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In deep geological repositories for disposing of high-level radioactive waste, various types of bentonite interfaces exist in the engineered barrier system. The hydromechanical resistances of the bentonite buffer rely on the sealing and healing of these interfaces, especially the assembled bentonite-bentonite interfaces that can heal spontaneously upon bentonite hydration (i.e., self-healing). This study explored the interfacial self-healing behavior of densely compacted Gaomiaozi bentonite via laboratory tests and evaluated the interfacial self-healing capacity in terms of the physical and hydraulic properties. In detail, the interfacial healing test results indicate that self-healing of the assembled bentonite interface initiated at low suction values (total suction s < 20 MPa) under confined conditions (when the assembled interface is compressed by the swelling pressure). The infiltration test results suggest an increased interfacial hydraulic resistance after long-time water infiltration and a slightly higher permeability than the saturated intact bentonite specimen with the same final dry density. The swelling pressure test results show that the bentonite assembly developed much lower swelling pressure than the intact bentonite specimen (for a given total suction) and achieved a rotated and slightly enhanced swelling pressure anisotropy compared with the saturated intact bentonite specimen with the same final dry density. The MIP test results reveal that the healed interfacial zone has similar pore structure as its adjacent intact zone. Thus, it is concluded that densely compacted Gaomiaozi bentonite has strong interfacial self-healing capacity in physical and hydraulic aspects. [ABSTRACT FROM AUTHOR]

Bentonite-based material (BBSM) is the preferred sealing material in deep geological repository (DGR) barrier systems for the long-term disposal of radioactive waste. Ensuring the safety of these systems hinges on the accurate prediction of BBSM properties during re-saturation. In response to these requirements, a hydro-mechanical (HM) process is employed to anticipate the response and behavior of BBSMs during re-saturation. In the context of this study, a novel HM model is developed that integrates a multiscale porosity model with a new swell model based on the Mohr–Coulomb failure criterion. By linking these components, the developed HM model proves capable of predicting changes in hydraulic properties, evaluating swelling strains, and assessing pressure induced by alterations in saturation levels. The developed model was calibrated and applied to bentonite materials of HM column experiments. Furthermore, the proposed HM model undergoes validation through a small-scale mock-up test involving a mixture of bentonite and sand samples. The results obtained from the model align closely with experimental measurements for hydraulic properties and swelling stresses, affirming its reliability. [ABSTRACT FROM AUTHOR]

The deep geological repository (DGR) system has been selected by most of the world's nuclear waste management organizations for the long-term disposal of radioactive wastes. The DGR mainly consists of a multi-barrier system—comprising the natural host rock and an engineered barrier system—to contain and isolate high-level radioactive waste, including used fuel containers (UFCs), to protect humans and the environment. Bentonite materials and host rock are the main components of the DGR's engineered and natural barrier system, respectively. It is crucial to understand the coupled behavior of bentonite and rock materials under various in situ conditions over long-term durations, as it supports safety assessments and enhances the overall safety level of DGR systems. This study presents a methodology for the numerical modeling of a hypothetical DGR using developed coupled models. The developed model was used to investigate the hydromechanical (HM) and thermomechanical (TM) response within the near-field (the area within a radius of 50 m near the UFC and multiple-barrier system) of a simplified hypothetical DGR, based on the proposed design concept of the Nuclear Waste Management Organization (NWMO) of Canada. The analysis results included the evolution of temperature, thermal stresses, saturation, and swelling pressure at different stages of the DGR system's lifetime. The results indicated that it could take up to 10,000 years to fully saturate the bentonite materials with a corresponding swelling pressure of 2.7 MPa associated with a decrease in the rock's strength/stress ratio near the placement room; however, the ratio did not indicate a significant system failure. Sensitivity analysis was also conducted to assess the impact of various parameters on the saturation time and the strength/stress ratio in a DGR. The results highlighted that saturation time was highly influenced by the permeability of both the rock formation and the bentonite, resulting in saturation times ranging from 500 to 20,000 years. Moreover, the strength/stress ratio was found to be sensitive to the model's parameters, particularly the maximum swelling pressure. The results of the TM analysis show that temperature development around the placement of rooms in a DGR is highly influenced by room spacing, with a lower factor of safety (FOS) as time and temperature progressed due to elevated temperature, while the rock remained stable over the 150-year analysis period. The inclusion of temperature-dependent mechanical properties produced negligible changes to the overall stability of the rock around the placement rooms of the DGR. [ABSTRACT FROM AUTHOR]

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Full-scale testing of lateral pressures in expansive clay under various saturation conditions is crucial to better understand the behavior of these soils and predict potential damage to structures. However, due to their complexity and cost, only a few full-scale physical testing studies on expansive soils have been reported in the literature. This study aims to provide new insight into the evolution of lateral swelling pressure in expansive soils under infiltration via full-scale physical testing. For this purpose, a heavily instrumented 3-m high masonry wall backfilled with an expansive clay was built and subjected to infiltration. The backfill was compacted in 95% of standard Proctor at a moisture content near optimal to simulate field conditions. The degree of saturation, pore-water pressure, temperature, suction, and lateral and vertical pressures were monitored at different locations during the test. Results showed that the development of lateral pressure is rapid during initial saturation and levels out as the clay approaches saturation levels. This finding highlights the importance of monitoring lateral pressure over time to accurately predict its behavior. The study also found that lateral pressure develops prior to vertical pressure, depending on the area and restraint. The lack of vertical pressure observed during the test is attributed to the continued displacement of the concrete block wall and settlement of the clay with increased area and wet weight of the soil. This finding is important for backfill against basement walls, retaining walls, and foundation units, where the mass of the expansive soil is limited, and effective stress is limited to one dimension. [ABSTRACT FROM AUTHOR]

