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Slope failures and slope slides of expansive soils are usually characterized by shallow sliding along the surface crack. Soilbag is an effective method to prevent and control slope failures and slope slides of expansive soil. Currently, soilbag protection for expansive soil slopes has been commonly designed using empirical methods, which led to many failures of soilbag-protected slopes, or high-cost. In this paper, a new design method of the soilbag-protected slopes in expansive soils is proposed based on the balance between the soilbag friction and the active lateral earth pressure induced by the swelling pressure of expansive soils. Specifically, the friction between the soilbags is assumed to be in direct proportion to the soilbag heap-up height. The active lateral earth pressure acted on a layer of soilbag is calculated along with the total height of the slope. Moreover, the width of soilbag layers is calculated from the balance of the sum of soilbag friction and the total active lateral earth pressure along with the soilbag height and expressed by the height of slopes. For the convenience of soilbag construction, the heap-up unit of soilbags is proposed for different slope heights of expansive soils.

The valorization of waste materials in the stabilization and reinforcement of soils is considered one of the most appropriate ways to reduce environmental pollution problems and to preserve natural resources, as it can also contribute to reducing the cost of produced materials. The main disadvantage of using fibres in geotechnical engineering remains their cost, which has limited their use in soil reinforcement. This paper focuses on the use of rubber fibres from used tires to reduce the potential for clay swelling, and the effect of this kind of fibre on swelling behaviour of soils. The reinforcement of the clays used in this work was made by the incorporation of rubber fibres at different weight contents; 0%, 1%, 2.5% and 10%. Eight mixtures were prepared and tested on swelling. The results of the experimental investigation show that the induction of rubber fibres at low percentages (1 and 2.5%) considerably reduces the amplitude and the swelling pressure of the clay. For a fibre content of 10%, the compressibility of the reinforced mixture becomes high. The obtained results also confirm the possibility of using the tires rubber waste as a material for reinforcing or stabilizing clay soils, which is very important in many applications especially in road engineering.

Structures constructed on expansive soils are experiencing higher upward pressure due to swelling- shrinkage nature of expansive soil. India has 15–20% expansive soil, which causes severe damage to the existing structure, including pavements, dams, multi-storey buildings, retaining walls. The aim of the study is to suitably reduce the distressed caused by the expansive soil on paved structures. The experimental result of expansive soil subgrade reinforced with and without coir geotextile mat has been presented in this paper. Lime and silica fume, treated and untreated coir geotextile mat with polypropylene fiber net has been used. A single and double layer of coir geotextile mat at various depths have been placed to evaluate the effect of reinforcement on expansive soil subgrade. The treatment was carried out to enhance the efficiency of coir geotextile for reducing the swelling pressure of the expansive soil subgrade. The chemical and microstructural components of expansive soil samples were investigated by using X-ray Diffraction (XRD) and Fourier Transform Infrared (FTIR). The constant volume swelling pressure, California Bearing Ratio (CBR) and large size direct shear (300 mm × 300 mm × 150 mm) tests have been carried out to evaluate the effect of treated and untreated coir geotextile on expansive soil subgrade. The experimental results analyzed indicates that the lime treated coir geotextile mat reduces the upward swelling pressure by 52.19% in single-layer and 81.89% in double-layer. The tangible improvement in the shear strength and bearing capacity of expansive soil subgrade was observed with the inclusion of lime treat coir geotextile. A lime treated coir geotextile in a single or double-layer can be used to stabilize the expansive soil subgrade. The improved property of reinforced expansive soil subgrade can reduce the thickness of the subbase and base course layer in paved structure.

In this study, the influence of rock fracture on the swelling behavior of compacted bentonite was investigated experimentally with bentonite compacted inside a hollow cylinder of fractured Beishan granite from China. During the test, hydration was allowed by letting water flowing into the compacted bentonite from the base plate, and air being expelled from the top plate. Along the sample, swelling pressure and relative humidity were monitored at different positions. Results showed that the presence of rock fracture significantly changed the hydration process of compacted bentonite. The evolutions of swelling pressure were directly related to the relative position to the rock fracture. At the same height, for the position closer to the rock fracture, a larger decrease in local dry density occurred, resulting in a larger loss in swelling pressure. This suggests that in field conditions of radioactive waste repository involving bentonite and rock, local filling of rock fracture by bentonite may occur, and the resulted bentonite swelling pressure decrease must be accounted for in the safety evaluation of the whole storage system.

Investigation of the swelling pressure of compacted bentonite is of great importance in evaluating the performance of the engineered barrier system in deep geological repositories for disposal of high-level radioactive waste. In this study, three methods including Cui method ( Cui et al., 2013 ), swell-consolidation method and constant-volume method were employed for determining the swelling pressure of compacted GMZ01 bentonite with infiltration of different concentrations of salt solutions. The swell-consolidation method gave higher value of swelling pressure, while the other two methods produced almost the same values. A critical void ratio was determined for separating the swelling induced by combination effects of double-layer swelling and crystalline swelling from that caused by the effect of crystalline swelling. Based on this, the salt solution effect on swelling pressure can be well explained. For specimens with a void ratio higher than this critical value, swelling pressure decreases with the increase of concentration of NaCl solution, due to the inhibition of the double-layer swelling and crystalline swelling. On the contrary, in case of void ratio near this critical value, the salt solution effects become negligibly. Conclusions reached on GMZ01 bentonite in this work are useful for determination of geological engineering parameters for construction of the Chinese deep geological repository.

