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Electro-osmotic drainage technology is especially suitable for low-permeability clay soil. The electrode–clay interface is believed to play a crucial role in electro-osmosis. Previous documents have highlighted the importance of the electrochemical processes at the electrode–clay interface, but few studies exist with respect to the influencing mechanisms. Therefore, the influencing mechanisms of the electrochemical processes on the electrode–clay interface have been thoroughly studied herein, both theoretically and experimentally. An interfacial resistance model in the electro-osmotic system is proposed based on the interfacial kinetic reactions of metal electrodes and graphite electrodes according to electrochemical theory. The reliability of the proposed model is demonstrated by chamber tests. The proposed model states that the most critical factor influencing interfacial resistance is the current density on the electrode surface. Other crucial influencing factors for interfacial resistance include the electrode material, surface status, pH of the pore solution, soil void ratio, conductive properties and adsorption properties. [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]

A method for the estimation of the non-linear, time-dependent settlement of piled raft foundations (PRFs) embedded in saturated clayey soils subjected to uniformly distributed load under the single-drainage condition was developed. A total of 20 different rectangular PRFs resting on four different types of normally consolidated to moderately overconsolidated clays (overconsolidation ratios of 1, 2 and 5) were analysed to quantify their short- and long-term settlements. Rigorous three-dimensional, elasto-plastic finite-element (FE) analyses were performed with the critical-state-based modified Cam Clay soil constitutive model. Biot's coupled consolidation theory was used to model the time-dependent dissipation of excess pore pressure under the single-drainage condition. The FE analysis results were used to investigate systematically the influence of time and various soil and PRF parameters on the settlement responses of piled rafts. Fitted equations correlating PRF settlements and the degree of consolidation with various influencing parameters were developed. The proposed equations predicted the immediate and primary consolidation settlements and the degree of consolidation with reasonable accuracy and can be used in initial design stages. [ABSTRACT FROM AUTHOR]

A novel graphical analysis-based method is proposed for analysing the responses of a cylindrical cavity expanding under undrained conditions in modified Cam Clay soil. The essence of developing such an approach is to decompose and represent the strain increment/rate of a material point graphically into the elastic and plastic components in the deviatoric strain plane. It allows the effective stress path in the deviatoric plane to be readily determined by solving a first-order differential equation with the Lode angle being the single variable. The desired limiting cavity pressure and pore pressure can be equally conveniently evaluated, through basic numerical integrations with respect to the mean effective stress. Some ambiguity is clarified between the generalised (work conjugacy-based) shear strain increments and the corresponding deviatoric invariants of incremental strains. The present graph-based approach is also applicable for the determination of the stress and pore pressure distributions around the cavity. When used for predicting the ultimate cavity/pore pressures, it is computationally advantageous over the existing semi-analytical solutions that involve solving a system of coupled governing differential equations for the effective stress components. It thus may serve potentially as a useful and accurate interpretation of the results of in situ pressuremeter tests on clay soils. [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]

The simple but profound standard equation given in BS 1377:1967 is revisited in this paper. According to the equation, plasticity index (PI) is 2.13 times (or simply twice) the linear shrinkage. This standard relationship is widely recognised and employed when determination of the liquid limit or plastic limit is difficult or not possible. The equation is also used as a basic means of checking the accuracy of test results for the Atterberg limits. Data of 180 natural soil samples were used to statistically evaluate the veracity of the equation. It was found that the BS 1377:1967 equation exhibits excellent accuracy and the equation's veracity for practical engineering use was confirmed. However, the method appears to be correct only up to PI values not exceeding 25% and has greater accuracy at lower PI values (<15%). Other studies in the literature also show that the equation may not apply to some soil types or to soils of particular clay mineral types. These possible limitations thus require further investigation. [ABSTRACT FROM AUTHOR]

