Sabrina Bonetto

The mechanical response of polymineralic rocks is the result of the combination of the individual strengths of all the mineralogical phases that are included in it. But which percentage of a softer mineral is sufficient to soften the mechanical strength of the entire rock? And, on the other hand, which percentage of a stronger material is enough to increase the strength of a soft rock? And do these percentages depend on the microstructure?Gypsum-anhydrite rocks have the requisites to answer these questions, due to the high mechanical contrast between anhydrite and gypsum mineralogical phases and to the high heterogeneity of microstructures that are usually present even in a single rock mass because of the low temperatures of the phase transition between gypsum and anhydrite.For these reasons, the present study investigated the strength and creep response under uniaxial compression of Triassic sulphates from the Italian Western Alps. The samples considered may be clustered in three main groups, depending on the occurring microstructural organization of gypsum and anhydrite mineralogical phases: i) pure gypsum, ii) gypsum with relicts of anhydrite at the nuclei of the crystals and iii) anhydrite with gypsum bordering the rims among the crystals.Results of mechanical tests showed that even a low percentage of anhydrite present at the nuclei of the gypsum crystals strongly controls the mechanical response, causing an increase in the uniaxial strength from 20-25 MPa to 50-70 MPa. On the other hand, the presence of small quantities of gypsum at the rim of anhydrite crystals implies a decrease of mechanical strength of up to 50% with respect to the values expected for pure anhydrite.Unlike the results about strength, creep strain rate data in gypsum showed a high predictability, suggesting that time-dependent deformation is mainly controlled by mechanisms occurring at the rim of crystals (e.g., pressure solution).

Sulphatic evaporites represent a critical challenge for underground engineering due to their high solubility, swelling potential, and sensitivity to changing hydraulic and thermal conditions. In this study, we investigate the temperature-dependent dissolution behavior and microstructural evolution of Triassic sulphate rocks consisting of anhydrite and minor portions of gypsum from the Western Alps. Twelve cylindrical samples were immersed in CaSO₄-saturated water solutions at 15 °C, 40 °C, and 60 °C for six months. Periodic mass and volume measurements were combined with Scanner Electron Microscope (SEM) imaging to quantify dissolution and document mineralogical transformations. All samples experienced progressive mass loss, whereas volumetric changes remained below measurement resolution. Dissolution pathways varied strongly with temperature. At 15 °C, dissolution occurred mainly along anhydrite grain boundaries, producing rounded crystal edges, while less effect was observed in the gypsum veins, leaving the intergranular layers preserved. In contrast, at 40–60 °C, gypsum was preferentially dissolved, generating porosity around comparatively unaltered anhydrite grains. These results qualitatively reproduce the temperature-controlled solubility inversion between gypsum and anhydrite predicted by thermodynamic models. No secondary gypsum precipitation or swelling features were observed. The experimental evidence highlights the role of temperature and hydraulic regime in controlling the stability of sulphate rocks and provides insights relevant to tunnel excavation, underground storage facilities, and geomechanical modeling in evaporitic settings.

For investigating and modeling the swelling potential of anhydrite rocks, it is important to define a fast but accurate, reliable, and repeatable procedure for mineral identification and quantification of anhydrite mineral in rock samples. We propose a quantitative evaluation of the applicability of two different SEM-based approaches (namely, image analysis and the use of the O/S atomic ratio) for the identification and quantification of anhydrite in polished slices of rock. We compare the results obtained with the bulk densities of the samples and with the outcomes of thermogravimetric analyses, demonstrating high convergence between the different data. We eventually propose a critical comparison between the proposed approaches and the existing methods, overall providing a practical guide for the selection of the best analytical procedure for the quantification of anhydrite content in rocks and, consequently, for the correct estimation of swelling potential.

