Despite daily progress over half a century, rock deformation leaves significant challenges in understanding their underlying mechanics and providing accurate models. Experimental geologists developed various approaches to deform rock samples, but coupling them with X-ray tomography marked a turn in monitoring failure precursors and interpreting stress-strain curves. X-ray transparent triaxial presses become more advanced and equipped yearly, allowing the complete rheological study of earth material.
The European Synchrotron Radiation Facility is the unique 4th generation synchrotron worldwide. Its Extremely Brilliant Source (EBS) allows the scan of samples encapsulated in thick autoclaves at high speed. It proposes a state-of-the-art fleet of triaxial presses capable of accurately measuring and observing the deformation of a rock sample while passively recording its acoustic emissions. It enables researchers to analyse fault movements, stress transfer, and energy release mechanisms at different sample sizes while precisely controlling stress, temperature, and deformation rates.
With comprehensive data analysis, such as crack segmentation and digital volume correlation coupled with acoustic events' time and spatial resolution, it is now possible to identify failure precursors at high spatial (X-rays) and soon temporal (acoustic) resolutions. One may also investigate phenomena with low amplitude or high frequency, which produce deformation but appear aseismic.
Here, we present the successful results of several teams that have used these devices and their latest technical developments.
How to cite: Cordonnier, B.: Cracking the Rock Mechanisms with the European Synchrotron Experimental Fleet., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18080, https://doi.org/10.5194/egusphere-egu25-18080, 2025.
Pore fluid pressure is known to significantly influence the mechanical strength of rocks. On one hand, an increase in pore fluid pressure may favor crack growth and thus trigger failure, while on the contrary, a decrease in pore fluid pressure will inhibit crack propagation and stabilize failure. On the other hand, whether pore fluid decrease or increases depends on the combination of: 1) pore-fluid pressure boundary conditions; 2) pore fluid pressure diffusion timescale relative to deformation timescales; 3) the latter governing the evolution of permeability and storage capacity within the system. Hence, whether pore fluid pressure will stabilize failure or not, via dilatant strengthening, will depend on a number of parameters, amongst which boundary conditions (drained or undrained), initial permeability, and strain rate must be included.
Here, we perform a comprehensive investigation into the mechanical strength of thermally cracked Westerly granite, in order to provide insights on pore fluid pressure evolution during rock failure. We conducted triaxial loading experiments on heat-treated Westerly granite samples (heated to 700 °C). In order to investigate the mechanical and hydraulic responses throughout the entire failure process, experiments were performed under both drained and undrained boundary conditions, at different strain rates (10-4, 10-5, 10-6, and 10-7 s-1) and initial effective confining pressures (5, 20, and 40 MPa). All experiments were conducted at an initial pore pressure of 50 MPa. During each experiment, stress, strain, as well as pore pressure (using 8 in-situ pore pressure transducers) were monitored. Acoustic emission and the evolution of elastic P-wave velocities were also recorded. So far, our experimental results demonstrate that:
- Water-saturated granites under undrained conditions show higher strength than drained ones, due to dilatant strengthening from reduced pore pressure at failure.
- Under drained conditions, the onset of pore pressure drop is governed by the competition between fluid diffusivity and volumetric strain rate.
- Dilatant strengthening under drained conditions is strain-dependent, with larger pore pressure drops at high (10-4 /s) vs. low (10-7 /s) loading rates.
Our results highlight the importance of dilatant strengthening during the failure of crystalline rock. For instance, it is possible that a number of former studies realized under nominally drained water saturated conditions may have underestimated the effect of water weakening, due to important – yet unobserved at the time- dilatant strengthening happening, resulting in strength of dry and saturated specimen being almost equivalent.
Dilatant strengthening being most efficient at high strain rate, we can safely extrapolate that it is most efficient just before or just after failure. In particular, by stabilizing failure, it may explain long foreshock and aftershock sequences, as seem to be the case in at least some of the recorded AE sequences during our experiments. Finally, whether thermal pressurization is or not able to balance out (because of high velocity frictional heating) dilatant strengthening during dynamic rupture remains to be investigated.
How to cite: Lin, G., Fan, C., Chapman, S., Fortin, J., and Schubnel, A.: The competition between fluid diffusion and volume dilatancy during the failure process of thermally cracked Westerly granite, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3048, https://doi.org/10.5194/egusphere-egu25-3048, 2025.
