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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]

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]

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]

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.

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]

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]

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]

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.

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]

The mechanical responses of two highly expansive plastic alluvial soils from Sudan are reported. When wetted from their in-situ state, such soils frequently lead to damage of civil engineering structures. Disturbed samples of a black cotton clay and a more plastic red clay were collected from two locations in the vicinity of Khartoum. Intrinsic properties were established from reconstituted samples using oedometer and triaxial apparatus. Natural undisturbed block samples of the black cotton clay were obtained and tested in an unsaturated state, as found in situ. Basic characteristics of both soils are presented. Detailed information on the intrinsic properties of both clay soils was established and found to conform with Burland's earlier published framework. Shear planes formed during shearing in almost all triaxial samples and strengths reduced to post-rupture values. -consolidated reconstituted samples exhibited a more brittle response to undrained shearing compared with isotropically consolidated samples. Peak failure conditions can be represented by linear failure envelopes for both soils, regardless of consolidation path, although those from shearing in extension do not pass through the origin: reasons for this are discussed. Oedometer tests on the intact black clay soil indicate a high potential for swelling on wetting (volumetric strains of almost 50%), decreasing with increasing stress level (swelling pressure of about 1 MPa). Unconsolidated undrained triaxial tests on the intact unsaturated samples show increasing strength and decreasing brittleness with increasing confining pressure. [ABSTRACT FROM AUTHOR]

The paper presents the main results of a research study into the very small strain shear stiffness of a clayey soil, as measured in vertical and horizontal directions, and , respectively, by means of T-shaped horizontal bender elements fitted in a stress-controlled triaxial system. The testing programme was designed to investigate the evolution of the anisotropy ratio / along isotropic ( = 0) and anisotropic ( ≠ 0) virgin radial paths. In particular, a reconstituted clay has been chosen as tested material in order to unequivocally relate the observed evolution of its stiffness anisotropy to the specific stress-strain histories imposed in laboratory. The results show that the small strain stiffness anisotropy smoothly adapts itself to the imposed strain history, achieving different constant values ranging from 1 to 1·2 for ranging from 0 to 0·8. The experiments show that the complete modification of the directional elastic properties of the soil requires the virgin radial compression path to be extended along a new direction up a stress level at least four times larger than that experienced previously. Finally, the variations in the clay elastic anisotropy have been related to the changes in clay fabric as investigated by means of scanning electron microscopy. In this context, the variation of the fabric orientation has been quantified through a specific digital image processing. [ABSTRACT FROM AUTHOR]

This note presents an energy-based isotropic compression relationship for cement-admixed soil. By assuming that the rate of destructuration is proportional to the rate of plastic work done during loading for a given soil, a relationship between the structure and the change in specific volume is derived. An approximate relationship is also derived for the case when the swelling index of the structured soil is small. By using experimental data, the main assumption introduced for deducing the relationship is validated. [ABSTRACT FROM AUTHOR]

A new apparatus for the determination of shrinkage limit is described. Two versions have been produced: a manually operated prototype 'version1' followed by an automated version named SHRINKiT. Test results using the former for British and overseas clay soils are described and comparisons made with the British Standards preferred method. A further set of test results is described for SHRINKiT. However, it was not possible to compare these with the BS 1377 method owing to the introduction of a ban on the use of mercury in the British Geological Survey's geotechnical laboratories. The new method is set in the context of the huge cost of shrink/swell-related subsidence damage in Britain and the relative disuse of both BS 1377 methods for shrinkage limit, for reasons of safety. The shrinkage behaviour of different soils types and sample states is discussed, in addition to the advantages and disadvantages of the new method. [ABSTRACT FROM AUTHOR]

The effect of consolidation on the undrained bearing capacity of both rough and smooth strip and circular surface foundations is investigated, examining the influence of the magnitude and duration of an applied preload and the initial over-consolidation ratio of the deposit. The investigation comprised small strain finite-element analysis, with the soil response represented by Modified Cam Clay. The results are distilled into dimensionless and generalised forms, from which simple trends emerge. Based on these results, a simple method for predicting the consolidated undrained bearing capacity is proposed. [ABSTRACT FROM AUTHOR]

