Hydro-mechanical Properties Research Articles

Using global sensitivity analysis to quantify the uncertainty of root reinforcement in vegetated slope stability

Abstract Aims Variabilities of vegetation and soil cause uncertainty to the factor of safety (FoS) of unsaturated vegetated slopes, yet the significance of these variabilities on the uncertainty of FoS is unclear. This study aims to quantify the effect of the uncertainties of root reinforcement and soil hydromechanical properties to the uncertainty of the FoS. Methods The variance‐based global sensitivity analysis was adopted to evaluate how the variance of FoS of vegetated slopes can be apportioned by the variabilities of soil and root parameters. A copula theory was applied to model the correlation amongst the parameters. Results For slip depths shallower than 0.30 m, the major source of the variance of the FoS included the parameters that define root reinforcement, followed by the parameters of soil shear strength. The variation of transpiration‐induced soil suction had limited effect on the FoS variance under heavy rainfall. Taking into account the correlations amongst the parameters had minor influence on their contribution to the variance of the FoS. Conclusions We observed threshold slip depths, where the relative contribution of uncertainties in root and soil parameters on the FoS uncertainty underwent a transition. Root reinforcement for slips as deep as 0.60 m can provide reliable slope stabilisation effects.

Induced polarization of clay-rich materials — Part 4: Water content and temperature effects in bentonites

Deep geological disposals (DGDs) are widely seen to be the best solution to contain high-level radioactive wastes safely. Compacted bentonite and bentonite-sand mixtures are considered the most appropriate buffers or sealing materials for access drifts, ramps, and shafts due to their favorable physicochemical and hydromechanical properties. Bentonite-sand mixtures are expected to swell and seal all voids when in contact with water, forming an impermeable barrier to radioactive elements. The parameters that will most affect the hydraulic performance of these seals are their water content, dry density, water salinity, and temperature. Monitoring and assessing these parameters are, therefore, crucial to confirm that the seals’ safety functions are fulfilled during the life of a DGD. Induced polarization (IP) is a nonintrusive geophysical method able to perform this task. However, the underlying physics of bentonite-sand mixtures has not been checked. The complex conductivity spectra of 42 compacted bentonite-sand mixtures are measured in the frequency range of 1 Hz–45 kHz in order to develop workable relationships between in-phase and quadrature conductivities versus water content and saturation, pore water conductivity, bentonite-sand ratio (10% to 100%), temperature (10°C–60°C), and dry density (0.97 to 1.64 [Formula: see text]). We observe that conductivity is mostly dominated by surface conductivity associated with the Stern layer coating the surface of smectite, the main component of bentonite. At a given salinity and temperature, the in-phase and quadrature conductivities obey power law relationships with water content and saturation. The in-phase and quadrature conductivities depend on temperature according to a classical linear relationship with the same temperature coefficient. A Stern layer-based model is used to explain the dependence of the complex conductivity with water content, dry density, water salinity, and temperature. It could be used to interpret IP field data to monitor the efficiency of the seal of DGD facilities.

Uncovering soil compaction: performance of electrical and electromagnetic geophysical methods

Abstract. Monitoring soil structure is of paramount importance due to its key role in the critical zone as the foundation of terrestrial life. Variations in the arrangement of soil components significantly influence its hydro-mechanical properties and therefore its impact on the surrounding ecosystem. In this context, soil compaction resulting from inappropriate agricultural practices not only affects soil ecological functions, but also decreases the water-use efficiency of plants by reducing porosity and increasing water loss through superficial runoff and enhanced evaporation. In this study, we compared the ability of electric and electromagnetic geophysical methods, i.e., electrical resistivity tomography (ERT) and frequency-domain electromagnetic (FDEM) method, to assess the effects caused by both heavy plastic soil deformations generated by a super-heavy vehicle and the more common tractor tramlines on silty-loam soils. We then tested correlations between geophysical response and soil variables (i.e., penetration resistance, bulk density, and volumetric water content on collected samples) at different homogeneous areas defined by k-means clustering. This work is intended to be a contribution to clarify expectations about the use of geophysical techniques to rapidly investigate soil compaction at various spatial scales, dissecting their suitability and limitations. It also aims to contribute to the methodological optimization of agrogeophysical acquisitions and data processing in order to obtain accurate soil models through a non-invasive approach. Electrical prospecting has finer spatial resolution and allows a tomographic approach, requiring higher logistic demands and the need for ground galvanic contact. On the other hand, contactless electromagnetic induction methods can be quickly used to define the distribution of electrical conductivity in the shallow subsoil in an easier way. In general, compacted soil portions are imaged as high-electrical-conductivity anomalies relative to the context. Results, validated with traditional soil characterization, show the pros and cons of both techniques and how differences in their spatial resolution heavily influence the ability to characterize compacted areas with good confidence.