Electrical signal changes in process of loading rock to fracturing is an important rock petrophysical phenomenon, which is of great significance for understanding the abnormal electric field, magnetic field and electromagnetic radiation related to rock fracturing, geohazards and tectonic earthquake. Positive holes (P-holes) activation due to the broken of peroxy defects is one of the important mechanisms causing rock current, and peroxy defects are common in most of the crust rocks. During the loading of rock specimen, the activation, transmission and accumulation of P-holes in different place inside the rock are bound to be variable, and present as the spatial difference in the changes of electrical signals. However, the spatial differences in the changes of electrical signals during loading rock to fracturing and the correlation between the electrical signal and the internal physical-and-mechanical states of rock have not been well studied so far.
Therefore, we carried out potential monitoring experiments in different areas of the rock under local stress and synchronous acoustic emission monitoring. The rock specimen was specially designed in 3D shape of cube-frustum. The lower cube acting as the loaded part was wrapped with copper foil and connect to the negative electrode of the potentiometers; while the upper square frustum acting as the free part were pasted with copper foil at three places and connect to the positive electrode of potentiometers, respectively, as in Fig. 1a.
The experimental results, as in Fig. 1b, showed that during the early rock loading, the characteristics of potential changes in each area were basically the same, with slight differences in amplitude, which were directly related to the size of micro-crack development area in the corresponding part. When the loaded rock reached to macroscopic fracturing and got failure, the characteristics of potential change in different areas were significantly different (Fig. 1c), which were directly related to the formation of macroscopic fracture inside. When no macroscopic fracture surface was formed at the intersection zone of the free part and the loaded part below the potential monitoring area, P-holes would transmit upward to the upper surface of frustum along the stress gradient, resulting in the rise in potential. Conversely, if a macroscopic fracture surface was formed at the intersection zone (Fig. 1d), the upward transmission of P-holes would be blocked, and more P-holes reached the surface of the loaded cube, resulting in the decrease in potential. Furthermore, we kept loading the rock fragments after macroscopic failure, and found that during the friction or the relative slip process between fragments, the combined influence of furrow effect, adhesive friction and slip shear also led to P-holes activation and dislocation sliding, resulting in potential rising again. The potential risings in different areas were related to the degree of friction and the distribution of macroscopic fracture surfaces in the corresponding parts.
Figure 1 Experimental schema diagram and results. (a) Diagram of the experimental schema; (b) The variations of potentials; (c) Potential changes when the rock got failure; (d) Failure pattern.
How to cite: Sun, L., Wu, L., Xu, Y., Zheng, T., Dong, G., Xie, B., and Mao, W.: Spatial Differences in Potential Changes of Rock Loaded to Fracturing: Characteristics and Mechanism, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5665, https://doi.org/10.5194/egusphere-egu25-5665, 2025.
Istanbul is a unique city spanning two continents and one of the world's most populous cities. There is a significantly increasing demand for the construction of deep engineering structures, particularly transportation and infrastructure tunnels because of a population exceeding 16 million. Numerous projects, including intercontinental strait crossings, will be implemented over the coming decades to meet the city's needs. Istanbul’s complex geological structure, rugged topography, and earthquake risk make construction efforts more challenging. Generally, deep engineering structures in Istanbul are primarily constructed within the classic and carbonate rocks, which are part of the Istanbul Paleozoic Sequence. These sedimentary rocks are intersected by dikes composed of andesite, diabase, and dacite, which exhibit varying geometries. Due to the different engineering properties of these rock units, which have different geological origins, their behavior in deep underground excavation openings also varies. Engineering problems such as rock bursts, water inflows, and TBM (Tunnel Boring Machine) jamming arise during tunnel construction, leading to both cost overruns and time delay. In this study, the effect of dyke geometries on tunnel stability was analyzed using ITASCA’s Particle Flow Code (PFC), which employs the discrete element method (DEM). Models were calibrated based on field experiences and laboratory data of the host rocks and dykes obtained during tunnel construction on the Anatolian side of Istanbul. The uniaxial compressive strength and elasticity modulus values of the host rocks and dykes are 28 MPa and 46 MPa, 12 GPa, and 16 GPa, respectively. Initially, a base two-dimensional model with dimensions of 4 by 4 meters was calibrated using the flat-joint model, and upscaled to 80 by 60 meters to represent the tunnel environment. Additionally, models featuring singular and dual dyke geometries with different orientations were utilized in an environment containing a tunnel opening with a radius of 4 meters. Analyses were carried out on a total of 18 models, which included seven single dyke geometries with a dip angle varying between 0 and 90 degrees in 15-degree increments, six geometries featuring a secondary dyke with a horizontal dip angle of 0 degrees intersected by another dyke at 15-degree increments, and five models with two dykes positioned at dip angles of 15, 30, 45, 60, and 75 degrees relative to each other. Each model was run for up to 100,000 cycles under gravitational loading conditions, and data on force chains, fragmentations, stress, and strain values were collected using measurement spheres positioned at 0, 90, 180, and 270 degrees around the tunnel opening. According to the results obtained from the models, the highest deformation in the tunnel section was observed at 60 degrees in single dyke geometries, while in double dyke geometries, it was observed at 0-30, 0-45, and 0-60 degrees.