Abstract The swelling soils, also known as expansive soils, increase in volume due to an increase in moisture content. The settlement of expansive soils could be the main reason for considerable damage to roads, highways, structures, irrigation channel covers, and the protective shell of tunnels that use bentonite for wall stability. Therefore, it is important to determine the amount of swelling pressure in expansive soils. This research uses two laboratory swelling test methods with constant volume (CVS) and ASTM-4546-96 standard, the swelling pressure of lime-stabilized bentonite soil has been estimated. Based on the key findings of this study, the swelling pressure values of pure bentonite samples tested using the ASTM-4546-96 method, compared to the constant volume swelling test, show an approximately 170% increase.

In some regions with hot and dry climate conditions, the temperature varies greatly between day and night. Therefore, the materials used in construction projects are exposed to a large number of thermal cycles daily. In this research, the application of sodium alginate polymer as an eco-friendly additive for soil stabilization and improvement of its geotechnical characteristics is studied. The study involves conducting geotechnical tests on both control and stabilized soil samples (with and without sodium alginate polymer) such as standard compaction test, swelling tests, and measuring Atterberg limits, while specimens were subjected to the same temperature variations as those recorded in the Khuzestan province, in the southwest of Iran. In fact, this study aims to investigate the effect of temperature ranges on the changes in the swelling potential of high plasticity clayey soils stabilized with sodium alginate polymer. Consolidation tests were carried out on compacted clay samples - containing different concentrations of sodium alginate polymer with treatment durations of 1 and 14 days - in accordance with method C of ASTM standard. The temperature range considered in this research was 23 to 45℃ due to the simulation of the temperature in Khuzestan province in the spring and autumn seasons. Observations indicated an increase in the swelling potential up to %13 in a sigmoidal manner with the repetition of temperature ranges and the stabilization of swelling changes, or so-called aging of swelling, which occurs with the repetition of temperature fluctuations. Additionally, the samples were analyzed using X-ray Diffraction (XRD), and X-ray Fluorescence (XRF) techniques to investigate the changes in their compositions. These methods revealed the formation of palygorskite minerals in specimens. This mineral intensifies the soil's swelling potential and is considered one of the contributing factors to the observed increase in swelling in the stabilized soil samples containing sodium alginate polymer.

Copyright of Journal of Shanghai Jiaotong University (Science) is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The swelling soils, also known as expansive soils, increase in volume due to an increase in moisture content. The settlement of expansive soils could be the main reason for considerable damage to roads, highways, structures, irrigation channel covers, and the protective shell of tunnels that use bentonite for wall stability. Therefore, it is important to determine the amount of swelling pressure in expansive soils. This research uses two laboratory swelling test methods with constant volume (CVS) and ASTM-4546-96 standard, the swelling pressure of lime-stabilized bentonite soil has been estimated. Based on the key findings of this study, the swelling pressure values of pure bentonite samples tested using the ASTM-4546-96 method, compared to the constant volume swelling test, show an approximately 170% increase. [ABSTRACT FROM AUTHOR]

In this study, the fuzzy logic method was used to determine the swelling pressure, which is an important engineering problem in clay soils. For this purpose, plasticity index, initial water content and dry unit volume weight values, which are among the parameters affecting the swelling pressure of clay, were taken into consideration. First of all, swelling pressure and affecting parameters are divided into fuzzy subsets. The fuzzy rule base was created and programmed in Fortran language. Then, constant volume swelling experiments were performed on three clay samples with high swelling potential. For swelling experiments, samples with six different initial water contents and seven different dry unit volume weights were prepared by compaction. The swelling pressure values obtained from the experiment were compared with the values obtained from the fuzzy logic model. In cases of high swelling pressure, the maximum error between the swelling pressures obtained from the fuzzy logic model and the experimental results was around 10%, while it was observed that the maximum error exceeded 30% at very low swelling pressure values. The average amount of error in inflation pressure estimation was obtained as 9.73%. When the experimental results are compared with the results obtained from the fuzzy logic method, it is seen that the fuzzy logic method can be used in estimating the swelling pressure in compacted clays. [ABSTRACT FROM AUTHOR]

