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This study investigates clayey soil from a road project situated in the district of Lodhran, Punjab, Pakistan. The subgrade prepared with the soil distorted due to heaving after a certain period of its construction. First, laboratory tests were conducted to explore the reason for this problem, examining the fundamental engineering properties of soil. The test results show that the soil acts as a soft material when water content reaches 30%, significantly reducing its strength. The soft soil is generally considered unsuitable for civil work due to its poor performance behaviour. So, the performance of clayey soil was examined in the study at its soft state by coupling it with stronger materials, such as polyethylene polymeric reinforcement and sand, developing laboratory-scale foundation models. Based on the model studies, the study proposes a sustainable polyethylene–sand–soft soil model, which shows 155 and 56% higher ultimate bearing capacity (BC) than soft soil and sand-reinforced soft soil foundations. The changes in BC occur due to the reinforcement action of the polyethylene reinforcement, which is associated with its tensile membrane action effects and interlock bonding at the soil-reinforcement interface. Practically, the study can reduce the dependency of industry practitioners on sand materials. Using polyethylene in civil work is viable for environmental sustainability. [ABSTRACT FROM AUTHOR]

The paper investigates the effect of hydrated lime on shear strength properties and behaviour of London clay, triaxial. Unconsolidated undrained tests were performed to identify the effect of lime dosage, compaction water content and curing time on the shear strength and stress–strain behaviour of the treated soil. The mineralogical and physicochemical transformations occurring during the curing of the soil were also monitored. The results showed that strength gain was strongly influenced by lime content and the curing period, whereas compaction water content was less influential. It was found that the strength evolution is likely to continue over long periods of time and result in very considerable strength gains on the hardening of pozzolanic reaction products. It was also shown that adequate early strength gains can be obtained with reduced material consumption, thus further increasing the sustainability of the treatment processes. The paper also highlighted the importance for engineering design of considering the brittle stress–strain response of the lime-treated soil, and the benefit of using lower amounts of lime to alleviate this undesirable effect. The implications of various aspects of soil brittleness in different situations merit further attention and should be explored by way of modelling in future work. [ABSTRACT FROM AUTHOR]

Troublesome events are related to the stabilisation of sulfate-rich soils with calcium-based materials. To overcome these inconveniences, research studies have been conducted applying modified and alternative treatments to soils containing low and high sulfate levels. This paper intends to assess the effects of mellowing period (MP) (2 and 4 days), Portland cement content (5%, 7% and 9%), density (15.75, 16.60 and 17.50 kN/m3) and curing time (14 and 28 days) on the performance of a clayey soil from the Paraguayan Chaco region containing high amounts of sulfates. A complete factorial design set was carried out to assess the unconfined compressive strength (UCS) and the one-dimensional free vertical swelling of compacted soil–cement–lime mixtures. The results showed a positive effect of the MP relative to the swelling of the stabilised soil. In addition, the curing period, the amount of cement and the dry unit weight were the most influential factors regarding the UCS. The stabilisation method addressed in this research – that is, extended mellowing combined with lime and Portland cement, seems to be of great importance for practical purposes on the stabilisation of soils containing high amounts of sulfates. [ABSTRACT FROM AUTHOR]

Class C fly ash, a byproduct of thermal power plants, is often preferred for the stabilisation of expansive soils. However, improper optimisation of the stabiliser may lead to the premature failure of treated soils during wet–dry cycles. This study demonstrates the volume change behaviour of fly ash-stabilised expansive soils subjected to wet–dry cycles. Furthermore, the effect of class C fly ash and lime–class C fly ash on the physical and engineering properties is also studied. The experimental results showed that addition of 20% fly ash to the expansive soil reduced the swell potential to 0% from an untreated swell value of 10.5%. However, when it was subjected to five wet–dry cycles, the initial cementitious effect of the fly ash on controlling the swell was partially lost, and therefore the volumetric deformation of the stabilised expansive soil increased from 0 to 14.5%. Furthermore, among the different additive combinations used for the treatment of expansive soils, it was observed that the combination of 4% lime and 20% fly ash resulted in the volumetric deformation of only 2.05% even after the fifth wet–dry cycle. Besides, the percentage of desiccation cracks has also reduced significantly from 29 to 0.5%. [ABSTRACT FROM AUTHOR]