This paper discusses the laboratory study of performance on expansive soil reinforced with polypropylene fiber and demonstrates that discrete and randomly distributed polypropylene fiber is useful in restraining the swelling tendency of expansive soils. Swelling characteristics of remoulded expansive soil specimens reinforced with varying fiber content (f = 0.2%, 0.3%, 0.4% and 0.5%) and aspect ratio (l/b = 15, 30 and 45) were studied. One dimensional swell-consolidation tests were conducted on consolidometer specimens. Reduction in heave and swelling pressure was the maximum at low aspect ratios at both the fibers contents of 0.2%, 0.3%, 0.4%, and 0.5%. Finally, the mechanism by which discrete and randomly distributed polypropylene fiber restrain swelling of expansive soil is explained with the help of soil-fiber interaction.

The swelling pressures of bentonites have been studied extensively due to their potential use as a barrier in radioactive waste disposal repository. Due to the radioactive decay of the waste, the temperature will increase in the repositories. Several experimental studies of the temperature dependence of the swelling pressure of smectites have been published while theoretical studies have received less attention. Atomic level simulations have been proven to be useful in broadening the understanding of clay materials in various conditions. Therefore, molecular dynamics simulations were carried out to predict thermal effects on the swelling pressure of a sodium smectite clay. The study focused on two temperature regimes. In the first regime, the clay was placed in a frozen environment and heated while the second regime involves heating the clay-water system from room temperature. At low temperatures gradual melting is observed and the onset of the swelling takes place around 250 K. At temperatures in the range of 300 K–600 K a slight increase in the swelling pressure is observed. The results can be used to rationalize experimental findings in the swelling pressure studies of smectite clays.

Alkali-silica reaction (ASR) of reactive aggregates is a major durability concern of concrete. The use of fly ash as a supplementary cementing material (SCM) shows a reliable way to control ASR expansion. This paper investigates the recent findings on effects of coal fly ash as a SCM on ASR of reactive aggregates. ASR is the reaction of amorphous silica of aggregates with highly alkaline pore solution in the binder matrix producing an expansive gel. The use of fly ash as cement replacement reduces pH of the pore solution by alkali binding and thus reduces the aggregate dissolution rate and swelling pressure of the ASR gel. The efficiency of fly ash primarily depends on its chemical composition with low calcium fly ash being more effective in mitigation of ASR expansion. Based on the available literature, this paper also analyses the ASR mitigation mechanisms of fly ash and provides some recommendations for future research. The degree of aggregate reactivity measurement, effect of alumina in fly ash, swelling properties of ASR gel in presence of fly ash and the long-term alkali contribution of fly ash on ASR are of particular importance.

This paper proposes a hydro-mechanical model of GMZ bentonite, based on the considerable amount of experimental research that has been developed recently. The model uses a double porosity approach based on the framework provided by the Barcelona Expansive Model to describe the deformability of the bentonite. A state surface was used to define its microstructural behaviour, based on the high-suction range data from water retention curves. The intra-aggregate (microstructural) and inter-aggregate (macrostructural) water contents were differentiated. The proposal was satisfactorily applied to simulate several constant stress swelling tests and swelling pressure tests, improving the confidence in the model. The use of this model has allowed not only reproduction of the experimental data but also improvement of our knowledge of GMZ bentonite behaviour.

A compacted mixture of Callovo-Oxfordian (COx) claystone/MX80 bentonite is a promising sealing material in the French Cigeo project for radioactive waste disposal at great depth. Over time, the sealing material will be saturated by the site water originating from the surrounding rock and the water chemistry can affect the performance of the sealing material. In this study, the effects of water chemistry and technological gaps on the hydro-mechanical property were investigated by performing hydration tests on the compacted claystone/bentonite mixture with technological gaps using deionised water and synthetic site solution for 10 and 590 days. After the tests, the dry density, water content and microstructure distributions were also determined to complement the program. Results show that the synthetic site solution did not affect the swelling pressure and hydraulic conductivity after a short term of 10 days. With the increase of hydration time, the specimens with technological gaps tended to be homogeneous, resulting in a reduction of hydraulic conductivity. Because of the cation exchanges and the decreased diffuse double layer thickness, the synthetic site solution reduced the swelling pressure and increased the hydraulic conductivity in long term, especially for the specimens with lower global dry densities.

The design of sealing/backfill elements in high level radioactive waste disposal repository often depends on the laboratory results in terms of swelling pressure and hydraulic conductivity. In this study, a series of swelling pressure test were performed on compacted specimens of MX80 bentonite and Callovo-Oxfordian (COx) claystone mixture with different initial stress state (with and without residual stress relaxation), aiming at investigating the effects of compaction induced residual lateral stress on the swelling pressure. Two methods named “Trimming” and “Transfer” were applied for the residual stress relaxation; whereas specimens were directly compacted in the hydration ring to simulate the case without residual stress relaxation. A higher swelling pressure was obtained on the specimens directly compacted in the testing ring compared to their counterparts with residual stress relaxation. Regarding to the relaxation methods, “Transfer” is more practical for specimen preparation in the laboratory, as it allows the relaxation of the stress without changes in specimens' diameter and mass.