The derivation of a new conceptual model for predicting the peak penetration resistance of circular footings installed vertically into sand overlying soft clay is presented in this paper. Based on visualisation experiments and finite-element analyses, a failure mechanism of a frustum of sand being forced into the underlying clay, with the outer angle reflecting the dilation in the sand, is assumed. The analytical basis of the new conceptual model follows the approach for silo analysis, and takes into account the stress level and dilatant response of the sand. A comprehensive analysis of the performance of the new model, and other existing analytical methods, in retrospectively predicting the peak resistance of a database of 49 geotechnical centrifuge tests is provided. Significant improvements over existing punching shear and load spread models are shown, as a result of incorporating the strength properties of the sand in a consistent manner. The new model has application to the offshore mobile 'jack-up' industry, where inaccurate predictions of peak capacity in layered soils continue to cause damaging punch-through failures. [ABSTRACT FROM AUTHOR]

When a jack-up spudcan foundation is installed on seabeds consisting of a sand layer overlying soft clay, the potential for 'punch-through' failure exists. This happens as a result of an abrupt reduction in bearing resistance when the foundation punches a block of sand into the underlying soft clay in an uncontrolled manner. This paper details an extensive series of 30 tests of flat circular and spudcan foundations continuously penetrated through samples of sand overlying clay, and performed under relevant stress conditions using a drum centrifuge. The large testing area of the drum centrifuge was used advantageously to produce test results that could be compared directly with tests covering a sand thickness over foundation diameter of 0·21 to 1·12. Results from retrospective finite-element analysis of the experiments are also described, with back-calculated values of the stress-level-dependent friction and dilation angles in the sand during peak penetration resistance shown to fit correlations in the literature. The back-analysis showed that larger values of peak resistance gave lower friction and dilation angles, which is consistent with gradual suppression of dilatancy under high confining stress. When compared with published results from visualisation experiments, the finite-element analysis showed a similar failure mechanism during peak resistance, with a frustum of sand forced into the underlying clay at an angle reflecting the dilation in the sand. [ABSTRACT FROM AUTHOR]

The article presents work and life experience of the Scott William Sloan, professor at the University of Newcastle at the New South Wales in Australia. It mentions the Sloan's seminal contributions development of higher order elements to allow the accurate prediction of collapse loads and the formulation of semi-explicit solution schemes with adaptive error control for integrating elastoplastic stress–strain relationships and automatic incrementation.

This work presents a novel, exact solution for the drained expansion of a cylindrical cavity in modified Cam Clay soil. Following the rigorous definitions for the mean and deviator stresses and therefore an exact constitutive relationship, the problem is formulated as a set of first-order simultaneous differential equations in the plastic zone with the aid of an auxiliary variable. The solution procedure proposed has the advantage over the conventional similarity method in that it is directly applicable to the cavity expansion problem of finite initial radius. Also the solution derived is sufficiently general to be applied to a more realistic situation of non-isotropic in situ stress condition and to the cavity contraction problem. Extensive parametric studies have been carried out to illustrate the effect of the overconsolidation ratio on the cavity expansion and stress distributions around the cavity, as well as on the stress path and specific volume change due to expansion. The present solution can and is used here as a benchmark for numerical solutions of cavity expansion in modified Cam Clay soil using Abaqus, the finite-element analysis commercial program. [ABSTRACT FROM AUTHOR]

This work presents an insight into double-structure effects on the coupled chemo-hydro-mechanical behaviour of a compacted active clay. In the first part, selected pore size distribution curves are introduced, to highlight the influence of solute concentration on the evolution of the microstructure of compacted samples. An aggregated structure with dual-pore network is induced by compaction even at relatively high water contents. This structural arrangement is enhanced by salinisation, and has a notable influence on transient volume change behaviour - that is, the occurrence of different stages of swelling upon pore water dilution and higher volume change rates upon salinisation. A coupled chemo-hydro-mechanical model, taking into consideration double-structural features from a chemo-mechanical viewpoint, is described and then used to interpret these behavioural responses and present complementary information on local transient processes. The model is designed to identify an intra-aggregate and an inter-aggregate domain, and assigns different values of hydraulic pressure and osmotic suction to each domain. Distinct constitutive laws for both domains are formulated, and the flow of salt and water between the two domains is accounted for by a physically based mass exchange term. The model is used to simulate salt diffusion tests run in an oedometer at constant vertical stress. Parameters used in the formulation are calibrated based on separate experimental evidence, both through direct test results and through back-analyses of laboratory experiments. [ABSTRACT FROM AUTHOR]