Understanding the amount of bentonite intrusion into rock cracks is necessary to evaluate the performance of natural barrier materials for geological disposal. In this study, assuming a possible chemical action in geological disposals, bentonite was immersed in various solutions to accelerate the chemical action, and a half-year swelling and intrusion experiment was conducted. The experimental results showed that the swelling pressure and intrusion distance of bentonite in a solution environment differed depending on the solution type and that both were smaller than those in a purified water environment. The swelling pressure of bentonite in the environments of the KOH, NaOH, MgCl2, and NaCl solutions decreased significantly, and it did not significantly enter into the gaps in these systems. This is undesired in situations where gaps such as the cracks of rock must be filled. Furthermore, a numerical analysis model was constructed that can simply represent the complex intrusion behavior of bentonite in cracks considering the balance of three forces acting on bentonite. The analysis results confirmed that under conditions where the external swelling pressure fluctuates over time, the intruding fluid fills the cracks more slowly than under conditions where the external swelling pressure is constant. It was also confirmed that under conditions where the viscosity of the intruding fluid decreases over time, the intruding fluid fills the cracks faster than under conditions where the upper limit viscosity is constant. The numerical results clarified that the governing equation for bentonite intrusion into closed cracks may express the long-term intrusive behavior of bentonite into cracks during geological disposal. [ABSTRACT FROM AUTHOR]

In the high-level radioactive waste geological disposal, the gaps between the waste canisters, buffer layer, and surrounding rock, will affect the hydro-mechanical behavior of bentonite blocks. In this paper, the gaps between the buffer layers were simulated by setting different technological void widths. The interaction between technological void width and the swelling pressure and hydraulic conductivity of compacted bentonite was investigated. Meanwhile, the effect of different boundary conditions on the hydration process of compacted bentonite simulated through stepwise pre-set technological void (SV) and completely pre-set technological void (CV) was studied. The results showed that, keeping the same dry density, the swelling pressure of compacted bentonite blocks with 33% technological voids remained unchanged compared to specimens without voids, while the hydraulic conductivity increased by 10%. Comparing the SV with CV specimens, the swelling pressure was similar, but the hydraulic conductivity of the latter increased by 6%. Microstructural test results indicated differences in overall homogeneity between compacted bentonite blocks with 33% technological voids and those without voids after complete hydration, and distinct differences were also observed between the void and block areas in specimens with voids. The SV method reduced the cumulative pore volume in the void area, resulting in a more uniform hydration process. [ABSTRACT FROM AUTHOR]

Because of the inherent rheological property of transparent gel, laponite has been proposed for soil densification to withstand seismic events. Since the swelling behaviors of laponite could affect the soil-nanoparticle structure, one of the most important research topics is the swelling capacity of nanoparticles, particularly laponite. Hence, the objective of this study is to investigate the swelling properties of fresh laponite and sand treated with different contents of laponite. The swelling characteristics of compacted laponite hydrogel were investigated using a one-dimensional consolidation test setup. Results showed that the swelling strain of compacted laponite increased with time and as the concentration of laponite increased in specimens. The initial swelling of fresh laponite took around 4 weeks to attain equilibrium, while in the reswelling tests, laponite reached equilibrium within 60 h. The reswelling strain of laponite was higher than the initial swelling of fresh laponite, with a distinct reswelling behavior compared to other clay minerals. This swelling strain of laponite was found to be consistent with other clay minerals in which the swelling strain is caused by interlayer and double-layer forces. Scanning Electron Microscope images revealed that the structures of swollen laponite are continuous sheet-like irregular structures with pore size. Moreover, the swelling strain of the sand-laponite mixture with 3% laponite reached equilibrium after 40 h, whereas the swelling strain of sand-laponite with 5% laponite specimen did not reach equilibrium even after 50 h. In this study, the water retention ratio and changes in laponite hydrogel characteristics due to repeated drying and wetting processes were also investigated. In addition, the swelling pressure of compacted laponite hydrogel was also estimated, which varied in a range of 5.6–8.6 kPa throughout the experiment. [ABSTRACT FROM AUTHOR]

Abstract The swelling pressure of bentonite and bentonite mixtures is critical in designing barrier systems for deep geological radioactive waste repositories. Accurately predicting the maximum swelling pressure is essential for ensuring these systems' long-term stability and sealing characteristics. In this study, we developed a constrained machine learning model based on the extreme gradient boosting (XGBoost) algorithm tuned with grey wolf optimization (GWO) to determine the maximum swelling pressure of bentonite and bentonite mixtures. A dataset containing 305 experimental data points was compiled, including relevant soil properties such as montmorillonite content, liquid limit, plastic limit, plasticity index, initial water content, and soil dry density. The GWO-XGBoost model, incorporating a penalty term in the loss function, achieved an R2 value of 0.9832 and an RMSE of 0.5248 MPa in the testing phase, outperforming feed-forward and cascade-forward neural network models. The feature importance analysis revealed that dry density and montmorillonite content were the most influential factors in predicting maximum swelling pressure. While the developed model demonstrates high accuracy and reliability, it may have limitations in capturing extreme values due to the complex nature of bentonite swelling behavior. The proposed approach provides a valuable tool for predicting the maximum swelling pressure of bentonite-based materials under various conditions, supporting the design and analysis of effective barrier systems in geotechnical engineering applications.