Understanding of desiccation-induced cracking in soil has improved over the last 20–30 years through experimental studies, but progress in predictive modelling of desiccation cracking has been limited. The heterogeneous structure of soils and the multi-physics nature of the phenomenon, involving emergence and propagation of discontinuities, make the mathematical description and analysis a challenging task. The authors present a non-local hydro-mechanical model for soil desiccation cracking capable of predicting crack initiation and growth. The model is based on peridynamics (PD) theory. Attempts to model soil desiccation cracking by PD are limited to a purely mechanical description of the process that involves calibration of the parameters. In contrast, the model presented in this paper describes soil desiccation cracking as a hydro-mechanical problem, where moisture flow and deformation are coupled. This allows for investigating and explaining the mechanisms controlling the initiation and propagation of discontinuities. The model is applied and tested against two sets of experimental data to explain the typical features of drying-induced cracking of clays. The validations use experimental parameters (Young's modulus, water retention characteristics) and avoid calibrations to test the accuracy of the model. The correlations between the shrinkage of soil clay, changes in displacement fields and crack growth are demonstrated. Crack initiation, propagation and ultimate crack patterns simulated by the model are found to be in very good agreement with experimental observations. The results show that the model can capture realistically key hydraulic, mechanical and geometry effects on clay desiccation cracking. [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]

Pile foundations for masts supporting overhead line equipment (OLE) on railways in Western Europe have traditionally been designed using empirical formulae derived from tests carried out in the 1950s under the auspices of the Union Internationale des Chemins de fer (UIC). Recent application in the UK of ostensibly more analytical approaches led to significantly increased pile lengths, which contributed to the high-profile cost over-run on the Great Western electrification programme. Further, the loads associated with some newer designs of mast are greater than those covered by the original field tests, and hence are outside the evidence base for the empirical approach. To address this, full-scale field tests were carried out on three, 610 mm dia. circular hollow-section steel piles installed in a railway embankment at the High Marnham test track (Nottinghamshire, UK). Each pile was designed according to the empirical OLE master index (OLEMI) method for a different form of modern OLE mast, and instrumented using Shape accelerometer arrays (SAAs) to determine pile deformations. The results provide valuable insights into the mechanisms of deformation of piles of different lengths, both at and beyond the expected in-service loads. p–y curves derived from the SAA measurements compare reasonably well with curves constructed using the American Petroleum Institute method for undrained clay soils. The tests also demonstrate the suitability of the OLEMI approach for large structures and loads; and that the Eurocode 7 partial factors on load and undrained shear strength applied to an undrained (total stress) limit equilibrium calculation are likely to be sufficient to meet serviceability requirements for standard single-and twin-track cantilever structures. [ABSTRACT FROM AUTHOR]

The article presents the discussion on novel elasto-viscoplastic formulation for compression behaviour of clays. Topics include model linearises the limiting compression curve (LCC) by using the logarithm of voids ratio; and immediate elastic strain at the draining boundary of a soil layer after load application producing an infinite spike in elastic strain rate.

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]

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]

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]

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]

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]

A detailed experimental programme was conducted to evaluate the liquefaction susceptibility of non-plastic and low-plasticity soils subjected to cyclic loading under undrained triaxial loading conditions. The study mainly focused on examining the influence of the amount of fines and plasticity indices on the liquefaction resistance of sands. After mixing silt and clay fractions into fine sand, 16 soil combinations were prepared. The silty sands contained up to 40% non-plastic fines and the low-plasticity soils contained a clay fraction of 5–40%. Each cylindrical soil specimen was constituted to a medium relative density and saturated specimens were subjected to a confinement pressure of 100 kPa. The consolidated specimens were then subjected to various levels of cyclic stress amplitudes using a sinusoidal wave load form at a frequency of 1 Hz. The results showed that both the non-plastic and low-plasticity clay soils were less resistant to liquefaction than the fine sand. The soils belonging to categories SM and SC (silty sand and clayey sand, respectively, as per Indian standard soil classifications) were susceptible to liquefaction if the fines passing through a 75 μm sieve were ≤ 40%, the liquid limit was ≤ 40%, the plasticity index was < 15 and the saturated water content was about 0.86 times the LL. [ABSTRACT FROM AUTHOR]

In the geotechnical community, the macroelement approach nowadays is largely considered to be a successful theoretical tool for solving soil–structure interaction problems. This approach is based on the definition of a generalised constitutive law putting in relation a small number of suitably defined generalised stress/strain variables. The macroelement formulations proposed in the literature take into consideration either drained or undrained cases, but disregard the hydro-mechanical coupling. In this paper, the authors intend to generalise the theory by introducing a new formulation for shallow foundations overpassing this limitation and capable of accounting for the influence of loading rate on the system response. To conceive and to calibrate the model, the authors numerically analysed the case of a shallow foundation positioned on a normally consolidated clayey soil stratum whose mechanical behaviour is reproduced by means of the modified Cam Clay model. Finally, the approach is discussed critically from the perspective of its use as a design tool according to approaches based on the ultimate limit state and displacement. [ABSTRACT FROM AUTHOR]