How to cite: Zengin, E. and Ündül, Ö.: Exploring Dyke Geometry Effects on Tunnel Stability Using Particle Flow Code, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7280, https://doi.org/10.5194/egusphere-egu25-7280, 2025.
Adsorption-induced deformation is common in porous rocks, but its role in stressed porous rocks remains unclear. These changes in elasticity have critical implications for geological stability, particularly in regions experiencing alternating droughts and wet conditions. This study investigates elastic deformation in fine-grained sandstone under cyclic loading over 34 days, with humidity increased to near dew point. Adsorption-induced weakening decreases from over 40% to less than 10% as overburden pressure rises from 1 MPa to levels below crack initiation. Similar trends are observed in fine-grained granite. A multi-scale model combining contact mechanics and nanopore adsorption explains these results, highlighting stress competition between adsorption effects and overburden pressure. Adsorption weakening becomes negligible beyond burial depths of 200 meters in sandstone and 700 meters in granite. These findings improve understanding of near-surface geological hazards, such as exfoliation, landslides, and cliff failure, under extreme climatic events.
How to cite: Wu, R., Kang, H., Gao, F., Li, B. Q., Leith, K., Lei, Q., Gor, G., Selvadurai, P. A., Peng, X., Dong, S., and Li, Y.: Elasticity control through overburden and adsorption competition in porous media, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1946, https://doi.org/10.5194/egusphere-egu25-1946, 2025.
The 660 km discontinuity serves as an important boundary for elucidating the dynamics of subducting slabs at this depth. Subducting slabs, characterized by their lower temperatures compared to the surrounding mantle, undergo distinct phase transitions. Harzburgitic compositions are the most gravitationally stable within the lower mantle transition zone, potentially incorporating up to 15 vol% akimotoite in their mineral assemblage. Recent experimental studies indicate that the transition from akimotoite to bridgmanite may be a critical factor in deciphering the complexities inherent to this region. Additionally, discoveries of iron-rich natural analogs of akimotoite and bridgmanite in Suizhou L6 chondrite have attracted considerable scientific attention regarding the stability of these iron-rich phases. These analogs, identified as Hemleyite (Fe2+0.48Mg0.37Ca0.04Na0.04Mn2+0.03Al0.03Cr3+0.01) SiO3 and Hiroseite (Fe2+0.44Mg0.37Fe3+0.1Al0.04 Ca0.03Na0.02) (Si0.89Al0.11) O3, provide critical insights into the geochemical behavior and phase stability of iron-bearing silicates under extreme conditions. In this study, first-principles computational methods based on density functional theory (DFT) were employed to investigate the stability fields of these iron-rich phases under high-pressure and high-temperature conditions, aiming to elucidate the effects of Fe²⁺ incorporation on slab stagnation behavior. The analysis demonstrates a positive correlation between acoustic velocity contrasts and increasing Fe²⁺ concentration at the phase transition boundary, while the transition pressure decreases significantly. Additionally, the findings suggest that the overall steepness of the Clapeyron slope remains largely invariant with increasing iron content.
How to cite: Pandit, P., Chandrashekar, P., and Shukla, G.: Impact of Fe²⁺ incorporation on the structural and thermodynamic characteristics of the akimotoite-to-bridgmanite phase transition, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-603, https://doi.org/10.5194/egusphere-egu25-603, 2025.
