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The swelling pressure of bentonite changes dramatically due to diffused nuclear radiation heat and underground osmosis, causing the failure of the buffer isolation layer in deep geological repositories for the disposal of high-level radioactive waste. A detailed overview of the relevant research results on the swelling pressure variation of bentonite under thermo-chemical effects is presented in this paper. The results showed that the values of the swelling pressure obtained by different test methods are dissimilar. The swelling pressure of bentonite decreased with the increasing pore solution concentration; nevertheless, the effect of temperature on the swelling pressure is still controversial. At the micro-level, crystal layer swelling and double- layer swelling are generally considered to be the main factors affecting the swelling pressure; the pore structure and water distribution of bentonite will change owing to thermo-chemical effects. At the macro-level, involving intergranular stress, a mechanical parameter was proposed to explain the mechanism of the changes in the swelling pressure of bentonite. Finally, future research directions for the study of the evolution of bentonite swelling properties under thermo-chemical effects are proposed, based on the current research results.

Compacted bentonite as an artificial barrier/backfill material is susceptible to heat when combined with the hyperalkaline conditions of deep geological repositories. In order to investigate the structural damage of compacted GMZ bentonite and its effect on swelling pressure deterioration, X-ray powder diffraction (XRD) and mercury intrusion porosimetry (MIP) tests were performed on bentonite specimens after immersed in hyperalkaline solution at 20–80°C. The results suggest that the increase in the number and pore sizes of macropores, and the decrease in the crystallinity degree of montmorillonite and silicate minerals are extremely obvious, which well characterises the structural damage of compacted bentonite on a microscopic scale. The structural damage parameter is facilitated by heat combined with hyperalkaline conditions. The structural damage of compacted bentonite is more susceptible to variations in the microscopic pore structure and the dissolution of silicate minerals than that of montmorillonite; and the structural damage of compacted bentonite will cause the long-term deterioration of swelling pressure. Hence, the long-term safety of HLW repository should be evaluated taking into account of the structural damage of compacted bentonite caused by heat combined with chemical conditions. [ABSTRACT FROM AUTHOR]

During the renovation of the Gotschna Tunnel from 2019 to 2020, prefabricated elements made of Compex were used for the first time as a deformable yielding zone in the invert zone. The client, construction management, construction company and supplier of the compressible elements worked closely together to implement the design specifications. Consequently, the expectations of the special building material in terms of the production quality of the prefabricated elements and handling on the construction site were more than met. The parties involved in the construction thus see potential for further applications and further developments of Compex. [ABSTRACT FROM AUTHOR]

Swelling soil leads to many types of constructional damages, deformations, and failures in the constructions' roads, shoulders, and foundations. Depending on the amount of swell, they can be insignificant, moderate, or massive. This paper presents a method for swelling soil stabilization by adding rice husk powder (RHP) in variable percentages of 0, 5, 10, 15, 20, and 25 by weight of dry soil. The properties of swelling soil stabilization were investigated by various lab tests such as consistency limits (plastic limit, liquid limit, and plasticity index), swelling potential, swelling pressure, free swelling, and free swell index. The swelling soil was also mineralogically examined using X-ray diffraction of clay mineralogy. This stabilization reduced the plasticity from 56% (extremely high plasticity) to 4.5% (low plasticity). Swelling potential (S) and swelling pressure (SP) decreased by 48% to 45.5, 44.7, and 34.6%, from 1003 kN/m2 to 800, 653, and 489 kN/m2 for the partial replacement of the soil by 5%, 10%, and 15% RHP, respectively. The results show that the present approach is very efficient for improving the swelling soil properties and that the optimal amount of added RHP of the swelling soil is 15%. It will also be a database aimed at reducing construction risks in the future. [ABSTRACT FROM AUTHOR]

Highly expansive clay is prone to cause extensive engineering damage, which can also be a potential construction material owing to the desirable characteristics of the active clay minerals in soils. Therefore, it is essential to understand the geotechnical characteristics of highly expansive clay. In this study, integrative apparatus was developed to examine the hydro-performance behavior of highly expansive clay, including the swelling ability and hydraulic and compression properties. Unlike that in the traditional method involving loading by a loading frame, a unique dual-piston system was used to convert the water injection pressure into the loading pressure with a static magnification factor of 0.729, and to transfer the real-time swelling pressure of the specimen in the vertical direction. A series of traditional tests were conducted on bentonite specimen using the proposed device, and aforementioned soil parameters were simultaneously or continuously obtained, i.e., the swelling pressure, saturated hydraulic conductivity, and deformation of the same specimen. The test results exhibited a high repeatability, and the test system was considered to be highly reliable. The integrative testing device can be an effective tool to examine the hydro-mechanical behaviors of highly expansive clay. [ABSTRACT FROM AUTHOR]

During the long-term operation of deep geological nuclear waste repositories, the swelling properties of compacted bentonites can be affected by canister temperature and electrolyte concentration in groundwater. The present article highlights the combined effect of temperature and electrolytes on the swelling pressure of monovalent Na-bentonite (predominant Na-montmorillonite) and divalent Ca-Mg bentonite (dominated by Ca-Mg montmorillonite and palygorskite minerals). A series of isochoric swelling pressure tests were carried out on compacted bentonites at a dry density of 1.7 Mg/m3 by applying temperatures of 25°C, 55°C, and 95°C and infiltrating with 0.1 and 1.0 M NaCl and CaCl2 electrolytes. The changes in the microstructure of bentonites were examined by using a Field Emission Scanning Electron Microscope (FESEM), X-ray diffraction (XRD), and mercury intrusion porosimetry (MIP). The experimental results indicated that the elevated temperature caused a marginal decrease and increase in the swelling pressure of monovalent and divalent bentonites, respectively. The infiltrated electrolytes caused a significant decrease in the swelling pressure of monovalent bentonite, whereas the effect was found to be negligible for divalent bentonite. At electrolyte concentrations of 0.1 and 1.0 M, the impact of CaCl2 was noted to be higher than that of NaCl. The coupled thermochemical effect caused a significant decrease in the swelling pressure of monovalent bentonite, whereas the effect was nominal for divalent bentonite. The FESEM, XRD, and MIP results confirmed that the thermochemical effect leads to a significant change in morphology, basal position of Na-montmorillonite, and pore structure of monovalent bentonite. The performance of Ca-Mg montmorillonite and palygorskite minerals as buffer material was noted to be better than that of Na-montmorillonite subjected to coupled conditions of elevated temperature and electrolyte concentration. [ABSTRACT FROM AUTHOR]

