The Tbilisi Area is located within the eastern segment of the Achara-Trialeti fold-and-thrust belt, which is itself a part of the Kura foreland basin system. The region is characterized by an active convergent tectonic regime resulting from the ongoing collision between the Eurasian and Arabian plates. The convergence has induced extensive deformation features, including large-scale folding, faulting, and uplift, which have influenced the stratigraphy and lithological compositions of the Eocene sedimentary rocks of the study area.

A detailed, interdisciplinary study of these Eocene sedimentary rocks was implemented, integrating petrographic, geochemical, geomechanical, and petrophysical analyses to comprehensively understand physico-mechanical properties, and their interrelation. For this purpose, samples taken from the field were analysed at the Institute of Applied Geosciences, KIT. Petrographic examinations reveal a heterogeneous lithological assemblage comprising predominantly fine-grained clay mineral matrix-rich arkosic wackes, lithic wackes, arkosic arenites, and lithic arenites often containing foraminifera and glauconite, implying marine deposition. Geochemical analyses indicate the most prominent elements of the rocks are Si, Al, and Ca. Their content ranges 23.2-29.6%, 7.1-10.1%, 1.7-11.6%, respectively.

The rocks exhibit notably low permeability, generally in the range of 10^-4 to 3*10^-1 millidarcies (mD), with permeability strongly dependent on porosity metrics (ranging from 1.1% to 10.3%). This low permeability is primarily controlled by clay matrix content and to a lesser extent on cementation processes. The heterogeneity and complexity of these formations are further confirmed by the wide range of uniaxial compressive strength (UCS), from 36.9 MPa to 208.8 MPa, reflecting variations in lithology, degree of cementation, and diagenetic modifications across different sections.

This work presents an initial effort to showcase the diverse rock properties from the Tbilisi Area, as the Eocene sedimentary rocks show distinct lithological heterogeneity and complex mineralogical and petrophysical characteristics, strongly influenced by their depositional and tectonic history with implications for engineering utilization of the lithologies.

Acknowledgement: This work was supported by the Joint Rustaveli-DAAD fellowship programme, 2025. We thankfully acknowledge assistance in the lab by Martin von Dollen (KIT).

How to cite: Giorgadze, A., Busch, B., Chen, Y., Cheng, C., Alania, V., Gorgidze, L., and Enukidze, O.: Petrographic, physico-mechanical, and geochemical characteristics of Eocene sedimentary rocks from the Tbilisi Area (Georgia), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-159, https://doi.org/10.5194/egusphere-egu26-159, 2026.

Rocks exhibit pronounced nonlinear viscoelastic behavior such as modulus softening and loading–unloading hysteresis, even under micro-strain dynamic loading. However, classical nonlinear elastic constitutive models based on higher-order expansions of Hooke’s law show limitations in capturing these nonlinear viscoelastic features. To address this, we extend the classical nonlinear elastic framework by incorporating strain-rate terms and formulate a nonlinear viscoelastic constitutive relation in which nonlinear elastic and viscoelastic parameters jointly describe modulus softening, dynamic response, and hysteresis loops. We use a copropagating acousto-elastic testing system to acquire time series of elastic modulus variation ΔM/E and the corresponding hysteresis loops for Crab Orchard sandstone at five dynamic strain levels. We then invert these data to estimate model parameters and test the constitutive relation. The model reproduces the main nonlinear viscoelastic features observed at all strain levels and, compared with two classical nonlinear elastic models without viscoelastic terms, better captures the phase information in the ΔM/E time series and the geometry of the hysteresis loops. The proposed nonlinear viscoelastic constitutive relation provides a practical way to constrain micro-strain nonlinear viscoelastic parameters of rocks in the laboratory and offers a basis for linking laboratory measurements with field relative velocity changes monitoring to study stiffness evolution during processes such as hydrological loading and fault slow slip.

How to cite: Bai, H., Feng, X., Fehler, M., Brown, S., and Bokelmann, G.: Nonlinear viscoelastic constitutive relation for rocks under micro-strain dynamic loading, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1712, https://doi.org/10.5194/egusphere-egu26-1712, 2026.

