The DIGIT experiment was launched at the Tournemire Underground Research Laboratory (URL) with the aim of determining the effects of temperature on the transfer of tracers mimicking the most mobile radionuclides in the Toarcian clay rock. The properties of this rock are similar to those of the host rocks being considered for a future deep geological repository for high-level radioactive waste (HLW). The experiment involves the monitoring of the interaction between a test water doped with stable halides and deuterium at constant concentration, and the porewater of the Toarcian clay rock under constant ambient conditions, as well as at higher temperature induced by artificial heating. This experiment seeks to partially address questions regarding the potential spread of contaminants during the thermal phase of HL waste packages. Specifically, the in situ experiment aims to evaluate the role of scale effects, thermodiffusion, a process that combines Fick's law, the Soret effect, and convection in the transfer of radionuclides. This paper is the second part of a companion paper dedicated to predictive calculations and the installation of the experimental device. It presents the main experimental and modeling results obtained since the beginning of the installation and after 20 months of heat at 70 degrees C. The test was carried out in five phases, finishing with a sampling campaign: a phase 0 called "initial conditions", followed by a pure diffusion phase (5 months), then three phases in a heated period lasting 1 year and 8 months. In total, 47 rock cores were analyzed, with approximately 170 samples tested by four diffusion methods (radial, outgoing, through and in vapor-phase) to determine the tracer concentrations in the porewater, their water content and their diffusive transport parameters. The results show a decrease in tracer concentrations with distance from the test zone, in the directions parallel and perpendicular to the stratification. The anisotropy of the medium results in greater migration in the direction parallel to the stratification. Thermal properties also confirm anisotropy with a higher thermal conductivity in the direction parallel to the stratification. Finally, an activation energy of 22.9 +/- 1.7 kJ & centerdot;mol-1 could be proposed by NMR for deuterium, indicating diffusion behavior following an Arrhenius law between 30 and 70 degrees C. The experimental data allowed for the calibration of a 2D axisymmetric numerical model using the commercial finite element software COMSOL Multiphysics (R). The Fick's law corrected by an Arrhenius law best reproduces the penetration of deuterium and anions. The Soret effect, integrated into certain scenarios, is only significant for anions' migration, using a fitted Soret coefficient of 0.1 K-1, as proposed in the literature for the Callovo-Oxfordian, the host rock of the Cig & eacute;o project in the east of France. The calibration of the simulated data with the experimental data allowed for the characterization of damaged and/or disturbed zones evolving over time. Simulations over 150 years, the duration of the thermal maximum for HLW packages, show that advection-modeled by Darcy's law-would have a negligible role in this context due to the low permeability of the upper Toarcian. In conclusion, the DIGIT test showed that, for the Upper Toarcian clay rocks at the Tournemire URL in France, diffusion, corrected for the effect of temperature, is the mechanism that characterizes the transport of radionuclide analogues. The study showed that thermodiffusion has a limited influence on deuterium migration but remains significant for anions in the case of a coupling between temperature correction and thermodiffusion. The test also highlighted the impact of temperature on the spatiotemporal development of a damaged and/or disturbed zone. These new and relevant results in the field will need to be confirmed later through additional experiments.

Cemented paste backfill (CPB) is a key material in underground mining, providing essential ground support while aiding in tailings management. However, current research has overlooked the combined effects of horizontal rockwall closure stress and vertical self-loading stress, referred to as multiaxial stress, on the CPB’s consolidation behavior and its mechanical properties development. Understanding and assessing these effects is critical because they directly affect the stability and performance of CPB structures. In this study, a novel multiaxial compressive stress curing and monitoring apparatus was used to simulate two horizontal rockwall closure scenarios with a consistent backfilling rate, under both drained and undrained conditions. Key parameters assessed included unconfined compressive strength (UCS), deformation during curing, stress-strain behavior, and modulus of elasticity. The results highlight that rockwall closure, combined with vertical stress, plays a pivotal role in the consolidation behavior of CPB, significantly affecting key mechanical properties. Higher horizontal stress from faster rockwall closure intensified compression during curing, leading to reduced porosity, enhanced particle rearrangement, and accelerated consolidation. This intensified consolidation leads to notable improvements in mechanical properties, including increased UCS, enhanced stiffness, and a higher modulus of elasticity, indicating improved load-bearing capacity. Moreover, the interaction between multiaxial stress and drainage conditions influenced stress-strain behavior and deformation, with drained conditions promoting earlier plasticity and higher peak stresses. These findings underscore the critical influence of multiaxial stress, combined with drainage conditions, on CPB performance, offering valuable insights for optimizing CPB design in underground mining applications.