This paper presents the results of centrifuge model tests and three-dimensional large-deformation finite-element analysis on axial pipe–soil sliding behaviour of partially embedded subsea pipelines. A three-dimensional re-meshing and interpolation technique with small strain approach was adopted using the Abaqus mesh-to-mesh solution mapping feature with the Cam Clay model. The parameters studied include soil properties, interface friction coefficient, embedment depth and post-lay reduction in vertical load. Embedment depth and post-lay load reduction were found to exercise the strongest influence on the post-consolidation and sliding behaviour. Empirical relationships correlating centrifuge experiments and numerical modelling are proposed for the embedment enhancement factor in terms of the embedment and vertical load ratios, under conditions of very slow sliding, corresponding to the drained condition. For very fast sliding, corresponding to effectively undrained conditions, similar relationships involving embedment and vertical load ratios and interface friction coefficients are also proposed. Finally, the variation of embedment enhancement factor with sliding velocity is expressed in terms of a relative enhancement index, Ψ, which can be adequately described by hyperbolic relationships for the complete range of consolidation history. These relationships provide a basis for the evaluation of the embedment enhancement factor corresponding to an arbitrary sliding velocity, which can be used in routine analysis and design of as-laid underwater pipelines in soft clayey soils. [ABSTRACT FROM AUTHOR]

A relationship between elastic anisotropy, as typically observed in clayey soils subjected to shear wave propagation tests, and plastic anisotropy, detected at yielding and leading to rotated yield loci, is proposed. Such a relationship is expected because both elastic and plastic anisotropies can be ascribed to the same directional ingredients that characterise the fabric of the soil at the microscale. The relationship takes the form of an analytical relation between an elastic and a plastic fabric tensor, the former entering a hyperelasticity theory while the latter is the rotational hardening variable of a clay plasticity theory. The elastic anisotropy can be measured experimentally by wave propagation along orthogonal planes, identifying the ratio of the corresponding elastic shear moduli while a sample is compressed at fixed stress ratio, and paired with plastic anisotropy obtained by the integration of its plastic fabric tensor evolution equation during the foregoing compression. Such experiments were available and used to calibrate and validate the proposed elastic–plastic anisotropy relationship. The findings have a two-way beneficial effect for the solution of a geotechnical boundary value problem, where one can easily measure initial elastic clay anisotropy in the field, which can be used to initialise the plastic anisotropy for the subsequent analysis of the problem, while the evolving plastic anisotropy can be used to update the elastic fabric tensor during deformation. [ABSTRACT FROM AUTHOR]

Estimated soil clay contents (P0.002) obtained from consistency limits were evaluated by means of comparison with the results of the conventional hydrometer test (P0.002h). In total, 180 soil samples were tested for Atterberg limits, linear shrinkage and clay content to generate the data used for statistical evaluation. It was found that there is a strong correlation between P0.002 and P0.002h, with realistic and valid statistical equality. However, the variability in P0.002 estimations – up to 50% – is quite high for practical purposes. Nevertheless, the findings of the study confirm the credibility of the hydrometer method. [ABSTRACT FROM AUTHOR]

Preloading with a surcharge is today commonly used together with prefabricated vertical drains for embankment construction on clayey soil to accelerate primary consolidation and increase strength. Because of considerable uncertainty related mainly to the rate of consolidation, there is a need to account for this in the vertical drain and surcharge design to ensure quality in the embankment construction. Addressing this issue, the paper presents a novel probabilistic design methodology that is compatible with the observational method. The procedure evaluates the suitable surcharge load to be used in combination with a vertical drain design in order to ensure that the established design criteria are satisfied with acceptable probability. [ABSTRACT FROM AUTHOR]

Realistic modelling of transverse (i.e. vertical and lateral) pipe–soil interaction plays an important role in predicting the behaviour of untrenched offshore pipelines that are designed to undergo controlled lateral buckling. The large plastic soil deformations and surface geometry changes that occur during this process mean that numerical analyses using the continuum-based finite-element method are difficult and computationally expensive. Furthermore, most previous research in this area has focused on undrained deformation of soft clay seabed soils. This paper uses the three-dimensional distinct-element method (DEM) to investigate the behaviour of a pipe segment that is partially embedded in sand. The simulation approach is validated against experimental results for a monotonic vertical penetration test, a monotonic sideswipe test, and a cyclic lateral loading test performed under constant vertical load. Other DEM analyses are performed to illustrate the growth, deposition and collection of soil berms, and to investigate the effect of varying the initial vertical overloading ratio and the pipe weight. The DEM simulations provide quantitative predictions of the vertical and horizontal forces acting on the pipe segment, and of the pipe displacement trajectory. Valuable qualitative insights into soil failure mechanisms occurring at a grain level are also obtained. [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]