Higher activity radioactive wastes represent a significant long-term human and ecological hazard. There is an international consensus that geological disposal of these materials is the most responsible approach to their long-term management, in order to safely contain and isolate them from people and ecosystems. Some higher radioactivity disposal concepts use a bentonite barrier to surround metallic waste containers. For bentonite to satisfy its function as a barrier material, it is required to protect waste containers from corroding agents, limit the release of radionuclides, provide stability against rock displacements, and ensure excess gas pressure build-up does not occur. Microbial processes within bentonites, if they develop, have the potential to alter the properties of the material and associated pore waters. This review therefore focuses on the microbial colonization of bentonite buffers, and in particular examines the roles of (i) sulphide-producing bacteria (SPB) and (ii) iron(III)-reducing bacteria (IRB). These groups are significant, since sulphide production is implicated in container corrosion and longevity and, the reduction of structural iron(III) in bentonite could affect its geo-chemical/physical properties. Conversely, microbial activity may have positive safety case-related functions, reducing radionuclide transport by transforming radionuclides into insoluble forms and reducing gas build-up by consuming hydrogen, for example. On balance the review indicates that preventing microbial activity within bentonite buffers, to avert any potential deleterious effects, is a higher priority than harnessing any potential benefits which may arise. In order to do this, bentonites used in a geological disposal context, e.g., in barrier systems, should be engineered so as to be able to attain a swelling pressure, on re-saturation, to an extent proven to disrupt microbial activity. Some uncertainty remains, however, in very long-term evolution of the bentonite, where degradation and loss of swelling pressure may occur in localized areas. Further research should consider the rates of microbial growth and metabolism under repository relevant conditions, through experimentation, study of natural analogues and numerical modelling.

Bentonite pellet-contained material (PCM) has been recognized as a candidate for the buffer/backfill material in deep geological high-level radioactive waste repository. The PCM has a more complex initial structure comparing with bentonite powder (BP). The difference in the initial structure may cause a difference in the swelling response. In the current work, the swelling pressure of the PCM and BP specimens with varying dry densities was investigated using the zero-swell method. The results showed that the swelling pressure of BP continuously increased. However, the swelling pressure of the PCM increased initially, followed by a decreasing period (i.e., collapse), and reincreased again until the final swelling pressure reached. Besides, the final swelling pressure of the PCM was larger than that of the corresponding BP. The deviation was further discussed based on the scanning electron microscopy images, pore size distribution curves, and the swell index tests.

The present study investigates the geotechnical characteristics of cemented clay-crumb rubber mixture through a series of compaction, UCS, STS, CBR, one-dimensional consolidation and swelling pressure tests. Crumb rubber (0.8–2 mm size) and cement content in the mixtures were 0%, 2.5%, 5%, 7.5%, and 10%, and 0%, 3%, and 6% by the dry weight of the specimens, respectively. The results of experimental research indicated that incorporation of crumb rubber in cemented clayey soil decreases the UCS and STS but prosperously able to overcome the brittleness of cemented clay in compression and tension. The CBR values of the composite having 6% cement were found to be propitious for its use as road sub-base with light traffic. It was also noticed that crumb rubber helps in reducing the swelling pressure and compression index of the mixes, which make it is a good candidate for lightweight fill material behind the retaining walls and embankment construction. Incorporation of crumb rubber in uncemented and cement clayey soil potentially reduces the reinforcement cost and deteriorating impact of waste tire disposal on the environment.

An extended reference fluid density approach/weighted correlation approximation (RFD/WCA) of density functional theory (DFT) for size-asymmetric electrolytes presented in part I is applied to calcu ...

Swelling pressure of dioctahedral smectites in the montmorillonite – beidellite series was investigated by molecular dynamics simulations. The pressure was found to correlate inversely with the magnitude of the layer charge in the range of −0.5 to −1.0 per unit cell. The beidellite type smectites were found to have lower swelling pressure than the montmorillonite type smectites. A clear effect of the type of interlayer cations on the swelling pressure was found. The sodium smectites sustained significant pressure even at longer interlayer distances, while in calcium smectites the pressure decreased soon after the initial swelling. The simulation results are in good agreement with experimental observations and provide a tool for predicting macroscopic swelling behavior in smectites.

Highly-compacted bentonite (HCB)-based sealing systems are being developed for potential use in nuclear fuel waste repositories because of their inherent physicochemical and rheological properties. Results from previous short-duration (40–90 days) studies with highly-compacted (HC), water infused, confined Wyoming MX-80 bentonite revealed that a uniform dry density ≥ 1.6 g/cm3 (resulting in a swelling pressure above 2000 KPa, water activity below 0.96 and an average pore size of

Bentonites are suitable candidates as buffer and backfill materials in HLW-repositories. A target of this research is to define the mineralogical alteration of bentonite caused by its interaction with iron powder, which simulates the contact of bentonite with a steel container. Compacted MX80 bentonite and Friedland clay (raw density of 1.6 g/cm 3 ) were used as the initial materials for clay/iron interaction experiments (10 wt.% of iron) involving percolation with NaCl or Mg-rich IP21 solution. These experiments were conducted at 25 °C, 60 °C, and 90 °C and a suite of analytical techniques was applied to identify the mineralogical transformations. Smectite was the main phase and was fully expandable in all reaction products, though the octahedral and tetrahedral compositions were altered. “Illitization” was found as a main process of smectite alteration and was caused by the percolation component of these experiments. Smectitization occurred only when Fe-oxidation was considerable. The alteration of smectite was mainly driven by the high alkaline pH-value resulting from Fe-corrosion. Different interstratified phases like kaolinite–smectite–dioctahedral vermiculite, berthierine–saponite, chlorite–saponite–trioctahedral vermiculite, and cronstedtite–saponite–trioctahedral vermiculite interstratifications were identified as neo-formed phases which were formed in minor amounts. Cementation of particles by Fe- or Si-precipitation was assumed to reduce swelling pressure and permeability.

