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This paper reports on the use of discrete element method to investigate the deformation and failure characteristics of an argillite consequent slope presenting signs of creeping and deformation. The proposed numerical model (based on Burgers model) takes into account the friction coefficient, bonding stiffness, and strength of the constituent materials, as well as the stiffness and strength of interlayer bonds. Weak plane bonding was identified as the key factor determining the sliding and deformation of slopes, with a far greater effect than the friction coefficient, bonding stiffness, or strength of interlayer weak planes. Nonetheless, continued monitoring and comparative analysis of all of these parameters may still be necessary to produce reasonable simulations of slope sliding behavior.

We report laboratory experiments to investigate the evolution of gas-transport properties of COx argillite along drying and wetting paths, in the context of deep underground nuclear waste disposal. The gas injection technique was used to simultaneously measure the variations of gas accessible porosity ( ϕ ag ) and gas permeability ( K g ) under different confining pressures ( P c ) and relative humidity (RH). Our results show that porosity (dry samples) and water saturation measured or derived by the gas injection technique are in good agreement with the conventional water vapor equilibration method, which confirms the quality and efficiency of the technique. Furthermore, the different changing magnitudes of ϕ ag and K g measured in the wetting and drying paths are attributed to the fact that the swelling deformation is greater than the shrinkage deformation. A coupling effect is observed between P c and RH. Specifically, when the sample is in a dry (or quasi-dry) state, relative gas accessible porosity ϕ rag does not (or negligibly) vary with P c , whereas the relative gas permeability ( K rg ) shows a strong sensitivity to P c . This is due to crack closure, which increases the tortuosity of the pores and/or causes part of the pores to be “crack closing”. However, in the highly saturated case, both ϕ rag and K rg become more and more sensitive to P c . This is caused not only by the crack closing but also by the softening of the material and the redistribution of saturation. Highlights This work aims to study the gas-transport properties of COx argillite during the drying and wetting paths. The gas injection technique was used to measure accessible gas porosity and effective gas permeability under different confining pressures and relative humidity. The porosity (dry samples) and water saturation derived by the gas injection technique are in good agreement with the conventional water vapor equilibration method. A coupling effect was observed between confining pressures and relative humidity.

Quantifying time-dependent rock mass degradation is critical for assessing long-term slope stability during open-pit mine closure. This study evaluates the geotechnical evolution of Paleoproterozoic arenites and argillites in the semi-arid Essakane Main Zone (Burkina Faso) over a 0–9-year atmospheric exposure period. Field characterization across 32 sampling stations included density measurements, point load testing (Is(50)), determination of the Geological Strength Index (GSI), and petrographic analysis. The results demonstrate a time-dependent reduction in physico-mechanical properties, modeled with a high correlation (R2 = 0.80–0.99). While density exhibited minor reductions, structural degradation was pronounced; the GSI decreased by 10 points for both lithologies, and Is(50) dropped significantly, particularly in argillites (4.1 to 2.3 MPa) relative to arenites (4.0 to 3.6 MPa). Petrographic evidence indicates negligible chemical weathering and mineral neoformation. Consequently, the degradation was attributed primarily to physical processes, specifically microcracking and discontinuity deterioration driven by thermal cycling and phyllosilicate sensitivity in argillites. These empirical relationships provide essential quantitative input for numerical slope stability modeling in semi-arid mine closure scenarios.

Bulk modulus is one of the mechanical properties used in any rock engineering related project. This property can be measured statically, where it is derived from stress–strain data, and dynamically, where it is derived from P- and S-wave velocities. The static bulk modulus is generally different from the corresponding dynamic bulk modulus. As the static bulk modulus is required in computation or modelling of the deformation of the rock when it is stressed hydrostatically, empirical relationships between the static and dynamic bulk moduli are needed to convert the dynamic bulk modulus to static values. In this study, the static and dynamic bulk moduli were measured simultaneously, at effective pressures up to 130 MPa, for dry and fluid-saturated argillites. The samples were collected from four different lithofacies within the upper Naparima Hill Formation, Trinidad. The results show that the dynamic bulk modulus is greater than the static bulk modulus, except for hard lithofacies under dry conditions where the static and dynamic moduli are approximately equal. Under saturated conditions, the porosity plays a key role in increasing the difference between the static and dynamic bulk moduli. A linear relationship with high correlation (R2 greater than 0.85) was established between the static and dynamic bulk moduli, which is dependent on the effective pressure and saturation state.

Fast drying (∼60 min) is useful for optimizing production processes by increasing productivity and reducing costs and environmental impacts, especially in red ceramic industries in Brazil. However, suitable clays are necessary and, currently, studies focused on the plastic behaviour of clays with compositions suitable for extrusion, especially for fast drying, are scarce. Therefore, in this study, three different clays from the same mineral deposit were studied for producing clay-based structural products via fast drying. The clays were characterized according to their chemical, mineralogical and thermal properties, particle size, cation-exchange capacity, specific surface area and open pore volume distribution. Ten formulations were developed using a simplex-centroid mixture design of experiments and their plasticity index (PI) values were determined. The response surfaces of the formulations were evaluated according to their PI, while the formation characteristics were determined according to their extrusion workability factor values. Formulations F5 (50.0 wt.% yellow clay and 50.0 wt.% green clay) and F8 (66.6 wt.% yellow clay, 16.7 wt.% grey clay and 16.7 wt.% green clay; PI = 15.5-16.6%) displayed optimal extrusion properties, followed by formulations F7 (33.3 wt.% yellow clay, 33.3 wt.% grey clay and 33.3 wt.% green clay) and F10 (16.7 wt.% yellow clay, 16.7 wt.% grey clay and 66.6 wt.% green clay; PI = 13.8-14.2%), which are within acceptable extrusion index values. Thus, the chosen formulations have significant potential for use in the manufacture of fast-drying red ceramics.