Impact of Wetting and Drying Cycles on the Hydromechanical Properties of Soil and Implications on Slope Stability

The soil-based infrastructure is the backbone of the global economy, connecting people, enhancing quality of life, and promoting health and safety. However, its vulnerabilities are becoming apparent due to climate change, mainly through frequent wetting and drying (wd) cycles. Despite few studies in the past, research showing the stability of flood embankments in the long term, incorporating the impact of wetting and drying cycles on the hydromechanical characteristics of soil, is scarce. This study aimed to assess the impact of controlled wd cycles on the hydromechanical properties of clay and silty sand soils and its implications for the stability of a typical flood embankment. Volumetric changes were monitored during the wd cycles. The soil water characteristic curve (SWCC), saturated hydraulic conductivity (ksat), effective cohesion (c′), and effective angle of internal friction (ϕ′) were measured at 1 and 10 wd cycles. The results indicated that the 10 wd cycles decreased the saturated moisture content and resulted in a flatter SWCC compared to the 1 wd cycle for clayey soil. The ksat value was also significantly higher at 10 wd cycles than 1 wd cycle for clayey soil. An insignificant difference was found in both the SWCC and ksat at 1 and 10 wd cycles for silty sand soil. The ϕ′ value for the clayey soil decreased from 28.5 to 20.1 as the wd cycles increased from 1 to 10, while c′ remained unchanged at 10 kN/m2. On the other hand, for the silty sand soil, ϕ′ increased from 34.6 to 37.5 with an increase in wd cycles from 1 to 10, and c′ remained constant at 1 kN/m2. Numerical modelling of transient water flow coupled with a slope stability analysis revealed that the stability of a flood embankment depends on the evolution of soil hydromechanical properties due to wd cycles and the duration of flooding. These findings underscore the need for proactive measures to mitigate landslide risks in regions prone to frequent wd cycles, thereby ensuring the safety and resilience of slopes and associated infrastructure.

Multi-directional deformation and hydraulic conductivity of expansive soils subjected to freeze-thaw cycles from three distinct initial saturation levels

Infrastructure construction in seasonally frozen regions, covering 23% of total land, faces challenges from freeze-thaw (F-T) induced damages. Expansive soils, as an important problematic soil undergo major hydromechanical properties changes influenced by F-T cycles. Sand-bentonite mixtures are extensively used for constructing earthen hydraulic barriers in cold regions. This study investigates the influence of F-T cycles on multi-directional strains and anisotropic hydraulic conductivity of different sand-bentonite mixtures prepared at optimum water content and experienced three distinct saturation levels. Results indicate that saturation level and bentonite content significantly influence volumetric strain under F-T cycles. The simultaneous effect of ice lens formation, expanding micro-voids, and suction generated by freezing processes cause different volumetric behaviors at varying saturation degrees. The dry specimen exhibits no strain under F-T cycles, while optimum and saturated specimens experienced final volumetric strains of 1.02% and 3.03%, respectively. Notably, during freezing, the specimen at optimum water content shrank, while the saturated specimen expanded. Increasing bentonite content from 40% to 70% developed freezing-induced shrinkage, from 1.73% to 4.72%, with higher thaw strain attributed to increased specimen plasticity. Also, dimensional variations revealed the cross-anisotropic nature of specimens, highlighting direct influence of water content on the shrinkage ratio. F-T cycles also increased hydraulic conductivity along both orthogonal directions by two orders of magnitude, while the anisotropy ratio decreased by about 3 after 9 F-T cycles, indicating altered pore structures. F-T cycles induce reduced swelling potential and compressibility over subsequent cycles. Microstructural observations also confirmed the F-T effects on the enhancement of porosity.