The swelling pressure of compacted bentonites plays an important role in the design of deep geological repositories. The current study highlighted the influence of compacted specimen dry density and water content on pore size distribution (PSD) and swelling pressure of two Indian bentonites. Constant volume swelling pressure tests were carried out on one divalent bentonite and one monovalent bentonite at three different dry densities such as 1.4, 1.6, and 1.8 Mg/m3 by varying three initial water contents of 8%, 12%, and 16%, respectively. The change in pore size distribution and morphology of the bentonites were investigated using mercury intrusion porosimetry (MIP) and field emission scanning electron microscopy (FESEM). The results indicate that the compacted dry density has significant role on macropore alteration of both bentonites; however, its effect is marginal on micropores. The macropore volume was noted to significantly decrease in monovalent bentonite due to increase in water content from 8 to 16%. The hydration phenomenon in compacted bentonites was found to be strongly dependent on both the clay fabric and the pore diameter. The high macropore volume of monovalent bentonite exhibited collapse behaviour during swelling process and developed a new family of big pores. However, collapse behaviour was not observed in divalent bentonite due to its small pore diameter. At a given dry density, the compacted divalent bentonite predominantly having Ca-Mg montmorillonite and palygorskite possesses a higher swelling pressure than monovalent bentonite, which has Na-montmorillonite as a predominant component. The effect of initial water content was noted to be negligible on swelling pressure of the monovalent bentonite at a lower dry density of 1.4 Mg/m3. On other hand, irrespective of dry density, the swelling pressure of divalent bentonite decreased with an increase in initial water content; however greater percentage reduction was noted at higher dry densities for both bentonites. [ABSTRACT FROM AUTHOR]

Structures constructed on expansive soils experience higher upward pressure due to their swelling characteristics. Various conventional treatment methods developed to counteract swell–shrink characteristics of expansive soil are deemed time consuming and not feasible for use in pavement. Geotextiles (GTs) have been used as a filtration and separation medium; however, their effect on swell pressure and shear strength of expansive soil has not been well explored. This study aimed to address these issues by using GT to control swelling behavior, drain moisture content, and provide support at the soil interface. Swell pressure and shear strength were quantified by constant volume swell pressure and direct shear and unconfined compressive strength tests, respectively. The influence of single-layer, double-layer, and triple-layer GTs at varying depths was studied. The higher tensile strength of the GT layer restrained the swell pressure mobilized by resisting internal soil movements and facilitating in-plane drainage conditions. Additionally, soil–geotextile interfacial interactions were observed to contribute to improvement in shear strength. Comprehensive statistical analysis using one-way analysis of variance (ANOVA) was carried out on swell and strength properties. The present study ascertained the use of GT for the dual function (i.e., strength and swell control) of stabilizing expansive subgrades. [ABSTRACT FROM AUTHOR]

Faults/weakness zones with gouge containing swelling clay (smectite) have in several cases caused serious stability problems in tunnels. The first part of this paper describes briefly some recent cases of instability/cave-in where swelling clay has been a main cause of the incident, followed by brief reviews of structure and properties of smectite and relevant laboratory test procedures. Main focus is placed on swelling pressure, which is a key parameter for understanding the potential problems that may develop when crossing a major fault/weakness zone, and a key factor also for analysis of stability and rock support requirement. Laboratory test results presented in this paper illustrate that swelling pressure may vary considerably between different locations of the same zone, and that test results based on standard laboratory preparation do not correspond well with results based on testing of in situ undisturbed samples. Swelling pressure based on laboratory testing, therefore, should not be used directly in stability analysis and rock support design. Recommendations on proper use of laboratory test data are given at the end of the paper. [ABSTRACT FROM AUTHOR]

Highly compacted bentonite is an ideal back-filling (buffer) material for the deep geological disposal of high-level radioactive waste. Montmorillonite is the main constituent mineral of it. The nanoscopic swelling characteristic of montmorillonite mineral particles greatly influences the macroscopic buffering performance of highly compacted bentonite blocks. Firstly, the montmorillonite suspension liquid was exfoliated by freeze-thaw cycles, the appropriate mineral particles were selected by atomic force microscope (AFM) for making colloidal probes. Then, the swelling pressure between mineral particles was measured by AFM, investigating the effects of interlayer distance, layer number, temperature, and interlayer cation type on the nanoscale swelling pressure. The experimental results showed that the swelling pressure of montmorillonite mineral particles peaks at about 0.7–0.8 nm interlayer distance. The swelling pressure of mineral particles with more layers is smaller. The higher the ambient temperature, the greater the swelling pressure. The swelling pressure of Ca-montmorillonite is significantly larger than that of Na-montmorillonite. The Laird model has a relatively good applicability with the interlayer distance of 0.6–1.2 nm; the DLVO theory has a good applicability with the interlayer distance greater than 1.5 nm. Finally, a predictive model was developed for the swelling pressure of nanoscopic mineral particles considering the effect of layer number. The research results provide data support and theoretical support for swelling pressure generation and cross-scale transmission mechanism of highly compacted bentonite hydration. • An experimental method for nanoscale swelling pressure of montmorillonite minerals. • The swelling characteristics of montmorillonite quasicrystals in nanoscale. • The applicability of nanoscale swelling theoretical models to montmorillonite minerals. • The swelling pressure prediction model of montmorillonite minerals during hydration. [ABSTRACT FROM AUTHOR]

