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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]

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]

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]

A series of centrifuge model tests has been conducted to investigate the bearing resistance of spudcan foundations of offshore jack-up rigs in sand overlying normally consolidated clay. The spudcan bearing-resistance profiles measured in most of the tests recorded a peak resistance at a shallow depth within the upper sand layer, followed by an abrupt post-peak reduction in resistance causing the spudcan to plunge into the underlying soft clay. This phenomenon is commonly termed as 'spudcan punch-through hazard', which potentially leads to severe structural damage of jack-up rigs in the field. The centrifuge test results revealed that the ratio of upper sand layer thickness over spudcan diameter and the ratio of bearing resistance between the upper sand and underlying clay affect the development of spudcan bearing resistance. The limitations of existing design methods, which were derived for the ultimate bearing capacity of pre-embedded shallow foundation to assess the spudcan bearing resistance-depth profile, are also identified. It is proposed that the profile may be assessed by focusing on three key characteristic bearing resistances. [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]

Investigation of micro-macro relationships in soils most often concerns granular soils in which both the elemental unit (the grain) and the physical laws governing inter-grain interactions appear to be better known. The situation is different for clays because the elementary unit and the inter-unit interactions at the micro-scale are more difficult to characterise. In fine-grained soils, it has been shown that an intermediate level, corresponding to the way clay and fine-grained particles are arranged together, had to be considered so as to link microscopic features to macroscopic behaviour. An investigation of the change in microstructure during compression carried out some time ago on a sensitive clay from Canada demonstrated that studying the changes in pore size distribution provides a satisfactory description of microstructure changes during compression. The analysis is applied here to six other sensitive clays. First, a careful examination of the intact and remoulded microstructure is conducted in order to understand better the relationship between microstructure and sensitivity. Second, an interesting correlation between the compressibility coefficient and the slope of the cumulative pore size distribution curve is observed in Champlain clays. This confirms the analysis conducted that compression in loose, low-plasticity soils can be attributed to the progressive and ordered collapse of pores, starting from the largest existing ones and progressively affecting smaller and smaller pores. A conclusion drawn from this work is that a micro-macro analysis in terms of changes of a rigid fragile porous matrix appears to be more relevant than a standard analysis based on the behaviour of individual grains, where the grains are taken to be the relevant elemental microstructure unit (a unit difficult to identify in natural clay soils). Also, further insight is provided for the interpretation of microstructure effects through comparing the compression curves of intact soil samples to those of remoulded samples. [ABSTRACT FROM AUTHOR]

A complete theoretical model for predicting the undrained behaviour of a rigid pipe in clay soils when subjected to combined vertical and horizontal loading is described. Physical modelling of a pipe on soft, lightly overconsolidated kaolin clay was conducted, with the experimental test programme specifically designed to establish the model parameters. The testing was conducted within the University of Western Australia's geotechnical drum centrifuge using an element of pipe 10 mm in diameter and 50 mm long, at an acceleration of 50 times the Earth's gravity. The model presented is expressed by the force resultants on the pipe and the corresponding displacements and allows predictions of response to be made for various vertical and horizontal load or displacement combinations. However, it is limited to monotonic loading and does not account for the influence of berms created by repetitive large lateral displacements. The model is verified in this paper by retrospectively simulating a selection of combined loading tests and comparing the output with the experimentally recorded results. [ABSTRACT FROM AUTHOR]

The causes of pipe damage that lead to leakages and bursts in water distribution networks are numerous, and the significance of each possible mechanism is not yet fully understood. This paper reports field monitoring and numerical modelling carried out to evaluate the potential for vegetation-induced desiccation to impose significant bending and therefore additional stress on buried water pipes. Over a period of two years, vertical and horizontal deflections were measured along two flexible pipes buried in London Clay in the vicinity of an oak tree. Meteorological measurements made at the site allowed soil moisture deficit to be computed, and these values were compared with regional values supplied by the UK national meteorological office. Finite difference continuum analyses were carried out in order to permit the interpretation of measured deflections in terms of the equivalent stress increases that would be imposed on a rigid cast iron water pipe. The calculated maximum tensile stress increase was found to be significant in terms of the residual strength of a corroded cast iron pipe. [ABSTRACT FROM AUTHOR]