Most models for dimensioning shallow geothermal heat exchangers consider that heat is only transferred by conduction. The ground water content is assumed to be constant with time. However, in the Vadose Zone (VZ) presenting important geothermal potential, the thermal properties of materials depend on the variable water content.
The literature review highlights that the relationships between thermal conductivity and water content are multiple and often very specific to certain nature of ground systems. The target of this work is therefore to characterize the thermal conductivity of a specific strongly heterogeneous site in order to discuss the limit of adaptability of these approaches and the robustness of the associated models.
Excavation of the Observatory of transfers in the Vadose Zone (O-ZNS) near Orléans (France) allowed us to extract VZ limestones from 7,20 to 20 m-depth, described as massive and weathered with heterogeneous fracture density. Two experimental approaches are used to determine thermal conductivity at different water content. The first is an empirical model that estimates thermal conductivity from acoustic velocity. P-wave acoustic velocities are obtained in dry and saturated conditions and then converted into thermal conductivity. These results are compared to direct thermal conductivity measurements obtained using the hot-wire method.
The indirect method seems to be well adapted for dry materials characterization. However, it presents inconsistencies for saturated or partially saturated materials. Indeed, we saw a conductivity decreases with water content, while theory predicts the opposite. The empirical model clearly shows its limitations when it comes to considering water in the pores of complex rocks. Nevertheless, on dry samples, the deduced thermal conductivity values are validated by direct measurements. The direct method makes it possible to observe the theoretical correlation between thermal conductivity and water content in order to adapt future models. Measurements show an increase in thermal conductivity with water content. But, in some samples, of rather massive appearance, poorly altered and fractured, water content has a relatively low impact on thermal conductivity. These variations raise questions about the effects of a specific microstructure on the correlation between water content and thermal conductivity. Indeed, on samples taken at 16.6 m-depth, the same mean value of thermal conductivity was observed regardless of water content, a behavior not observed on other samples.
The thermal conductivity data will be integrated in a new thermo-hydro model of the O-ZNS site, currently under development : i) to test the stability and consistency of the models and compare results with experimental data, and ii) to later calibrate the chosen model and apply it to different contexts.
How to cite: Dupuis, M., Abbar, B., Mallet, C., Voirand, A., Philippe, M., and Azaroual, M.: Caracterising Thermo Hydro Mechanical properties in complexe limestone formation (OZNS, Beauce aquifer, France), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2713, https://doi.org/10.5194/egusphere-egu25-2713, 2025.
Currently, there is insufficient confidence in the application of soft rock in major projects, leading to overly conservative design of foundation bearing capacity. Clarifying the stress distribution and failure process of soft rock foundation with depth offer guiding significant for determining the bearing capacity of soft rock foundation in practical geotechnical engineering. Based on the arch foundation project of the Fifth Bridge of the Lantian Yangtze River, this paper investigated the bearing capacity of soft rock foundations and its depth correction rule by analyzing field test results and numerical simulations. A formula inversion model was established referencing current standards and relevant literature, and the depth correction coefficient k2 for soft rock foundation bearing capacity was calculated based on field test measurements. Using finite element software PLAXIS 3D, a numerical model of soft rock foundations with variables including load plate burial depth and lateral limiting conditions was created under field conditions and calculate the simulated bearing capacity of soft rock foundations. By combining results from both methods, the variation rule of soft rock foundation bearing capacity influenced by depth factors is analyzed, and the applicability of different research methods is discussed. It is found that within a certain range, the bearing capacity of soft rock foundations has a linear positive correlation with burial depth, and after reaching 15d, it shows a gradual trend. Finally, recommended values for the depth correction coefficient are 2.5 (for undetailed or poor foundation conditions) and 8.0 (for good foundation conditions with low weathering degree), with different values adopted according to site conditions. Furthermore, the bearing capacity of soft rock foundations with free surfaces was discussed, offering a valuable reference for similar future engineering scenarios. After the bearing capacity measurement and foundation deformation performance analysis, it was concluded that there is still a significant bearing capacity reserve, which provides essential data support for dimensional optimization. This paper further substantiates that the bearing capacity of soft rock foundation can be significantly enhanced through in-depth modification, thereby offering meaningful reference and guidance for practical engineering applications.
How to cite: Yang, X., Gong, W., and Yang, H.: In-situ test and numerical verification of bearing capacity of soft rock foundation with depth, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10931, https://doi.org/10.5194/egusphere-egu25-10931, 2025.