Bentonites are considered as a suitable buffer material for the high-level radioactive waste disposal. The long-term stability of the hydromechanical properties of the bentonite barrier at high temperature is one of the key conditions for the proper functioning of the bentonite barrier. This paper presents an experimental study of the swelling pressure evolution of compacted samples of BCV bentonite exposed to high temperatures. The samples at constant volume were fully saturated at room temperature from the as-compacted state and then rapidly heated to constant temperatures of 50–150 °C. Temperatures were then held constant and the swelling pressure evolution was measured for the next 30 days. In the next stage, temperatures were decreased back to laboratory conditions and the equilibration of the swelling pressures was monitored. Finally, hydraulic conductivity of the selected samples was determined at room temperature. An additional test was performed to investigate the effect of saturation after heating on swelling pressure development. The results showed a significant decrease in the swelling pressure with time at elevated temperatures in all the samples (denoted as thermal relaxation). This decrease was more significant at higher temperatures and at temperatures above 100 °C the swelling pressure did not reach a steady state value until the end of the high temperature stage. The rate of swelling pressure decrease was quantified by the coefficient of relaxation C rel. A permanent decrease in swelling pressure due to thermal relaxation was identified after cooling. The swelling pressures decreased to 90–41% of the original swelling pressures determined before heating. The magnitude of the swelling pressure reduction increased with the applied temperature. Similar behaviour was observed for samples of different dry densities. The same effect of thermal relaxation was observed for samples saturated before and after heating. Thermal relaxation did not affect the hydraulic conductivity of the bentonite after temperature cycle, which was similar to that of thermally untreated BCV samples. • Significant thermal relaxation (swelling pressure decrease with time) of BCV bentonite was observed. • Decrease in swelling pressure accelerates with applied temperature. • Thermal relaxation resulted in permanent reduction of swelling pressure. • No effect of temperature cycle on hydraulic conductivity was observed. [ABSTRACT FROM AUTHOR]

Many countries are planning to host long-lived high- and intermediate-level radioactive waste in disposal facilities sited in deep argillaceous formations. Bentonite, as a swelling material, is often chosen as engineered buffers due to its low permeability and high swelling capacity. However, its properties can be influenced by the hydraulic/gas conditions prevailing in-situ that are expected to change throughout the duration of the repository. The objective of this work is to estimate the effect of partially water-saturated conditions on the mobility of water and ions in compacted MX-80 bentonite in relation to the evolution of its swelling pressure. For that purpose, (i) diffusion of water and ions (I− and Na+) and (ii) the swelling pressure of compacted bentonite samples partially water-saturated were studied by means of the osmotic technique that allows controlling the suction from 9 to 0 MPa. Results showed that (i) water diffusivity remained unchanged independently of the degrees of saturation (70, 84 and 100%) and (ii) iodide diffusivity decreased by a factor of 12 (from 100 to 70%), while (iii) Na+ diffusion was reduced by a factor of more than 70 (from 100 to 70%), associated to a drop of the distribution factor by a factor of 16. Comparison of these results with diffusion data already acquired in clayey materials whose porous structure evolves little with suction (i. e. compacted kaolinite and intact Collovo-oxfordian clay-rocks) underlined how the bentonite porous structure whose organization evolved with the degree of saturation is a key parameter. This statement is supported by mechanical tests, which indicated a distinct evolution of the swelling pressure curves depending on the degree of saturation. At 70% saturation, mechanical tests indicate (i) a preservation of the large inter-aggregate porosity where water can diffuse in both vapor and liquid phases, and (ii) a final swelling pressure 1.5 to 2 times lower than at full water saturation, meaning that a part of swelling clay particles was not accessible to water ingress and so to 22Na+. Conversely, at 84 % and 100 % saturation, change in swelling pressure curves was explained by a collapse of bentonite inter-aggregate porosity, in favor of expanding the inter-particle and interlayer porosities where 22Na + diffusion is enhanced by surface diffusion phenomenon. • Diffusive rate of water tracer is similar in bentonite for water saturation from 1 to 0.7 • Strong reduction of diffusive rate and adsorption of sodium by 73 and 16, resp. in bentonite for water saturation from 1 to 0.7 • The tortuosity of iodide diffusive paths in bentonite increases by only 1.4 times for water saturation from 1 to 0.7 • Diffusive behavior is linked to the bentonite saturation-dependent microstructure changes • Mechanical data are in agreement with the diffusion findings [ABSTRACT FROM AUTHOR]

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. • A design method of the soilbag-protected slopes for expansive soils is proposed considering the swelling pressures. • Determinations for the width of soilbag arrays and the heap-up unit of soilbags are introduced. • Standardization method of soilbag technology for expansive soil slope protection. [ABSTRACT FROM AUTHOR]