Bentonite has been considered as a potential buffer material in engineering barriers of high-level radioactive waste disposal systems. The intrusion of groundwater and heat from the waste change the temperature and chemical composition of the bentonite, consequently can alter the mechanical properties of the bentonite. In this study, thermochemical effects on the swelling behaviors were observed in compacted Ca-bentonite samples. Laboratory tests were conducted on Korean Gyeongju bentonite blocks that were compacted at different dry densities. Swelling pressure tests at various temperatures between 30 °C and 90 °C were carried out by supplying de-ionized water, NaCl solution, and CaCl2 solution. The study revealed that at higher temperature the bentonite swells faster, but the final swelling pressure decreases in the higher temperature condition. As for the chemical effect, the final swelling pressure at the same temperature shows an order: CaCl2 > De-ionized water > NaCl. In addition, the swelling behavior of the bentonite during a thermal loading cycle was experimentally investigated. The swelling pressure at the same temperature revealed different values depending on whether the bentonite was heated up or cooled down. The result demonstrated that the temperature change history should be a significant factor in determining the swelling pressure of bentonite buffers.

The swelling of clay at high temperature and pressure is important for applications including nuclear waste storage but is not well understood. A molecular dynamics study of the swelling of Na montmorillonite in water at several temperatures (T = 298, 400, and 500 K) and water environment pressures (Pe = 5 and 100 MPa) is reported here. Adopting a rarely used setup that enables swelling pressure to be resolved with an accuracy of ~1 MPa, the swelling pressure was computed at basal spacings 1.6–2.6 nm (or 2–5 water layers between neighboring clay sheets), which has not been widely studied before. At T = 298 K and Pe = 5 MPa, swelling pressure Ps oscillates at d-spacing d smaller than 2.2 nm and decays monotonically as d increases. Increasing T to 500 K but keeping Pe at 5 MPa, Ps remains oscillatory at small d, but its repulsive peak at d = 2.2 nm shifts to ~2.0 nm and Ps at different d-spacings can grow more attractive or repulsive. At d > 2.0 nm, Ps is weakened greatly. Keeping T at 500 K and increasing Pe to 100 MPa, Ps recovers toward that at T = 298 K and Pe = 5 MPa, however, the repulsive peak at d = 2.0 nm remains the same. The opposite effects of increasing temperature and pressure on the density and dielectric screening of water, which control ion correlations and thus double layer repulsion, are essential for understanding the observed swelling pressure at elevated temperatures and its response to environment pressures.

Interlayer swelling pressure of smectite minerals was investigated at atomic level using molecular dynamics simulation method. Four different alkaline-earth cations were used as interlayer cations for simulated montmorillonite and beidellite minerals. The swelling pressures of the smectite minerals were obtained as function of interlayer cation, layer charge, charge location, dry density and d-spacing. The swelling pressure of the homoionic smectites follows the trend Mg2+ > Ca2+ > Sr2+ > Ba2+. Layer charge and charge location have also a notable effect on swelling pressure. Octahedrally substituted smectites show higher swelling pressure than tetrahedrally substituted, while lower layer charge lead to higher pressure than higher layer charge. The results have practical implications in the selection and predicted behaviour of backfilling clay materials for geodisposal of high-level radioactive waste.

The hydro-mechanical properties of the buffer material play an important role in the design of deep geological repositories. This paper presents the effect of various electrolyte concentrations on swelling pressure, consolidation characteristics and hydraulic conductivity of two different Indian bentonites. Constant volume swelling pressure tests on compacted bentonite specimens as well as consolidation tests on saturated bentonite specimens were carried out by supplying 0, 0.1, 0.5 and 1.0 N NaCl and CaCl2 solutions. The change in morphology and microstructure of bentonite specimens were examined by Scanning Electron Microscope (SEM) and XRD analysis. The hydraulic conductivity was calculated based on consolidation test results. At a dry density of 1.4 Mg/m3 both swelling pressure and hydraulic conductivity of divalent bentonite were found to be approximately 2.9 and 7.3 times higher than that of monovalent bentonite when saturated with deionized water. The electrolyte solutions altered the morphology, microstructure and hydro-mechanical properties of the monovalent bentonite significantly; however, the effect was found to be negligible for divalent bentonite. An empirical equation is proposed to predict the hydraulic conductivity of the bentonites. A good correlation between experimental and predicted hydraulic conductivity of bentonites is obtained. The divalent bentonite was found to be better suitable engineered barrier material in the electrolyte environment, whereas monovalent bentonite was found preferable at low salinity conditions.

The lumped mass model is derived from a one-mode Galerkin discretization with the Gauss–Lobatto quadrature applied to the non-linear swelling pressure term. Our reduced-order model of the problem is then analyzed to study the essential dynamics of an elastic cantilever Euler–Bernoulli beam subject to the swelling pressure described by Grob’s law. The solutions to the initial value problem for the resulting nonlinear ODE are proved to be always periodic. The numerical solution to the derived lumped mass model satisfactorily matches the finite difference solution of the dynamic beam problem. Including the effect of oscillations at the base of the beam, we show that the model exhibits resonances that may crucially influence its dynamical behavior.

Interlayer cations largely determine the swellability of expansive clays. An atomic level study was carried out to determine the effect of monovalent interlayer cations on the swelling behavior of two different smectite minerals to establish their swelling pressure trends. Montmorillonite and beidellite clay minerals were simulated with five different alkaline metals as interlayer cations: Li+, Na+, K+, Rb+, and Cs+. A molecular dynamics simulation method was employed with varying charge balancing cations, layer charges and charge locations. The swelling pressure of homoionic smectite decreased as the interlayer cation progressed down the group from Li+ to Cs+ yielding the following trend: Li+ > Na+ > K+ > Rb+ > Cs+. The effects of layer charge and charge location were also evident. The outcome of this study is useful for the selection of smectite buffer materials for use in high-level radioactive waste disposal repositories.