In deep underground mines, cemented paste backfill (CPB) is subjected to complex multiaxial stress conditions, including vertical self-loading and horizontal rockwall closure, which can significantly influence the evolution of pore water pressure (PWP). Understanding PWP development under these conditions is essential for ensuring barricade stability and the long-term performance of CPB structures. This study investigates the development of PWP in CPB under realistic deep mine conditions, particularly focusing on multiaxial stress loading and drainage availability. A novel multiaxial stress curing and monitoring apparatus was employed to simulate these coupled conditions and comprehensively capture the evolution of both positive and negative PWP within CPB throughout a 28-day curing period. Although the apparatus can impose field-like temperature histories and drainage boundaries, the present tests fix temperature to isolate mechanical and drainage effects. Groundwater inflow is not explicitly simulated; instead, controlled drainage boundaries are employed to bracket typical deep-mine backfill drainage conditions. Results indicate that horizontal rockwall closure stress significantly amplifies the magnitude and prolongs the duration of positive PWP by actively confining and entrapping pore water, resulting in notably higher peak PWP values and stress-induced pore pressure coefficients (Cn) compared to CPB subjected solely to vertical stress. Practically, this means that even at the same filling rate, CPB material subjected to additional horizontal rockwall closure in deep mines can experience significantly higher positive PWP, thereby increasing the load exerted on barricades at early curing stages and elevating the risk of barricade failure. As curing progresses and positive PWP dissipates, it eventually drops below zero, leading to the development of negative PWP (suction). To interpret this suction development, the study adopts the concept of the air-water interface (meniscus) from unsaturated soil mechanics, illustrating how curing-induced changes in pore structure influence meniscus curvature and consequently affect suction magnitude. Horizontal closure stress promotes consolidation and densification of CPB-supported by mercury intrusion porosimetry (MIP) and thermogravimetric (TG) analyses-which reduces pore size and enhances pore water consumption. This densification leads to smaller pore sizes, generating menisci with smaller radii of curvature, thereby increasing suction (negative PWP). However, rapid and high-magnitude horizontal stresses (rockwall closure 2) at later curing stages can induce a "resaturation effect," partially reversing this beneficial suction increase, whereas moderate horizontal closure stress (rockwall closure 1) allows stable suction development throughout curing. Furthermore, introducing drainage under multiaxial stress conditions significantly mitigates elevated positive PWP by facilitating rapid dissipation of excess pore water. Drainage also effectively prevents the "resaturation effect" even under high horizontal closure stresses (rockwall closure 2), maintaining higher and more stable suction in CPB throughout curing. These findings underscore the critical influence of multiaxial stress conditions on pore water pressure in CPB, emphasizing the necessity of accounting for these coupled factors in order to manage pore pressure effectively, ensure barricade safety, and enhance the overall stability of CPB in deep mining operations.