Existing electro-osmotic calculation models are mostly based on the assumption of a porous medium with uniform pores, whereas natural soil has pores of different sizes. This is especially significant in the case of low-permeability soil, whose pore size can vary over five or six orders of magnitude, from the nanometre to the millimetre scale. Experimental results have revealed significant differences in the electro-osmotic flow characteristics of soils with various pore sizes, indicating a strong dependence on pore size distribution (PSD). This dependence is termed the pore size effect (PSE) on electro-osmosis. In this paper, a series of one-dimensional electro-osmosis experiments on three types of low-permeability clay soil are conducted to quantify the PSE on electro-osmosis. Based on the experimental results and an analysis of electro-osmotic characteristics, a modified analytical approach considering the actual soil PSD and its effect on electro-osmosis is proposed and thereby two modified analytical models are established. Using the experimental results, the modified models are compared with the existing Helmholtz–Smoluchowski model and other models that assume uniform pores. The results show that the PSE increases with increasing thickness of the electric double layer and that the modified models can be used to reasonably calculate the electro-osmotic permeability of low-permeability soil. [ABSTRACT FROM AUTHOR]

This paper describes a one-dimensional (1D) computational model for the analysis and design of laterally loaded monopile foundations for offshore wind turbine applications. The model represents the monopile as an embedded beam and specially formulated functions, referred to as soil reaction curves, are employed to represent the various components of soil reaction that are assumed to act on the pile. This design model was an outcome of a recently completed joint industry research project – known as PISA – on the development of new procedures for the design of monopile foundations for offshore wind applications. The overall framework of the model, and an application to a stiff glacial clay till soil, is described in a companion paper by Byrne and co-workers; the current paper describes an alternative formulation that has been developed for soil reaction curves that are applicable to monopiles installed at offshore homogeneous sand sites, for drained loading. The 1D model is calibrated using data from a set of three-dimensional finite-element analyses, conducted over a calibration space comprising pile geometries, loading configurations and soil relative densities that span typical design values. The performance of the model is demonstrated by the analysis of example design cases. The current form of the model is applicable to homogeneous soil and monotonic loading, although extensions to soil layering and cyclic loading are possible. [ABSTRACT FROM AUTHOR]

Triaxial tests were performed on artificially cemented gravel–silty clay mixed soils and remoulded samples under consolidated drained conditions. The aim was to investigate the effects of the content of silty clay and confining pressure on the stress–strain, volumetric strain and other mechanical characteristics of the cemented and remoulded samples. The test samples were prepared with different fines contents and effective confining pressures. The results showed that both the confining pressure and the fines content had a great effect on the mechanical properties of the cemented and remoulded samples. During triaxial shearing, the cemented samples underwent dilation and strain-softening, accompanied by the appearance of shear bands at a confining pressure lower than 100 kPa and fines content less than 30%. Otherwise, the cemented samples showed strain-hardening and contraction, accompanied by bulging failure. All the remoulded samples showed strain-hardening and contraction, accompanied by bulging failure during triaxial shearing. The shear strength decreased with increasing fines content and the influence of the fines content increased with an increase in confining pressure. It was also found that, the higher the fines content, the lower the cohesion and friction angle of the cemented and remoulded samples. [ABSTRACT FROM AUTHOR]

When saturated, clayey soils are subjected to compressive stress and there is a time lag between the applied stress and the extrusion of pore water; there is thus a lag in the settlement. Soils under structures such as silos, tanks and so on may be subjected to cyclic loading. The theories that can be used for the calculation of consolidated settlement under cyclic loadings, such as triangular cyclic loading, contain errors due to the assumptions used in the derivations of mathematical equations. Thus, using these theories can create significant errors. The characteristics of the cyclic load, the surcharge and the specimen can affect the consolidation settlement as well as the time to achieve a steady state. Thus, in this research, one-dimensional consolidation of clay subjected to triangular cyclic loading was experimentally investigated under several conditions. The results showed that the ultimate consolidation settlement of a clay layer and the time to reach this state decreased with an increase in surcharge and an increase in cyclic time. Furthermore, the experimental results showed significant differences from the results obtained using theoretical methods. [ABSTRACT FROM AUTHOR]