The chemical characteristics of water present in the pores and fractures of the rock mass and the mineralogical rock composition determine the chemical processes that may take place in a geological formation. The chemical reactions occurring in a geotechnical problem play an important role because their development can influence on the mechanical and hydraulic behaviour of rock masses. For example, a change in the concentration of dissolved salts in groundwater can lead to a modification of the swelling potential or trigger and expansive or shrinkage response of clayey formations (Yustres et al., 2017). Therefore, a good knowledge of the chemistry involved in the rock mass is relevant both to understand and to predict the response of the geological media. This is of great importance in the case of the construction of critical civil infrastructures like energy and nuclear waste storage facilities.
Chemical effects are expected to occur in soils and rocks, and several variables may affect the intensity at which they take place. The literature describes several case histories in rocks where the effects of chemistry are more intense than in soils. Tunnels and foundations may respond hydraulically and mechanically under the influence of the chemical processes of the dissolution/precipitation of soluble minerals present in the rock. These phenomena are capable of leading to severe and rapid expansions that can result in infrastructure and building damage. The extreme expansions observed in anhydritic rocks are one example in which dissolution and precipitation processes affect the geotechnical behaviour (Alonso et al., 2013, Ramon & Alonso, 2018).
A coupled numerical model has been developed to address the chemical processes coupled to thermo-hydro-mechanical (THM) problems in geological media. The numerical model is capable to simulate general chemical processes and the associated hydraulic and mechanical effects. The formulation of the chemical interactions is implemented in a coupled manner within a Finite Element code for THM analysis in geological media (CODE_BRIGHT). The presentation will describe the details of the equations and hypothesis considered in the model. The simulation of a real case will be also analysed.
Alonso, E.E., Berdugo, I.R. and Ramon, A. (2013). Extreme expansive phenomena in anhydritic-gypsiferous claystone: the case of Lilla tunnel. Géotechnique 63 No. 7, 584 – 612
Ramon, A. and Alonso, E. E. (2018) Heave of a Building Induced by Swelling of an Anhydritic Triassic Claystone. Rock Mech. Rock Engng.: 51, Issue 9, pp 2881–2894.
Yustres, A., Jenni, A., Asensio, L., Pintado, X., Koskinen, K., Navarro, V., Wersin, P. (2017). Comparison of the hydrogeochemical and mechanical behaviours of compacted bentonite using different conceptual approaches. Applied Clay Science, 141: 280-291.
How to cite: Ramon, A. and Olivella, S.: Numerical analysis of the effects of chemistry on the THM behaviour of rocks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21626, https://doi.org/10.5194/egusphere-egu25-21626, 2025.
In rocks, brittle deformation depends on loading rating. With increasing rates, usually greater than ~102 s-1 rock strength increases significantly that results intense fragmentation. Dynamic conditions necessary for rate dependent brittle failure can occur during impact events, seismic ruptures and landslides. Among the geoscientist and rock engineers, Split Hopkinson Pressure Bar (SHPB) is often used for the study of dynamic behavior of rocks under high strain rate condition. Present study focuses on strength behavior of sandstone over the range of strain rate (3.6×10-5 - 2.4×102 s-1) using compression testing machine and Split Hopkinson Pressure Bar (SHPB). The failure mode is also captured by high speed camera. The result demonstrates that dynamic compressive strength increases with increasing strain rate and follows Kimberley’s universal theoretical scaling relationship. Dynamic increase factor (DIF) also shows strong dependency on strain rate. The degree of fragmentation is also compared with existing theoretical fragmentation models. The average fragments size shows strong strain rate dependency over the entire testing range. With the increasing strain rate more pulverized state were observed after the failed specimens. Moreover, the mean fragment sizes are well described by power law function of strain rate.
How to cite: Gupta, N., Sharma, M. L., Iqbal, M. A., and Tripathi, A.: Dynamic Strength of rock under High strain rates, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1033, https://doi.org/10.5194/egusphere-egu25-1033, 2025.