This study has the main purpose of investigating the micro-mechanisms involved in the expansion of anhydrite, a phenomenon that often occurs during excavations and may cause serious technical problems to civil tunnelling and other infrastructures (e.g., buildings, bridges, underground caverns). For this purpose, we developed an experimental investigation aimed at observing microscale changes occurring in anhydrite samples during water immersion by means of X-ray Computed Tomography (CT). We prepared six cylindrical specimens (diameter 10 mm and height 20 mm) of Triassic anhydrite from the Western Alps. Each of them was wrapped with an impervious cellophane sheet and partially submerged in calcium-sulphate saturated water. The upper surfaces were left in direct contact with air to force the water to cross the specimens. The specimens were put in water on the 15th of December 2023. Then, they were periodically scanned – over a total period of 1 year – through X-ray tomography using the CoreTOM scanner (TESCAN XRE) at Ghent University Centre for X-ray Tomography (UGCT), with a voxel size of 10 µm, as an EXCITE TNA project.The elaboration of CT scans allowed to evaluate the volume and phase changes occurred during the test. All the specimens consistently showed a total expansion between 2% and 3% in volume. In addition, the multitemporal scans were examined using an algorithm of Digital Volume Correlation to deepen the mechanisms driving the expansion by visualizing the position where the expansion prevalently occurred.The improved knowledge of the mechanism driving the process of expansion in anhydrite provides elements for a more accurate forecasting of the entity and the times of the phenomenon in real contexts (e.g., civil tunnelling, mining, slope stability, underground energy storage), driving to the possible refinement of existing constitutive models.

The mechanical and technical characterization of bimunits (i.e., chaotic units consisting of hard blocks within a softer matrix), represents an untrivial challenge for researchers and practitioners. The main existing methods for their characterization require the estimation of the Volumetric Block Proportion (VBP). In real contexts, the VBP is typically estimated from point, linear, or areal measurements, making it strongly dependent on the availability of accessible outcrops and/or borehole data. To address this limitation, we evaluated the potential of geophysical (geoelectrical) methodologies for quantifying the Areal Block Proportion (APB) in bimunits. Specifically, we propose an approach for the analysis of electrical resistivity tomographies (ERTs) on bimunits, as outlined by Caselle et al. (2024). This approach is based on the fundamental research assumption that the electrical contrast between blocks and the matrix enables the discrimination of rock blocks in ERTs, provided their sizes exceed the resolution of the ERT. When block sizes are smaller, the ERT homogenizes the blocks-matrix mixture, producing an overall resistivity signature. This signature shows a positive proportionality with the percentage of blocks and can be used to estimate the ABP while still providing valuable information for bimunits characterization. This hypothesis was tested through numerical simulations and real ERTs, offering a preliminary validation of the proposed approach. Caselle, C., Comina, C., Festa, A., Bonetto, S. 2024. Electrical resistivity tomography for the evaluation of Areal Block Proportion (ABP) in bimunits: Modelling and preliminary field validation, Engineering Geology, 333, 107488, https://doi.org/10.1016/j.enggeo.2024.107488.

This study focuses on the investigation of the chemical reactions involved in the phenomenon of anhydrite swelling, that is a well-known issue that may affect the functionality of underground infrastructures.The study was performed on Triassic gypsum and anhydrite samples collected from an Alpine location (Signols, Oulx in the Susa Valley, Piedmont, Italy) and involved the investigation of the behavior of this material immersed in different aqueous solutions at various temperatures.The influence of different aqueous solutions (distilled water, water with CaSO4, water with MgCl2, and water with NaCl) on the solubility and precipitation of new crystals was evaluated at different temperatures (15°C, 40°C, and 60°C).Both macro- and micro-scale observations were conducted before water immersion and after different time intervals. Macro-scale observations included the measure of the volume and the mass and the capture of photographical images with a camera. Micro-scale analyses involved the use of SEM-EDS to determine the mineralogical composition and examine the changes in micro-scale morphological features (e.g., growth of new crystals).The experiment seeks to identify potential mineralogical transformation, particularly the hydration of anhydrite into gypsum, under the specified conditions. The findings will contribute to understanding the mechanisms influencing anhydrite swelling and its implications for geological and engineering applications.