The work studies not salted Sarmatian clays from the Central Moldova. Laboratory modeling of a long-time influence the water has on clays is executed. Changes of structure and properties of Sarmatian clays owing to diffusive leaching for 3 months are analyzed. Typification of a clays according to their resistance to flood is developed and the technique of the forecast of durability indicators of the clays which are exposed to flood in foundations of buildings and constructions is offered.

Swelling anhydritic rock can cause severe damage to tunnels. Even though this phenomenon was first observed more than a century ago, many knowledge gaps persist concerning the swelling mechanisms caused by the transformation from anhydrite to gypsum. One of these gaps is the relationship between swelling pressure and swelling strain. This paper presents experimental research results concerning the stress dependency of the swelling caused by anhydrite to gypsum transformation.

This study has evaluated the swelling of meniscal test samples associated with altered osmotic environments. Meniscal samples were cut and weighed, then placed in one of 3 solutions: deionized water, phosphate buffered saline (PBS) or 2× concentration PBS. The amount of swelling in meniscal samples was solution independent with average swelling greater than 20%. The effect of this swelling on the mechanical properties of the samples was evaluated under confined compression testing. Samples were measured using a photogrammetric technique at the time of sample preparation and again after 1 h in PBS. Meniscal samples used for mechanical testing swelled on average 18% in thickness after 1 h in isotonic PBS. Free-swollen tissue was 1/3 as stiff at equilibrium as those that were recompressed to their original thickness prior to testing. Secant moduli at peak stress were nine times greater in the recompressed samples than the free-swollen samples. Relaxation times were faster in swollen samples, indicating increased permeability compared to recompressed specimen. Swelling pressure in the tissue averaged 14.4 kPa in isotonic PBS, identifying that the menisci are pre-stressed structures within the knee joint. Histological analysis identified that the quantity of swelling is related to both the osmotic pressure generated by proteoglycans and the local collagen architecture in the sample. This is the first study to quantify the amount and swelling in meniscal test samples. This swelling behavior significantly influences the properties of the tissue in compression and should be addressed in future mechanical testing and protocol development for the menisci.

The Danish Tertiary Holmehus clay belongs to the series of illite-smectite mixed-layer clays in northern Europe and has a potential to serve as an effective engineered barrier for isolating hazardous waste. Mineralogical specification was made of the components illite/smectite mixed-layer and dioctahedral vermiculite/smectite mixed-layer structures. The lower content of expandable phase than of smectite- rich clays like MX-80 gives somewhat higher hydraulic conductivity and somewhat lower swelling pressure but both are deemed suitable for isolating canisters with high-level radioactive waste in deeprepositories for densities at water saturation of at least 1900 kg/m3. The lower swelling pressure, the potential of being chemically more stable, and the high buffer capacity by providing dissolved Si makes Holmehus clay a candidate for use in both deep and near-surface repositories. Validerad; 2015; Nivå 2; 20140310 (svek)

The swelling capacity is one of the most characteristic properties of bentonites. This property, along with others, made bentonite a candidate material for the safe disposal of high-level radioactive waste (HLRW). For HLRW-barrier systems the swelling pressure is of particular interest because it basically controls sealing properties (a large swelling pressure generally results in low permeability). Commonly, the swelling pressure is investigated as a function of compaction and hence plotted against the density, usually the dry density. Different dry density/swelling pressure relations of bentonites were published. Therefore, the aim of the present study was to identify reasons for these differences. To be able to compare a significant set of different bentonites, a small scale swelling pressure device was developed which is based on measuring a swelling pressure related value of 500 mg bentonite powder. This device allowed recording about 200 single values (in duplicate) and hence dry density/swelling pressure relations of thirty six different bentonites. The differences of the dry density/swelling pressure plots of different bentonites could be explained by i) different ways to obtain a range of dry densities (either constant load or constant water content), ii) different portions of uncompactable porosity of the different bentonites, and iii) different smectite contents.

This paper aims to theoretically investigate and characterize the failure mechanism of hydrated bentonite plugs, when used as a sealing material in wellbores. Using the proposed theoretical models, it was determined that when hydrated bentonite plugs failed due to friction at the walls, created by internal swelling pressure or through internal shear failure, the resulting failure pressure was linear with the plug height (H), coefficient of friction or internal shear strength, and inversely proportional to plug diameter (D). On the other hand, if the friction at the walls was created by plug weight then the failure pressure was a function of H2/D. However, in this case, the frictional strength increased parabolically with height, and, at reasonable plug heights, the frictional strength became greater than shear strength, and resulted in failure due to internal shear failure, which also made the failure pressure a function of H/D. This suggests that plug strength is usually a linear function of H/D. Moreover, the coefficient of friction and internal shear strength are dependent on final moisture content of the hydrated plug, the salinity of the hydration water, pressure, temperature and hydration time. The strength of a bentonite plug is inversely proportional the total volume by which it expands during hydration and takes in excess of 185 days to achieve this state. Plug strength decreased in saline water, although even at elevated concentrations sufficient strength remained to produce and adequate seal.From very limited data, shown here, Queensland bentonite, from the 5D zone of Amcol's Gurulmundi mine, appeared to have similar plugging strength as Wyoming bentonite.

A series of unsaturated tests on the GMZ bentonite–sand mixture at different dry densities and sand ratios are analyzed. This mixture is proposed as buffer/backfilling material in the Chinese concept for radioactive waste disposal. The water retention properties were studied under both confined and unconfined conditions; the results show that the water retention capacity is independent of the confined conditions and dry density if the suction is greater that about 4–5 MPa, and by contrast, at low suctions ( 3 or sand ratio increasing from 30% to 50%, always lower than 2.0 × 10 − 12 m/s. Furthermore, the swelling pressure at different position of specimen was monitored during the infiltration process, and the dry density distributions have also been determined at the end of the tests. Therefore, this method can be used for engineering purposes to predict the unsaturated hydraulic parameters at an early stage of a design to get an idea of the required design and hence, cost.