The release of CO2 into the atmosphere is thought to be a major factor contributing to global warming, and technology for separating and recovering CO2 from the gases emitted from large-scale sources and storing it in deep underground aquifers (hereafter referred to as CCS: Carbon dioxide Capture and Storage) is already being used commercially in other countries as a measure to combat global warming. When starting a CO2 geological storage project, as part of risk management, it is necessary to consider whether there is a potential threat of causing seismic activity or ground deformation that could have a negative impact, and to plan and implement countermeasures. The Japan islands located in the convergent zone of four tectonic plates and are known as one of the most earthquake-prone countries in the world. Evaluating and predicting the impact of great earthquakes on reservoirs and cap rocks and disseminating this information to society is considered to be one of the important issues in terms of gaining social acceptance at the project planning stage. The authors are currently developing an earthquake response analysis method for evaluating the stability of CO2 geological storage sites in advance in the event of a great earthquake, but one of the issues is the physical properties of the ground to be input into the analysis model. It is well known that brittle rocks under atmospheric pressure show plasticity under confining pressures of tens to hundreds of MPa, and it is easy to imagine that soft sedimentary rocks also show similar mechanical behaviour. However, there are only a few cases of published high-pressure triaxial compression tests using drilling core samples collected from deep underground, for example. In this study, triaxial compression tests were conducted using sandstone and mudstone block samples (comprising the middle Pleistocene to the upper Pliocene) collected from outcrops and shaped into specimens (height 100 mm, diameter 50 mm) in the laboratory under confining pressures equivalent to CO2 storage sites. Regardless of the age of the sediment, the principal stress difference in mudstone increased to 1-2% axial strain, after which it remained almost constant. There was no clear yield point in the ‘stress-strain curve’, and the mudstone showed strain-hardening behaviour. The pore water pressure increased as the axial strain increased. In the sandstone, no clear shear surface was formed even at an axial strain of around 5%. The specimens did not become barrel-shaped after testing, but instead showed a shape of overall shrinkage. The volume change continued to decrease as the axial strain increased. This is thought to be because the difference in the principal stress did not reach its maximum strength. In the future, we plan to conduct experiments that take into account the pressure history (depositional depth and overburden) that the specimens have been subjected to in the past, before loading tests.
How to cite: horikawa, S., takemura, T., and kusunose, K.: High pressure triaxial compression test in soft sedimentary rocks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3958, https://doi.org/10.5194/egusphere-egu25-3958, 2025.
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.
How to cite: Giordano, E., Caselle, C., Costa, E., Bonetto, S. M. R., Paschetto, A., and Mosca, P.: Experimental analysis of crystal growth in anhydrite and its impact on swelling quantification, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6576, https://doi.org/10.5194/egusphere-egu25-6576, 2025.
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.
How to cite: Caselle, C., Ramon, A., Schröer, L., Cnudde, V., Bonetto, S. M. R., Mosca, P., Costa, E., Giordano, E., and Paschetto, A.: Volume and phase changes of swelling sulphates revealed through multitemporal micro-CT imaging , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4306, https://doi.org/10.5194/egusphere-egu25-4306, 2025.
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.
How to cite: Bonetto, S., Comina, C., Festa, A., and Caselle, C.: Evaluation of Aereal Block Proportion (ABP) for the mechanical characterization of bimunits using Electrical Resistivity Tomography , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11515, https://doi.org/10.5194/egusphere-egu25-11515, 2025.
In many geotechnical and tectonic settings, a fundamental understanding of the inelastic behavior of porous rocks under polyaxial compression is necessary. In this study, we present new true triaxial compression data obtained in the ductile regime on Bleurswiller sandstone with the size of 100mm X 50mm X 50mm. The deformed samples show a range of failure modes qualitatively similar to what was reported by earlier experimental studies performed in conventional conditions (axisymmetric compression). In particular, visual inspection and X-ray Computed Tomography imaging reveal compaction localization in all our deformed samples. The pore collapse model of Zhu et al. (2010) is extended to include the role of the intermediate principal stress and our new data for the onset of shear-enhanced compaction are in basic agreement with this extended model that includes three stress invariants. At constant minimum principal stress, the onset of shear-enhanced compaction tends to decrease slightly with increasing intermediate principal stress.
Published true triaxial data obtained in the brittle regime highlights the impact of the intermediate principal stress on the onset of dilatancy. The predictions of the conventional sliding wing crack model extended to true triaxial conditions are in poor agreement with these data. Our analysis suggests that the observed discrepancies are related to the influence of the intermediate principal stress on the effective shear stress on the wing cracks. Another energetic approach pioneered by Wiebols & Cook (1968) shows a better agreement with the experimental results, and predicts that at constant minimum principal stress, the onset of dilatancy would not be a monotonic function of the intermediate principal stress. Our new data and analysis will help the interpretation of inelastic deformation under polyaxial compression in various geotechnical and tectonic settings.