The paper presents a chemo-mechanical model for expansive clays that takes into account the effects of cation content and cation exchange. These factors play a key role in the mechanical behaviour of very active clays, particularly with regard to volumetric behaviour. The model is based on an existing double-structure formulation that distinguishes specifically between microstructure and macrostructure. Chemical effects are defined at the microstructural level, the seat of the basic physico-chemical phenomena affecting highly swelling clays. The microstructural model accounts for changes in both osmotic suction and in cation content. Microstructural strains are considered to be reversible; material irreversibility arises from the interaction between the two structural levels. The formulation is developed for general unsaturated conditions; saturation is considered as a limiting case. The model is successfully applied to the reproduction of experimental behaviour observed in oedometer tests on saturated bentonite subjected to chemo-mechanical loadings, and in hydration tests of unsaturated bentonite performed using different solute concentrations. [ABSTRACT FROM AUTHOR]

Bentonites are clay soils characterised by a high specific surface and a permanent negative electric charge on their solid skeleton. Their common use as hydraulic and contaminant barriers for landfill and soil remediation applications, including the final disposal of nuclear waste, needs to be supported by adequate theoretical modelling of their mechanical behaviour and transport properties, in order to assess the expected performance in the long term. To this end, a theoretical approach has been proposed in order to derive constitutive equations for their coupled chemical-hydraulic-mechanical behaviour. The phenomenological parameters that govern the transport of electrolyte solutions through bentonites - that is, the hydraulic conductivity, the reflection coefficient (which is also called the chemico-osmotic efficiency coefficient), and the osmotic effective diffusion coefficient - have been measured through laboratory tests on a bentonite with porosity of 0·81, over a range of sodium chloride concentrations in the pore solution that varied from 5 mM to 100 mM. The relevance of the osmotic phenomena has been shown to decrease when the salt concentration increases. The obtained results have been interpreted by assuming that the microscopic deviations of the pore solution state variables from their average values are negligible. In this way, it is possible to interpret the macroscopic behaviour on the basis of the physical and chemical properties of the bentonite mineralogical components. [ABSTRACT FROM AUTHOR]

Engineering issues for which the understanding of the chemo-mechanical behaviour of soils is relevant include wellbore stability problems, the salinification of groundwater, and nuclear waste storage. However, despite the vast number of situations in which couplings between chemistry and mechanics occur, the available constitutive models rely on limited experimental evidence. This paper presents the results of an experimental programme on the chemo-mechanical behaviour of a non-swelling illite. The osmotic suction is controlled through the ion concentration of sodium chloride in the pore water. Stress paths include mechanical loading at a constant osmotic suction, and an increasing osmotic suction at a constant mechanical stress. The experimental results point out a correlation between the osmotic suction and initial oedometric modulus, as well as between the osmotic suction and yield stress. A constitutive framework for soils is extended to take the observed chemo-mechanical couplings into account. The numerical model has been calibrated for the illite using the parameters obtained through the tests under mechanical loading at a constant concentration, and validated using more elaborate stress paths. The presented experimental and constitutive investigation builds a basis for the assessment of engineering issues in which pore liquid chemistry plays a major role. [ABSTRACT FROM AUTHOR]

Current developments in deepwater offshore oil production in the Gulf of Guinea (GoG) make it necessary to characterise the mechanical behaviour of the GoG deepwater sediments better. This paper examines some aspects of the strain-rate-dependent behaviour of intact and reconstituted GoG clay specimens. Results from isotropic compression and undrained shearing laboratory tests with changing rates of stress and strain are presented. They show that the soil generally follows an isotach behaviour, with clear strain-rate dependence of the stress-strain behaviour and pore pressure response in the undrained shear tests. The effects of structure and its degradation on the time-dependent response of the sediments seem to confirm general trends observed in other structured clays. [ABSTRACT FROM AUTHOR]