This paper discusses the strength characteristics of cement-treated soil cured at extremely low temperatures ranging from 5°C to −20°C. To examine how extremely low curing temperatures affect the strength of cement-treated soil, a field study of cement stabilisation executed in the severe winter of Hokkaido, Japan, is presented in the first part of this paper. This study reveals that extremely low air temperatures prevented the shallow part of the cement-treated ground at the site from solidifying sufficiently. Then the influence of extremely low curing temperatures on the strength characteristics of cement-treated soil is discussed, based on the results of laboratory cement mixing and other tests. It is found that cement-treated soils cured at lower temperatures (−20°C, −5°C, 0°C and 5°C) have lower unconfined compressive strengths (UCSs) than that cured at 20°C (a standard curing temperature according to the Japanese Geotechnical Society Standard). Cement-treated soils cured at −5 and −20°C showed almost no gain in UCS. For cement-treated soils cured at 0°C or above, the UCS increased with an increase in maturity. Finally, based on the above experimental results, points to be noted in the construction of cement stabilisation in winter in cold regions are proposed. [ABSTRACT FROM AUTHOR]

Desiccation cracking in clay soils is a combined mechanical and hydraulic problem and such soils can be improved by various methods including reinforcement with fibres. The relationships between tensile strength, cracking resistance and water-retention properties of fibre-reinforced fine-grained soils lack coverage in the literature to date. In this study, these three properties are evaluated and connected by way of a series of tensile strength and desiccation cracking tests on fibre-reinforced London clay. The results confirm that increased fibre addition delays the occurrence of peak stress and changes failure behaviour from brittle to ductile. The tensile strength increment gets higher as water content decreases, and reaches a maximum value of 460 kPa when the water content is 12%. The crack intensity factor reduces from 7.20% to 0.89% when 12 mm long fibre is used at a ratio of 0.9%. Fibre reinforcement also changes the crack development pattern by reducing the size of large cracks and increasing the proportion of small individual cracks. However, the presence of fibres was not observed to change the water-retention properties of the soil, indicating that the tensile improvement comes from the pull-out resistance of the fibres rather than suction changes. [ABSTRACT FROM AUTHOR]

Soils containing organic matter exhibit low shear strength and high compressibility. Lime stabilisation has been shown to improve the engineering properties of clayey soils. An attempt was made to study the effect of organic matter (starch and peat) on the shear strength of lime-stabilised clayey soils subjected to longer curing periods (up to 180 days). Most studies have reported the strength behaviour of lime-stabilised organic soils up to 60 days. Vane shear tests were carried out on artificially prepared organic soil mixtures treated with 6% lime after different curing periods (0, 7, 30, 60, 90 and 180 days). The results indicate that the improving effect of lime is deteriorated in the presence of organic matter as the curing period increases. It was observed that, for lime-stabilised clayey soils containing organic matter, the strength seemed to increase up to 30 days, after which it ceased. The strength reduction in lime-stabilised clayey soils containing organic matter depended on the pH and functional groups present in the soil. Fourier transform infrared spectroscopy of cured samples was also carried out to examine the microstructural changes responsible for the strength change in lime-stabilised clayey soils. [ABSTRACT FROM AUTHOR]

In this research study the effects of calcium and magnesium ions on stabilisation of a clay soil were studied by conducting a set of laboratory tests. A special apparatus was employed for carrying out the tests under constant voltage and time. During the tests, solutions of calcium chloride (CaCl2) or magnesium chloride (MgCl2) with different concentrations were injected into the soil samples. The electro-osmotic and electrokinetics methods were used for stabilisation of the soil and the results were compared with each other. In the electro-osmotic technique, distilled water was used as pore fluid, but in the electrokinetic method, calcium chloride or magnesium chloride solutions with various concentrations were injected into the pores of soil samples. The results revealed an increase in strength of the soil in both methods. In the electrokinetic method, the amount of increase in strength was a function of concentration of the solution that was used. The results also indicated that a solution of calcium chloride is more effective in increasing the strength, discharge flow and electro-osmotic permeability than a magnesium chloride solution at various concentrations. In addition, the variations of these properties are a function of the concentration of the given solution. [ABSTRACT FROM AUTHOR]