Natural stones used in most buildings undergo degradation due to their exposure to outdoor environments, particularly to sometimes extreme variations in temperature and humidity conditions. In historical buildings, consolidants are often used to restore the strength of the damaged building materials and prevent further deterioration. The most commonly used consolidant in this context is ethyl silicate but it is incompatible with salt-contaminated stone. A salt-compatible alternative, lithium silicate, has been developed but remains rarely used. This is partly due to the limited number of available scientific studies and the difficulty of detecting lithium using conventional analytical methods. The aim of this study was to compare the effectiveness of these consolidants on two porous limestones subjected to thermal and mechanical stresses. Saint-Maximin and Leitha limestones were selected for this study because both rocks were widely used as building stones, in France and Austria, respectively. Cylindrical samples of 40 mm in length and 20 mm in diameter were prepared from large blocks. The average porosities of our Saint-Maximin and Leitha limestones were 38% and 41%, respectively. The permeability of both limestones was greater than 1 Darcy. Three groups of samples were tested: intact samples, samples thermally treated up to 400°C and samples deformed uniaxially to the peak stress. Consolidants were introduced in these samples through imbibition experiments that lasted a minimum of 48 h. Within the limestones, the consolidants underwent hydrolysis and condensation reactions to first form a gel on the pore surface. This gel progressively polymerized to form a thin solid layer on the pore surface. Treated samples were typically left to cure in a dry environment for at least a month. Minor variations of the porosity and permeability were observed in all the consolidated samples. The Uniaxal Compressive Stress (UCS) of the intact samples predictably increased by a factor of two for both rocks and both consolidants. After thermal treatment up to 400°C, the UCS of samples of Saint-Maximin and Leitha typically decreased by about 25% due to the thermal expansion of the grains and thermal microcracking. We found that consolidation with ethyl silicate erased this weakening effect. For lithium silicate, the samples also recovered part of their strength, but the effect was less pronounced. When damage was introduced into the rocks through uniaxial compression, ethyl silicate produced a more significant strengthening effect than lithium silicate. In the context of cultural heritage conservation, it is essential that consolidated stones present petrophysical properties similar to the original material in order to prevent further mechanical alterations. Both products exhibit a consolidating effect, but stones consolidated with lithium silicate display properties closer to those of the original rock.

How to cite: Baud, P., Schloegel, P., Surma, F., Reuschle, T., and Heap, M.: The impact of consolidants on the properties of intact and damaged porous limestones, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3035, https://doi.org/10.5194/egusphere-egu26-3035, 2026.

CO₂ geological storage is key to combat global warming. During the site screening process, impact of seismic activity on the storage site is required [1]. As 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 especially important issues in terms of gaining social acceptance at the project planning stage.

　The authors are 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 the input physical parameters of the cap and storage rocks under in-situ stress condition are not enough obtained. 

As the most of Japanese candidate storage sites are at young sedimentary formations, we prepare specimens (height 100mm, diameter 50mm) from Early Pleistocene sandstone and mudstone block sampled from outcrops. Triaxial compression tests were conducted under confining pressures corresponding to the depths of CO₂ storage sites. The loading rate was performed at strain rates of 180%/min, 100%/min, and 10%/min. For instance, when a mudstone specimen was loaded at an effective confining pressure of 14 MPa, a back pressure of 9 MPa, and a strain rate of 180%/min, the maximum strength (approximately 6 MPa) appeared near an axial strain of 1%, after which a gradual softening trend was observed. Distinct strain-softening characteristics were not observed in this experiment. The pore pressure reached its peak slightly earlier than the maximum strength. Although it decreased thereafter, a slight upward trend was observed despite the decrease in axial deviator stress.

   In this presentation, we will report the strength and pore pressure characteristics of rocks based on rock types and loading rates, and propose strength parameters effective for dynamic analysis.

[1] International Organization for Standardization,2026, ISO standard 27914; Carbon Dioxide Capture, Transportation and Geological Storage – Geological Storage.