The installation and extraction of jack-up spudcans may induce significant stresses in the adjacent piles supporting the permanent jacket platforms at an offshore site. In the present study, centrifuge model tests were conducted to investigate the effects of spudcan movements on the lateral and axial behaviour of adjacent fixed-head piles embedded in soft clay. Parameters such as jack-up operation period, clearance between the spudcan and pile, and the embedment length of the pile are examined. The test results show that the most critical period for platform piles is at the end of spudcan installation, and the lateral pile behaviour is more severely affected than the axial pile behaviour. During spudcan installation, the induced bending moment on a pile located one-quarter spudcan diameter away from the spudcan edge is about 2·4 times that of a pile located one spudcan diameter away. For a deeply buried spudcan with penetration of over three-quarters spudcan diameter, the induced bending moment on longer piles is much smaller than that on shorter piles. The experimental findings provide further insights into the underlying mechanisms governing spudcan-pile interaction in soft clay under various configurations and conditions. [ABSTRACT FROM AUTHOR]

The ultimate bearing capacity of a rigid, plane-strain pipe segment embedded in undrained clay is studied using numerical limit analysis. The pipe is considered to be 'wished in place' at invert penetrations ranging from zero to five pipe diameters, thus providing coverage of both on-bottom (partially embedded) and trenched (fully embedded) offshore pipelines. The soil is modelled as a rigid-plastic Tresca material with either uniform strength or strength proportional to depth. The effects of soil weight, interface roughness and interface tensile capacity are investigated in a systematic manner. All calculations are performed using the finite-element limit analysis code OxLim, which uses adaptive mesh refinement to compute tightly bracketed lower- and upper-bound plasticity solutions. The velocity fields from the upper-bound analyses provide the corresponding failure mechanisms. The paper initially focuses on purely vertical loading (penetration and uplift), and then addresses combined vertical and horizontal loading. A comprehensive set of design curves and failure envelopes is presented, with the results explained in terms of the changing failure mechanisms. These results are immediately applicable in practice. In particular, current industry-standard procedures for design against pipeline upheaval are critically reviewed, and are shown to have potentially unconservative shortcomings. [ABSTRACT FROM AUTHOR]

Seasonal cycles of soil water content cause shrinking and swelling in clay soils, which can in turn contribute to strain-softening and progressive slope failure. This paper presents and analyses six years of field measurements of soil water content and pore water pressures in the upper layers of a lightly vegetated London Clay slope near Newbury, UK, and shows how they can be related quantitatively to the climate using a water balance model. The field observations are set in the context of a 40-year run of rainfall data for the site. Moderately extreme rainfall and drought events were experienced over the period 2003-2008, allowing almost the full variation in likely pore water pressures to be characterised. Pore water pressures were found to return to near hydrostatic during most winters. Variations in summer rainfall, particularly during June-August, are shown to have a large influence on the magnitude of the cycles of pore water pressure and effective stress. The 40-year rainfall dataset is used to calculate approximate return periods for the observed soil conditions, and provides a benchmark for calculating the impacts of expected climate change on similar sites. [ABSTRACT FROM AUTHOR]

This paper presents an exact semi-analytical analysis for cylindrical cavity expansion in modified Cam Clay critical state soil under the undrained condition. By assuming small-strain deformation in the elastic region and large-strain deformation in the plastic region, the formulation of the problem is reduced to solving a system of first-order ordinary differential equations for the radial, tangential and vertical effective stresses in the plastic zone. The pore pressure distribution can subsequently be determined from the radial equilibrium equation in terms of the total stresses. The semi-analytical solution derived in this paper follows the rigorous definitions for the two effective stress invariants instead of approximate ones, as usually assumed in the existing literature, and applies to the more general case where the out-of-plane (vertical) in situ stress may be different from the in-plane (horizontal) one. The results show clearly that the stress history (overconsolidation ratio) has a significant influence on the stress and pore pressure distributions around the cavity. The present solution provides an exact and realistic theoretical framework for predicting the soil behaviour around the cylindrical cavity, with applications to the interpretation of pressuremeter tests and to pile installation problems. It also serves as a valuable benchmark for verifying various cavity expansion numerical methods involving the critical state plasticity model. [ABSTRACT FROM AUTHOR]