This paper presents heave and pullout studies of plain granular pile-anchors (GPAs) and geogrid-encased GPAs. Experiments were conducted in California bearing ratio (CBR) moulds and fabricated moulds of size 381 × 381 × 457 mm in expansive clays. The GPA method is an innovative technique developed for reducing heave and improving bearing capacity and pullout capacity. In this study, GPAs were encased in geogrids to augment the engineering performance of the system. Tests were conducted in CBR moulds and fabricated larger moulds to study and compare the heave and pullout behaviour of plain GPAs and geogrid-encased GPAs. The results indicated that the clay beds reinforced with geogrid-encased GPAs showed better heave and pullout behaviour. Heave decreased by 90.8% and 92.5%, respectively, in the case of plain and geogrid-encased GPAs installed in the CBR moulds and by 95.12% and 98.3% in the case of plain and geogrid-encased GPAs installed in fabricated large moulds. Pullout load on geogrid-encased GPAs in CBR moulds improved by 42.17% over that on plain GPAs and pullout load on geogrid-encased GPAs in the fabricated large moulds improved by 52.25% over that on plain GPAs. [ABSTRACT FROM AUTHOR]

A programme of experiments was conducted to study the use of the electro-kinetic technique to transport a stabilising chemical agent through a clay soil. The experimental tests were undertaken on a clay soil in a special apparatus by applying a constant voltage gradient across the sample to introduce a solution of calcium chloride (CaCl2) with different concentrations in the soil. The variations of shear strength across the sample resulting from the electro-kinetic process were determined. The experiments were conducted in two groups. In the first group, the electro-osmosis method was used for soil samples with distilled water. In the second group, the electro-kinetic technique was applied to the soil to transport the solution of calcium chloride with varying concentrations through the pores in the soil. The results showed that the strength of soil increased for both groups and the amount of increase in the second group was dependent on the concentration of calcium chloride injected into the soil. The injection of this stabiliser also increased the electric current and electro-osmotic permeability. [ABSTRACT FROM AUTHOR]

Few studies have reported the effect of cement content and surcharge pressure on the drying−wetting durability of cement-stabilised clayey soil. The aim of this research was thus to understand the effect of these two factors on the drying−wetting durability of cement-stabilised clayey soil. Clayey soil, dredged from Taihu Lake in Wuxi, China, was stabilised with three different cement contents. Drying−wetting tests were performed on the cement-stabilised clayey soil under five different surcharge pressures and direct shear tests were conducted using a modified conventional direct shear device. The cement content was found to have a significant effect on the drying−wetting durability of the cement-stabilised clayey soil. Drying−wetting appears to decrease the shear strength of clayey soil with a low cement content, whereas drying−wetting appears to increase the shear strength of clayey soil with a high cement content. The variation in shear strength of the cement-stabilised clayey soil is attributed to drying-induced bond damage and drying-temperature-induced hydration and pozzolanic reactions. The surcharge pressure had a significant impact on the drying−wetting durability in a certain range. The findings are interesting from a practical perspective for earthworks involving cement-stabilised clayey soils. [ABSTRACT FROM AUTHOR]

Electrokinetic (EK) treatment is becoming increasingly important in the geotechnical field, especially for treating fine-grained soils. Above all, dredged sediments (slurries) need to be treated in order to be reutilised. Applying an electric potential difference within the soil, three phenomena take place: electrophoresis, electro-osmosis and electromigration. Negative particles move towards the positive electrode while water and cations move towards the negative electrode. Although the literature is full of cases describing the parameters that affect the EK process, there is a need to understand its limits and fields of application. This paper summarises the results collected from several case studies to understand the influence of some parameters on the efficiency of EK treatment, specifically in terms of dewatering rate. Soil conditions (soil type, pH, pore fluid salinity and water content) and set-up design parameters (electrode materials, configurations and operational mode) are analysed. Finally, parameter ranges for assessing the acceptability of electro-osmotic treatment are proposed. The results show that there are optimum values for the previously mentioned parameters that improve the dewatering and thus enhance the behaviour of the treated soils. EK treatment can be effective when applied on dredged sediments with low salinity. [ABSTRACT FROM AUTHOR]

This paper reports the strength and ductility behaviour of rubber-granulate-reinforced cemented clayey soil and rubber-fibre-reinforced cemented clayey soil. The load–deformation behaviour of specimens was analysed in terms of absolute toughness and toughness index (TI) for further screening of the curves. A 5·08 and 3·46% improvement in the unconfined compressive strength and 16·74 and 8·60% improvement in the split tensile strength of the clayey soil was observed with the addition of rubber granulates and fibres up to 2·5 and 5%, respectively. However, increasing the content of granulates and fibres led to reductions in strength. The rate of strength reduction in granulate-reinforced soil was found to be higher than in that containing fibre. The absolute toughness and TI of soil mixed with 5 and 7·5% of granulates and fibres were found to be higher compared to values for other inclusions. Overall, the inclusion of rubber particles led to a decrease in initial stiffness, improved ductility and strain hardening in specimens subject to compressive load. However, in comparison with the ductile behaviour of fibre-reinforced soil under tensile loads, granulates were found to be ineffective in changing the soil's brittle behaviour. [ABSTRACT FROM AUTHOR]

