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IIT Madras

Lime is the most commonly used chemical admixture for the treatment of the expansive soils. But the intrusion of sulfate contaminant into the lime treated soil will always results in deterioration of the treated soil. The intrusion of sulfate occurs through acid rains, effluent from tannery industries or mine wastes, intrusion of sea water, construction waste, intrusion of leachate from solid waste fills and sulphate rich groundwater. Therefore, this paper aims at bringing out the effect of sodium sulfate (Na2SO4) solution on the compaction and strength behavior of the lime treated expansive soil. Further, the effect of compaction delay and curing period on the sulfate contaminated lime treated soil is also brought out in this paper. Lime contents of 2.5 (initial consumption of lime (ICL) −1%), 3.5 (ICL) and 4.5% (ICL +1%) were used in this study. The sulfate contamination was limited to 5000, 10000 and 20000 ppm. The experimental results showed that the sulfate contamination decreased the maximum dry density and optimum moisture content of the lime treated expansive soil. Further, the intrusion of sulfate solution into the lime treated expansive soil decreased the strength of the lime treated expansive soil. © 2019, Springer Nature Switzerland AG.

Department Of Civil Engineering

World University root node

Sustainable Civil Infrastructures

Effect of Sulfate Contamination on Compaction and Strength Behavior of Lime Treated Expansive Soil

In the present study, the cyclic triaxial tests and resonant column (RC) tests were carried out, to study the effect of frequency on reconstituted marine clay saturated with distilled water and NaCl solutions. Slurry consolidated samples were prepared at 50 kPa vertical stress. Samples were isotropically consolidated at three different effective confining pressures i.e. 80, 150 and 300 kPa. The loading frequencies adopted for the study were 0.1 Hz and 1 Hz with a number of 100 loading cycles. The results show that the effect of frequency could affect the shear modulus of clay soil reconstituted with varying pore fluid chemistry. The shear modulus increases and damping ratio decreases with increase in loading frequency for clay soil reconstituted with concentrated saline solution. Furthermore, the seismic response analysis was conducted to study the effect of frequency on marine clay soil reconstituted with distilled water and electrolyte solutions using one dimensional equivalent linear DEEPSOIL software. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.

International Journal of Geotechnical Engineering

Effect of frequency on cyclic response of marine clay saturated with various pore fluids

Compacted expansive soils are widely used as engineered barriers in waste contaminant applications like landfills, brine ponds, and nuclear waste disposal sites. These liners are designed for very low hydraulic conductivity (&lt;1 × 10−7 cm/s). Percolation of chemical waste or leachate results in physicochemical changes in compacted expansive soils which increases the hydraulic conductivity. This paper brings out the changes in swelling behavior and hydraulic conductivity of compacted expansive soil induced with osmotic gradients using NaCl and CaCl2 solutions. Multiple identical soil specimens placed in oedometer assemblies were inundated with distilled water, 0.4 and 4 M NaCl (monovalent cations), and 0.4 and 4 M CaCl2 (divalent cations) salt solutions and allowed to swell under a surcharge pressure of 12.5 kPa. Void ratio–water content plots were also traced during swelling process. Falling head permeability tests were conducted on swollen soil specimens in rigid wall oedometer permeameters under a hydraulic gradient (i) of 20. The experimental results showed that the swell potentials reduced and hydraulic conductivity increased with the increase in induced osmotic suction. © Springer Nature Singapore Pte Ltd 2019.

GENERAL

Lecture Notes in Civil Engineering

Effect of induced osmotic suction on swell and hydraulic conductivity of an expansive soil

The volume change during drying of compacted expansive soils occurs in the form of reduction in overall volume and development of cracks. Accurate determination of volume of shrunken soil specimens becomes essential to understand the shrinkage behaviour of compacted expansive soils. Mercury displacement method available for the bulk volume measurement of cylindrical small samples suffers from the serious limitations such as the restrictions of using the mercury as it is a hazardous material and the size of specimens is limited to small samples/portions. In the past few years, the digital camera images have been successfully utilised in studying the crack pattern and various parameters associated with reconstituted soils dried from slurry state. Fewer works have been carried out to quantify the cracks in the compacted soils, especially in compacted expansive soils. In this paper, simple methods for the determination of the volume of shrunken soil specimens excluding the volume of cracks are proposed based on the digital camera images captured on thin oedometer shrunken soil specimen along with the vernier calliper method. The results were compared with the mercury displacement method. Cracks which extended from top to bottom of the shrunken specimen during drying assisted in employing these methods. The effect of cracks on shrinkage deformations during second drying cycle and at the end of five drying cycles under a vertical stress of 12.5&nbsp;kPa was studied.