How to cite: Horikawa, S., Takemura, T., and Kusunose, K.: High Pressure Triaxial Compression Test in Soft Sedimentary Rocks　—Relationship Between Loading Rate and Strength-Deformation properties—, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15718, https://doi.org/10.5194/egusphere-egu26-15718, 2026.

Across the central and western expanses of China, where soft rock formations dominate the geological landscape, arch bridges have long reigned supreme as the preferred structural choice. Their foundations, ingeniously engineered with a stepped-block configuration, boast exceptional overall rigidity—striking a masterful balance between structural integrity and economic efficiency by curbing infrastructure costs without compromising on deformation resistance. Drawing upon the foundational engineering of the Lantian Yangtze River Five Bridges, this study embarks on a profound investigation into the load-bearing behavior of stepped block foundations embedded within soft rock strata. It introduces a refined rigid-flexible judgment criterion and unveils an advanced, standard-anchored Optimization Specification C Method for stress-displacement analysis—a paradigm shift in computational precision. A novel analytical formula for the local shear failure angle is derived, shedding light on the underlying mechanics of shear collapse, while the verification framework for foundation deformation characteristics is meticulously enhanced. The culmination of this research is a comprehensive, high-fidelity bearing performance analysis system, exquisitely tailored for practical engineering application. Key findings reveal that both the rigid-flexible classification and the Optimization Specification C Method are eminently suited for assessing the bearing capacity of stepped arch foundations in soft rock environments, with design protocols firmly advocating for rigid foundation behavior under displacement-controlled criteria. The newly developed computational model transcends traditional limitations by delivering multidimensional output—capturing not merely singular values but the intricate spatial distribution of stress and displacement across the foundation zone. Remarkably, the Optimization Specification C Method achieves a 34% reduction in relative error compared to conventional standards, underscoring its superior accuracy, reliability, and real-world applicability. Critically, under conditions of global horizontal sliding of the arch structure, localized shear failure may initiate within the frontal rock mass adjacent to the stepped foundation. Furthermore, four distinct failure modes have been identified, each intrinsically linked to specific geometric configurations of the stepped block foundation—implying that optimal design must be guided by precise evaluation of the failure angle. By integrating bearing capacity assessments with stringent displacement control benchmarks, a holistic evaluation of foundation performance is achieved. While the current arch bridge foundation design successfully satisfies all load-bearing requirements, its deformation response reveals considerable untapped potential for refinement. Engineering case analyses further confirm that conventional single-dimensional performance checks, though inherently conservative and generally safe, fall short of capturing the full complexity of foundation behavior.

How to cite: Yang, X., Deng, W., and Yang, H.: A Masterful Symphony of Strength and Stability: An Exquisite Analysis System for the Load-Bearing Behavior of Stepped Block Arch Bridge Foundations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18283, https://doi.org/10.5194/egusphere-egu26-18283, 2026.

Digital Rock Physics (DRP) methods are increasingly used to link high‑resolution 3D imaging with the numerical determination of rock properties. In this work, we present new results from the SimBoL project, which applies this approach to drill cuttings from a borehole in Traunreut, southern Germany. The goal is to evaluate the potential of non‑core material for reliable petrophysical characterization relevant to geothermal applications.​

High‑resolution X‑ray computed tomography (CT) scans were segmented to obtain representative digital samples of carbonate cuttings, from which mineral composition, thermal conductivity and permeability were derived. A subset of these properties was computed using an updated numerical solver that incorporates periodic boundary conditions, enabling the treatment of irregular cutting geometries without relying on subvolumes or sample reshaping, and thereby allowing the use of larger rock volumes and a more realistic representation of heat and fluid transport processes than previous approaches restricted to cubic domains.​

The ongoing simulations yield quantitative estimates of rock properties that are compared with available borehole data and complemented by observations from thin sections. The analysis illustrates how digital twins of rock cuttings can deliver additional information on the internal architecture of reservoir rocks, reducing dependence on costly core material and strengthening the conceptual basis for geothermal reservoir characterization.