How to cite: Meng, F., Shi, L., Hall, S., Baud, P., and Wong, T.: Onset of Pore Collapse and Dilatancy in Porous Sandstone Under True Triaxial Compression: Experimental Observation and Micromechanical Modeling , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8113, https://doi.org/10.5194/egusphere-egu25-8113, 2025.
The swelling behavior of clay-sulfate rocks poses significant challenges in geotechnical engineering due to complex hydro-mechanical and chemical interactions. This study introduces a hybrid framework combining finite element modeling (FEM) with machine learning (ML) to efficiently analyze and predict the nonlinear behavior of swelling processes. We generated synthetic datasets representing swelling phenomena at the Staufen site, Germany, using a coupled hydro-mechanical FEM simulation in OpenGeoSys. A parametric analysis was conducted to systematically vary critical parameters, including Young's modulus, permeability, maximum swelling pressure, and air entry pressure, to capture the inherent uncertainty and variability of swelling processes. A constrained CatBoost ML model was trained on the FEM outputs to predict porosity, saturation, and displacement under varying hydro-mechanical conditions. Results demonstrate strong alignment between the ML surrogate and FEM simulations, achieving high accuracy while significantly reducing computational demands. Sensitivity analysis indicated the dominance of swelling pressure and Young's modulus in influencing swelling-induced deformation, while Monte Carlo simulations quantified prediction uncertainties. This contribution discusses the potential of integrating FEM with ML for site-specific risk assessment and mitigation planning in geotechnical engineering.
How to cite: Taherdangkoo, R., Mollaali, M., Ehrhardt, M., Nagel, T., and Butscher, C.: Integrating Finite Element Modeling and Machine Learning for Hydro-Mechanical Analysis of Swelling in Clay-Sulfate Rocks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8168, https://doi.org/10.5194/egusphere-egu25-8168, 2025.
Understanding the microstructural details of concrete is crucial for improving their material properties in structural applications within civil engineering. Digital Rock Physics (DRP) refers to a modern technique that enhances the understanding of the physical behavior of rocks or respectively concrete through microscale imaging of their internal structures. Based on the non-destructive method of high-resolution X-ray computed tomography (XRCT), which is still widely underestimated, it is possible to obtain information e.g., on phase distributions, volume characteristics like pore spaces and furthermore microstructures such as microcracks can be visualized. Here we used the XRCT to investigate the influence of external mechanical loading on concrete. XRCT images with different resolutions were performed under confining pressures of 0.1 MPa to 46 MPa. The generated and analyzed CT images of unloaded and loaded (i.e., due to external stress) concrete are compared with respect to any potential microstructural changes. We specifically examined the segmentation process and its impact on the determined effective material properties. Despite the many possibilities enabled by XRCT technology, there are still challenges in identifying microstructures or phases correctly, due to its relatively low resolution, which also complicates the assignment of their physical properties based on numerical simulations. For the interpretation of the concrete’s CT images, additional methods are needed. This applies in particular to grain and phase boundaries of individual aggregates, transition zones or very fine-pored phases. For this reason, the high-resolution image-based data from XRCT is combined with standard polarization and scanning electron microscopy (SEM). Together with these additional fundamental laboratory techniques, it is possible to receive more detailed information of the structure, detect internal changes at all scales and to get an optimal spatially segmented image of the concrete samples. It is possible to determine realistic synthetic scenarios for different loading situations, which enables the application of advanced numerical approaches. This study demonstrates the importance of understanding the internal microstructure of concrete-based structures to analyze the XRCT images and to identify the effects of external stresses in concrete and thus the factors that influence the accuracy of physical measurements at elevated pressure conditions.
How to cite: Beiers, L. M., Balcewicz, M., Lebedev, M., and Saenger, E. H.: Digital concrete physics - High-resolution X-ray computed tomography (XRCT) and microstructural investigations of concrete under confining pressures, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11880, https://doi.org/10.5194/egusphere-egu25-11880, 2025.