Compacted bentonite/sand mixture have been considered as possible sealing/backfilling material in the deep geological disposal of high-level radioactive nuclear waste. The swelling pressure of the compacted bentonite/sand mixture is of significance in the design of the geological repository, which requires good consistency between data obtained by laboratory and field measurement. In this work, a series of swelling pressure tests were performed on compacted MX80 bentonite/sand specimens prepared by methods commonly adopted in laboratory (As-compacted, Transferred) and those mimicking the real block manufacturing process (Trimmed, Inserted). Results shown that with identical dry density (especially when the dry density was larger than 1.70 Mg/m3), largest swelling pressure was obtained in specimens prepared by method Inserted, followed by method As-compacted, Transferred and Trimmed. The distinct difference between the swelling pressure could be largely attributed to the effects of residual post-compaction lateral stress. More interestingly, specimens prepared by methods Trimmed and Transferred followed a similar swelling pressure-dry density relationship. From this point of view, method Transferred without causing mass loss, change of bentonite content and possible technological voids effect was recommended in lieu of method Trimmed for specimen preparation in laboratory. [ABSTRACT FROM AUTHOR]

Soil adjustment has been executed for improving the properties like the mud soil. Since the volume of waste is created on the planet has expanded because of the over populace. To improve the dirt compaction the manner in which mud soil has less security. It this test study we will find out the quality of soil by adding the coconut shell powder. To expand the dependability of coconut shell powder. Various tests were directed on soil with differing level of coconut shell powder (2%, 4%, 6% and 8%). To incorporate ideal dampness content, greatest dry thickness and CBR esteem. By worldwide popular development is compelling social orders to build on any dirt kind open inside their locale including mud soils. Adjustment of the dirt is one of the traditional and most ideal approaches to improve the properties of the sort of soil. Many research papers are shown that there is improving like clay soil properties of soil by adding the coconut shell powder. [ABSTRACT FROM AUTHOR]

Hydrogels are cross-linked polymer networks able to absorb or to release large amounts of water. The water uptake is associated with a considerable volume change but also with changes of optical properties like the refractive index. The swelling can be excited by a large spectrum of different physical (e.g. temperature, electrical voltage, magnetic field) and chemical factors (e.g. pH value, concentrations of chemical or biochemical species). The particular sensitivity can be adjusted by tailoring the composition of the hydrogel or via its functionalization. If the interaction between hydrogel and analyte to be measured is reversible then such hydrogels are becoming a promising candidate for miniaturized, cost-effective and inline-capable sensors. [ABSTRACT FROM AUTHOR]

Buffer/backfill material is an important engineering barrier in a deep geological repository of high-level radioactive waste (HLW). Its thermo-hydro-mechanical (THM) performance is very important for the safe and stable operation of the HLW repository system. Natural graphite powder mixed with sodium bentonite forms a buffer/backfill material that can dissipate heat quickly and provide strong isolation. In this paper, the THM characteristics of bentonite–sand–graphite–polypropylene fiber (BSGF) mixtures, used as a buffer/backfill material, were studied through a series of laboratory tests. The influence of graphite and polypropylene fiber contents on thermal conductivity, swelling pressure, hydraulic conductivity, and strength properties of BSGF mixtures with different sand contents was analyzed. Experimental results indicated that the graphite content, the maximum graphite mesh number, and the initial dry density of bentonite–graphite mixtures influenced the thermal conductivity of bentonite–graphite mixtures. The addition of polypropylene fiber was found to enhance the shear strength and inhibit cracking without significantly affecting the expansivity, permeability, and thermal conductivity of the BSGF mixtures. This study provides a new buffer/backfill material that can improve the stability, functionality, and thermal efficiency of the HLW repository. [ABSTRACT FROM AUTHOR]

In recent years, the need for land has been increasing due to the increasing population, especially in big cities. In addition to the use of lands that meet sufficient criteria in terms of foundation soils, it has become compulsory to use lands that do not meet these criteria. In lands that do not meet sufficient criteria in terms of basic soils, improvement is made by using classical additives such as lime, fly ash, blast furnace slag. However, these additives are not environmentally friendly as they increase CO2 emissions in nature. Therefore, in recent years, there has been an interest in new environmentally friendly additives alternative to these additives. One of these additives is Bacillus Sp. which provides improvement in the soils by producing CaCO3 in the soil where it is injected. In this study, strength and swelling pressures were investigated under freeze-thaw cycles on high plasticity clay (CH) and sandy clay (SC) soils injected with Bacillus Sp. According to the results, it was determined that Bacillus Sp. contributed positively to the improvement of the strength and swelling pressure parameters of soils. [ABSTRACT FROM AUTHOR]

Technology gaps are inevitable parts of the buffer barriers in the high-level radioactive waste (HLW) repositories. The mechanical properties, permeability and water-solute-radionuclide migration of buffer barrier are different when considering the gaps. The present study was designed to investigate the sealing effect of joint between the compacted blocks with two types of sealing materials, a bentonite paste (P) and a bentonite particles and powder mixture (P/P) both from the macro- and micro-aspects. A series of laboratory test was conducted to study the hydro-mechanical properties of bentonite blocks after backfilling the joint between blocks. Both the intake and outflow water volume, and the pressure on radial and axial direction were monitored during the hydration. Following the permeability test, the joint's sealing was evaluated by a final dry density, water content distribution and microstructure evolution. The results showed that the axial and radial pressure of blocks backfilled with bentonite P and bentonite P/P mixture were higher than that of blocks with a blank joint. Pressure preferentially increased in the low-stress areas (the joint areas), contributing to sealing of the joint. The hydraulic conductivities for backfilled bentonite blocks were almost on the same order of magnitude as to intact bentonite blocks, revealing a clear sealed hydraulic behavior. The final dry density decreased in the block area and increased in the joint area after hydration, forming a transition zone with a certain width. A smaller difference was found between the block and joint area in the backfilled block. The mercury intrusion porosimetry (MIP) test and scanning electron microscope (SEM) test showed that backfill decreased the numbers of inter-aggregates pores ranged between 8 and 15 μm compared with that in the blank joint. The comprehensive data showed that a joint backfilled with a bentonite P/P mixture has a higher swelling capacity, lower permeability, and denser structure compared with joint backfilled with bentonite P. The results suggested that joint backfilling improved the integrity of the blocks and enhanced the swelling property and impermeability compared with that of the non-backfilled blocks. Both bentonite P and bentonite P/P has satisfactory sealing performance of compacted block joints, with better effect of the later. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to apply the correlations to evaluate the risk of soil swelling in the area of the north-west part of Algeria. On this basis, 84 soil samples were collected from laboratories in the region, plus a reading of the main publications on swelling soils in the area of the north-west part of Algeria, and then different types of regressions were applied to this data. The results show that the plasticity index has a high degree of influence on the swelling pressure; the swelling potential and the swelling coefficient compared to the clay content. New empirical relationships were found between the swelling pressure and swelling potential; these correlations are good concordances with the literature. Cubic; quadratic and multiple models of regression seem are in good concordances better adapted compared to simple linear regression models in the presented study. [ABSTRACT FROM AUTHOR]