Cemented paste backfill (CPB) is a sustainable construction material produced by mixing mine tailings, water, and a small proportion of binder to fill underground mine voids. Widely used in modern underground mining operations, CPB provides critical ground support, enhances mining safety by reducing void spaces, improves ore recovery, and minimizes the environmental risks associated with surface tailings storage. In this context, slag-based alkali-activated binders have emerged as promising low-carbon alternatives to Portland cement for CPB applications; however, the hydration mechanisms governing hybrid carbonate–hydroxide activation under the high water-to-binder conditions typical of CPB remain insufficiently understood. This study investigates the hydration mechanisms, microstructure evolution, physical property development, and strength performance of slag-based CPB activated with blended sodium carbonate (SC) and sodium hydroxide (SH). A systematic evaluation of SC/SH ratios and total activator dosages was conducted under realistic CPB conditions. To elucidate early-age hydration kinetics and matrix densification processes, a multi-parameter monitoring framework integrating electrical conductivity (EC), volumetric water content (VWC), and matric suction (ψ) was implemented. Hydration products and phase assemblages were characterized using X-ray diffraction (XRD), while physical properties and uniaxial compressive strength (UCS) were evaluated over extended curing periods. Results show that hybrid SC–SH activation fundamentally alters hydration pathways relative to Portland cement systems, promoting the formation of a composite phase assemblage dominated by amorphous C-(A)-S-H gels, calcite, and hydrotalcite-like phases. The hydration process follows a distinct two-stage mechanism consisting of an initial ionization–retardation stage with elevated ionic concentration and limited water consumption, followed by a deionization–acceleration stage characterized by rapid gel precipitation, progressive water binding, and pore structure refinement. Balanced SC/SH ratios significantly shorten the retardation period and enhance matrix densification, as indicated by decreasing EC and VWC and increasing matric suction. Among the formulations investigated, the SC/SH 50/50–10

The incorporation of supplementary cementitious materials (SCMs), such as blast furnace slag (BFS) and fly ash (FA), provides a promising strategy to optimize cemented paste backfill (CPB) by reducing operational costs, enhancing durability, and reducing the carbon footprint. This study systematically investigates the effects of partially replacing cement with BFS or FA on the autogenous self-healing behavior of the CPB system. Four binder blend ratios (i.e., cement/SCM mass ratio of 100/0, 80/20, 50/50, and 20/80) were evaluated based on crack closure observations, uniaxial compressive strength, hydraulic conductivity, and porosity-related parameters. Results show that the appropriate BFS contents promote self-healing efficiency at early and long-term healing stages compared with cement-only CPB, attributed to the secondary latent hydraulic reactions between BFS and calcium hydroxide, leading to the formation of calcium–(alumino)–silicate–hydrate (C–(A)–S–H) gels and microstructural densification. The pre-cracked Portland cement type I (PCI)/BFS 50/50 specimens exhibited the highest healing efficiency at 28 d of self-healing, with strength exceeding the uncracked control by 17.2

This paper investigates solute transport processes in the bentonite buffer of a Deep Geological Repository (DGR) for used nuclear fuel, using the Canadian concept as an example. The design relies on a multi-barrier system in which the used fuel container (UFC) provides containment and the surrounding bentonite buffer protects the UFC while retarding radionuclide migration following a potential breach. Solute transport in the buffer is strongly influenced by coupled thermal-hydraulic-mechanical (THM) processes. A coupled THM-transport model was developed to evaluate (1) reactive transport of bisulfide (HS^-) from the host rock to the UFC and associated UFC corrosion; and (2) radionuclide migration following a hypothetical UFC breach. The model builds on previous verification and validation and is further assessed against laboratory-scale bisulfide transport experiments and a large-scale thermal diffusion experiment at the Tournemire Underground Research Laboratory (France). The results show that temperature-dependent diffusion is the dominant transport mechanism, significantly enhancing solute migration, whereas hydraulic desaturation has limited influence and the Soret effect is negligible at repository scale. Under the reference conditions, adsorption and FeS precipitation delay detectable HS− flux to the UFC until approximately 5 × 105 years and limit the predicted corrosion depth to 0.05 mm after one million years. In the breach scenario, the buffer effectively delays and attenuates moderately/strongly sorbing radionuclides (e.g., 135Cs, 237Np). The effectiveness in retarding radionuclides' migration is most sensitive to bentonite diffusivity and sorption capacity.