Geotechnical engineering data are usually small-sample and high-dimensional, which brings a lot of challenges in predictive modeling. This paper uses a typical high-dimensional and small-sample swell pressure (Ps) dataset to explore the possibility of using multi-algorithm hybrid ensemble and dimensionality reduction methods to mitigate the uncertainty of soil parameter prediction. Based on six machine learning (ML) algorithms, the base learner pool is constructed, and four ensemble methods, Stacking (SG), Blending (BG), Voting regression (VR), and Feature weight linear stacking (FWL), are used for the multi-algorithm ensemble. Furthermore, the importance of permutation is used for feature dimensionality reduction to mitigate the impact of weakly correlated variables on predictive modeling. The results show that the proposed methods are superior to traditional prediction models and base ML models, where FWL is more suitable for modeling with small-sample datasets, and dimensionality reduction can simplify the data structure and reduce the adverse impact of the small-sample effect, which points the way to feature selection for predictive modeling. Based on the ensemble methods, the feature importance of the five primary factors affecting Ps is the maximum dry density (31.145%), clay fraction (15.876%), swell percent (15.289%), plasticity index (14%), and optimum moisture content (13.69%), the influence of input parameters on Ps is also investigated, in line with the findings of the existing literature.

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. [ABSTRACT FROM AUTHOR]

Phyllite residual soil is a typical regional soil formed from the weathering of phyllite rock formations, characterized by poor engineering properties. The swelling pressure could pose a threat to roadbed stability and other geological engineering disasters during the rainy season. Therefore, studying the swelling pressure of phyllite residual soil is critical for ensuring the sustainable development of both human society and the natural environment. In this study, a series of swelling pressure tests were conducted on the phyllite residual soil to determine its swelling pressure, and nuclear magnetic resonance (NMR) test was applied to assess the evolution of soil fabric in both the initial unsaturated state and saturated state. The results indicate that the swelling rate of phyllite residual soil is negatively correlated with the initial water content and positively correlates with the dry density. The denser or drier the phyllite residual soil is in its initial state, the higher the equilibriumswelling pressurewill be. The analysis of T2 distribution curves reveals that during the wetting process in phyllite residual soil, water fills micropores prior to macropores until water fills up all pores. [ABSTRACT FROM AUTHOR]

Swelling rocks and soils can generate significant swell or swelling pressure upon contact with water due to their special mineralogical composition, and thus a reliable determination of their swelling property is essential when evaluating the long-term safety and stability of adjacent geotechnical infrastructure. In this work, the swelling pressures of Yanji mudstone before and after seasonal wetting–drying (WD), freezing–thawing (FT) and wetting–drying–freezing–thawing (WDFT) processes were experimentally determined by zero-swell, load-swell, and swell-consolidation methods. It was found that the seasonal processes significantly reduced the swelling pressures determined by different methods because of the contraction of aggregates and the appearance of large pores and fissures/cracks. Due to the more intensive microstructure change, the WDFT process had a more detrimental influence on the swelling pressure of Yanji mudstone than separate WD or FT cycles. Moreover, a comparison among three determination methods showed that a larger swelling pressure was measured by the swell-consolidation method owing to the greater resistance of the even microstructure after hydration under a low vertical stress and the possible friction with cell wall during consolidation compared with the load-swell and zero-swell methods. With the increase of WDFT cycles, this difference method decreased because the large pores and fissures/cracks could increase the compressibility of swollen specimens in the swell-consolidation tests and accelerate the water infiltration in the zero-swell and load-swell tests. [ABSTRACT FROM AUTHOR]

This article aims at presenting the results of an experimental study using limestone waste from a mining operation in order to reduce the swelling potential of clay soil. Initially, the physical and mineralogical characterization of the materials were conducted. Next, tests were carried out to assess the percentage of heave and swelling pressure. Oedometric compression tests were performed with flooding stress of 5 kPa, 60 kPa and 120 kPa. The tests were carried out in pure soil (S), waste (limestone powder—LP) and waste/soil mixtures at mass proportions of 40%LP/60%S, 60%LP/40%S and 80%LP/20%S. The results showed that pure clay soil exhibited high swelling potential and swelling pressure. On the other hand, the limestone powder shows no expansion. Swell pressure and percent of heave decrease with the increase of the residue content in the mixture. The results obtained demonstrate that the use of 60% waste can stabilize clay soil against swelling when submitted to a minimum stress of 62 kPa, and that incorporating 40% waste stabilizes the soil when submitted to stresses above 280 kPa. [ABSTRACT FROM AUTHOR]

This paper presents the parametric analysis of a combined system of a low-volume concrete pavement, base layer and reinforced expansive soil, subjected to the stresses due to wheel loading and swelling of the soil. A soil-structure Interaction model is considered for the analysis, in which the pavement and the reinforcement are idealized as a finite beam, with plane-strain conditions, whereas a base layer and the expansive soil are modelled as Winkler Springs of different stiffnesses. During the analysis, it was taken into account that the geosynthetic reinforcement, which could be in the form of a geogrid, geocell, or a combination of both, possesses bending stiffness and is placed at the interface between the base layer and the expansive subgrade. The reinforcement layer is subjected to stresses due to wheel load, self-weight of pavement slab and surcharge load of the base layer at the top and the swelling pressure from the subgrade at its bottom. The governing differential equations for the flexural response of the model are derived and a closed-form solution is presented in a non-dimensional form. The outcomes of the parametric analysis highlight that the flexural response of the pavement is predominantly affected by the relative stiffness of the base layer and the expansive subgrade. In contrast, the relative flexural rigidity of the upper and lower beams has a comparatively minor impact on the model's response. Additionally, parameters like the depth of placement of the lower beam, unit weight of the upper soil layer, and the self-weight of the upper beam also contribute to influencing the response of the pavement model. The study suggests that, while designing for the concrete pavement, opting for an increase in the modulus of subgrade of expansive soil may be a preferable choice over reinforcing the foundation of the pavement. [ABSTRACT FROM AUTHOR]