Determination of volumetric shrinkage of an expansive soil using digital camera images

This paper presents a case study of a two-storey building in Oragadam, near Chennai (India), which has undergone distress due to the presence of expansive soil. Undulations in the floors, cracks in partition walls and non-uniform heave in the pavement are some of the failure patterns noticed in and around the structure. Undisturbed soil samples were collected from the site to identify the cause of distress. From the field inspection and laboratory testing it was found that the use of unsuitable fill material (expansive soil) followed by the ingress of excess water from the garden and improper planning of the location of the rainwater-harvesting system were the causes of the initiation of distress in the building. © 2018 ICE Publishing: All rights reserved.

Proceedings of the Institution of Civil Engineers: Forensic Engineering

Distress of an industrial building constructed on an expansive soil: A case study from India

The effect of pore fluid chemistry on the cyclic behaviour of fine grained soil is studied by performing strain controlled undrained cyclic triaxial tests on reconstituted marine clay with 0.4 M sodium chloride solution and distilled water. Specimens using different pore fluids were prepared by slurry consolidation method at vertical stress of 50 kPa. The influence of physico-chemical factors on the cyclic behaviour of reconstituted marine clay was brought out by studying the effect of number of cycles on the cyclic shear modulus degradation of clay. The effective confining pressure was taken as 150 kPa, loading frequency as 1 Hz, number of loading cycles as 100, and the strain range is kept in between 0.3% to 1%. The experimental results show that, with 0.4 M sodium chloride solution as the pore fluid, the shear modulus increases at lower strain range. The variation of damping ratio with the cyclic shear strain was also brought out in this study. © 2018 American Society of Civil Engineers.

Geotechnical Special Publication

Effect of Pore Fluid on Cyclic Behaviour of Reconstituted Marine Clay

The phenomenon of collapse assumes significance in the geotechnical engineering applications such as earth dams and highway and railway embankments as the compacted soils in these applications are susceptible to wetting-induced failures. Therefore, the present study focuses to understand the influence of placement conditions and vertical stress on the wetting-induced collapse behaviour of compacted red soil through series of single oedometer collapse tests. The loading–collapse (LC) curves of compacted red soil for different dry unit weights were established over a large range of matric suctions in order to analyse the experimental results in the context of Barcelona basic model (BBM) elasto-plastic framework and also the experimental results were supported using the concept of LC curves defined in the BBM framework. The experimental results showed a path-dependent relationship of collapse potential with the water content at a given dry unit weight and vertical stress. The position of LC curves of the compacted specimens with respect to the wetting path illustrated a decrease in the soil collapse with the increase in dry unit weight. Thus the present experimental results demonstrate that the BBM framework aids in predicting the nature of volume change and the point of maximum collapse.

Department of Mechanical Engineering

Collapse behaviour of compacted red soil

Physico-chemical effects assume significance in geoenvironmental engineering applications where compacted soils and natural soil deposits interact with chemical contaminants. The physico-chemical interactions occur at the microstructural level and affect the macrostructure and thus the volume change behaviour. This paper brings out the physico-chemical effects on the compressibility and collapse behaviour of compacted red soil. The physico-chemical effects were induced by using different fluids for specimen preparation and inundation. Salinisation of compacted specimens prepared with distilled water induces outward osmotic flow and causes induced osmotic consolidation. In addition, the diffusion of saline solutions into the compacted specimens leads to microstructural contractions at the clay particle level and results in an increase in the irreversible macrostructural strains. Consequently, the macrostructure experiences plastic hardening and this results in greater collapse strains. Scanning electron micrographs showed an increase in the size of macrovoids (loose macrostructure) with the increase in pore fluid osmotic suction owing to the microstructural contractions. Therefore, this paper also provides an insight into the behaviour of specimens prepared with saline solutions with respect to the initial loading–collapse (LC) curves and collapse behaviour when subjected to inward osmotic flow and no osmotic flow conditions. The specimens prepared with saline solutions yielded at lower vertical stress in comparison with the specimens prepared with distilled water, and the elastic response of the compacted soil was found to be independent of both matric and pore fluid osmotic suctions. The osmotic swelling, which occurs owing to dilution of pore fluid at the microstructural level, resulted in slightly lower collapse potentials in specimens subjected to inward osmotic flow condition in comparison with the no osmotic flow condition. © 2017 Thomas Telford Ltd.

