Italy). Uniaxial compressive strength (UCS) tests were performed in order to obtain reference mechanical parameters. More rapid and economic point load test (PLT) and ultrasonic pulse velocity (UPV) measurements were additionally performed to verify their applicability as complementary/alternative methods for site characterization. Rock-type specific PLT-UCS and UPV-UCS relationships were established. A wide dispersion of the mechanical parameters was observed due to the heterogeneities of the studied material. Consequently, compositional, textural and microstructural observations on selected samples were performed. Two main material classes were recognized based on average grain size and total gypsum content, underlining the significant influence of the grain sorting on the measured mechanical properties. Keywords: Gypsum, Uniaxial compressive strength (UCS), Point load test (PLT), Mechanical properties, Geological heterogeneit
Nonlinear strain effects induced by thermal forcing on jointed rock masses
No full textThe study of the deformative response to cyclical thermal stresses of rock masses is considered crucial in geological risk mitigation relative to those instabilities that can configure high hazard slope instability scenarios due to their impulsiveness and high frequency of occurrence. Under specific climatic conditions, the superposition of heating and cooling cycles can influence the mechanical behavior of rock masses. Temperature fluctuations can exert slight yet repeated perturbations of stress fields resulting in a day-to-day cumulative effect, contributing to lead rock slopes toward prone-to-failure conditions over wide time scales. As a direct consequence of the thermal expansion-contraction cycles, the stress field of rock masses undergoes such perturbations capable of inducing both the genesis of new cracks and the growth of preexisting ones (i.e., subcritical crack–growth). These processes can induce inelastic deformations that can trigger shallow slope instabilities, such as rockfalls and rock topples. A multimethodological approach based on environmental, thermal, microseismic, and ambient seismic noise monitoring was designed for the purpose of identifying and characterizing nonlinearity of thermally-induced deformation on jointed rock masses at different dimensional scales. Two different case studies—a massive 10.000 m3 natural rock arch and a 20 m3 intensely jointed rock block—were selected to investigate the influence of repeated thermal cycles on their stability. In particular, their complex 3D geometries, different volume sizes and jointing conditions were considered to be of great interest to better comprehend the effectiveness of shallow thermal stresses interacting with different rock mass dimensional scales.
Passive seismic monitoring techniques (i.e., ambient seismic noise and microseismic monitoring) allowed to obtain interesting insights on the interaction between the investigated rock masses and the periodic fluctuations of their temperature fields. The analysis of ambient seismic noise was aimed at investigating the possible wandering of resonance frequencies within short- to long-duration monitoring surveys, and highlighted the existence of thermally-driven, in-phase daily and seasonal fluctuations, but no irreversible modifications in their valuespotentially related to a progressive damaging process and acceleration toward failure of the structurewere observed. For what concerns the analysis of local microseismicity, a semi-automatic approach was implemented to identify possible irreversible clusters of fracture-related microseismic events over long-term monitoring windows. Based on the collected data, the here presented analyses highlighted not trivial insights on the role played by continuous near-surface temperature fluctuations and extreme thermal transients in influencing the stability of rock masses. In particular, the comparison of monitoring periods characterized by the most intense microseismic activity pointed out a peculiar distribution of microseismic events during heating and cooling phases of the rock mass in relation to different environmental conditions. These behaviors can be interpreted as the consequence of different driving mechanisms at the base of local failures.
Along with the study of the seismic response of these jointed rock systems, Infrared thermography surveys were carried out at both sites for the characterization of their thermal behavior through different methodological approaches (i.e., 2D and 3D). The multitemporal acquisition of thermograms at Wied Il-Mielaħ allowed to achieve a preliminary characterization of the thermal behavior of the rock arch in response to the continuous fluctuation of near-surface temperatures at the daily and seasonal scale, highlighting the importance of considering the effect solar radiation and its interaction with complex morphological settings. Besides, a simplified method integrating Structure from Motion and Infrared thermography techniques was adopted at the Acuto field laboratory. The obtained results revealed that through the generation and co-registration of thermal and optical point clouds, the transfer of temperature attributes from low- to high-density point clouds can provide a detailed 3D representation of geometric features and surface temperature distributions and evolutions. The accurate reconstruction of 3D temperature fields will allow to obtain further insights for the assessment of the role played by thermal stresses in the concentration of elastic and plastic deformations in jointed rock masses, giving the possibility to weight the contribution of lighting and shadowing effects on entire slopes or isolated block volumes characterized by variable exposures and hence differentially heated by the solar radiation.
The combination of different approaches can provide new insights on the effects related to near-surface thermal stresses fluctuations by allowing the investigation of the mechanical behavior of rock masses from fracture-scale to joint-isolated rock blocks, and the characterization of the spatio-temporal evolution of near-surface thermal fields
Microseismicity of an unstable rock mass:from field monitoring to laboratory testing
No full textThe field‐scale microseismic (MS) activity of an unstable rock mass is known to be an important tool to assess damage and cracking processes eventually leading to macroscopic failures. However, MS‐event rates alone may not be enough for a complete understanding of the trigger mechanisms of mechanical instabilities. Acoustic Emission (AE) techniques at the laboratory scale can be used to provide complementary information. In this study, we report a MS/AE comparison to assess the stability of a granitic rock mass in the northwestern Italian Alps (Madonna del Sasso). An attempt to bridge the gap between the two different scales of observation, and the different site and laboratory conditions, is undertaken to gain insights on the rock mass behavior as a function of external governing factors. Time‐ and frequency‐domain parameters of the MS/AE waveforms are compared and discussed with this aim. At the field scale, special attention is devoted to the correlation of the MS‐event rate with meteorological parameters (air temperature and rainfalls). At the laboratory scale, AE rates, waveforms, and spectral content, recorded under controlled temperature and fluid conditions, are analyzed in order to better constrain the physical mechanisms responsible for the observed field patterns. The factors potentially governing the mechanical instability at the site were retrieved from the integration of the results. Abrupt thermal variations were identified as the main cause of the site microsesimicity, without highlighting irreversible acceleration in the MS‐event rate potentially anticipating the rock mass collapse
Preliminary data on fossil rodents from the vertebrate sites Moncucco and Verduno (post-evaporitic Messinian, Piedmont, NW Italy)
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