This paper presents experimental studies on a compacted expansive soil, from Nanyang, China for investigating the at-rest lateral earth pressure σL of expansive soils. The key studies include (i) relationships between the σL and the vertical stress σV during soaking and consolidation, (ii) the influences of initial dry density ρd0 and moisture content w0 on the vertical and lateral swelling pressures at no swelling strain (i.e. σV0 and σL0), and (iii) evolution of the σL during five long-term wetting-drying cycles. Experimental results demonstrated that the post-soaking σL-σV relationships are piecewise linear and their slopes in the passive state (σL > σV) and active state (σL

Clayey soils exhibit significant volumetric changes in response to variations in water content. The swelling pressure of clayey soils is a critical parameter for evaluating the stability and performance of structures built on them, facilitating the development of appropriate design methodologies and mitigation strategies to ensure their long-term integrity and safety. We present a dataset comprising maximum swelling pressure values from 759 compacted soil samples, compiled from 16 articles published between 1994 and 2022. The dataset is classified into two main groups: 463 samples of natural clays and 296 samples of bentonite and bentonite mixtures, providing data on various types of soils and their properties. Different swelling test methods, including zero swelling, swell consolidation, restrained swell, double oedometer, free swelling, constant volume oedometer, UPC isochoric cell, isochoric oedometer and consolidometer, were employed to measure the maximum swelling pressure. The comprehensive nature of the dataset enhances its applicability for geotechnical projects. The dataset is a valuable resource for understanding the complex interactions between soil properties and swelling behavior, contributing to advancements in soil mechanics and geotechnical engineering. [ABSTRACT FROM AUTHOR]

Copyright of SDU Journal of Engineering Sciences & Design / Mühendislik Bilimleri ve Tasarım Dergisi is the property of Journal of Engineering Sciences & Design and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Expansive soils pose significant challenges to structural integrity, primarily due to volumetric changes that can lead to detrimental consequences and substantial economic losses. This study delves into the intricate dynamics of expansive soils through loaded swelling pressure experiments conducted under diverse conditions, encompassing variations in the sand content, initial dry unit weight, and initial degree of saturation. The findings underscore the pronounced influence of these factors on soil swelling. To address these challenges, a novel method leveraging machine learning prediction models is introduced, offering an efficient and cost-effective framework to mitigate potential hazards associated with expansive soils. Employing advanced algorithms such as decision tree regression (DTR), random forest regression (RFR), gradient boosting regression (GBR), extreme gradient boosting (XGBoost), support vector regression (SVR), and artificial neural networks (ANN) in the Python software 3.11 environment, this study aims to predict the optimal applied stress and dry unit weight required for soil swelling mitigation. Results reveal that XGBoost and ANN stand out for their precision and superior metrics. While both performed well, ANN demonstrated exceptional consistency across training and testing phases, making it the preferred choice. In the tested dataset, ANN achieved the highest R-squared values (0.9917 and 0.9954), lowest RMSE (7.92 and 0.086), and lowest MAE (5.872 and 0.0488) for predicting optimal applied stress and dry unit weight, respectively. [ABSTRACT FROM AUTHOR]

The long-term geological disposal of high-level radioactive waste relies on predictions of future changes in a disposal facility's hydro-mechanical characteristics to assess potential leakage through fractures in the excavation damaged zone (EDZ) after backfilling the facility. This study evaluated the transmissivity of EDZ fractures using in situ hydraulic tests around the area of a full-scale, experimental, engineered barrier system in the Horonobe Underground Research Laboratory, Hokkaido, Japan. After their installation, the buffer blocks swelled, altering the stresses within the EDZ fractures. The effects of these changing stresses on the fractures' transmissivity were assessed over a period of 4 years. The transmissivity continuously decreased in this period to about 41% of its value measured prior to the swelling. Using the Barton–Bandis normal-stress-dependent fracture-closure model, the decrease in transmissivity is quantitatively attributed to closure of the EDZ fractures, which was caused by the swelling pressure increasing up to 0.88 MPa. Evidence of fracture closure came from seismic tomography surveying, which revealed a slight increase in seismic velocity in the study area with increasing swelling pressure. The results show that EDZ fractures were closed by swelling of the full-scale buffer material. They also demonstrate the applicability of the Barton–Bandis model to preliminary estimation of the long-term transmissivity of EDZ fractures in facilities for the geological disposal of radioactive waste. [ABSTRACT FROM AUTHOR]