Hydromechanical properties of metachronal swimming in polychaetes

Free-swimming polychaetes are common in marine habitats and exhibit a unique form of swimming whereby a metachronal wave occurs simultaneously with a bending body wave. This body wave is unusual among swimming animals because it travels in the same direction as the animal’s swimming direction. However, we currently lack a mechanistic understanding of this unusual form of locomotion. In this study we use a combination of high-speed, high-resolution video and particle image velocimetry (PIV) to quantify kinematics and fluid dynamics for three species of swimming polychaetes, spanning two orders of magnitude in size. We find that in all species, flows generated by metachronal waves of parapodia dominate while typical flows associated with body bending is absent. However, the parapodia are less flexible than propulsive structures in other metachronal swimmers. This creates a localized, but substantial upstream flow during the recovery stroke. Using body bending, the recovery stroke can occur mostly beneath the bulk flow from the power strokes, resulting in minimal inference while the subsequent power stroke can benefit from the pressure field generated during recovery. These results may have implications for future vehicle designs that incorporate metachronal locomotion.

Experimental investigation of failure mechanism of fissure-filled sandstone under hydro-mechanical conditions

Fissure fillings are critical to the hydro-mechanical properties of jointed rock masses in rock engineering. In this study, triaxial seepage tests were performed on standard cylindrical fissure-filled sandstone. The characteristics of stress–strain relationships, absorption and consumption of energy, variations in deformation resistance, and permeability evolution during the experimental process, along with the crack development observed in post-failure computed tomography scan images of the sandstone specimens were analyzed. The results demonstrate that the fillings improve the energy capacity and reduce the damage accumulation of sandstone specimens, with sand-filled specimens performing better than mud-filled specimens, especially at lower bridge angles. The fillings can reduce the depth of crack extension and lessen the influence of prefabricated fissures on sandstone failure, with this effect diminishing as the rock bridge angle increases. Permeability decreases in the pre-peak failure stage as the fillings improve the deformation resistance of the sandstone specimens. In the post-peak failure stage, the fillings and rock debris generated by the sandstone failure move within the developed fractures, causing significant fluctuations in permeability. These findings deepen the understanding of the hydro-mechanical properties of jointed rocks and provide a scientific basis for stability analysis in rock engineering.

Experimental investigation of collapsible soils under oedometric loading: effect of internal erosion

Collapsible soils, geological formations characterized by pronounced structural instability upon saturation, present a significant challenge in geotechnical engineering. This experimental study aims to deepen our understanding of the mechanisms governing the behavior of these soils, which are particularly prevalent in arid and semi-arid regions subject to extreme hydrological cycles. Collapsible soils, sensitive to climatic variability, undergo profound alterations in their hydromechanical properties due to alternating periods of prolonged drought and intense rainfall events. These fluctuations induce significant modifications in the soil's pore structure, promoting the development of internal erosion phenomena such as suffusion. The results obtained from this experimental investigation on reconstituted samples highlight the combined influence of various factors, such as water content, dry density, particle size, and flow rate, on the collapse potential. It appears that fine particles play a predominant role in the formation of fragile structures, susceptible to collapse upon saturation. Moreover, the intensity and duration of infiltration significantly influence the propagation velocity of ultrasonic waves, thus offering a promising tool for monitoring the evolution of damage within the soil mass. Furthermore, this study provides essential insights for assessing the risks associated with collapsible soils and contributes to the development of more reliable characterization and modeling methods. It emphasizes the need to consider the complex interactions between the physical, chemical, and mechanical properties of the soil, as well as the influence of environmental conditions, for better control of the risks associated with these materials.