Rockwall closure in deep underground excavations commonly develops at different rates along two horizontal directions, leading to anisotropic stress conditions during the curing of tailings-based cementitious composites (commonly referred to as cemented paste backfill, CPB). However, the influence of such directional stress paths on the mechanical development of these composites during stress-assisted curing remains insufficiently quantified. This study systematically investigates how unequal horizontal closure rates generate horizontal stress anisotropy and thereby govern strength development, deformation behavior, matric suction evolution, and failure characteristics of a tailings-based cementitious composite cured under multiaxial stress conditions. Using a multiaxial stress-curing apparatus, specimens were subjected to identical vertical stress histories while horizontal stresses were applied with different directional balances, representing isotropic horizontal confinement (RC100:100), moderate horizontal anisotropy (RC100:50), and extreme horizontal anisotropy (RC100:0). The results demonstrate that the directional balance of horizontal confinement fundamentally controls how curingstage stresses are translated into the evolving mechanical performance of the cementitious matrix, even under comparable cumulative stress exposure. Isotropic horizontal confinement consistently produced the highest unconfined compressive strength (UCS) at all curing ages, reflecting efficient three-dimensional densification and enhanced structural continuity of the hardened composite. Moderate horizontal anisotropy resulted in reduced but sustained strength development, whereas extreme horizontal anisotropy led to pronounced late-age strength degradation despite high applied horizontal stress. These findings indicate that strength evolution is governed not only by stress magnitude or duration, but critically by the directional balance of horizontal confinement during curing. Matric suction measurements provide complementary pore-scale insight into hydration-driven and deformation-induced microstructural evolution. Although anisotropic stress paths generated higher suction magnitudes than isotropic confinement over much of the curing period, increased suction did not necessarily translate into higher UCS. Under extreme anisotropy, damage-dominated pore evolution suppressed late-age resaturation and limited the mechanical contribution of suction enhancement. Deformation measurements further revealed that increasing anisotropy progressively reduces compaction efficiency: isotropic horizontal confinement achieved the largest volumetric strain (10.03%), moderate horizontal anisotropy produced intermediate densification (8.15%), and extreme horizontal anisotropy resulted in the lowest volumetric strain (6.28%) despite large directional deformations. Stress-strain responses and failure observations confirmed that unequal horizontal confinement fundamentally alters deformation and failure behavior of the hardened composite. Overall, this study establishes a mechanistic framework linking curing-stage stress anisotropy to the evolving microstructure, mechanical performance, and structural integrity of tailings-based cementitious composites under realistic multiaxial confinement conditions.

Cemented paste backfill (CPB) is an innovative cementitious construction material widely used in modern underground mining to provide ground support while enabling the sustainable management of mine waste (tailings). However, the formation of cracks within CPB structures remains a persistent challenge that threaten long-term mechanical stability and durability. Recent studies increasingly demonstrate that CPB possesses a promising self-healing capacity, allowing recovery of mechanical strength and permeability without external intervention. This review presents a comprehensive and critical synthesis of current advances in the understanding of self-healing behaviour in CPB, integrating experimental evidence with fundamental concepts established for conventional cementitious materials. The mechanisms governing crack formation in CPB are systematically examined, followed by an in-depth review of autogenous and autonomous healing pathways, with particular emphasis on continued hydration, carbonation, and mineral precipitation processes. The influences of key governing parameters, including curing age, crack geometry, temperature, drainage conditions, stress state, and chemical environment, are comprehensively assessed. Special attention is given to the role of mineral additives (e.g., blast furnace slag and fly ash) and emerging biological approaches based on microbially induced calcite precipitation, while identifying important knowledge gaps related to silica fume and conventional chemical admixtures. Experimental techniques employed to characterize CPB self-healing are synthesized, encompassing crack closure, mechanical strength and permeability recovery, microstructural imaging, and chemical and mineralogical analyses. By consolidating fragmented knowledge across disciplines, this review clarifies the mechanisms controlling CPB self-healing, identifies limitations of existing laboratory-scale studies, and outlines priorities for Multiphysics modeling, field-scale validation, and the development of hybrid self-healing systems. This paper establishes self-healing as a quantifiable and design-relevant property of CPB, supporting the advancement of more resilient, durable, and low-carbon underground backfill systems.