The aim of this paper is to investigate the behaviour of laterally loaded pile groups with a rigid head, and correlate the response of a pile group to that of a single pile. For this purpose, a computationally intensive study using three-dimensional non-linear numerical analysis was carried out for different pile group arrangements in clayey soils. The responses of the pile groups were compared with that of the single pile, and the variation of the displacement amplification factor was then quantified. The influence of the number of piles, the spacing and the deflection level on the group response is discussed. A previously proposed relationship for predicting the response of a pile group, based on its configuration and the response of a single pile, has been modified to allow for soil shear strength that was found to affect the group response. The modified relationship provides a reasonable prediction for various group configurations in clayey soils. [ABSTRACT FROM AUTHOR]

A simplified method is proposed for the stability analysis of clayey slopes subjected to pore pressure changes. The method is based on the infinite slope model and takes advantage of an analytical solution to evaluate the changes in pore pressure at the potential (or pre-existing) failure surface directly from the pore pressure measurements at a piezometer which is installed above this surface. A case study documented in the literature is analysed as an application. [ABSTRACT FROM AUTHOR]

The article discusses the small-scale model tests used to explore the deformations caused by two kinds of piling auger in clay soil. It notes on the result of the small-scale model tests on two types of full-displacement piling auger with the goal of improving the evaluation of the risk in clay soils. It also notes that similar lateral movement patterns were observed in the model and full-scale auger tests despite the probability of an occurrence of partial drainage.

The article discusses the numerical simulation pushover tests on a model jack-up platform on a clay. Analysis of the test models have represented the numerical predictions of the jack-up pushover experiments which is an integrated structural modelling method using standard Abaqus beam elements. It also assesses the method for the prediction of the capacity of a model jack-up platform subjected to pushover tests on soft clay where the predictions manifest the versatility of the spudcan model.

This feasibility study examines the use of in situ microbial gas production to engineer the consolidation properties of clayey soils by changing the settlement-time profile. A simple analytical model has been proposed to assess the swelling of the soil during the steady-state gas production, and to predict immediate settlements due to loading at the end of this process. For experimental validation of the suggested technique, Clostridium acetobutylicum, an anaerobic fermentative microorganism, was mixed into clayey-sand samples, fed with a nutrient-rich medium, and allowed to produce gas in situ. A series of standard oedometer tests was performed on gas-containing and gas-free soil specimens. Results showed that, in agreement with the model predictions, in situ gas production caused negligible swelling of the samples, while shifting a significant portion (up to 50%) of total displacement from primary consolidation settlement to immediate settlement without changing total displacements or the coefficient of consolidation. [ABSTRACT FROM AUTHOR]

The article presents a study on pressure distribution in stone columns reinforced with crushed basalt in soft clay, under foundation loading and consolidation. A 60 millimeter (mm) in diameter footing was used to test the stresses on stone columns in a 300 mm diameter by 400 mm high clay samples under drained conditions and loading. Results show that the pressure distribution on the columns have shown complex behavior during loading and negative skin friction has developed after unloading.

The article discusses a study which investigated the aspects of the compacted soils' behaviour along wetting paths. The study conducted wetting and oedometric loading tests on clayey compacted soils. Results revealed the effect of compaction stress and compaction water content on wetting paths. It notes that when compaction stress is higher, the soil's swelling is larger.

The article presents a study on the effects of the maximum soil aggregates size and wetting-drying cycles on the stiffness of a compacted lime-treated clayey soil. The study used an air-dried soil that was ground into a target maximum soil aggregates size and the soil specimen was covered by plastic film to prevent soil moisture changes. Results showed that soil stiffness was dependent on aggregate size following a lime-treatment and the wetting-drying cycles increase the soil stiffness.

The article presents a study that investigates the pullout capacity factor of a plate anchor in clays. The study performed finite-element (FE) analyses for anchor pullout capacity solutions and considered coupling effects including the anchor inclination, clay self-weight, and non-homogeneity. Results vary in both empirical and numerical forms in facilitating the use to solve practical design problems.