Significantly elevated U, Mo, Zn and Pb contents characterize the Early Ordovician black shales in the Sillamäe area, NE Estonia. The presence of silty interlayers with sulphidic mineralization and authigenic carbonates suggests unique physicochemical conditions for metal enrichment in this location. We investigated metallogenesis of these shallow-water black shales based on high-resolution mapping of element distribution in the Sõtke drill core and nearby Päite outcrop using X-ray fluorescence spectroscopy, inductively coupled plasma mass spectrometry and organic elemental analysis, complemented by optical microscopy and scanning electron microscopy of selected samples. Enriched metals in the black shales of the study area show dissimilar distribution trends with sharp vertical concentration gradients. The recorded variance ranges were 88–275 ppm for U, 70–2467 ppm for Mo, 85–1600 ppm for V, 21–17 283 ppm for Zn and 95–26 549 ppm for Pb, while total organic carbon varied from 0.5 to 13 wt%. In most cases, the metals showed no clear covariance with organic matter or other major compounds such as S or P. The development of a sulphate reduction zone near the sediment–water interface with a sharp decrease in Eh, production of H2S, elevated alkalinity and pH, and (re)distribution of phosphorus probably controlled the syngenetic capture of Mo and U. Enhanced transfer of fluids and solutes in coarse-grained permeable beds facilitated the accumulation of metals, while the deposit probably acted as a semi-open geochemical system throughout its geological evolution. Local Zn and Pb enrichment developed due to the intrusion of late diagenetic metal-bearing fluids and the entrapment of metals in beds that contained authigenic carbonates.

The chemical extraction of rare-earth elements (REEs) from Estonian graptolite-argillite (GA) and phosphate rock (Phosphorite, PH) samples has been conducted and analyzed. For the initial leaching process, HCl and HNO3 with different concentrations were used to extract REEs from GA and PH. Different extraction agents, including ionic liquids, were examined for the extraction of REEs from acidic aqueous solutions in the liquid–liquid extraction step. After leaching and extraction, all samples were characterized using the inductively coupled plasma mass spectrometry method (ICP-MS/MS). The highest REE extraction efficiencies from GA were established with 1-ethyl-3-methyl imidazolium diethyl phosphate (EMImDEPO4) and from PH using bis(2-ethylhexyl) phosphate (D2EHPA).

Lower Paleozoic black shales from Estonia, Sweden, and Russia were analyzed for major and trace elements to reconstruct the provenance, tectonic setting, and paleoweathering conditions of these shales. The black shale is highly enriched in U, V, Mo, and Pb (except in samples from Sweden where Pb is slightly enriched), slightly enriched in SiO2, Fe2O3, K2O, and TiO2 and highly depleted in CaO, Na2O, and MnO, with respect to average shales. The provenance signatures (Th/Sc versus Zr/Sc, Al2O3 versus TiO2, Zr versus TiO2 plots, and Zr/Sc ratio) of the Baltoscandian black shales suggest that they were derived from rocks of intermediate to felsic composition and from recycled sediments. The likely provenance region was the Paleoproterozoic igneous and metamorphic basement of southern central and southern Finland, which consists predominantly of felsic to intermediate metamorphic (acidic to intermediate gneisses, felsic volcanics, microcline granites and migmatites) and igneous rocks (small granitic intrusions and large rapakivi granite intrusions), and reworked older Ediacaran and Lower Cambrian sediments; however, the proportion of clastic input from these sources is not uniform in the three regions studied. The discrimination of the tectonic settings of source materials of the black shale using the SiO2 versus K2O/Na2O plot and a new discriminant method (APMdisc) favors a passive margin setting. The Chemical Index of Weathering (CIW) indicates that the clastic material in the black shale of the studied regions has experienced an intense degree of chemical weathering. Weathering indices (Chemical Index of Alteration CIA and CIW) also show that the black shale has experienced significant secondary potassium enrichment.

This work presents the results of a multi-technique comparative investigation aimed at assessing the mineralogical composition and radioactivity levels of two stone fragments from different areas of the archaeological site of Halaesa (Sicily, Italy). The analysis employed an integrated approach combining μ-energy-dispersive X-ray fluorescence (μ-EDXRF) spectroscopy, µ-Raman spectroscopy, X-Ray Diffraction (XRD), ion chromatography (IC), High-Purity Germanium (HPGe) gamma spectrometry, and E-PERM electret ion chamber methods. By examining the stone composition at both the elemental and molecular scales, with support from ion chromatography data, potential degradation patterns linked to post-depositional weathering and external decay agents were identified. Moreover, the specific activity of radionuclides (226Ra, 232Th, and 40K) and the 222Rn exhalation rates were measured, enabling the estimation of a set of radiological indices that assess potential health hazards associated with prolonged exposure to these lithic materials. The findings highlight how a multidisciplinary approach can foster the assessment of stone deterioration mechanisms, supporting the design of optimized conservation strategies aimed at preserving the archaeological heritage of Halaesa and ensuring the safety of both the public and onsite personnel.