Human interaction has always influenced the structure of watercourses, often resulting in changes that disrupt their morphological balance and the associated river habitats. In Europe, the earliest river reconfiguration efforts date back to Roman times. Since then, distinct stages of river management have emerged. The most significant alterations to waterways occurred during the 20th century, particularly after World War II, driven by industrial and urban growth.This project aims to assess the anthropogenic impacts on river morphodynamics in three alpine water basins located northwest of Turin, Italy, focusing on the past 150 years, from the pre-industrial phase to the present.Using a Geographic Information System (GIS)-based approach, the study investigates how human activities, such as urbanization, agriculture, and infrastructure development, have influenced the physical characteristics and behaviour of river systems. The methodology involves collecting spatial data from 1850 to 2022, digitizing it, and applying morphological indices to evaluate changes in river settings, shapes, and sediment transport. For the entire period, major changes in river morphodynamics were correlated with land use patterns. Statistical analyses were subsequently employed to assess variations in river morphology over time. This approach provides a robust framework for evaluating anthropogenic pressure on river morphodynamics.The results reveal significant changes in river patterns, sediment transport, and habitat availability. Notably, a general narrowing of channels was observed, along with a transition in their layout from sinuous to straight and from braided to single-thread channel configurations.By comparing the outputs of different indices with major land use changes in the territory, the study highlights the critical interplay between human development and riverine morphodynamics. These findings contribute to a deeper understanding of how human interventions reshape natural water systems, offering valuable insights for future environmental management and conservation strategies.

Europe's pursuit of climate neutrality by 2050 necessitates innovative strategies in renewable energy deployment. The European Union has championed policies to harness clean energy sources as hydroelectric energy. This study delves in Piedmont region (North-West of Italy), evaluating its residual potential for run-of-river hydroelectric plants. More in detail, the research focuses on the Sangone catchment, aiming at performing a regional-scale study made to identify the best sites for potential hydroelectric plants. To ensure alignment with European Union biodiversity and environmental conservation directives, particularly the Habitats Directive and Birds Directive, the research prioritizes sites that are not in areas dedicated to environmental protection.Moreover, the study includes landscape analysis and evaluation of geological and geomorphological constraints, such as landslide and hydraulic hazard, and technical and economic feasibility of plants.After that, utilizing freely accessible data encompassing temperature, precipitation, land use, and soil characteristics specific to Piedmont, the study employed the Soil and Water Assessment Tool (SWAT).This GIS-integrated hydraulic model extrapolated flow rate metrics for water catchment areas devoid of direct measurement, optimizing site selection for maximal hydroelectric energy yield.The simulation used 17 years of meteorological data from 42 measuring stations and the model was run over the Sangone stream catchment. The model has also been calibrated to simulate runoff in the Sangone catchment. The outputs divide the stream in sections with equivalent potential power production. Preliminary findings underscore the effectiveness of SWAT by using free data and free tools. It can be a useful planning tool for hydropower implementation by locating sites suitable for run-of-river plants, considering environmental impact and geo-hydrological hazard. As Europe navigates its green transition, such integrative approaches emphasize the feasibility and sustainability of hydroelectricity as a linchpin in the continent's renewable energy matrix.

Coniolo and Brusaschetto, are two small towns located in the Monferrato area of the Alessandria Province, northern Italy. These communities have similar histories related to development and subsequent abandonment of marl quarry activity that began more than a century ago and continued until recently. Quarrying occurred until soil conditions, water infiltration, and excessive depth made cost of extracting and7 lifting material prohibitive. Quarries consisted of tunnels located directly beneath the towns at about 150 m below ground surface. Collapse of the tunnels led to surface subsidence and destruction of overlying homes and much of the municipal infrastructure. In the early Twentieth Century, regulations pertaining to mine and quarry safety were typically deficient, entirely absent, or not followed. Extractive activities of non-energy mineral resources from quarries and mines were and continue to be widespread in Italy, which currently ranks fifth among what are now countries of the European Union (EU). Mining sites are present in all regions of Italy, particularly in the northern part of the country and along coasts, often in areas of geohydrogeological risk. Consequences of anthropogenic pressures that alter the natural environment, such as the physical size of aquifer drawdowns, are linked to issues for a number of extractive sites across the country. This report analyzes historical and technical documents, conducts a geomorphological analysis of hilly slopes surrounding these communities, and examines urban planning and geophysical surveys to determine the impact of subsurface quarrying activities on the overlying ground surface. The study highlights significant problems that are applicable to other localities globally. This research demonstrates: (a) the importance of geological considerations to development and abandonment of mining activity in inhabited areas; (b) the importance of establishing and following safety protocols; and (c) the manner in which economic interests can take precedence over the well-being and lives of those employed to extract resources.