The article presents an analysis of the potential application of anisotropic creep model (ACM) and isotropic creep models (ICM) to soft soils. It states that the parameters were obtained through the use of a constant rate of strain (CRS). It suggests the inapplicability of ACM to peat and organic clays while ICM variant has high potential to soft soils.

This paper presents an analysis of the cone penetration test in multi-layered clays using the commercial finite-element code Abaqus/Explicit. The von Mises yield criterion and its associated flow rule are assumed to model the plastic behaviour of elastoplastic undrained clays. An arbitrary Lagrangian-Eulerian scheme and an enhanced hourglass algorithm are adopted to preserve the quality of mesh throughout the numerical simulation. Initially, the behaviour of the penetration resistance is examined in a soil with only two layers. The bottom layer is the weaker of the two and the behaviour of the penetration resistance when the cone approaches the lower layer is studied. The investigation is then extended to study the cone penetration test in a multi-layered clay by sandwiching a weaker clay layer between two stronger clay layers. The thickness of the weaker clay layer is varied and the behaviour of the penetration resistance is studied in relation to the thickness and relative strength of the soil layers. The results are discussed with respect to the soil mechanisms that are present when the cone moves past the relevant layer boundaries so that the position of these boundaries can be determined more accurately. [ABSTRACT FROM AUTHOR]

Difficulties in obtaining high-quality soil samples from deepwater sites have necessitated increasing reliance on piezocone, T-bar and ball penetration tests to determine soil properties for design purposes. This paper reports the results of an international collaborative project in which a worldwide high-quality database of lightly overconsolidated clays was assembled and used to evaluate resistance factors for the estimation of intact and remoulded undrained shear strength from the penetration resistance of each device. The derived factors were then compared with existing theoretical solutions to evaluate the influence of particular soil characteristics. The overall statistics showed similar levels of variability of the resistance factors, with low coefficients of variation, for all three types of penetrometer. However, correlations of the resistance factors with specific soil characteristics indicated that the resistance factors for the piezocone were more influenced by soil stiffness, or rigidity index, than for the T-bar and ball, while the effect of strength anisotropy was only apparent in respect of resistance factors for the T-bar and ball relative to shear strengths measured in triaxial compression. In the correlation between the remoulded penetration resistance and remoulded strength, the resistance factors for remoulded strength were found to be higher than those for intact strength and with a slight tendency to increase with increasing strength sensitivity but insensitive to soil index properties. Based on an assessment of the influence of various soil characteristics, resistance factors are recommended for the estimation of intact and remoulded undrained shear strength from the penetration resistances of each device for soil with strength sensitivity less than six. [ABSTRACT FROM AUTHOR]

This paper presents results of an analysis of a set of high-quality, side-by-side piezocone penetration test (CPTu) and standard penetration test (SPT) data for examining mechanical behaviour-based classification of soils. The results show that the soil behaviour type index ( ), either defined by Jefferies and Been (denoted herein as ) or by Robertson and Wride (denoted herein as ), is an effective parameter for mechanical behaviour classification. Additionally, an effort is made to find the most suitable cut-off (or boundary) value that can delineate cohesionless (sand-like) soils from cohesive (clay-like) soils. The Robertson and Wride's formulation, = 2·67 is found capable of delineating these two classes of soils. Similarly for the Been and Jefferies' formulation, = 2·58 is found to be the most suitable cut-off value for such classification purpose. These cut-off values for distinguishing sand-like soils from clay-like soils are found to be reliable in a case study of liquefaction susceptibility. [ABSTRACT FROM AUTHOR]

The characterisation of soils for civil engineering purposes depends on removing sufficiently high-quality samples from the ground. Accurate evaluation of sample quality is therefore important if reliable design parameters are to be determined. This paper describes the use of unconfined shear wave velocity ( ) and suction ( ) measurements to assess sample quality rapidly in soft clay. Samples of varying quality from three well-characterised soft clay sites are initially assessed using conventional techniques, and their results compared with and measurements performed on the same samples. It is observed that the quality of samples indicated by these measurements is very similar to those inferred from traditional disturbance measures, with being the more reliable indicator. A tentative empirically derived criterion, based on samples tested in this project, is proposed to quantify sample disturbance combining both and measurements. Further work using this criterion on different materials is important so as to test its usefulness. [ABSTRACT FROM AUTHOR]