Soil swelling in road layer is the complex phenomenon. The paper aims to derive a concise expression for two challenging design parameters when the subgrade layer is expansive in geotextile-reinforced unpaved road. The design parameters considered in the present study are the mobilized bearing capacity and swelling pressure for expansive soil. Herein the dimensional analysis via Buckingham’s π method is applied to derive the design parameters by forming the dimensionless group for prototype and model system. The model testing for the swelling pressure and mobilized bearing capacity are carried out in the laboratory by using consolidometer ring and CBR set up. The test results reveal the swelling pressure of 22.03kN/m2 for the soil sample having 76% as degree of saturation. A linear relation is observed between swelling pressure and degree of saturation and becomes equal upon surcharge. The mobilized bearing capacity for the expansive soil sample is 0.47kg/cm2. The failure pattern observed during testing is general shear failure in unsoaked condition and punching soil failure in soaked condition. The paper provides geometric ratio of 1:6 for model and prototype and also suggests modification in Giroud and Han generic equation by including the developed dimensionless group.

Expansive soils pose major geotechnical challenges due to significant volume changes. This research investigates an innovative stabilization approach using sand, expanded polystyrene (EPS) beads, and jute fibres to enhance the properties of expansive soil. The purpose is to utilize the unique characteristics of these admixtures to restrict swelling potential and improve strength and load-bearing capacity. Experimental testing quantified improvements through parameters like unconfined compressive strength (UCS), swelling pressure, California bearing ratio (CBR), compaction characteristics, and Atterberg limits. Soil samples were prepared with individual and combined admixtures at optimum proportions and extensively tested after proper curing. Quantitative results indicated that including sand, EPS beads, and jute fibres increased the soil’s UCS by 41, 29, and 23%, respectively. The swelling pressure, on the other hand, decreased by 14, 18, and 11%, respectively. Maximum improvements were achieved with combined admixtures: UCS increased by 65%, swelling pressure reduced by 23%, and CBR improved from 5 to 6.5%. Regression analysis indicated a strong correlation (R 2 = 0.96) between admixture proportions and resultant UCS. The key achievements are effective swelling control, a marked increase in shear strength parameters, and synergy between admixtures in enhancing expansive soil properties. This sustainable stabilization method using industrial by-products presents a promising solution for constructing stable civil structures even in problematic expansive soil regions.

This study aims to investigate the wetting and swelling pressure characteristics of unsaturated compacted Ca-bentonite in contact with a cement-equilibrated fluid, focusing on the interface between the bentonite buffer and host rock. Water retention and swelling pressure tests were conducted on unsaturated compacted Ca-bentonite and Ca-converted bentonite specimens with varying initial dry densities and water contents using deionized (DI) water and the 0.02 M Ca(OH)2 solution as hydrating fluids. The results showed that the total suction decreased as the degree of saturation increased, whereas the degree of saturation increased with higher dry densities. A slight difference in the water retention (absorption) capacity was observed when using either DI water or the 0.02 M Ca(OH)2 solution as the hydrating fluid, depending on the degree of saturation. The swelling pressure increased with increasing initial dry density but decreased with increasing initial water content at a given dry density. Contact with the 0.02 M Ca(OH)2 solution slightly lowers the swelling pressure, which could be attributed to an osmotic effect caused by chemical potential differences, indicating the effect of a small fraction of Na in the interlayers. In addition, chemical alterations in bentonite had minimal impact on the swelling pressure because of limited interactions. These findings improve the understanding of swelling behavior at the interface between the bentonite buffer and host rock, emphasizing the significance of hydrating fluids, bentonite properties, and hydration processes. [ABSTRACT FROM AUTHOR]

Granular bentonite has been considered as candidate sealing material of various technological gaps in deep geological repository of high-level radioactive waste (HLW). Large inter-pellet pores inside the granular bentonite potentially work as preferential migration pathways of water, gas and radionuclides. During the long-term operation process, the inter-pellet pores will be filled by swollen pellets with the infiltration of groundwater, but it is still unclear how the inter-pellet pores evolve upon saturation and whether the mixture can reach a full homogenization. In this study, a series of constant-volume hydration tests and mercury intrusion porosimetry (MIP) tests were performed on bentonite pellet mixture and compacted bentonite powder. Results revealed that the development curve of swelling pressure for bentonite pellet mixture exhibited a double-peak shape. The first peak value of the pellet mixture was lower than that of the compacted powder at a given dry density, but their final swelling pressures were similar. At the initial hydration stage, the water content, dry density and degree of saturation profiles along the sample height showed obvious gradients, resulting in an apparent heterogeneity of the pore structures. As hydration proceeded, the gradients in the water content and dry density profiles tended to decrease. Simultaneously, the pellet mixture gradually evolved from a trimodal porosity to a bimodal one. The pellet mixture and the compacted powder both exhibited a similar bimodal porosity at nearly saturated state. The homogenization process of the pellet mixture was quantitatively analyzed by a heterogeneity coefficient related to microstructural evolutions. [ABSTRACT FROM AUTHOR]