Geotechnique

Physico-chemical effects on collapse behaviour of compacted red soil

Physico-chemical effects have a significant impact on the behavior of clay barriers due to the interactions between the pore fluid and clay particles, and they pose a great challenge because the efficiency of clay barriers and cover systems may be altered. Therefore, this paper highlights the effect of physico-chemical factors on shrinkage behavior of compacted expansive clay. To achieve this, the compacted clay specimens were inundated with distilled water, NaCl, and CaCl2 salt solutions in separate oedometer cells at a vertical pressure of 6.25 kPa and allowed to swell. The swollen specimens were gradually shrunk until the specimens attained constant mass, and the changes in void ratio and water content were monitored during drying. The experimental results showed that magnitude of induced osmotic suction and type of pore fluid had a significant impact on shrinkage behavior of compacted clay specimens due to the changes in soil structure. The average pore size of compacted specimens significantly decreased with the induced osmotic suction due to the reduction in size of micropores owing to the suppression of double layers. The discussions are supported by scanning electron microscopy images. Also, the experimental shrinkage data were fitted using modified van Genuchten and Fermi mathematical models, and the results showed that these models fit well with an adjusted R2 higher than 0.9962. © 2016 American Society of Civil Engineers.

International Journal of Geomechanics

Physico-chemical effects on shrinkage behavior of compacted expansive clay

The present study examines the relevance of placement conditions on the behaviour of polypropylene fiber reinforced bentonite. The laboratory testing program includes conducting standard and modified Proctor compaction tests, tracing shrinkage behaviour, performing hydraulic conductivity and unconfined compression strength tests on both unreinforced and fiber reinforced bentonite. An overall acceptable zone in terms of water content and dry unit weight is established by considering the hydraulic conductivity, strength and volumetric shrinkage criteria. The experimental results showed that the volumetric shrinkage criterion controlled the overall acceptable zone for unreinforced and fiber reinforced bentonite specimens in compacted state. However, the hydraulic conductivity values of fiber reinforced bentonite specimens subjected to wet-dry cycles show that the shrinkage criteria may not be appropriate for materials such as bentonite and bentonite-enhanced clays which possess good self sealing properties; and for such materials the hydraulic conductivity needs to be evaluated after wet-dry cycles. As the basic ingredient of geosynthetic clay liners (GCLs) is bentonite clay, the relevance of the placement conditions is discussed for the GCLs. © 2017 Elsevier B.V.

Applied Clay Science

Polypropylene fiber reinforced bentonite for waste containment barriers

Sequential permeation of calcium chloride and sodium hydroxide solutions into the soil mass leads to the formation of lime in the in-situ soil mass owing to chemical reactions. Previous studies have demonstrated that the lime precipitation modifies the expansive soil properties both by lime modification and pozzolanic reactions. However, the independent contributions of either calcium chloride solution or sodium hydroxide solution in stabilizing the expansive soil are not known. Therefore, an attempt is made in the present investigation to examine the relative efficiencies of calcium chloride solution, sodium hydroxide solution and lime precipitation in stabilizing the expansive soil by comparing the physico-chemical and index properties, oedometer swell potentials and unconfined compressive strength of treated specimens. The present investigation also brings out the relative efficiencies of hydrated lime and precipitated lime in stabilizing the expansive soil. The experimental results showed that treating the expansive soils with calcium chloride and sodium hydroxide solutions independently promoted only the short-term reactions whereas the sequentially treating the expansive soil with calcium chloride and sodium hydroxide solutions resulted in the formation of lime precipitation, which could mobilize both short-term lime-modification reactions and long-term soil-lime pozzolanic reactions. © 2016 Taylor & Francis.