The thermo–hydro–mechanical response of a bridge pile foundation–soil system subjected to degrading permafrost conditions was investigated using an integrated numerical framework that explicitly coupled heat transfer, moisture migration, phase change, and mechanical behaviour. A representative bridge along the Inuvik–Tuktoyaktuk Highway was analyzed under three projected climate warming scenarios over a 75-year design period. The model quantified the long-term evolution of ground temperature, active layer thickness, thaw settlement, adfreeze bond degradation, axial pile capacity, and lateral pile displacement under combined thermal and mechanical effects. The results showed progressive warming and deepening of the active layer, leading to intensified thaw settlement and substantial loss of ice-bond resistance along the pile–soil interface. The axial bearing capacity decreased by up to 14

Pile foundations in cold and seasonally freezing regions are frequently subjected to simultaneous vertical and lateral loads, while soil properties evolve with temperature due to freeze–thaw processes. Conventional design approaches commonly treat axial and lateral responses independently and often neglect temperature-induced variations in soil–pile interaction, potentially leading to inaccurate performance predictions. This study develops a fully coupled thermal–hydro–mechanical (THM) multiphysics model to investigate pile behaviour under combined vertical and lateral loading in thermally variable soils. The model incorporates temperature-dependent soil properties, an elastoplastic constitutive relationship, and an explicit soil–pile interface formulation that accounts for frictional contact and temperature-sensitive adfreeze bonding. Gravity and pore-water pressure effects are included to ensure physically consistent stress evolution. The governing equations are implemented in COMSOL Multiphysics. The model is validated against two independent physical model tests involving freeze–thaw cycles and combined loading conditions. It is then applied to simulate the seasonal response of a free-head pile embedded in representative Ottawa soils under unfrozen, frozen, and partially frozen states. Parametric analyses demonstrate that both axial and lateral capacities increase as temperature decreases due to ice formation and enhanced interface bonding. Lateral loading is found to improve axial capacity across thermal regimes, whereas the influence of axial loading on lateral capacity is temperature-dependent and not consistently beneficial. The proposed framework provides a comprehensive tool for evaluating pile performance under interacting mechanical and thermal effects and offers insight into foundation design in seasonally cold regions subject to evolving climate conditions.

Abstract This study investigates the influence of realistic summer daily thermal cycles on the mechanical, hydraulic, and microstructural properties of cement-stabilized sensitive marine clay (SMC), a problematic marine soil widely found in Eastern Canada. SMC samples treated with 5% and 20% cement were subjected to two curing regimes: constant temperature (20 °C) and simulated daily thermal cycles, and tested after 1, 3, 7, and 28 days of curing. Unconfined compressive strength (UCS) and secant modulus tests were performed to assess mechanical performance, while matric suction monitoring, thermogravimetric analysis (TG/DTG), and mercury intrusion porosimetry (MIP) were used to evaluate hydration behavior and microstructural evolution. Results show that daily thermal cycles significantly accelerate strength and stiffness development at early curing stages by enhancing cement hydration, leading to finer pore structures and higher matric suction due to rapid self-desiccation. However, a “crossover effect” was observed in TG/DTG results, where prolonged thermal cycling reduced hydration product formation at later stages. MIP results, in contrast, showed continued microstructural densification, likely due to a dilution effect associated with high water-to-cement ratios. These findings provide practical insights for optimizing curing strategies and binder dosages in road and infrastructure projects involving sensitive marine clays under fluctuating thermal conditions.

This paper investigates the long-term evolution of the engineered barrier system of a deep geological repository (DGR) for used nuclear fuel in Canada, focusing on coupled thermo-hydro-mechanical (THM) processes in bentonite buffer materials. A fully coupled THM mathematical model was developed, verified against analytical solutions, and validated using experimental data from laboratory and in situ tests. The model was then applied to simulate the near-field response of the EBS within a granitic host rock, focusing on key performance indicators such as temperature distribution, resaturation time, swelling pressure development, and stress on the used fuel container (UFC). The results provide insights into the interactions between thermal, hydraulic, and mechanical processes in the bentonite buffer material, a crucial component in maintaining the repository's integrity. Results indicate that temperature evolution, buffer resaturation, and swelling pressures remain within established safety criteria. Overall, the modeling framework provides a reliable tool for assessing the THM behavior of the Canadian DGR and offers insights into optimizing design parameters to enhance repository safety over extended time scales. These findings contribute to a deeper understanding of the multi-physics interactions governing EBS performance, ultimately supporting informed decision-making in deep geological disposal of nuclear waste.