Enhancing biocementation performance in low permeability clayey soil through sand column strategy

Soil erosion is a common phenomenon which causes lots of geological and engineering disasters. Clayey soil erosion control is a hot research topic and a challenging issue for its low permeability and lack of effective infiltration of treatment solutions. In this study, a coupling microbially induced calcium carbonate precipitation (MICP)-sand column method was proposed as a promising and sustainable technique to mitigate surface clayey soil erosion with adjustable treatment depth. Seven groups of soil samples were prepared, including pure soil, MICP-treated soil, and MICP-sand column method-treated soil. A series of disintegration tests and penetration tests were conducted to investigate the method feasibility and adjusting mechanism of erosion mitigation with varying sand column heights and diameters. Compared to pure soil sample, sample treated by MICP-sand column (6 cm-height and 3 cm-diameter) method could reach a maximum reduction of 50 % in ultimate disintegration rate and a 30 % increase in the highest penetration resistance. The sample has a 7.9 cm effective treatment depth, which is 5.3 times of the MICP-treated sample. The mechanism of erosion mitigation can be attributed to that the sand column serves as a favorable path for the bacteria suspension and cementation solution in low-permeability-clayey soil and improves the effective depth of MICP treatment. Adjusting the height and diameter of sand column can change the calcium carbonate distribution, especially at the locations near the surface and around the sand column. In this study, the optimal height and diameter are 6 cm and 3 cm, respectively, and finally form a U-shape three-layer structure. The structure significantly increases the proportion of the hard crust layer and weak-cemented layer with high hydro-mechanical properties. In conclusion, the coupling MICP-sand column method with reasonable height and diameter of sand column shows the ability to control surface erosion of soil and has better long-term mitigation performance.

Effects of CO2-saturated brine imbibition on the mechanical and seepage characteristics of Longmaxi shale

Supercritical carbon dioxide (SC– CO2) serves as a promising anhydrous fracturing fluid that has the potential to simultaneously enhance shale gas recovery and accomplish CO2 sequestration within shale reservoirs. However, the hydromechanical properties of shale are considerably affected by CO2-brine-shale interaction. This study conducted shale imbibition experiments involving subcritical/supercritical CO2 saturated brine (Sub/SC-CO2+brine). Triaxial compressive strength tests were performed to evaluate the impact of Sub/SC-CO2+brine imbibition on the mechanical properties of shale, as well as the influence of SC-CO2+brine imbibition on shale permeability. The results indicate that, after SC-CO2 brine imbibition, noticeable macroscopic cracks are formed parallel to the bedding plane. The imbibition of Sub/SC-CO2+brine results in the reduction in axial stress and Young's modulus, while simultaneously increasing the axial strain of shales. Compared to Sub-CO2+brine, SC-CO2+brine exhibits a higher imbibition pressure and a more intense geochemical reaction with shale. Due to increased compressibility sensitivity, the averaged permeability after SC-CO2+brine imbibition shows a reduction of nearly 70 % compared to that before imbibition. The insights from this research are expected to provide theoretical support for shale gas recovery and CO2 geological sequestration.

Multi-scale variations of subglacial hydro-mechanical conditions at Kongsvegen glacier, Svalbard

Abstract. The flow of glaciers is largely controlled by changes at the ice–bed interface, where basal slip and sediment deformation drive basal glacier motion. Determining subglacial conditions and their responses to hydraulic forcing remains challenging due to the difficulty of accessing the glacier bed. Here, we monitor the interplay between surface runoff and hydro-mechanical conditions at the base of the Kongsvegen glacier in Svalbard. From July 2021 to August 2022, we measured both subglacial water pressure and till strength. Additionally, we derived median values of subglacial hydraulic gradient and radius of channelized subglacial drainage system from seismic power, recorded at the glacier surface. To characterize the variations in the subglacial conditions caused by changes in surface runoff, we investigate the variations of the following hydro-mechanical properties: measured water pressure, measured sediment ploughing forces, and derived hydraulic gradient and radius, over seasonal, multi-day, and diurnal timescales. We discuss our results in light of existing theories of subglacial hydrology and till mechanics to describe subglacial conditions. We find that during the short, low-melt-rate season in 2021, the subglacial drainage system evolved at equilibrium with runoff, increasing its capacity as the melt season progressed. In contrast, during the long and high-melt-rate season in 2022, the subglacial drainage system evolved transiently to respond to the abrupt and large water supply. We suggest that in the latter configuration, the drainage capacity of the preferential drainage axis was exceeded, promoting the expansion of hydraulically connected regions and local weakening of ice–bed coupling and, hence, enhanced sliding.