International audience; Pre-compacted elements (disks, torus) of bentonite/sand mixture are candidate materials for sealing plugs of radioactive waste disposal. Choice of this material is mainly based on its swelling capacity allowing all gaps in the system to be sealed, and on its low permeability. When emplaced in the gallery, these elements will start to absorb water from the host rock and swell. Thereby, a swelling pressure will develop in the radial direction against the host rock and in the axial direction against the support structure. In this work, the swelling pressure of a small scale compacted disk of bentonite and sand was experimentally studied in both radial and axial directions. Different swelling kinetics were identified for different dry densities and along different directions. As a rule, the swelling pressure starts increasing quickly, reaches a peak value, decreases a little and finally stabilises. For some dry densities, higher peaks were observed in the radial direction than in the axial direction. The presence of peaks is related to the microstructure change and to the collapse of macro-pores. In parallel to the mechanical tests, microstructure investigation at the sample scale was conducted using microfocus X-ray computed tomography (μCT). Image observation showed a denser structure in the centre and a looser one in the border, which was also confirmed by image analysis. This structure heterogeneity in the radial direction and the occurrence of macro-pores close to the radial boundary of the sample can explain the large peaks observed in the radial swelling pressure evolution. Another interesting result is the higher anisotropy found at lower bentonite dry densities, which was also analysed by means of μCT observation of a sample at low bentonite dry density after the end of test. It was found that the macro-pores, especially those between sand grains, were not filled by swelled bentonite, which preserved the anisotropic microstructure caused by uniaxial compression due to the absence of microstructure collapse. © 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences.

International audience; Bentonite has been adopted as a buffer/sealing material in most high-level radioactive waste disposal programs. After emplacement in the repository, bentonite will undergo alkaline chemical effects due to cement degradation, changing its hydro-mechanical behaviour. In this study, the swelling pressure of compacted GMZ bentonite at an initial dry density of 1.7 Mg/m3 was investigated with two synthetic cement solutions (Young Cement Water -YCW and Evolved Cement Water -ECW) at temperatures of 20 and 60 °C. After swelling tests environmental scanning electron microscope (ESEM), mercury intrusion porosimetry (MIP) and X-Ray diffractometry (XRD) tests were also performed to analyse the morphology, microstructure and mineralogy characteristics of the specimens.Results show that the swelling property of bentonite would degrade with time under the in-situ pore water and temperature conditions of repository. With cement solutions injection, a mass of macro-pores in compacted bentonite transforms into micro-pores, especially, in case of YCW with higher temperature. Cation exchanges, smectite dissolution and secondary minerals formation (some zeolites and C-S-H gels) are found to occur in compacted GMZ bentonite. Increasing temperature accelerates the smectite dissolution rate. The dissolution of montmorillonite and the formation of secondary minerals should be the fundamental reasons for the swelling pressure decline, and then microstructure change.

MX80 bentonite/Callovo-Oxfordian (COx) claystone mixture has been proposed as a sealing/backfilling material in a deep geological repository of radioactive waste in France. A good understanding of the swelling behaviour of this mixture is essential when evaluating the long-term performance of the repository. In this work, the swelling pressure of MX80 bentonite/COx claystone mixture was investigated by the constant-volume method for a full range of bentonite fraction. Results show that the swelling of claystone in the mixture can be inhibited by bentonite and its contribution to the global swelling pressure depends on the bentonite fraction. For the mixture with >70% bentonite, claystone behaves as an inert material, and its contribution to the global swelling pressure can be ignored. However, for the mixture with less bentonite, the swelling of claystone will significantly contribute to the global swelling pressure. A method was proposed allowing the swelling pressure of bentonite/claystone mixture to be predicted in the full range of bentonite fraction.

Ageing effects on the swelling properties of compacted GMZ01 bentonite are investigated in this paper. Samples were compacted to prescribed dry densities and water contents and kept for ageing under constant volume and K0 confined conditions for target days of 0, 1, 7, 15, 30 and 90. Then, swelling deformation and swelling pressure tests were performed on the aged samples. Results indicate that both the swelling deformation and swelling pressure decrease with ageing time, with a more significant decrease at the first few days of ageing. Ageing effects are more pronounced for samples with large dry density and high water content. At the same initial dry density and water content, samples aged under constant volume conditions show much smaller decrease of swelling pressure compared to that of samples aged under K0 confined conditions. The decrease of swelling potential of samples with ageing days is mainly attributed to the bonding effects and the internal redistribution of water within the bentonite, which was confirmed by the changes of microstructure of samples with ageing.

An approach to estimate the swelling pressure of compacted bentonite (Bent) using Gouy–Chapman diffuse double layer theory is presented. Several laboratory swelling pressure tests on compacted Bent (MX80 and Calcigel) under constant volume conditions were performed and compared with the calculated swelling pressure using the original theory. The study revealed that at low dry density the as prepared total void ratios are less than theoretical void ratios using diffuse double layer theory, however, reverse behavior has been noticed for high compaction dry densities. Based on the experimental results of Bent with different valences, the relationship between the theoretical void ratio from diffuse double layer theory and as prepared total void ratio were determined. New equations were derived on the basis of diffuse double layer theory and experimental swelling pressure data. The method categorizes the different Bents into two groups depending upon the weighted average valency. A good agreement was observed in all the cases between experimental and estimated swelling pressure using derived equations. The applicability of the proposed method was investigated by comparing the estimated swelling pressure results with the additional reported in literature laboratory results on swelling pressure of compacted Bent.