Numerous engineering cases have demonstrated that the expansive soil channel slope remains susceptible to damage with the implementation of a rigid or closed protective structure. It is common for the protective structure to experience bulging failure due to excessive swelling pressure. To investigate the swelling pressure properties of expansive soil, the constant volume test was employed to study the influence of water content and reserved expansion deformation on the characteristics of swelling pressure in strong expansive soils, and also to explore the evolution mechanism of the swelling pressure. The findings demonstrate that the swelling pressure-time curve can be classified into swelling pressure-time softening and swelling pressure-time stability type. The swelling pressure-time curve of the specimen with low water content is the swelling pressure-time softening type, and the softening level will be weakened with increasing reserved expansion deformation. Besides, the maximum swelling pressure Psmax decreases with increasing water content and reserved expansion deformation, especially for expansion ratio η from 24% to 37%. The reserved deformation has little effect on reducing Psmax when it is beyond 7% of the expansion rate. The specimen with low water content has a more homogeneous structure due to the significant expansion-filling effect, and the fracture and reorganization of the aggregates in the specimens with low water content cause the swelling pressure-time softening behavior. In addition, the proposed swelling pressure-time curve prediction model has a good prediction on the test results. If necessary, a deformation space of about 7% expansion rate is recommended to be reserved in the engineering to reduce the swelling pressure except for keeping a stable water content. [ABSTRACT FROM AUTHOR]

Bamboo is a plant with various applications. As a natural, renewable material that exhibits good mechanical performance, it seems to be an interesting alternative to wood, which has become a scarce and expensive commodity. However, comprehensive knowledge of its properties is necessary to maximise its potential for various industrial purposes. The swelling behaviour of bamboo is one of the features that has not yet been sufficiently investigated. Therefore, in this research, we aimed to measure and analyse the swelling pressure and kinetics of bamboo blocks. The results show that similar to wood, the swelling kinetics of bamboo depend on its density: the denser the tissue, the higher the maximum swelling value recorded. The maximum tangential swelling measured was about 5%–6%, which is lower than the value for the most commonly used wood species. Swelling pressure ranged from 1.16 MPa to 1.39 MPa, depending on the bamboo density: the denser the sample, the shorter the time required to reach maximum swelling pressure. Like in wood, the smallest linear increase in size due to swelling was observed in the longitudinal direction (0.71%). However, opposite to wood, more pronounced swelling was recorded in the radial direction (over 7%) than in the tangential direction (nearly 6%). The results show that bamboo's swelling behaviour makes it a good material for use in variable humidity conditions, being more favourable than the unmodified wood of many species. [ABSTRACT FROM AUTHOR]

Expansive soils are one of the most problematic soils faced by civil engineers in various construction activities. It has the property to swell with the addition of water and shrink on water removal. The volume change behavior of expansive soil occurs vastly during seasonal changes in moisture conditions and can be significantly attenuated by chemically stabilizing the soil. In this study, calcium lignosulphonate (LS), a biopolymer, is added to the soil to curtail the swelling nature of the soil. Lime (L) is also used to treat the soil, and a comparative study is carried out to examine the effectiveness of LS. The expansive soil is treated with several combinations of cushion layers with 1.5% LS, 2% L, 4% L, and combination of 1.5% LS and 2% lime. To counter the swell pressure of the expansive soil, the treated soil and additive composites are placed as a cushion layer over the expansive soil with the replacement ratio of 1:1 and 1:2, represented as configuration "a" and "b." The swelling pressure of the proposed arrangement is evaluated through the constant volume swell apparatus. The soil layers are inundated from the bottom upwards, and the swell pressure is determined for the various configuration adopted. The effectiveness of the stabilized soil cushion over expansive soil is analyzed through the numerical software PLAXIS 2D for further extension to field conditions. As the replacement thickness of stabilized soil increases, the swell pressure decreases. Nevertheless, the lime-treated soil layer depicted lesser swell than the LS-treated soils. Analyzing the conditions for field situations in numerical analysis yielded consistent results with the laboratory inferences. [ABSTRACT FROM AUTHOR]

The findings revealed that the addition of nanoalginate and lime had distinct effects on various soil properties. Specifically, the liquid limit (LL) and plastic limit (PL) decreased when sodium nanoalginate and lime were added, while the plasticity index (PI) and shrinkage limit (SL) increased. Furthermore, the soil classification was altered when sodium alginate and lime were introduced to the control soil. Regarding the standard Proctor test, it was observed that adding sodium nanoalginate increased the maximum dry density and reduced the optimal moisture content, whereas lime had the opposite effect by decreasing the maximum dry density and increasing the optimal moisture content. The free swelling and swelling pressure tests indicated that the incorporation of sodium nanoalginate and lime reduced both free swelling and swelling pressure. The most significant reduction was observed in the sample containing 7% sodium nanoalginate and 5% lime. Additionally, the study highlighted the influence of processing time, showing that an increase in the curing time led to a decrease in free swelling and swelling pressure in samples mixed with 3% sodium nanoalginate and lime. The XRD test showed that adding sodium nanoalginate reduced primary minerals, forming SAH, while lime reduced quartz and calcite, creating CSH. Overall, the results suggest that sodium nanoalginate can be a more environmentally friendly alternative to lime for soil stabilization projects. [ABSTRACT FROM AUTHOR]