Effect of Drying and Wetting Cycles on the Surface Cracking and Hydro-Mechanical Behavior of Expansive Clays

Expansive clays present serious issues in a variety of engineering applications, including roadways, light buildings, and infrastructure, because of their notable volume changes with varying moisture content. Tough weather conditions can lead to drying and shrinking, which alters expansive clays’ hydro-mechanical properties and results in cracking. The hydro-mechanical behavior of Al-Ghatt expansive clay and the impact of wetting and drying cycles on the formation of surface cracks are addressed in this investigation. For four cycles of wetting and drying and three vertical stress levels, i.e., 50 kPa, 100 kPa, and 200 kPa, were investigated. The sizes and patterns of cracks were observed and classified. A simplified classification based on main track and secondary branch tracks is introduced. The vertical strain measure at each cycle, which showed swell and shrinkage, was plotted. The hydromechanical behavior of the clay, which corresponds to three levels of overburden stress as indicated by its swell potential and hydraulic conductivity was observed. It was found that at low overburden stresses of 50 kPa, the shrinkage is high and drops with increasing the number of cycles. Al-Ghatt clay’s tendency to crack is significantly reduced or eliminated by the 200 kPa overburden pressure. The results of this work can be used to calculate the depth of a foundation and the amount of partial soil replacement that is needed.

A novel framework for deriving water retention behavior of multimodal unsaturated soils based on pore size distribution data

The soil water retention curve (SWRC) strongly influences the hydro-mechanical properties of unsaturated soils. It plays a decisive role in geotechnical and geo-environmental applications in the vadose zone. This paper advances a novel framework to derive the water retention behavior of multimodal deformable soils based on the pore size distribution (PSD) measurements. The multiple effects of suction on the soil pore structure and total volume during SWRC tests are considered. The complete picture of soil microstructure is quantitatively described by the void ratio (for the pore volume) and a newly defined microstructural state parameter (for pore size distribution) from a probabilistic multimodal PSD model. Assuming a reversible microstructure evolution, a unique PSD surface for wetting and drying links the SWRC and PSD curves in the pore radius-suction-probability space. A closed-form water retention expression is obtained, facilitating the model's implementation in particle applications. The model is validated using the water retention data of four different soil types, showing a strong consistency between the measurement and the reproduced curve. The proposed method provides new insights into the pore structure evolution, the water retention behavior and the relationship between them for multimodal deformable soils.

Emulation and evaluation of tumor cell combined chemotherapy in isotropic/anisotropic collagen fiber microenvironments.

The rapid emergence of anisotropic collagen fibers in the tissue microenvironment is a critical transition point in late-stage breast cancer. Specifically, the fiber orientation facilitates the likelihood of high-speed tumor cell invasion and metastasis, which pose lethal threats to patients. Thus, based on this transition point, one key issue is how to determine and evaluate efficient combination chemotherapy treatments in late-stage cancer. In this study, we designed a collagen microarray chip containing 241 high-throughput microchambers with embedded metastatic breast cancer cell MDA-MB-231-RFP. By utilizing collagen's unique structure and hydromechanical properties, the chip constructed three-dimensional isotropic and anisotropic collagen fiber structures to emulate the tumor cell microenvironment at early and late stages. We injected different chemotherapeutic drugs into its four channels and obtained composite biochemical concentration profiles. Our results demonstrate that anisotropic collagen fibers promote cell proliferation and migration more than isotropic collagen fibers, suggesting that the geometric arrangement of fibers plays an important role in regulating cell behavior. Moreover, the presence of anisotropic collagen fibers may be a potential factor leading to the poor efficacy of combined chemotherapy in late-stage breast cancer. We investigated the efficacy of various chemotherapy drugs using cell proliferation inhibitors paclitaxel and gemcitabine and tumor cell migration inhibitors 7rh and PP2. To ensure the validity of our findings, we followed a systematic approach that involved testing the inhibitory effects of these drugs. According to our results, the drug combinations' effectiveness could be ordered as follows: paclitaxel + gemcitabine > gemcitabine + 7rh > PP2 + paclitaxel > 7rh + PP2. This study shows that the biomimetic chip system not only facilitates the creation of a realistic in vitro model for examining the cell migration mechanism in late-stage breast cancer but also has the potential to function as an effective tool for future chemotherapy assessment and personalized medicine.