A mechanistic model is developed to predict the swelling pressure of fully saturated, bentonite-based materials in distilled water or dilute saline solutions over a large range of final dry densiti ...

This paper presents the results of a subsurface site investigation that was performed to characterize different soil and rock formations along Sheikh Zayed canal with particular emphasis on the swelling characteristics of the clays in that area. Site-specific empirical correlations were developed to predict the clay swelling potential and pressure from simple and economic laboratory test results. The data were input into a Geographic Information System (GIS) framework to provide interactive maps that show the spatial distribution of the variables and identify their characteristics. These maps are then used to easily identify the values of swelling pressure/potential at various locations. This research provides a tool that is based on simple index tests that can be used to provide data that otherwise would require elaborate and costly investigations; the GIS framework allows storing, retrieving and updating these data easily to assist taking supported decisions dynamically.

International audience; SEALEX is a research project aiming at identifying the key factors that affect the long-term performance of bentonite-based sealing systems with an initial technological void. In this context, a series of in situ experiments have been performed in field conditions. Meanwhile, a small-scale test (1/10) was carried out in controlled conditions in the laboratory, aiming at providing useful information for analyzing the in situ tests in terms of saturation time and sealing effectiveness. In this paper, the results of the small-scale test are presented along with the results from the first in situ test (PT-N1). It was observed that during the saturation process, the evolution of the injected water volume followed a hyperbolic relationship with time in both the laboratory and field conditions. In the laboratory conditions, a decrease in axial swelling pressure occurred due to filling of the technological void. By contrast, this decrease has not been observed in the field conditions. Comparison of the injected water and the axial swelling pressure between the two different scales enabled the definition of a same time upscaling ratio of 2.5 (in situ experiment/small-scale test). Accordingly, the saturation duration of the in situ experiment was estimated to be equal to two years. For the small-scale test, a swelling strain evolution rate of 0.588 mm/day was identified in the case of infiltration from two sides of the sample. This is useful when predicting the evolution of swelling strain in the case of failure of the sealing plug. After filling of an additional 20% void, a swelling pressure of 0.18 MPa was obtained, indicating the favorable sealing capacity of the material after filling the technological void.

Problems associated with swelling soils are faced by practitioners and researchers all over the world. Swelling soils incur large deformations and swelling induced pressures associated with changes to their moisture content or pore water chemistry. A combination of swelling soil and climatic conditions conspires to add additional design considerations for infrastructure founded in swelling soil. Difficulties are encountered in laboratory testing as well as analysis of applications that incorporate swelling soils. In this paper a two-part approach is used to characterize the swelling potential of Bearpaw clayshale. Traditional swelling pressure tests as well as specialized triaxial swelling tests are reported and interpreted using a unifying framework for characterizing swelling potential. The results indicate that the swelling potential of Bearpaw increases with depth corresponding to a decrease in moisture content and void ratio. The combination of swelling pressure tests and triaxial swelling tests allows the interpretation of the swelling potential for general conditions.

Adequate design of engineered barriers, including canister, buffer and backfill, is important for the safe disposal of high-level radioactive waste. Three-dimensional computer simulations were carried out under different condition to examine the thermal and mechanical behavior of engineered barriers and rock mass. The research looked at five areas of importance, the effect of the swelling pressure, water content of buffer, density of compacted bentonite, emplacement type and the selection of failure criteria. The results highlighted the need to consider tensile stress in the outer shell of a canister due to thermal expansion of the canister and the swelling pressure from the buffer for a more reliable design of an underground repository system. In addition, an adequate failure criterion should be used for the buffer and backfill.

Cement and clay will be used extensively in geological disposal facilities for radioactive wastes, but the long-term interaction of hyperalkaline pore fluids from cement with clay may be detrimental to the latter's containment properties (swelling pressure, hydraulic conductivity, etc.). An evaluation of the thermodynamic stability of minerals in the cement-clay system shows that mineral alteration will depend to a large degree upon the specific characteristics of the rock-groundwater system at a disposal site.

A mixture of bentonite and sand has been proposed for use as a buffer/backfill material in the disposal of high-level radioactive waste in many countries. In China, it is necessary to quantify the influence of the sand content ratio and the initial dry density on the swelling characteristics of GMZ bentonite–sand mixtures, and to collect test data useful in the design of buffer/backfill materials. To accomplish these goals, this study conducted laboratory tests on the swelling pressure and swelling deformation of GMZ bentonite–sand mixtures consisting of different sand contents of 0, 10, 20, 30, 40 and 50%. The results indicate that swelling occurs in three distinct phases: inter-void swelling, primary swelling and secondary swelling, where both swelling pressure and swelling strain follow a sigmoid relationship with time. With constant initial water content, the maximum swelling pressure presents an exponential increase with increased initial dry density, and the maximum swelling strain increases linearly. As the sand content ratio increases, the maximum swelling pressure decreases exponentially while the maximum swelling strain follows a quadratic decrease. In the introduction of the concept, the effective clay density (ρB), an expression which includes both initial dry density and sand content ratio was derived. New equations for evaluating the relationship between effective clay densities and swelling characteristics are proposed. Furthermore, a prediction method for the swelling characteristics of compacted GMZ bentonite–sand mixtures is presented by combining the expression of effective clay density and the new equations. The applicability of this method was investigated by comparing the fitted curves with laboratory test results of the swelling pressure and swelling deformation of compacted GMZ bentonite–sand mixtures. Experimental data has shown satisfactory results, so these equations can predict the swelling characteristics of GMZ bentonite–sand mixtures with various sand content ratios and initial dry densities within a certain numeric area.