As underground mining advances to greater depths, cemented paste backfill (CPB) is increasingly subjected to complex thermo-mechanical loading conditions, including multiaxial stress states and elevated temperatures. This study investigates the coupled effects of field-representative vertical self-weight and horizontal rockwall closure stresses, along with in-situ temperatures, on the mechanical behavior and pore water pressure (PWP) evolution of CPB. Experiments were conducted using a novel apparatus capable of controlling multiaxial stress and temperature during curing, replicating in-situ stress paths and thermal profiles typical of deep mine environments. Results show that multiaxial stress enhances CPB strength and stiffness by promoting denser particle packing, reducing porosity, and increasing frictional resistance. Elevated temperatures independently accelerate early-age cement hydration, further improving bond strength and stiffness. When combined, multiaxial stress and elevated temperature produce a synergistic enhancement in unconfined compressive strength (UCS) and elastic modulus, as confirmed by two-way ANOVA and synergy index analysis. PWP responses were also highly sensitive to thermo-mechanical conditions. The evolution of positive and negative PWP was governed by the interplay of thermal expansion, hydration-induced desaturation, and mechanical compaction. Multiaxial stress amplified early positive PWP and delayed its dissipation, whereas elevated temperature accelerated hydration and reduced pore pressure, leading to enhanced suction at later ages. A transient “stress-induced resaturation” effect was observed under late-stage excessive horizontal stress but was mitigated by elevated temperatures. These findings provide critical insights into the coupled mechanical and hydraulic behavior of CPB under realistic field conditions and offer guidance for optimizing backfill design, binder content, and barricade stability in deep mining applications.

This paper investigates solute transport processes in the bentonite buffer of a Deep Geological Repository (DGR) for used nuclear fuel, using the Canadian concept as an example. The design relies on a multi-barrier system, where the used fuel container (UFC) ensures containment, and the surrounding bentonite buffer seals gaps between the container and host rock. The buffer serves two key functions: (i) protecting the UFC against processes that may compromise containment, and (ii) retarding radionuclide migration in the event of UFC breach. Solute transport in the buffer is strongly influenced by coupled thermal-hydraulic-mechanical (THM) processes. A fully coupled THM-transport model was developed to evaluate two scenarios: (1) reactive transport of bisulfide \(\:\left({HS}^{-}\right)\) from the host rock to the UFC and its implications for long-term corrosion; and (2) radionuclide migration toward the host rock following a hypothetical breach. The model builds on previous verification and validation and is further validated here against laboratory-scale bisulfide transport experiments and a large-scale thermal diffusion experiment at the Tournemire Underground Research Laboratory (France). Model–data agreement demonstrates that adsorption and \(\:FeS\) precipitation significantly retard bisulfide migration, delaying detectable flux to the UFC by ~ 5×10⁵ years and limiting copper corrosion to ~ 0.05 mm over 1 Myr. Temperature-dependent diffusion is the dominant transport mechanism, while the Soret effect is negligible at repository scale. In the breach scenario, the buffer effectively delays and attenuates moderately/strongly sorbing radionuclides (e.g., 135 Cs, 237 Np). Overall performance is most sensitive to bentonite diffusivity and sorption capacity, highlighting key parameters for design and safety assessment.

This study investigates the rheological properties of cemented paste backfill (CPB) incorporating high-volume slag and fly ash (FA) as sustainable substitutes for Portland cement type I (PCI). The research aims to enhance CPB flowability while maximizing the reuse of industrial byproducts. Rheological tests were conducted on CPB samples composed of silica tailings with varying PCI/slag/FA ratios to assess their effects on yield stress and viscosity. Using a central composite design and response surface methodology, mathematical models were developed to quantify and predict the relationships between rheological parameters and binder composition. Microstructural and monitoring analyses revealed that slag and FA influence CPB flowability through particle size, shape, and hydration characteristics. Results indicate that replacing up to 80 % of PCI with slag and FA reduces yield stress and viscosity by 4.2 %-21.7 % and 0.7 %-5.0 %, respectively, improving flowability for mine filling applications. However, excessive slag and FA contents (90 %) increase fine particle interactions, elevating yield stress and viscosity. Time-dependent rheological changes were observed, with yield stress and viscosity increasing by 40 %-66.7 % and 3.9 %-7.1 % during two hours of curing, driven by hydration product formation. The optimal binder ratio (10.15 % PCI, 20.3 % slag, and 79.7 % FA) achieves a desirable balance of low yield stress (137.4 Pa) and viscosity (2.91 Pa & sdot;s) with over 90 % industrial waste reutilization. This study provides a robust framework for optimizing CPB formulations, addressing key challenges in sustainable mining practices, and guiding the large-scale reuse of industrial wastes.