The expansive soil and sand dunes are abundant in desert areas at which new cities have been constructed. One of the effectively mitigation techniques for the expansive soil is to mix it with a non-swelling soil. This paper aims to study the influence of different sand dunes fractions, varying from zero to 50%, on the behaviour of the highly expansive clay. The clay-sand mixtures were also chemically stabilized by 10% of lime. The samples were remoulded according to the modified AASHTO compaction tests results. Swelling and strength tests were performed on each mixture. The results showed that mixing sand dunes with expansive clay reduced its swell potential and swelling pressure. The reductions increased as the increment of sand fraction. The swell potential and swelling pressure of the clay reduced to approximately the one-third when utilizing 50% sand. But mixing lime and sand with clay caused further significant reductions in swell properties. The swell potential and the swelling pressure of the clay were approximately suppressed when it was stabilized by 50% sand and 10% lime. Adding sands to clays had a negative effect on the strength. The CBR and UCS values of the clay-sand mixture decreased with increasing sand fractions. Once adding lime to the clay-sand mixtures, the CBR and UCS after 8-weeks curing time increased. The increments raised with increasing of sand fraction. The existence and the increment of sand dunes in clay influenced effectively on the chemical reactions with lime. [ABSTRACT FROM AUTHOR]

The usage of bentonites and sand-bentonite mixtures as liners has become prevalent due to their low permeability. However, these materials are scarce and prohibitively expensive in India. Black cotton clay (BCC) was chosen as an alternative clay liner for this research due to its abundance in India and its mineralogical composition. Since heavy metals accumulation in municipal landfills is a rising issue with devastating effects on the ecosystem and human health, in this investigation, two heavy metals (lead and cadmium) were intended as permeants at three different concentrations (100, 500, and 1000 ppm) to imitate the impact of heavy metal leachate on BCC. The essential index and engineering properties of BCC were evaluated and compared under these two permeants from the liner perspective. Experimental results revealed that the free swell index, Atterberg limits, swelling and swelling pressures were reduced for a rise in concentration irrespective of metal type. However, this reduction was more with cadmium permeants compared to lead. The measured swelling data was compared with predicted swelling data using a rectangular hyperbola model, and a good correlation was achieved. The hydraulic conductivity ( k ) and unconfined compressive strength (UCS) values were increased for a rise in concentration with both metal permeants. At 1000 ppm concentration, the k values were raised to 3.5 and 6.7 times, and UCS values were enhanced by 8.3 and 5.5% for lead and cadmium permeants, respectively. At high concentrations, field emission scanning electron microscopy (FESEM) results showed the formation of huge voids and aggregation.

Using industrial waste materials in the treatment of problematic soils is an environmentally friendly and cost-effective technique. It helps in decreasing disposal issues induced by various industrial wastes. Also, it is crucial to understand the behaviour of these waste products before use. This paper presents experimental research in the treatment of expansive soil by the utilization of iron furnace slag. Laboratory program was performed to examine the effect of iron furnace slag on enhancing the engineering properties of expansive soil. Several tests included liquid limits, plastic limits, free swell percentage, swelling pressure, and unconfined compressive strength were conducted on untreated and treated soils. The efficiency of adding 0, 2, 4, and 6 percentages of iron slag to the soil was investigated. The results of the natural and iron slag stabilized soils showed that iron slag has a notable effect on strength parameters and considerable improvement in plasticity and swelling properties. The addition of iron slag to the soil increased the unconfined compressive strength while reduced the swelling potential of soil. It is concluded that the utilization of iron slag to improve the properties of expansive soil is successful and useful

Geotechnical engineering like any other engineering field has to develop and cope with new technologies. This article intends to investigate the spatial relationships between soil’s liquid limit (LL), plasticity index (PI) and Liquidity index (LI) for particular zones of Sulaymaniyah City. The main objective is to study the ability to produce digital soil maps for the study area and determine regions of high expansive soil. Inverse Distance Weighting (IDW) interpolation tool within the GIS (Geographic Information System) program was used to produce the maps. Data from 592 boreholes for LL and PI and 245 boreholes for LI were used for this study. Layers were allocated into three depth ranges (1 to 2, 2 to 4 and 4 to 6) m. A total of 1396 observations were used for producing the maps for both LL and PI, and 371 data for LI. Based on the results, the IDW method gives reasonable predictions depending on the results of R2 and RMSE. The results also showed that the study area has relatively large zones of high expansive soil that must be taken into considerations before performing any construction activity. These maps are essential for helping geotechnical engineers in making decisions and visualizing soils’ behaviors.