The China-mock-up test is to evaluate the performance of the compacted Gaomiaozi (GMZ) bentonite under coupled thermo-hydro-mechanical (THM) conditions in deep geological disposal. A numerical study of the test is conducted in this paper. The principal THM characteristics of the bentonite are presented at first. A THM model is then presented to tackle the complex coupling behavior of the bentonite. The model of Alonso-Gens is incorporated to reproduce the mechanical behavior of the bentonite under unsaturated conditions. With the proposed model, numerical simulations of the China-mock-up test are carried out by using the code of LAGAMINE. The time variations associated with the temperature, degree of saturation, suction and swelling pressure of the compacted bentonite are studied. The results suggest that the proposed model is able to reproduce the mechanical behavior of the bentonite, and to predict moisture motion under coupled THM conditions.

One of the major functions of a bentonite buffer for a HLW repository is to provide the buffer with a self-sealing capacity through its ability to swell on contact with free water. Swelling pressure measurements were carried out to investigate the swelling behavior of Ca-bentonite. Experimental results showed that the swelling pressure increased with an increase in dry density, and its dependence on dry density increased at higher dry densities beyond 1.6 Mg/m 3 . The effect of salinity on the swelling pressure for the Ca-bentonite was different from that for Na-bentonite. The swelling pressure of the Ca-bentonite was higher in a diluted concentration of NaCl solution (0.04 M) compared with de-mineralized water, and it then decreased with an increase in the concentration of the NaCl solution beyond 0.04 M. Such a swelling behavior of the Ca-bentonite was explained by the ion-exchange of Ca 2 + for Na + from the solution followed by hydration with water molecules and osmosis due to the differences in concentrations of the NaCl solutions.

International audience; A mixture of the MX80 bentonite and the Callovo-Oxfordian (COx) claystone were investigated by carrying out a series of experiments including determination of the swelling pressure of compacted samples by constant-volume method, pre-swell method, zero-swell method and swell-consolidation method. Distilled water, synthetic water and humidity controlled vapour were employed for hydration. Results show that upon wetting the swelling pressure increases with decreasing suction; however, there are no obvious effects of synthetic water chemistry and hydration procedure on the swelling behaviour in both short and long terms. For the same initial dry density, the swelling pressure decreases with increasing pre-swell strain; whereas there is a well defined logarithmic relation between the swelling pressure and final dry density of the sample regardless of the initial dry densities and the experimental methods. It was also found that swelling pressure depends on the loading-wetting conditions as a consequence of the different microstructure changes occurred in different conditions. Furthermore, it was attempted to elaborate a general relationship between the swelling pressure and the final dry density for various reference bentonites.

The swelling behavior of argillaceous rocks is a complex phenomenon and has been determined using a lot of indexes in the literature. Determining the required modeling indexes that need to be performed requires expensive tests and extensive time in different laboratories. In some of the cases, it is too difficult to find a relation between the effective variables and swelling potential. This paper suggests a method for modeling the time dependent swelling pressure of argillaceous rocks. The trend of short term swelling potential during the first 3 days of the swelling pressure testing is used for modeling the long term swelling pressure of mudstone that is recorded during months. The artificial neural network (ANN) as a power tool is used for modeling this nonlinear and complex behavior. This method enables predicting the swelling potential of argillaceous rocks when the required indexes and also correlation between them is unattainable. This method facilitates the model of all studied samples under a unique formulation.

Tunneling in weakness zones containing swelling clay represents one of the most difficult conditions in hard rock tunneling. Evaluation of rock support requirements in such zones is normally empirical, i.e. mainly based on experience. In this paper, rock supports in a major weakness zone containing swelling clay is analysed based on monitoring results and numerical analysis in order to enrich the experience of support evaluation under such conditions. The Finnfast subsea road tunnel is used as a case. Laboratory tests of the gouge material from the actual zone indicate that the swelling pressure is moderate. All instrumentation data and simulation results show that the loading on the sprayed concrete is far less than its compressive strength, even for the rock support without the reinforced sprayed concrete rib. This suggests that such zones may often be excessively supported when the swelling clay is not very active. It is also found that for reliable stability control through such zones the instrumentation should be installed as close to the excavation face as possible.

This paper describes a new controlled swelling device fabricated to measure the corresponding swelling pressure of meat immersed in brine throughout salting. To set up the proposed device, swelling in pieces of pork meat immersed in a 5% (w/w) NaCl brine was studied. It is well known and described in literature the influence of NaCl on the water holding capacity of meat. The increase in that value has been related with the existence of swelling pressures in the protein matrix. The obtained results indicated that the developed device provides swelling pressure values which are in accordance with the measured changes in composition, weight and height of non-constrained samples.

This paper focuses on the determination of the swelling pressure of polymeric hydrogels by variation of the composition of the monomer mixture used for synthesis via free radical polymerization. The method used is based on the principle of determining the swelling pressure at a given final volume of swelling. Data for different types of low swollen hydrogels based on weakly crosslinked poly(acrylic acid)/poly(sodium acrylate) copolymers are presented for swelling in deionised water. For polymer volume fractions ϕ P between 0.03 and 0.30, swelling pressures p in the range of 0.20–4.23 MPa were obtained. No effect on the swelling pressure could be found by variation of monomer concentration and crosslinker content. In contrast, the content of sodium acrylate had an effect on the swelling pressure. The results are discussed based on the effect of counterion condensation.