Granular layers are often placed over weaker clay soils to improve the bearing capacity of working platforms and spread foundations. Their design requires the calculation of a two-layer bearing capacity. The commonly used existing calculation models are quite empirical with imprecise input parameters and can err on the non-conservative side in some situations. Other proposed methods tend to involve multiple design charts and are suited only to either strip or circular foundations. In this paper a new and highly practical design method is proposed whose input parameters are derived directly from the shear strengths of the two layers without the need for empirical-based charts. The output can be obtained either from a single chart or a few equations that are straightforward to implement into a spreadsheet. It can be applied quite generally to both surface and shallow embedded foundations, circular and rectangular and with dry or saturated granular layers, and also to working platform design for tracked plant. The method was validated using three independent numerical studies and centrifuge testing. The results showed that, although errors can increase for foundation shapes towards square or circular and with increasing overburden, the errors are smaller than those of the commonly used existing methods and are also conservative. [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]

The aim of the study reported in this paper was to develop practical correlative models capable of predicting the compaction characteristics of clay soils blended with rubber from waste vehicle tyres. Four different clay soils, ranging from intermediate to high plasticity, were adopted for the test programme and each was blended with four different percentages of ground rubber waste. The test programme consisted of cone penetration (consistency limits) and standard Proctor compaction tests. As a result of ground rubber inclusion, the consistency limits and compaction characteristics all exhibited a linear decreasing trend with increase in rubber content. The rate of decrease, however, was greater for the high-plasticity clays. Simple correlative models, linking the compaction characteristics to the consistency limits, were suggested and validated by statistical techniques. The proposed models provide a practical procedure towards predicting the compaction characteristics of ground rubber–clay blends without the hurdles of conducting laboratory compaction tests, and thus can be implemented in practice for preliminary assessments. [ABSTRACT FROM AUTHOR]

A series of lateral tests conducted in a centrifuge on displacement piles in kaolin is used to examine the effects of pile shape, pile end-condition and clay overconsolidation on the lateral load transfer (p–y) curves in soft clay. These experimental tests are supported by finite-element analyses, which examine the responses of the circular, square and H pile sections used in the centrifuge tests. The experimental and numerical results reveal an important effect of pile shape on p–y curves, but no discernible effect of the pile end condition. These results also indicate comparable dependencies of net ultimate pressures on normalised depth and undrained shear strength. The findings enable development of a new formulation for p–y curves in soft clay, which incorporates the effects of pile shape and uses the triaxial compression consolidated undrained shear strength as the reference undrained strength. [ABSTRACT FROM AUTHOR]

In this article, authors have presented a thorough and careful review in relation to laboratory tests and other approaches employed in the determination of the consistency limits of clayey soils. It highlights their use and misuse for fine-grained soil classification purposes and in existing correlations.

Retrogressive or progressive landslides in slopes with highly sensitive quick clays may extend several hundred metres from where the slide was initiated. Reintroducing high salt contents to the pore water of leached low-saline quick clays may inhibit the development of such large landslides. Wells filled with potassium chloride (KCl) were installed in a quick-clay deposit at Dragvoll, Trondheim, Norway, to investigate the impact of changed pore-water chemistry on the geotechnical properties. The clay ceased to be quick due to favourable changed ion composition in the pore water, even at low salt contents, thus inhibiting retrogressive development. The apparent pre-consolidation stress ( p′c) increased with increasing salt contents and the immediate collapse in structure typically seen in quick clays was avoided at loads just beyond p′c by changing the pore-water chemistry. Quick clay treated with KCl may therefore work as a barrier against retrogressive development and reduce the risk of initiation of progressive landslides. [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]

The characteristics of clay soil in the Saga Plain in Japan, as well as the effect of the depositional environment on its engineering properties, have been investigated. While the clay was being deposited there were several large-scale volcanic eruptions in the region. A considerable amount of volcanic ash settled into the clay, which had a marked effect on its engineering properties. The soil is strongly structured and the sedimentation compression curves are well above the sedimentation compression line proposed by Burland, which indicates some degree of cementation. The compression index is high - even for soil samples with in situ vertical effective stresses of 200-300 kPa, the index can be as high as 2·3. The rate of permeability reduction with void ratio is higher than most reported data in the literature. The reason considered is that the compression process involves not only gradual compression of the pores but also breaks down relatively large pores into smaller pores, which can cause rapid reduction of permeability. The stiffness is lower, with results of unconfined compression tests showing that the ratio of undrained shear strength to secant modulus is about 150. [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]