Cemented paste backfill (CPB), a mixture of mine tailings, water, and binder, is widely used to provide structural support in underground mines. However, early-age CPB is particularly vulnerable to dynamic loading events, such as earthquakes and rockbursts, which can compromise mine safety and increase the risk of failure. This paper presents a novel coupled chemo-mechanical constitutive model that captures both the time-dependent enhancement of structure during binder hydration and its subsequent degradation under cyclic loading. The model introduces several original features: (i) a hydration-sensitive Phase Transformation Line (PTL) to characterize dilatancy behavior, evolving with curing and degrading with destructuration; (ii) internal variables for bonding and structural strengths, which degrade with accumulated plastic strain to simulate progressive debonding; (iii) a generalized bounding surface and plastic potential formulation that extends into both compression and extension stress states; and (iv) direct chemo-mechanical coupling through hydration-dependent evolution of key mechanical parameters (e.g., structural strength, PTL slope). These advancements are embedded in a unified, bounding surface plasticity framework, specifically designed to simulate early-age CPB under cyclic loading conditions. The model is successfully validated against a series of laboratory cyclic triaxial tests, demonstrating strong predictive capabilities. By capturing the coupled chemical and mechanical processes that govern early-age CPB behavior, this model provides a robust and physically meaningful tool to assess the performance of backfill structures under dynamic conditions. The proposed framework offers new insights into liquefaction susceptibility and structural reliability of CPB under cyclic conditions, contributing to safer and more cost-effective designs of CPB structures in underground mines.

Indoor air pollution constitutes a public health problem due to the long time that individuals spend in enclosed spaces every day. The present study aims to investigate the level of volatile organic compounds (VOCs) in indoor air in households in Senegal, and to assess health risks related to residents’ exposure. Of the 17 VOCs identified, 16 were detected in Medina accommodations versus 14 in Darou Khoudoss. Toluene levels reached 70.9 μg/m3 in Medina and 18.5 μg/m3 in Darou Khoudoss, which were the highest compared to other compounds. The sum of Benzene, Toluene, Ethylbenzene, o-Xylene, and 1,2,4-trimethylbenzene concentrations were two times higher in Medina (79.57 µg/m3 versus 37.1 µg/m3). Furthermore, VOCs were found at higher levels in living rooms compared to other living spaces. The highest benzene and acetone concentrations were estimated at 13.6 µg/m3 and 8.4 µg/m3, respectively, in households where incense was burnt daily, while the highest formaldehyde levels were observed in households using incense seasonally (6.8 µg/m3). As regards the health risks associated with exposure of residents, the lifetime cancer risks were all above the WHO tolerable limit (10−5–10−6). Exposure to benzene (8.5 µg/m3) associated with a lifetime risk of leukemia (51.3 per million people exposed) was higher in Darou Khoudoss, while the risk of nasopharyngeal cancer (600 per million people exposed) associated with exposure to formaldehyde (4.23 µg/m3) was higher in Medina.