Lime is an effective substance to decrease the swelling of expansive soils. The effective use of lime as a stabilizing agent in the presence of sulfate under some circumstances has been questioned due to the formation of ettringite. In this research, the effect of the addition of rice husk ash (RHA) on the swelling pressure of a bentonite soil (B) modified with lime (L) and calcium sulfate or gypsum (G) was investigated. Nine groups of twin compacted samples, namely, bentonite soil (B), B + L (3% by dry weight), B+3%L+ 5%G, B+3%L+RHA (5, 10 and 15% by dry weight, respectively) and B+3%L+5%G+RHA (5,10 and 15%, respectively), were prepared and tested immediately for 1-D constant volume swelling pressure measurements. Similar groups of samples were prepared and tested after 7 and 28 days of curing. The results indicated the effect of RHA in decreasing the magnitude of swelling pressure in comparison with untreated and treated soil without RHA

Bentonite pellet mixtures are candidate material for the sealing of galleries in radioactive waste disposals. The hydromechanical behaviour of assemblies of bentonite pellets is investigated upon partial hydration through (1) suction-controlled swelling pressure tests in the laboratory and (2) discrete element method simulations. The combination of these experimental and numerical approaches highlights that, before the mixture homogenization, the swelling pressure develops in two phases. The first phase is characterized by an increase in contact forces between pellets. The second phase is characterized by plasticity at contacts between pellets and is controlled by the progressive decrease in pellet strength and stiffness upon hydration. In addition, numerical results highlight that the swelling pressure measured in the laboratory can be influenced by the sample preparation, the cell size, and the diameter of the pressure sensor. [ABSTRACT FROM AUTHOR]

Buffer/backfill material is an important part of engineered barriers in deep geological repositories of high-level radioactive waste (HLRW). A good buffer material not only possesses good heat conductivity, expansion, and sealing characteristics, but also exhibits enough strength. Its thermomechanical performance can significantly influence the safety and stability of a HLRW repository. Polypropylene fibers were mixed with bentonite-based mixtures (bentonite–sand–graphite) to form a buffer material with high strength, good heat dissipation capacity, and strong isolation capacities. The effects of fiber content, fiber length, and sand particle size on the shear strength, swelling pressure, and thermal conductivity of fiber–bentonite-based (BSGF) mixtures were analyzed under given graphite and sand contents. Detailed analyses of the shear, expansion, and heat transfer mechanisms of BSGF mixtures were performed to understand the behavior. The results indicated that the strength of BSGF material improved significantly with the addition of fiber content, whereas swelling potential and thermal conductivity were reduced. With an increase in sand particle size, cohesion and maximum swelling pressure decreased, whereas internal friction angle and thermal conductivity increased. The optimum fiber content, fiber length, and sand particle size were determined based on the thermomechanical performance of BSGF mixtures. These findings help in the field application of buffer materials with different fiber contents, fiber lengths, and sand particle sizes. [ABSTRACT FROM AUTHOR]

This paper presents the effects of fine sand and fly ash on the swelling of an expansive clay. Fine sand and fly ash were used as additives at varying quantities. Free swell index (FSI), swell potential and swelling pressure were determined for the additive contents of 0%, 5%, 10%, 15%, 20% and 25%. FSI decreased by 29% and 50.32% respectively when fine sand content and fly ash content increased from 0 to 25%. Swell potential decreased by 80.4% and 32.7% respectively when fine sand content and fly ash content increased from 0 to 25%. While swelling pressure decreased by 84.6% when fine sand content increased from 0 to 25%, it did not show any trend with fly ash content. [ABSTRACT FROM AUTHOR]

Featured Application: Adopting enzyme induced calcite precipitation technique to reduce swell, permeability and contaminant remediation of soils. Soil treatment methods to cope with ever-growing demands of construction industry and environmental aspects are always explored for their suitability in different in-situ conditions. Of late, enzyme induced calcite precipitation (EICP) is gaining importance as a reliable technique to improve soil properties and for contaminant remediation scenarios. In the present work, swelling and permeability characteristics of two native Indian cohesive soils (Black and Red) are explored. Experiments on the sorption and desorption of multiple heavy metals (Cd, Ni and Pb) onto these soils were conducted to understand the sorptive response of the heavy metals. To improve the heavy metal retention capacity and enhance swelling and permeability characteristics, the selected soils were treated with different enzyme solutions. The results revealed that EICP technique could immobilize the heavy metals in selected soils to a significant level and reduce the swelling and permeability. This technique is contaminant selective and performance varies with the nature and type of heavy metal used. Citric acid (C6H8O7) and ethylene diamine tetra-acetic acid (EDTA) were used as extractants in the present study to study the desorption response of heavy metals for different EICP conditions. The results indicate that calcium carbonate (CaCO3) precipitate deposited in the voids of soil has the innate potential in reducing the permeability of soil up to 47-fold and swelling pressure by 4-fold at the end of 21 days of curing period. Reduction in permeability and swell, following EICP treatment can be maintained with one time rinsing of the treated soil in water to avoid dissolution of precipitated CaCO3. Outcomes of this study have revealed that EICP technique can be adopted on selected native soils to reduce swelling and permeability characteristics followed by enhanced contaminant remediation enabling their potential as excellent landfill liner materials. [ABSTRACT FROM AUTHOR]