Relative efficiencies of electrolytes in stabilization of an expansive soil

Coal ash is a by-product produced from the thermal power plants. It is characterized with low unit weight, high shear strength and low compressibility and finds a major application as an alternate material in the geotechnical engineering applications. However, some coal ash fills are susceptible to wetting-induced collapse due to the loss of capillary suction which stabilizes the inter-granular bonds. The present study examines the influence of placement conditions, vertical stress and pore fluid concentration on the collapse behaviour of compacted fly ash specimens. The experimental results showed that the maximum collapse potential for the coal ash specimens compacted to relative compaction of 80 % and water content of 15 % was in the range of 8.6–13 % at vertical stress of 100 kPa, which indicates that the apparent preconsolidation stress for the coal ash specimens is equal to 100 kPa. Among the coal ashes, the compacted fly ash specimens are more susceptible to wetting-induced collapse in comparison to bottom ash and pond ash specimens which is attributed to the higher silt size fraction in the fly ash. This study also presents the collapse behaviour of lime stabilized compacted coal ash. © 2016, Springer International Publishing Switzerland.

Fulltext

International Journal of Geosynthetics and Ground Engineering

Collapse Behaviour of Compacted Coal Ashes

The present investigation examines the efficiency of an in situ lime precipitation technique in stabilizing expansive soil through laboratory-scale model tests. Expansive soil was compacted in a cylindrical mold and sequentially permeated with CaCl<inf>2</inf> and NaOH solutions into the expansive soil through a central hole filled with coarse sand. Successive permeation of CaCl<inf>2</inf> and NaOH solutions into the compacted expansive soil resulted in precipitation of lime in the expansive soil mass. The precipitated lime reduced the plasticity index, controlled the swell-shrink potentials, and increased the unconfined compressive strength of the expansive soil by both strong lime modification reactions and soil-lime pozzolanic reactions. The results are corroborated with microfabric studies on lime precipitation treated specimens, which showed the formation of cementation bonds. © 2014 American Society of Civil Engineers.

Journal of Materials in Civil Engineering

Laboratory investigations of in situ stabilization of an expansive soil by lime precipitation technique

Depending on the relative chemical concentrations of clay pore water and landfill leachate, three osmotic flow scenarios may be anticipated to dissipate the osmotic suction gradient: outward osmotic flow, inward osmotic flow and no (osmotic) flow. This study examines the volume change behaviour of clay subjected to all osmotic flow conditions. Results show that osmotic suction gradient decreases swelling strains when the osmotic flow is outward, whereas swelling strains increase in case of inward osmotic flow. The increase or decrease in effective stress from osmotic suction gradient is transient and reduces to zero with dissipation of matric suction and osmotic suction gradient. In the no (osmotic) flow condition, the swelling strains are governed by matric suction and pore fluid osmotic suction. The experimental results bring out the dependency of swelling strains on applied stress, stress paths and osmotic suction gradient.

Environmental Geotechnics

Osmotic flow in compacted expansive clay

The experimental results of the present study on compacted expansive clay illustrate that matric suction increases with the increase in pore fluid osmotic suction due to changes in soil structure. Scanning electron micrographs show that particle stacking (aggregations) increases with increase in pore fluid osmotic suction and cation valence due to reduction in diffuse double layer thickness, and thus results in a reduction in micro pore size with a corresponding increase in macro pore size. At a given water content, the macro pore degree of saturation reduces with the increase in osmotic suction owing to the increase in macro pore size and leads to an increase in matric suction, as the matric suction is characteristic of the macro pore and the degree of saturation of the macro pore. The matric, osmotic and total suction measurements using the filter paper method also confirm that the matric and osmotic suction components are additive. This demonstrates that the method of obtaining matric suction from the difference between total suction and pore fluid osmotic suction determined using non-contact filter papers is reliable. © 2015, ICE Publishing. All rights reserved.

Effect of pore fluid osmotic suction on matric and total suctions of compacted clay

In geoenvironmental engineering applications, the compacted fills often come in contact with hazardous chemical contaminants and are subjected to physico-chemical changes. These changes alter the mechanical behaviour of compacted soils due to the physico-chemical interactions at the clay particle level, which are reflected as a variation in the yield stress at the macrostructural level. Therefore, the current experimental investigation presents the effect of pore fluid osmotic suction on the compressibility and collapse behaviour of compacted clayey sand (red soil). Compaction of salt solution remoulded soil leads to the development of larger macropores owing to the microstructural contractions. The macroporosity increases with the increase in the pore fluid osmotic suction due to greater microstructural contractions. Thus, the yield stress decreases with the increase in the pore fluid suction, and the relationship between them was found to be logarithmic. The micro- and macro-structural changes occurring from the physico-chemical changes also affect the collapse, as the phenomenon of collapse is associated with macrostructural deformations. In order to eliminate the osmotic flow during collapse, no osmotic flow condition was adopted. Experimental results illustrate that the collapse increases with the increase in the pore fluid suction on account of increase in matric suction and macroporosity.