How to cite: Serje Gutierrez, A., Siegert, M., Gurris, M., and Saenger, E. H.: From Rock Cuttings to Physical Properties: Integrating Digital Rock Physics and Borehole Data from Traunreut, Southern Germany., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20706, https://doi.org/10.5194/egusphere-egu26-20706, 2026.

We compare and contrast physical properties (density, P-wave velocity) of volcaniclastic sediments with other uncemented marine sediments. We study cores collected by International Ocean Discovery Program (IODP) Expedition 398, which recovered more than 2200 m of volcaniclastic deposits from 12 sites and 28 holes from Santorini Caldera, Greece, and the surrounding rift basins in the South Aegean Volcanic Arc. The grain density (mass of solids divided by their volume, including any isolated vesicles) of volcaniclastic deposits is typically lower than that of volcanic glass and crystals and is sometimes less than 2 g/cm³, indicating the preservation of isolated gas-filled vesicles in erupted and then deposited materials. To complement bulk measurements, we also measured the total and isolated porosity in individual lapilli-sized volcanic clasts from four different volcanic deposits. We use xray computed tomography to image isolated pore space. Collectively, these measurements confirm that volcaniclastic sediments can preserve vesicle textures and isolated porosity for hundreds of thousands of years and at depths >500 m below sea-level and > 100 m below the seafloor

Volcaniclastic deposits typically have higher P-wave velocities but lower bulk densities than oozes and other marine sediments. In volcaniclastic deposits, lapilli have higher P-wave velocities and lower bulk density than ash, the opposite trend of most sediment in which higher density is correlated with higher seismic velocity. We use granular physics models to show that the higher volcaniclastic P-wave velocity originates from two effects: 1) lower pore volume outside clasts that increases elastic moduli and P-wave velocity and 2) isolated gas vesicles in volcanic clasts that lower bulk density with proportionally less effect on elastic modulii. In volcaniclastic sediments there is relatively little change in physical properties to depths of several hundred meters below the seafloor, which we attribute to rough grain surfaces and lower intergranular (external) porosities that resist compaction and the decrease of intergranular pore space relative to background marine sediment.  These trends lead to distinctive signatures of volcaniclastic sediments in reflection seismic images.

How to cite: Manga, M., Wright, V., Cadena, T., Susman, I., Escogido, C., Ward, S., Kelly, L., Fauria, K., McIntosh, I., Preine, J., Tominaga, M., Nomikou, P., Druitt, T., Kutterolf, S., Ronge, T., Hübscher, C., Karstens, J., and Yamamoto, Y. and the IODP Expedition 398 Scientists: Contrasting seismic velocity and compaction of marine calcareous oozes and volcaniclastic deposits, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4113, https://doi.org/10.5194/egusphere-egu26-4113, 2026.

Geothermal exploration drilling plays a crucial role in advancing the energy transition. To make the prospecting process more economical and time-efficient, the EU-funded GeoHEAT project has set the goal of developing methods that allow for obtaining the maximum amount of information about the subsurface with as little expense as possible. The project includes the development of a ground-penetrating radar (GPR) that can be used during borehole logging at elevated ambient temperatures. For the accurate interpretation of the GPR data, as well as for estimating the porosity and water content of the rocks surrounding the borehole, properties such as permittivity and electrical conductivity of these rocks are required. Here, we want to present the current progress of our research, which aims to determine the aforementioned characteristic properties using digital rock physics (DRP). Moving away from standardized cylindrical samples and using irregularly shaped by-products of the drilling process, known as drill cuttings, we can provide a more comprehensive understanding of the subsurface, thereby improving the characterization of potential geothermal reservoirs.

Core sampling during exploration drilling is costly and time-consuming, as it interrupts the operation. In addition, cores are often taken from only a few sections in order to keep the added costs low. However, these samples are necessary for laboratory testing, as sufficiently large and smooth contact surfaces must be available to ensure that the respective measurement devices deliver accurate results. No such requirements exist in DRP, as simulations are performed at the pore scale and therefore very small samples without flat surfaces, such as irregular drill cuttings, can be used.