The application of laser technology for drilling rocks has drawn the attention of scientists and engineers for decades (Xu et al., 2003; Buckstegge et al., 2016; Jamali et al., 2019; El Neiri et al., 2023), promising a revolution in well-drilling operations of the oil and gas industry and geothermal energy sector. High-power lasers can penetrate hard rock formations with greater rate and precision, without physical contact with the rock which eliminates wear on drill bits and subsequently reduces significantly drilling time and well completion costs. This work is a part of the DeepU Project that addresses problems of conventional drilling in search of cheaper and environmentally friendly drilling technique for the exploitation of geothermal energy. A series of laboratory-scale experiments were performed with the Ytterbium fiber laser with a wavelength of 1070±10nm, operating in continuous mode within a power range of 170-30000W. The temperature of the lasing process and IR imaging were recorded by thermo-camera FLIR GF77a with HSM mode allowing for gas visualization. The craters in laser-affected rocks were further investigated by photogrammetry and electron microscopy while ejected particles were collected and characterized. This comprehensive study has revealed the nature of petro-thermo-mechanical phenomena occurring during laser irradiation of rocks. The three observable processes are: thermal spallation, melting and vaporization. They are controlled mainly by power density (delivered to the rock surface), irradiation time and lithology (texture, mineral and chemical composition). The photogrammetric analysis of laser-affected rocks has shown the efficiency of the laser drilling process, expressed by the rate of penetration and specific energy i.e., the amount of energy necessary to remove a unit of volume. The microscopic study of lased surfaces has revealed the impact of the laser on the rock samples. Depending on the drilling regime the result was: 1) smoothly cut craters with shallow fractures generated by thermal spallation at lower power or 2) a rugged glass layer of vitrified molten rock formed by melting and vaporization at higher power. The power-dependent transition between the processes, thus drilling regime was defined for granite, sandstone and limestone. These results allowed to design and apply a DeepU thermal spallation laser system to successfully drill larger diameter boreholes (<10cm), and bring closer to the successful application of laser technologies in the geothermal field.
This research is funded by the European Union (G.A. 101046937). However, the views and opinions expressed are those of the author(s) only and do not necessarily reflect those of the European Union or EISMEA. Neither the European Union nor the granting authority can be held responsible for them.
References
Buckstegge F., Michel T., Zimmermann M., Roth S., Schmidt M., 2016, PP, v. 83, p. 336–343, doi:10.1016/j.phpro.2016.08.035.
El Neiri M.H., Dahab A.S.A.H., Abdulaziz A.M., Abdelghany K.M., 2023, JEAS, v. 70, p. 98, doi:10.1186/s44147-023-00260-2.
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Xu Z., Reed C.B., Leong K.H., Parker R.A., Graves R.M., 2003, ICALEO, Laser Institute of America, p. P531, doi:10.2351/1.5060167.
How to cite: Slupski, P., Cerwenka, G., Chorowski, M., Di Sipio, E., Galgaro, A., Mallin, K., Manzella, A., Pasquali, R., Romanowski, A., Sassi, R., Steinmeier, O., and Pockele, L.: Laser-rock interactions, is drilling rocks possible with a laser?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19025, https://doi.org/10.5194/egusphere-egu25-19025, 2025.
The aim of the present study is to understand the strength behaviour of thermally treated sandstone under compression and tensile loading conditions, both in quasi-static and dynamic states. The sandstone specimens were thermally treated in a furnace for 24 hours at a heating rate of 5°C/min and then allowed to cool within the furnace. The specimens were divided into five temperature groups: 25°C, 200°C, 400°C, 600°C, and 800°C. Using a Universal Testing Machine (UTM) and a Split Hopkinson Pressure Bar (SHPB), the quasi-static and dynamic compressive and tensile strengths were determined. The study validates the applicability of Kimberley's universal scaling relationship for thermally treated sandstone under both loading condition. Additionally, the characteristic strain rate remains unchanged up to 400°C and significantly decreases thereafter. High-speed photography provided crucial insights into the failure characteristics under both compression and tensile loading conditions as the temperature increased. The findings are applicable to various geotechnical projects involving high temperatures and dynamic loading conditions.
How to cite: Tripathi, A., Khan, M. M., Pain, A., and Rai, N.: Strength Behavior of Thermally Treated Sandstone Under Quasi-Static and Dynamic Loading Conditions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19456, https://doi.org/10.5194/egusphere-egu25-19456, 2025.