Effect of pore fluid on compressibility and collapse of clayey sand

Previous investigation showed that sequential mixing of calcium chloride and sodium hydroxide solutions with an expansive soil resulted in lime precipitation in the soil mass, which controlled the swelling potentials and increased the unconfined compressive strength of treated specimens through strong modification and pozzolanic reactions. However, expansive soils in the field are subjected to cyclic wetting and drying due to environmental conditions, which affects the swell-shrink behaviour. Therefore, the present investigation examines the efficacy of the lime precipitation technique in controlling the swell-shrink potentials and strength characteristics of expansive soils subjected to cyclic wetting and drying. Expansive soil is mixed sequentially with different concentrations of calcium chloride and sodium hydroxide solutions to yield a range of lime precipitation contents, and cured for different time periods. The cured specimens were subjected to cyclic wetting and drying in modified odeometer cells, and the swell-shrink potentials were monitored. The unconfined compressive strength of cured specimens was also determined after different cycles of wetting and drying in a sand bath. The laboratory results showed that the second swell potential was the maximum for untreated and lime precipitation treated specimens, in comparison with other wetting cycles. The equilibrium state was reached after about four to five cycles of wetting and drying. The equilibrium bandwidth reduced as the percentage lime precipitation and curing period increased. The unconfined compressive strength reduced with wetting and drying cycles, which indicated the loss of cementation after one wetting and drying cycle. © 2014, Thomas Telford Services Ltd. All rights reserved.

Proceedings of the Institution of Civil Engineers: Ground Improvement

Swell-shrink behaviour of lime precipitation treated soil

Compacted clay soils are used as barriers in geoenvironmental engineering applications and are likely to be exposed to salinization and desalinization cycles during life of the facility. Changes in pore fluid composition from salinization and desalinization cycles induce osmotic suction gradients between soil-water and reservoir (example, landfill/brine pond) solution. Dissipation of osmotic suction gradients may induce osmotic swelling and consolidation strains. This paper examines the osmotic swelling and consolidation behaviour of compacted clays exposed to salinization and desalinization cycles at consolidation pressure of 200 kPa in oedometer assemblies. During salinization cycle, sodium ions of reservoir fluid replaced the divalent exchangeable cations. The osmotic swelling strain developed during first desalinization cycle was 29-fold higher than matric suction induced swelling strain of the compacted specimen. Further, the diffusion controlled osmotic swelling strain was 100-fold slower than matric suction-driven swelling process. After establishment of ion-exchange equilibrium, saturated saline specimens develop reversible osmotic swelling strains on exposure to desalinization cycles. Likewise the saturated desalinated specimen develops reversible osmotic consolidation strains on exposure to cycles of salinization. Variations in compaction dry density has a bearing on the osmotic swelling and consolidation strains, while, compaction water content had no bearing on the osmotic volumetric strains. © 2012 Springer Science+Business Media Dordrecht.

Geotechnical and Geological Engineering

Osmotic Swelling and Osmotic Consolidation Behaviour of Compacted Expansive Clay

Department Of Biotechnology

Communications in Computer and Information Science

Preface

Compacted expansive clays swell due to crystalline swelling and osmotic/double layer swelling mechanisms. Crystalline swelling is driven by adsorption of water molecules at clay particle surfaces that occurs at inter-layer separations of 10-22 Å. Diffuse double layer swelling occurs at inter-layer separations >22 Å. The tendency of compacted clay to develop osmotic or double layer swelling reduces with increase in solute concentration in bulk solution. This study examines the consequence of increase in solute concentration in bulk solution on the relative magnitudes of the two swelling modes. The objective is achieved by inundating compacted expansive clay specimens with distilled water and sodium chloride solutions in free-swell oedometer tests and comparing the experimental swell with predictions from Van't Hoff equation. The results of the study indicate that swell potential of compacted expansive clay specimens wetted with relatively saline (0.4, 1 and 4 M sodium chloride) solutions are satisfied by crystalline swelling alone. Comparatively, compacted clay specimens inundated with less saline solutions (0.005-0.1 M sodium chloride) require both crystalline and osmotic swelling to satiate the swell potential. © 2013 Springer Science+Business Media Dordrecht.