Bentonite pellet mixtures are considered as one of the candidate sealing materials for deep geological disposals of radioactive waste. One of the particularities of this material is the initial heterogeneous distribution of pellets and porosity within the mixture, leading to complex hydro-mechanical behaviour. In this paper, the hydro-mechanical properties of GMZ bentonite pellet mixtures were investigated in the laboratory by carrying out water retention tests on pellet mixtures under constant-volume condition and single pellets under free swelling condition, as well as a infiltration test on a column specimen of pellet mixture. In the infiltration test, the relative humidity and radial swelling pressure were monitored at five heights, the axial swelling pressure was also recorded. The instantaneous profile method was applied to determine the unsaturated hydraulic conductivities. Results show that, in high suction range (> 10 MPa) the water retention curve of pellet mixture under constant-volume condition was comparable to that of a single pellet under free swelling condition, while in low suction range (< 10 MPa) the latter exhibits a much higher water retention capacity. Due to clogging of large pores, the unsaturated hydraulic conductivity decreases as suction decreases to around 25 MPa. However, with further suction decrease, the hydraulic conductivity increases continuously until the value at saturated state, as in the case of most unsaturated soils. The radial swelling pressure at different heights develops with local sudden increase and decrease, which was attributed to local rearrangement of pellets upon wetting. By contrast, as the axial swelling pressure was measured on the global surface of the specimen, it develops in a more regular fashion. [ABSTRACT FROM AUTHOR]

Constructing over expansive soils often severely damage the structure due to high swellshrinkage behaviour and loss of strength owing to fluctuating water content. Due to the above reasons construction on or using expansive soils is considered to be unsafe. The technique of such soil, improvement by installation of granular piles (also known as stone columns) is popular to marshy lands, marine clays, loose sand, silty or clayey sand, and compressible soils. Granular piles improve swelling properties of expansive soil. In the present study six expansive soils were used. The one of them was the naturally available black cotton soil and others were derived from it by mixing bentonite in different proportions. Test beds of these soils were prepared at different initial moisture contents and the granular pile of sand was installed in these beds by the method of removal. Besides initial moisture content, properties of expansive soils, the spacing between the piles (expressed by s/d ratio; s = spacing between the piles and d = diameter of a pile) and the relative density of granular pile forming material were the variables of the study. Multiple linear regression analysis on the test data has been performed and equations for predicting swelling pressure of soil bed without pile and inclusion with granular pile have been developed. [ABSTRACT FROM AUTHOR]

In the nuclear fuel cycle of nuclear power generation, reprocessing generates high-level radioactive waste. Geological disposal is a widely accepted disposal method for high-level radioactive waste. This method can isolate waste from the human environment for a very long time. Geological disposal utilizes bentonite as a buffer material in order to suppress the transfer of radioactive materials to groundwater. In practice, waste may be exposed to a high-temperature environment due to decay heat or geothermal heat, or heated groundwater may permeate the water. Nonetheless, few studies consider the effect of heat on bentonite, and it is difficult to understand the long-term swelling performance of bentonite material under these conditions. Therefore, it is necessary to investigate the effect of temperature on bentonite. In this study, swelling properties of bentonite were investigated by performing a swelling pressure test considering temperature history and temperature change. Results demonstrated that swelling pressure tended to increase with increasing temperature. Furthermore, a threshold value for the equilibrium swelling pressure may exist. [ABSTRACT FROM AUTHOR]

A series of temperature-controlled swelling pressure and swelling strain tests were performed on Gaomiaozi (GMZ) bentonite to study the temperature effects on the swelling behavior. The influence of sample dry densities (for swelling pressure tests) and applied various vertical stresses (for swelling strain tests) were taken into account. Emphasis was put on the stress-dependent properties of temperature effects. Results show that at a certain temperature, there is a unique relationship between the stress level and the void ratio of saturated bentonite specimens for either the swelling pressure or swelling strain tests. This relationship could be defined as "swelling stable line" (SSL), which was bilinear shaped and reflects a stress-dependent swelling behavior of compacted bentonite. This stress-dependent swelling behavior is attributed to the different hydration mechanisms under lower and higher stresses. A comparison of SSLs at different temperatures shows an obvious stress-dependent behavior of temperature effects on swelling properties. These stress-dependent temperature effects on swelling behavior of GMZ bentonite are further confirmed by data collected from literatures on various types (i.e., Ca- or Na-bentonite) of bentonites: regardless of the predominant cations, the elevation of temperature increased the swelling potential in the lower stresses part of SSL, whereas it reduced the swelling potential in the higher stresses part. This phenomenon is related to the influences of temperature on the swelling processes (i.e., hydration, diffuse double-layer repulsion, and separation of elementary layers) under different stress levels. [ABSTRACT FROM AUTHOR]

The light weight structure built over potentially expansive soils may suffer damage due to the uplift pressure exerted by the soil after moisture increase. The measurement of the swelling pressure can be made in laboratory using direct methods based on the oedometer tests. This test is long time consuming and implies high costs. There is an increasing trend in predicting the value of swelling pressure based on routinely determined geotechnical parameters like dry unit weight, initial water content, clay content, Atterberg limits, cation exchange capacity. This article presents the results of correlation and regression made with the Statistica V.13 software, on 50 soil samples collected from nine countries. The analyses show a high coefficient of correlation (R) of swelling pressure with the plasticity index followed by the liquid limit and clay content. Also, this paper provides empirical equations for indirect estimation of swelling pressure based just on a single soil parameter (PI, LL) or two parameters (PI and LL, PI and Cl). [ABSTRACT FROM AUTHOR]