Waste containment facilities, such as landfills and tailings storage facilities, rely on barrier (liner, cover) materials to prevent hazardous contaminant migration. Recently, polymer-enhanced paste tailings (PP) barriers, made from a compacted mixture of paste tailings and superabsorbent polymer (SAP), have emerged as a promising solution for sustainable waste containment due to their low permeability. However, although compacted PP shows promising hydraulic properties, its mechanical characteristics relevant to barrier functionality, such as consolidation behavior and shear characteristics, are not yet understood. No studies have assessed these mechanical characteristics. This study investigates the consolidation behavior and shear strength characteristics of polymer-paste tailings (PP) barriers incorporating superabsorbent polymers (SAPs). Compacted PP samples with different concentrations of SAP (0.0 %, 0.2 %, 0.5 %) were prepared, and the samples were subjected to consolidation and shear tests. Consolidation behavior was investigated using oedometer tests, monitoring settlement over time under different stress conditions. In addition, shear characteristics were assessed by direct shear tests to evaluate the material's resistance to shearing and deformation under different normal stresses. The results indicated that increasing SAP content accelerates the consolidation process. In contrast, the shear strength of the material increases with SAP content up to 0.2 %, after which it decreases when the SAP content reaches 0.5 %. This means that the shear strength of the compacted PP is strongly dependent on the amount of SAP concentration. Specifically, the cohesion increases with higher SAP content, whereas the friction angle decreases with increasing SAP content. These findings highlight the importance of balancing SAP content to achieve a stable and efficient barrier system. The findings position this PP material as an attractive option for barrier design, offering the benefits of minimizing waste management and lowering the expenses associated with tailings management at the earth's surface.

Argillaceous rocks have many favourable characteristics for deep geological disposal of high-level radioactive waste (HLW) such as low permeability resulting in slow solute transport dominated by diffusion processes. However, waste-generated heat can increase pore pressure through Thermal-Hydraulic-Mechanical (THM) coupled processes, potentially enhancing advective transport. In this study, the authors developed a mathematical model to simulate a laboratory and a large-scale in situ experiment at an underground research facility (URF), to investigate (1) T-solute transport coupling (via the Soret effect and temperature-dependent diffusion coefficient) and (2) THM-solute transport coupling in argillaceous rock. The findings suggest that the Soret effect is significant in the laboratory experiments with relatively high thermal gradient, but negligible in the URF experiment where the thermal gradient is much smaller. Instead, the effect of temperature on the diffusion coefficient appears to play a more crucial role for the URF experiment. In addition, the advection enhancement due to thermal pressurization as a result of THM processes shows an insignificant effect on solute transport. The modelling of the URF experiment, as confirmed by observational evidence, shows the importance of anisotropy of the THM-transport properties as well as the effects of the excavation damage zone (EDZ). Finally, the model captures the key features of both experiments, highlighting its capability in enhancing comprehension of transport processes from a deep geological repository (DGR) built in argillaceous rocks. This improved understanding is valuable for safety assessments of DGRs in such rock types.

There is currently no research examining the rheological properties of cementitious paste backfill (CPB) materials containing aluminium oxide nanoparticles (nAlO). Knowing the yield stress and viscosity of CPB containing nAlO is crucial, especially when applying nano-CPB technology in underground mines. The purpose of this work is to thoroughly examine how nAlO affects the rheological characteristics of CPB and how those characteristics change over time. Yield stress and viscosity measurements are performed on CPB samples with different compositions (e.g., nAlO content, binder type, and superplasticizer content) at intervals of 0 min, 20 min, 1 h, 2 h, and 4 h. The study also includes measurements of the pH and zeta potential of the materials, microstructural studies (TG/DTG and XRD), and electrical conductivity (EC). The findings show that adding nAlO to CPB significantly changes its rheological properties, which in turn affects flowability. The yield stress and viscosity of CPB samples are greatly increased by the incorporation of nAlO, with the degree of influence varying based on variables including water content, curing duration, and type of binder. Because of the nAlO-induced microstructural changes in the CPB material, the interaction of nAlO and a larger fraction of nAlO, along with an increase in curing time, raises rheological characteristics and decreases paste flowability. The results of EC, DTG, and XRD, which show that binder hydration improves with nAlO dosage, corroborate this. Moreover, as nAlO content increases, the zeta potential decreases in magnitude, resulting in stronger repulsion forces and reduced flowability. However, EC, XRD, and DTG analyses suggest that the addition of 0.125% superplasticizer counteracts the flowability reduction caused by nAlO, as the superplasticizer slows down the cement hydration rate at very early curing stages. Moreover, the increase in the slag percentage from 0% to 50% and 75% of the binder content slightly decreases viscosity but greatly increases yield stress. The study’s fresh perspectives contribute to the advancement of nano-CPB technology and have important ramifications for the practical use of this technology in underground mine backfill operations.