To construct an engineering barrier in a deep geological repository, bentonite generally should be laid out in blocks, which are commonly pre-prepared through uniaxial static compactions. The way of compaction and installation of the bentonite blocks will inevitably influence swelling performance of the bentonite compacted and eventually buffer functions of the engineering barrier system constructed. In this article, a new experimental apparatus was developed and cubic GMZ bentonite specimens with different initial suctions and dry densities were statically compacted. Swelling pressures were measured parallel to and perpendicular to the compaction direction/axis of the cubic specimens prepared in different ways. Results confirmed existence of the residual lateral stress and sidewall friction. The swelling pressure parallel to is higher than that perpendicular to the compaction axis, and its anisotropy coefficient tends to decrease to a certain degree upon hydration. Specimen with higher initial suction swells much quicker and exhibits a more significant intermediate period. The initial suction effects on anisotropy coefficient depend on hydration. The measured swelling pressure significantly increases with increasing dry density with about a 9.6- times increase as the density increased from 1.5 to 1.9 Mg/m3. The anisotropy coefficient of swelling pressure increases at first and then decreases a little bit with increasing dry density (e.g., the final anisotropy coefficient exhibited a 1% decrease while dry density changed from 1.8 to 1.9 Mg/m3). [ABSTRACT FROM AUTHOR]

A typical deep geological repository (DGR) design consists of a multi-barrier system, including the natural host rock and the engineered barrier system. Understanding the swelling behavior of bentonite-based sealing materials (BBSM), as a candidate material for the engineered barrier system, is crucial for DGR's long-term safety. In this study, a hydromechanical (HM) column-type test was designed to model the hydration of BBSM from the underground water and determine the resulting swelling pressure in vertical and radial directions. Five hydration tests were carried out on identical compacted samples of 70% bentonite and 30% sand (70-30 bentonite-sand) mixtures with a dry density of 1.65 g/cm3 for varied durations of hydration, between 1 day and 120 days. The experiments were performed parallel to the compaction direction. Following each HM column-type test, the advancement of the wetting front was determined for each test. After 120 days, 56,339 mm3 of water infiltrated the sample and the wetting front reached over 50% of the sample height. The evolution of axial swelling pressure revealed an initial increase in swelling pressure with time in all tests, followed by a reduction in the rate at later times. After early stages of swelling, radial sensors showed an increase in swelling pressure. After 120 days, the radial pressure sensor closest to the hydration front showed 52% more radial pressure than the axial swelling pressure. [ABSTRACT FROM AUTHOR]

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.

Phyllite soil and red clay belong to the soils that negatively impact the engineering performance of railway subgrade and may cause subgrade bulges, uneven subgrade settlement, and other subgrade distresses. In order to make full use of these two soils, a collaborative improvement plan was proposed. A series of tests were conducted to analyze the synergistic effects of lime and red clay on the improvement of phyllite soil. The tests included the no loading swelling ratio, swelling pressure, consolidation, and direct shear tests. Additionally, scanning electron microscopy was used to investigate the role of lime and red clay in soil improvement. The test results show that a red clay ratio of 60% + lime content of 3% is the optimal composite improvement scheme. The scheme led to a 93% reduction in the no loading swelling ratio and an 88% reduction in swelling pressure. Additionally, cohesion, the internal friction angle, and the compression modulus increased by 345%, 73%, and 373%. Red clay and lime had weak synergistic improvement effects on the no loading swelling ratio, the swelling pressure, and the internal friction angle of phyllite soil, that is, the synergistic improvement effect of red clay and lime was less than the sum of the single improvement effect but greater than the single improvement effect. Red clay and lime had a strong synergistic improvement effect on the cohesion and the compression modulus of phyllite, that is, the synergistic improvement effect of red clay and lime was greater than the sum of the single improvement effect. The microstructure analysis test results show that red clay can fill the pores of phyllite soil and improve its immediate strength. Through hardening and cementation, lime can enhance the strength of phyllite soil as well as address the issue of the reduced engineering properties of phyllite soil and red clay when exposed to water. Red clay and lime promote each other's reactions and have a synergistic improvement effect on phyllite soil. [ABSTRACT FROM AUTHOR]

Expansive soils, characterized by their propensity to undergo volume changes in response to moisture variations, pose significant challenges to civil engineering due to the presence of the montmorillonite mineral. This mineral exhibits a high capacity for water absorption, leading to volumetric expansion and consequent soil heave. This study aims to provide a comprehensive understanding of the behavior of expansive soils, focusing on variations induced by different proportions of bentonite enrichment. In this research, both experimental and theoretical approaches are employed. Experimentally, the swell percentage, liquid limit, plastic limit, shrinkage limit, maximum dry density, and optimum moisture content are determined for three bentonite-enriched soil samples: clay with 40%, 60%, and 80% bentonite. Theoretically, the validity of existing empirical equations is assessed in light of the experimentally observed behavior of the bentonite-enriched soils. This dual approach allows for a nuanced understanding of the behavior of expansive soils and provides a foundation for the development of more accurate predictive models. Through this integrated analysis, this study contributes to the body of knowledge on the impact of expansive soils on civil engineering structures and offers a pathway towards more effective management of these challenges. [ABSTRACT FROM AUTHOR]