In this study, swelling properties of fine grained soils that surfacing around Güdül and its environments were studied in order to determine causes of cracks and plaster spills on 1 and 3 storey buildings in Güdül district of Ankara. 19 boreholes with a depth of 5 m to 15 m were drilled. Groundwater was not observed except BH-4, BH-9 and BH-16. 21 standard penetration test samples and 30 undisturbed soil samples were taken from these boreholes. Swelling pressure tests, swelling percent tests, soil classification and index tests were carried out with these samples. The SPT N60 blow counts from which samples were taken are ranging between 12 and 49 and the mean average N60values are determined as 25 blow counts.%59 of the soil samples are determined as low plastic clay (CL) low plastic silt (ML) or low plastic organic material (OL). %41 of the soil samples are determined as high plastic clay (CH)-High plastic organic material (OH) or high plastic silt (MH). The mean swelling pressure is 45.83 kPa and the highest swelling pressure is 111.29 kPa determined from the swelling pressure tests. Activity, swelling potential, swelling pressure maps of Güdül and its surrounding were prepared. While the activity of soil is 0.5 arround the Emirler district, the activity of the soils is 1.4 arround Yeni district which locates 5 km north of Emirler district. Likewise, the swelling potential and swelling pressure values are 1.5% and 25 kPa around Emirler district, while 6% and 65 kPa around Yeni district. Except for the location of BH-17, there is a significant increase in swelling percentage and swelling pressure values from south to north direction. If the foundation soils interact with water, swelling pressure may cause risk for 1-3 storey buildings. [ABSTRACT FROM AUTHOR]

In this study for factors effecting the swelling pressure of jerash expansive soils were investigated in this study, effect of initial dry density and effect of initial water content on the jerash expansive soil were investigated. It show that as the initial dry density decrease from 1.85 gm/cm³ to1.25 gm/cm³, the swelling pressure also decrease are from 3.1 gm/cm²(to 0.25 gm/cm²(also it show that, as the initial water content increase from 0%to 15%, the swelling pressure of jerash expansive soil decrease from 2.65 gm/cm²(to 1.35kg/cm². [ABSTRACT FROM AUTHOR]

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Various methods have been reported in the literature to measure the swelling pressure of clayey soils. These methods generally include experimental measurements of the swelling pressure of the soil using indirect methods by conventional oedometer apparatus; while the measurement of swelling pressure of compacted samples using direct method has been less considered. Direct methods involve constant volume swell method with initial vertical stress and without applying vertical stress. Indirect methods consist of swell-consolidation (Free-swell and Restricted-swell) and zero swell experiments. In the present study, in addition to using conventional oedometer, an experimental technique using a modified loading frame was employed to directly measure the swelling pressure. It is observed that the swelling pressure measured by direct method is greatly affected by the vertical stress at which the sample is inundated. The measured swelling pressures obtained from direct and indirect methods are compared with each other. The results indicate that zero swell method slightly overestimates swelling pressure compared to the direct method of constant volume swell without initial vertical stress. Furthermore, the methods of free swell-consolidation and restricted swell-consolidation excessively overestimate the swelling pressure. Regarding the actual conditions of the soil in practical works, it seems that the swelling pressure measured by the method of constant volume swell with initial vertical stress is closer to the true value. The effects of initial conditions such as dry unit weight and initial water content on the swelling pressure are also evaluated in all methods. [ABSTRACT FROM AUTHOR]

Pavement structures constructed on the expansive soil subgrade experience a higher upward pressure compared to any other subgrade material. The upward pressure is caused due to high swelling and shrinkage characteristics of expansive clay soil. The present study has investigated and identified the mechanisms by which a remolded expansive soil can be modified to reduce the upward pressure and swelling (heave). To achieve this, a lightweight, environmentally friendly, and high pressure resistive expanded polystyrene (EPS) granules have been used with expansive soil s from three different locations of Madhya Pradesh state, India. The study has been performed to understand the swelling and strength characteristics of soil with and without the use of EPS (density = 21.6 kg/m3) as per ASTM specifications. The chemical and microstructural components of the expansive soil were investigated using autotuned total reflectance Fourier transform infrared (ATR-FTIR), X-ray diffraction (XRD), and scanning electron microscope (SEM). Several laboratory experiments, including optimum moisture content, maximum dry unit weight, grain-size distribution, liquid limit, plastic limit, shrinkage limit, free swell index, unconfined compressive strength, and pressure swelling tests were carried out on the statically compacted expansive clay soil specimen with and without EPS (0.25%, 0.50%, 1.00%). The maximum addition of EPS was considered as 1% as the very high expansion was observed, and beyond this, further addition of EPS was not feasible. The results show that the swelling pressure, expansion percentage, and time rate of swell decrease, whereas the unconfined compressive strength (UCS) increases with the addition of EPS. The inclusion of EPS in expansive clay soil exponentially reduced the heave and the upward pressure, whereas the maximum UCS was observed at 0.5%. [ABSTRACT FROM AUTHOR]

The present article brought out the effect of compaction pressure and temperature on the swelling pressure of two Indian bentonites. The isochoric swelling pressure tests were carried out using a modified oedometer at ambient and elevated temperatures. The effect of compaction pressure on swelling pressure of compacted bentonite was studied by conducting constant volume swelling pressure tests on two bentonites for a range of dry densities between 1.3 and 1.8 Mg/m3. The effect of temperature on the swelling pressure of bentonites was evaluated by conducting tests on three different conditions, such as isothermal, incremental and decremental temperature conditions. The isothermal swelling pressure tests were performed at three different temperatures such as 25 °C, 55 °C and 95 °C at a dry density of 1.6 Mg/m3. In incremental and decremental temperature conditions swelling pressure tests were performed at various temperatures in a stepwise manner. The effect of temperature on swelling pressure of compacted bentonites was investigated theoretically using Diffused double layer theory. A correlation between the compaction pressure, dry density and swelling pressure of bentonites is presented based on the experimental results. Further the correlation equation was validated with literature-reported results of three bentonites. In isothermal condition, an increase in temperature resulted in increase and decrease in swelling pressure for divalent bentonite-A and monovalent bentonite-B, respectively. In the incremental temperature condition, swelling pressure was found to increase slightly for both the bentonites. During the decremental temperature condition, the swelling pressure was noted to decrease significantly for both the bentonites. The theoretically calculated swelling pressure was found to increase with an increase in temperature for both the bentonites. [ABSTRACT FROM AUTHOR]