The DRP workflow consists of three main steps. First, high-resolution computed tomography scans are taken of a small sample. These are then processed into a digital twin using segmentation, where the individual phases, such as minerals or pores, are distinguished from one another so that specific properties can later be assigned to them in this location-dependent volume. In combination with our finite volume method code, which solves a stationary potential equation, this digital model can be used to simulate the desired effective properties.

In previous studies, an early implementation of our code demonstrated reliable results for frequencies greater than 1 MHz. By implementing preconditioners, we now simulate lower frequencies with highly accurate results where before the increase in polarization led to code instabilities. Additionally, we fully validated the code on comparative data, such as analytical solutions and laboratory measurements of a high-porosity sandstone and a low-porosity granite. In the future, we will investigate how changes during the creation and transport of drill cuttings influence the accuracy of the results, thereby contributing further to a more efficient approach to geothermal exploration.

How to cite: Kerkmann, N., Siegert, M., Finger, C., Shakas, A., and Saenger, E. H.: Frequency-Dependent Effective Electrical Properties of Suboptimal Rock Samples through Digital Rock Physics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8989, https://doi.org/10.5194/egusphere-egu26-8989, 2026.

The Dogger geothermal reservoir of the Paris Basin is one of the most actively exploited carbonate aquifers in France and serves as a key target for sustainable district-heating systems. It consists mainly of Middle Jurassic carbonates deposited on a ramp, where sedimentary facies and diagenetic overprinting produce strong spatial heterogeneity. Understanding the heterogeneous petrophysical distributions is essential for predicting fluid circulation and designing subsequent geothermal operation plan. However, petrophysical interpretations derived from geophysical methods remain scale-dependent: laboratory acoustic measurements, well logs, and seismic data have different resolutions, making it challenging to reconcile acoustic signatures and to map heterogeneity consistently across scales.

To address these challenges, we conducted ultrasonic transmission experiments on core fragments taken from the SEIF-01 geothermal well in Melun area to determine Vp and Vs across key facies types. We further measured pressure-dependent Vp-Vs variations on cylindrical plugs, to better understand how the sedimentary microstructures and crack closure control the seismic velocity. Using seismic rock velocity models, we interpret the influence of pore shape (measured by pore aspect ratio) and fluid on the seismic velocity, to provide a quantitative link between micro-scale pore geometry and macroscopic elastic properties.

Finally, we will integrate the laboratory results with in-situ sonic logs and 2D seismic reflection data to bridge acoustic observations across scales. This multi-scale integration provides new insights into the internal heterogeneity of the Dogger reservoir and improves the interpretation of geophysical datasets for geothermal development. Our results highlight the potential of combining ultrasonic experiments, well logs, and seismic data, to better constrain reservoir properties and support more reliable geothermal resource assessment in heterogeneous carbonate systems.

How to cite: Wang, H.-M., Bailly, C., Brigaud, B., Bordenave, A., Issautier, B., Pwavodi, J., Samuel, C., Fortin, J., Le Romancer, C., Ould braham, R., Hamm, V., Maurel, C., Bonte, D., Sosio, G., and Stopin, A.: Integrating the multi-scale elastic velocities for interpreting and predicting the Dogger carbonate geothermal reservoir, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13896, https://doi.org/10.5194/egusphere-egu26-13896, 2026.

     The thermal conductivity and thermal diffusivity of minerals and rocks under high temperature and pressure can provide data supporting for historical simulation of geological processes, and they are also necessary parameters for establishing the thermal structure of deep layer under a stable state.

     Amphibolite is a crucial component of the continental crust and subduction zone. The physical properties of amphibolite are of great significance for understanding the physical structure of the continental crust and subduction zones. In this study, using a thermal properties testing platform on a hinged cubic press, the thermophysical properties of two types of amphibolite were studied at 0.5-1.5 GPa and 300-973 K by the transient plane heat source method. The experimental results show thermal conductivity and thermal diffusivity decrease with the increasing of temperature and increase with the increasing of pressure. The influence of temperature on these parameters is much greater than that of pressure. Under fixed pressure, the thermal conductivity can vary up to 15.1% with temperature changes, while the thermal diffusivity can vary up to 40.0%. Under fixed temperature, the influence of pressure on the thermal conductivity can reach up to 23.4% and the influence on the thermal diffusion coefficient can reach up to 15.7%. The experimental data were successfully fitted using empirical formulas. The thermal conductivity and thermal diffusivity of garnet amphibolite in this study is notably higher than those of amphibolite without garnet and those reported in previous studies, so it is believed that the presence of garnet significantly enhances the thermal conductivity of amphibolite.