Assessing the hydromechanical control of plant growth.

Multicellular organisms grow and acquire their shapes through the differential expansion and deformation of their cells. Recent research has addressed the role of cell and tissue mechanical properties in these processes. In plants, it is believed that growth rate is a function of the mechanical stress exerted on the cell wall, the thin polymeric layer surrounding cells, involving an effective viscosity. Nevertheless, recent studies have questioned this view, suggesting that cell wall elasticity sets the growth rate or that uptake of water is limiting for plant growth. To assess these issues, we developed a microfluidic device to quantify the growth rates, elastic properties and hydraulic conductivity of individual Marchantia polymorpha plants in a controlled environment with a high throughput. We characterized the effect of osmotic treatment and abscisic acid on growth and hydromechanical properties. Overall, the instantaneous growth rate of individuals is correlated with both bulk elastic modulus and hydraulic conductivity. Our results are consistent with a framework in which the growth rate is determined primarily by the elasticity of the wall and its remodelling, and secondarily by hydraulic conductivity. Accordingly, the coupling between the chemistry of the cell wall and the hydromechanics of the cell appears as key to set growth patterns during morphogenesis.

Experimental investigation of tail void grouting pressure evolution for super-large diameter shield tunnels

The shield tunneling method is widely used in underground construction. Factors such as the variations in grouting pressure and stiffness/strength evolution over space and time directly affect ground deformation and system stability. To investigate the effect of grouting pressure variation, grouting influence zone, and hydromechanical properties on the model responses (e.g., surface settlement and lining forces), an innovative model test setup was developed to simulate the tunneling process wherein the lining could settle or float during grout injection. This setup included tunnel shrinking, loading-unloading, grout injection, and sample preparation systems. The experimental results show that the grouting pressure evolution law may be significantly affected by the tunnel translation. When the tunnel centerline was fixed in the traditional model tests, the resulting grouting pressure in the tail void was lower than that when the tunnel was free to move. This is because the tunnel translation changed the shape of the annular gap and contributed to the measured grouting pressure. The proposed setup is capable of revealing a more realistic law of grouting pressure evolution, and the subsequent spatio-temporal grouting-induced soil/lining behavior is currently being investigated.

Impact of Fluid Distribution and Petrophysics on Geophysical Signatures of CO2 Storage Sandstone Reservoirs

AbstractCarbon Capture and Storage (CCS) is a key element to achieving net‐zero energy challenge timely. CCS operations require the integration of geophysical data, such as seismic and electromagnetic surveys, numerical reservoir models and fluid flow simulations. However, the 10–100s m resolution of seismic imaging methods complicates the mapping of smaller scale rock heterogeneities, while borehole measurements commonly show large fluctuations at sub‐cm scales. In this study, we combine laboratory data, well‐logging, rock physics theories and a proof‐of‐concept time‐lapse seismic modeling to assess the effect of pore‐scale fluid distribution and petrophysical heterogeneities on the expected performance of whole‐reservoir CCS operations in deep saline aquifers, by analogy to the Aurora CCS site, North Sea. We monitored the elastic and electrical properties of three sandstone samples with slightly different physical and petrographic properties during carbon dioxide (CO2) flow‐through tests under equivalent in situ effective pressure. We inferred the CO2‐induced damage in the rocks from the variations of their hydromechanical properties. We found that the clay fraction, CO2‐clay chemical interactions, and porosity were the main factors affecting both the CO2 distribution in the samples and the hydromechanical response. We used seismic modeling of well‐log data and the laboratory results to estimate the reservoir‐scale time‐lapse seismic response to CO2 injection and to assess the effect of the rock heterogeneities in our interpretation. The results show that disregarding the effect of rock heterogeneities on the CO2‐brine fluids distribution can lead to significant misinterpretations of seismic monitoring surveys during CCS operations in terms of both CO2 quantification and distribution.