The effects of alkali-activated slag on the engineering properties of clayey soil were investigated. The mix proportion parameters were chosen by using Taguchi's experimental design methodology. Four factors (ground-granulated blast-furnace slag content, concentration of sodium hydroxide solution, sodium hydroxide-to-sodium silicate weight ratio and alkaline solution-to-slag weight ratio) were assessed in order to obtain the greatest compaction properties, uniaxial compressive strength and California bearing ratio (CBR). Significant improvements were observed in the mechanical properties (unconfined compressive strength (UCS) and CBR) of the clayey soil with addition of the stabilisers. Optimal values (15% slag content, sodium hydroxide concentration of 6 M, sodium hydroxide-to-sodium silicate ratio of 0·5 and alkaline solution-to-slag ratio of 2·5) increased the UCS of the compound from 8 to 100 kg/cm2 at 7 d. The excessive addition of alkaline solutions weakened the strength parameters of the soil. The results showed that the most influential factor was the alkaline solution-to-slag weight ratio. The Taguchi method is an effective and suitable experimental method for optimising alkali-activated slag parameters. [ABSTRACT FROM AUTHOR]

Electrokinetic (EK) treatment is a possible attractive way to speed up the consolidation of fine-grained dredged sediments. The effectiveness of this method depends on the complex physical–chemical interaction between soil particles, interstitial fluid and pollutants. This paper presents the experimental laboratory results obtained by inducing mechanical and EK consolidation in a fine-grained dredged material. Then, a finite-difference numerical code implemented by the authors able to solve the large and small strain consolidation equations (Lassec1), including the electro-osmotic flow, is described along with the theoretical simplifications adopted and the calibration procedure required. The experimental results have been numerically simulated, showing the ability of Lassec1 to reproduce the coupled mechanical and electrical consolidation processes, highlighting that under very low stress levels it is necessary to take into account the highly non-linear soil behaviour, and thus the large strain theory is needed to obtain a reliable prediction of the consolidation process. With this aim, special laboratory devices are necessary for a good calibration of the permeability function and of the stress–strain relationship at very low stress levels. [ABSTRACT FROM AUTHOR]

Cement-stabilised self-compacting earth (CSCE) is a mixture of soil, water, stabiliser and chemical admixture, with sufficient fluidity to mould earth walls and structures without the need for mechanical densification. The application of the CSCE technology demands a better understanding of the influence of polycarboxylate-based superplasticiser in the mechanisms of particle dispersion, and the microstructure formation of the CSCE. Therefore, for two soil mixtures, sandy soil + cement + water + admixture and clayey soil + cement + water + admixture, the following tests were applied: calorimetry, thermogravimetry, Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, compressive strength and water absorption capacity. The results demonstrated that the use of superplasticiser in the CSCE exhibits efficiency of fluidity, mobility, segregation control and exudation control in the mixture. Regardless of the soil type, the influence of the superplasticiser on the CSCE mixtures is more relevant to aspects such as the action of electrostatic dispersion of soil and water and of the particles that induce steric hindrance; also the adsorption reactions of admixture by clay minerals are discrete in the CSCE, resulting in a system with physicomechanical behaviour stabilised and compatible for earth-based construction through the use of superplasticiser in the range of 0·8–1·6 and minimum water/soil ratio with proximity to the liquid limit. [ABSTRACT FROM AUTHOR]

Solid waste management is a serious problem worldwide as the amounts of produced wastes are increasing annually. For example, the disposal of waste gypsum plasterboard, used as dry walling across the world, represents a serious environmental issue. Therefore, this study examines the potential for reusing plasterboard wastes as a stabiliser material for earthwork projects, especially for organic soft clay soil. Recycled plaster, mixed with cement or lime at different ratios was used as a stabiliser for tested soil. Atterberg limits, scanning electron microscopy, x-ray diffraction, compressive strength, and secant moduli tests were conducted to evaluate the improvement in stabilised soil properties. The results indicate that the inclusion of plaster-cement (B-C) or plaster-lime (B-L) admixtures improved the geomechanical properties of the stabilised soil, with higher admixture concentrations leading to greater improvement. Moreover, the soil specimens stabilised using the B-L admixture exhibited a higher strength gain rate and reduction in plasticity index and water content than those stabilised by the B-C admixture. The development of cementation compounds in a stabilised soil matrix has a considerable effect on permanent strength enhancement. It is concluded that the proposed stabilising technique can be valuable for both waste management and construction industries. [ABSTRACT FROM AUTHOR]