     Combining high-temperature and high-pressure data from previous studies as well as this study and the parameters of the thermal lithosphere model, the thickness of the thermal lithosphere in different regions of the North China Craton under different surface heat flows was calculated. The results reveal that within a surface heat flow range of 50-80 mWm^-2, the thermal lithosphere thickness of the Bohai Basin varies between 49.8 and 145.7 km, the thickness of the central orogenic varies belt between 53.3 and 201.5 km, and the thickness of the Ordos Basin varies between 54.4 and 231.2 km.

How to cite: Yi, L. and Ma, W.: Thermal properties of garnet-bearing amphibolite at high temperature and pressure and its impact on the thermal structure of the lithosphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15505, https://doi.org/10.5194/egusphere-egu26-15505, 2026.

A swarm of m-scale dikes, made of diabase and porphyritic microgranite, related to a ca. 420 Ma bimodal tholeiitic magmatism crops out in the Rocroi Inlier, a Lower Paleozoic inlier exposed in the Ardenne Allochton (western Rhenohercynian Zone, European Variscan Belt). These dikes are affected by a more or less penetrative cleavage and their magmatic mineralogy has been replaced to various degrees by secondary minerals such as albite, chlorite, sericite, epidote and calcite, as a consequence of Pennsylvanian Variscan deformation and associated low-grade metamorphism. The thickest dikes (thickness from 3-4 to 10-15 m) display a deformation gradient from the border zones which has a penetrative cleavage to the core which is little or even apparently not deformed.

We have conducted measurements of the anisotropy of magnetic susceptibility on samples collected along transversal sections across five thick dikes from the Rocroi Inlier, two made of diabase and three of microgranite. The bulk magnetic susceptibility (K_m) has typical paramagnetic values, 5.8-14.0 x 10^-4 SI in the diabase and 0.4-6.4 x 10^-4 SI in the microgranite, except in the core of one diabase dike where magnetite occurs, ca. 580-890 x 10^-4 SI. The corrected anisotropy degree (P’) tends to have high values, up to ca. 1.8, in the deformed border zones and decreases towards the core. This parameter is therefore a proxy of the petrofabric strength. The shape parameter (T) reveals a predominantly oblate magnetic fabric, which suggests a prevailing coaxial deformation, in agreement with a previous finite strain study.

Magnetic foliation in the deformed border zones is parallel to dike margin, as well as to cleavage both in diabase or microgranite and in metapelites at the contact with the intrusion. It rotates a few degrees when moving away from the dike walls. Magnetic lineation is orientated down-dip on the foliation plane and is therefore also slightly deflected across the dikes. The mean magnetic foliation dip, hence the mean lineation plunge is ca. 30-60° to the S-SE. This orientation is roughly similar to that of the main (Variscan) cleavage in the metapelitic host rocks which bears a down-dip stretching lineation. However, magnetic fabric in the dikes and petrofabric in the country rocks outside the contact zone with the intrusions are slightly oblique (up to ca. 30°). Such a discrepancy possibly results from fabric refraction due to competence contrast with the host rocks. Incomplete transposition of the magmatic fabric by the Variscan deformation, as observed in particular in some microgranite samples, could also play a role here, by influencing the orientation of the magnetic fabric.

How to cite: Bolle, O., Bopda Tala, N., and Custine, E.: Heterogeneous Variscan deformation in late Silurian–early Devonian diabase and microgranite dikes of the Caledonian Rocroi Inlier (Ardenne Allochthon, France) quantified using anisotropy of magnetic susceptibility (AMS), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18866, https://doi.org/10.5194/egusphere-egu26-18866, 2026.