Structural, soil-water, and dynamic characteristics of clay with different moisture and temperature histories

Variations in the hydro-mechanical properties of pavement subgrade soils are complex under long-term, repeated, and interlaced moisture and temperature (M-T) effects, such as wetting-drying (WD) and freeze-thaw (FT) processes. This study compares the soil structure, soil-water characteristic curves, and accumulated plastic strain (ɛ p) of compacted Heilongjiang clay with three different M-T histories. Experimental results demonstrated that (i) after M-T actions, structural pores develop while textural pores shrink, leading to a reduction in the water retention capacity and an increase in the desaturation rate. Following the stabilization of the M-T effects, the soil structure and soil-water characteristics of specimens with different M-T histories become similar; (ii) at high moisture content (w), ɛ p is more sensitive to moisture changes (including w and suction, s). Following the FT cycles, ε p and ε pa (the difference between the ε p at 5000th and 3000th cyclic loading) become more sensitive to moisture changes; (iii) after M-T effects, the ε pa-w relationship is nonlinear while the ε pa-logs relationship is linear. Different M-T histories generated differences in only the ε p at the beginning of the FT processes while such differences disappear after M-T effects have stabilized. The experimental data presented in this paper could prove valuable in understanding the behaviors of pavement soils under complex environmental conditions.

Hydro-mechanical analysis of slope stability using anisotropic constitutive model

This study introduces a novel and robust numerical approach to analyzing rainfall-induced landslide hazards, incorporating coupled hydro-mechanical behavior, anisotropic properties of unsaturated geomaterials, and soil–atmosphere interaction. The advanced hyperbolic Mohr-Coulomb model with anisotropy is adopted for mechanical responses, while generalized Darcy’s law is employed for hydraulic behaviors. This approach allows for anisotropic specification of hydromechanical properties like stiffness, strength, and intrinsic permeability. Atmospheric boundary conditions enable analysis of soil–atmosphere interactions, encompassing infiltration and runoff during extreme rainfall. Parametric analyses were conducted to evaluate slope safety factors under various anisotropic angles.

Understanding the creep behavior of bentonite-sand mixtures as buffer materials in a low-level radioactive waste repository in Taiwan

This study investigates the creep behavior of bentonite-sand mixtures as potential buffer materials for low-level radioactive waste (LLW) repositories, with a specific case study in Taiwan. To assess the long-term hydro-mechanical properties, constant-volume swelling pressure, hydraulic conductivity, strain-controlled shear, and stress-controlled shear tests were conducted on MX80 and KV1 bentonite-sand mixtures. The experimental results indicate that MX80-sand 70/30 mixtures are prioritized as the buffer materials with 2.10 MPa swelling pressure and 1 × 10−13 m/s hydraulic conductivity. However, the shear strength of mixtures was reduced by almost 50 % when fully saturated. Furthermore, this study proposed a novel stress-controlled direct shear apparatus to retrieve the creep model parameters. The numerical method based on the creep model efficiently supports and simulates the saturation process and creep displacement. The finite element method (FEM) result predicts that the buffer of both bentonite-sand mixtures will achieve an average degree of saturation of 95 % at the end of three decades and full saturation in 100 years. The simulated creep displacement results at key nodes suggest that both top and bottom parts in the buffer, assembled from MX80-sand 70/30 mixtures or KV1-sand 70/30 mixtures, will have almost equivalent values of 4 mm in the horizontal and 2 mm in the vertical directions eventually.