The collapsibility of soils is one of the various phenomena by which soils pose threats to structures built upon them. This behaviour is more pronounced in clays and some silty sands in arid and semi-arid zones. In this study, an attempt was made to decrease the collapsibility of three different clay soils (soil I, soil II and soil III with different clay content and plasticity indices) by treatment with cement-polymeric fibres as an admixture at various percentages (1, 2, 3, 4 and 5%). The collapsibility potential of all soils was found to be 'moderate to high' in the remoulded initial state. Standard double oedometer tests were conducted to measure the collapsibility of the soils before and after stabilisation. It was found that an increase in the cement:fibre ratio and/or the admixture content percentage significantly decreased the collapse strain at inundation. Moreover, the collapsibility index decreased on increasing the admixture content beyond 3% for soil I and 2% for soils II and III. For an admixture content of <2-3%, the reduction in the collapsibility index was found to be negligible. For all soils used in this study, with a 5% admixture content and a cement:fibre ratio of 6:1 by weight, the soils were found to change from the very high collapsibility range to the almost no-collapsibility range. [ABSTRACT FROM AUTHOR]

Dispersive soils exhibit erosive behaviour in contrast to normal clayey soils. Several chemical stabilisers have been identified as being capable of stabilising these soils. However, the effect of brown coal fly ash (BFA) on the stabilisation of dispersive soil has not yet been investigated adequately. BFA is known to be a weak contributor to strength development. In this work, the stabilisation mechanism of BFA for strength improvement and erosion resistance over time was investigated using two different dispersive soils. The experimental results revealed that the selected BFA is an effective stabiliser in enhancing the erosion resistance of the tested dispersive soils in the short-term. On the other hand, it was found that the addition of hydrated lime further enhanced the strength development of dispersive clayey soils and facilitated early strength gain. Furthermore, soil samples treated with an effective combination of BFA and hydrated lime were investigated at the micro-level by means of energy dispersive x-ray spectroscopy and scanning electron microscopy. The micro-level investigations revealed that the cation exchange rate was higher in soils with a low calcium/sodium ratio. [ABSTRACT FROM AUTHOR]

Stabilisation of expansive soil using lime or sand is an effective improvement technique as it reduces the swelling ability of the soil. The aim of this paper is to study the influence of different lime fractions and lime-sand mixtures on the behaviour of highly expansive clay by performing swelling and strength tests on each mixture. Calcium (Ca)-bentonite is utilised as highly expansive clay. All samples were remoulded according to the results of the modified compaction Aashto test. Non-treated bentonite possesses high values of swelling and strength. Mixing lime and sand with clay causes significant reductions in swelling characteristics. The reductions increase effectively with the increase in lime and sand content. The swell potential and the swelling pressure of the clay almost vanish when stabilised by 10% lime and 50% sand. Generally, adding only lime into clay leads to an increase of its California bearing ratio (CBR) and unconfined compressive strength (UCS), whereas mixing clay with both lime and sand leads to an increase in the CBR values. The CBR values increase significantly with the increment of their content. For a >30% sand content, the UCS of the lime-clay mixtures decreases on increasing the sand fractions, whereas the UCS values increase with a longer curing time. The CBR and UCS-56 d curing time of the stabilised clay with 10% lime and 50% sand increase to twice the values for the non-treated clay. [ABSTRACT FROM AUTHOR]

This paper summarises the evaluation of previously existing and recently developed bearing capacity estimation methods for spread footings resting on aggregate pier reinforced clay. A load test database of full-scale footings resting on stone columns was used to generate an accurate ultimate limit state design model for bearing capacity and characterise the associated model uncertainty. Different levels of variability in area replacement ratio, slenderness ratio, length of pier, depth of footing embedment, and undrained shear strength, were incorporated in the resistance factor calibration in order to account for possible uncertainty in the load test database and future construction. Resistance factors were calibrated as a function of the ratio of dead to live load, reliability index, and total variability in the nominal bearing capacity. The operational factor of safety was computed for comparison to allowable stress design procedures and indicated that typical factors of safety associated with current practices can continue to be used for soil deposits with moderate variability. [ABSTRACT FROM AUTHOR]