The installation of jet-grouted columns in soft ground can induce lateral displacement resulting from injection of a great amount of water and grout into the ground, which may then lead on to further significant effects. This paper presents an approach to estimate the lateral displacement due to the installation of a jet-grouted column in clayey soils. Assuming that the installation of a jet-grouted column is represented by the expansion of a cylindrical cavity with a uniform radial stress applied at the plastic-elastic interface in a half-plane, the analytical solution developed by Verruijt is adopted in this study to calculate the lateral displacements attributable to the expansion of the cylindrical cavity. An empirical equation that accounts for the jetting parameters (jetting pressure, flow rate of the fluid and rod withdrawal rate) and soil properties (soil type and its undrained shear strength) has been developed to determine the radius of the plastic zone. Three case histories analysed in this paper demonstrate that the proposed method can be used for estimation of the lateral displacement caused by installing jet-grouted columns in clayey soils, despite minor discrepancies from the group column installation case between the predicted and measured values. These minor discrepancies can most likely be attributed to the omission of the effect of installation sequence and rheological properties of the grout in the calculation. [ABSTRACT FROM AUTHOR]

Expansive clayey soils, which are prevalent across the surface sediments of the earth, are considered problematic for the structures and infrastructure founded in them. These soils are also challenging for environmental engineers involved in the design and construction of municipal and nuclear waste liners, petroleum engineers dealing with shale oil and gas, and agricultural scientists. Because their overall behaviour is controlled by molecular-level processes and interactions, a behaviour model encompassing the contributions from these interactions is required to predict the behaviour of these soils. This interaction becomes increasingly complex for natural expansive clays where a complex composition of clay and non-clay minerals exists. Unfortunately, none of the existing constitutive models pertaining to expansive clays comprehensively incorporates all the factors contributing to volume change behaviour of naturally occurring expansive soils. This study led to the development of a nano-level constitutive model for natural expansive clays through a three-phase study consisting of macro-level swell potential testing on laboratory control and natural field samples, micro-investigation of the pre- and post-swell specimens, and molecular level modelling through molecular mechanics, molecular dynamics and Monte Carlo techniques. This swell potential behaviour model incorporates all the major contributing factors such as moisture content, density, cation exchange capacity, exchangeable cations and interaction of clay minerals with non-clay minerals. The developed models have been successfully validated through close prediction of the swell potential behaviour of the laboratory control samples and natural field samples. [ABSTRACT FROM AUTHOR]

Clayey soils exhibit a very pronounced time-dependent behaviour owing to their viscous properties. To analyse and to quantify these properties, two rounds of tests have been performed on a compacted clay. The first round, consisting of constant-strain-rate compression, stress relaxation and creep, shows that viscous properties are not influenced by different levels of stress and strain. Moreover, the influence of the loading frequency on the viscoelastic modulus is evidenced by the cyclic tests performed at very small strain amplitudes. The results of the second round, consisting of creep and stress-relaxation tests performed at different levels of stress and strain in triaxial loading-unloading-reloading phases and analysed by way of the viscoplastic mechanism terms from Perzyna's over-stress theory, show the existence of a primary yield mechanism activated at the maximum loading point. A kinematic mechanism becomes activated during the unloading and reloading phases, controlling from this moment on the viscoplastic behaviour within the primary yield locus. [ABSTRACT FROM AUTHOR]

This note presents a novel approach for controlling the degree of saturation during one-dimensional compression of unsaturated soils. This technique offers a simple and versatile way to study the hydro-mechanical response of unsaturated soils as well as the unsaturated-saturated soil transition. By using a multi-stage approach, the same specimen can be used to evaluate the compressibility of unsaturated specimens at different degrees of saturation, which may reduce the long testing periods commonly required for unsaturated soil testing. The experimental results described in this paper show that the proposed technique is capable of controlling the degree of saturation within reasonable limits and provides an interesting approach to analyse the coupled hydraulic and mechanical behaviour of unsaturated soils. [ABSTRACT FROM AUTHOR]