Installation of independent-legged jack-up rigs in sea-bed sediments where a strong layer overlays weaker soil can lead to catastrophic 'punch-through', with potential leg buckling or toppling of the unit. Although approximate methods of analysis exist for estimating the penetration resistance, these do not account for the distortion of the upper layer as it punches through into the lower layer and there has been only limited visual depiction of the failure mechanism that occurs for the case of strong clay overlying weaker soil. This paper reports results of centrifuge model tests undertaken to provide insight into spudcan foundation behaviour during undrained vertical penetration through a stronger clay layer into weaker material, varying the strength ratio between lower and upper soil layers, the thickness of the upper layer relative to the spudcan diameter and the strength gradient of the lower layer. The model tests included half-spudcan tests against a transparent window, allowing the soil flow to be captured continuously by a digital camera and subsequently quantified through particle image velocimetry (PIV) analysis, and separate full-spudcan tests to measure the penetration resistance. Four interesting aspects of the soil flow mechanisms were identified: () vertically downwards motion of the soil and consequent deformation of the layer interface; () trapping of the stronger material beneath the spudcan, with this material being carried down into the underlying soft layer; () delayed back-flow of soil around the spudcan into the cavity formed above the spudcan; () eventual localised flow around the embedded spudcan. The effect of normalised layer soil properties and geometry on the soil flow mechanisms and the form of the penetration resistance profile is discussed in the context of the likelihood and severity of punch-through failure. Typical critical failure modes involved punching shear, with clear shear planes in the shape of a truncated cone forming in the upper layer below the spudcan. Potential punch-through, with a peak in penetration resistance followed by some reduction, occurred for almost all cases investigated. The reduction in resistance became more severe as the strength ratio of the underlying layer to the upper layer reduced, and also as the upper layer thickness increased. The failure modes assumed by the currently available recommended practices are not consistent with those observed from the study, suggesting a more rational approach is needed. [ABSTRACT FROM AUTHOR]

This paper presents results of large deformation finite element (LDFE) analyses that investigate the penetration response of deep-penetrating spudcan foundations in stratified soil comprising a strong clay layer overlying weaker clay. Such strength profiles give rise to potential punch-through failure, with a local maximum penetration resistance followed by some reduction. The paper is a companion paper to one that presents results from centrifuge model tests of the same problem, with the overall aim being to investigate the potential for punch-through failure and its severity, as a basis for improving design methods for evaluating spudcan penetration. The LDFE analyses have simulated continuous penetration of smooth and rough spudcan foundations from the sea-bed surface. A detailed parametric study has been undertaken, exploring the relevant range of layer thickness (relative to the spudcan diameter), strength ratios and spudcan base roughness. The results have been validated against previously published results and the centrifuge test data presented in a companion paper. Excellent agreement was obtained between the results from LDFE analyses and centrifuge tests. As the ratio of the shear strength of the bottom layer to that of the top layer decreased, upwards soil flow around the spudcan shoulder became less pronounced and the failure mechanism was dominated by a steep-sided plug of soil from the top layer being forced deep into the lower layer. The potential for severe punch-through was demonstrated by a significant reduction in the resistance profile as the spudcan approached the interface between the two layers. A preliminary design chart is proposed to estimate the cavity depth above the penetrating spudcan, which was significantly greater than that for a single layer clay. The penetration responses have been presented in terms of profiles of normalised net bearing pressure for a range of layer geometries and soil properties. Potential punch-through occurred for all cases where the strength ratio was less than or equal to 0·6, with the reduction in resistance being greater the lower the strength ratio of the underlying layer to the upper layer, and the thicker the upper layer, but reducing as the strength gradient in the lower layer increased. The current approach suggested in offshore design guidelines is shown to underestimate the penetration resistance significantly, in most cases, and give poor estimates of the likelihood and severity of spudcan punch-through. [ABSTRACT FROM AUTHOR]

T-bar and ball full-flow penetrometers have important potential in evaluating the remoulded shear strength in situ, by means of cyclic penetration tests. This paper presents numerical investigations into repeated penetration and extraction of the penetrometers in soft clay, using a large deformation finite element method. This approach was able to uncover remoulding mechanisms and resulting gradual strength degradation of soil from intact to fully remoulded states by modelling the entire process of cyclic penetration and extraction. Analyses showed that a cyclic range of three diameters of the penetrometers was sufficient to avoid overlap of the failure mechanism at the extremes and mid-point of the cyclic range. The resistance degradation curves could be fitted accurately by simple expressions consistent with the strain-softening soil model adopted. The strain-rate dependence was similar in non-softening or post-cyclic soil for a given rate parameter. The resistance factor for the post-cyclic condition is higher than that for the initial conditions, depending to some degree upon soil sensitivity and brittleness parameter. [ABSTRACT FROM AUTHOR]

A numerical simulation of laboratory model tests was carried out to develop an understanding of the behaviour of geocell-reinforced sand, and soft clay foundation beds under a circular footing. The influence of the geometrical parameters of the geocell (width, and height, ) on the overall performance of the footing was investigated and the pressure-settlement responses of geocell-reinforced foundation beds were predicted and compared with the unreinforced test results. Simulations were also carried out on conventional-type planar geogrid reinforcement to study the relative performance of both reinforcement forms. The influence of the boundary constrains on the behaviour of the foundations was also studied. In all the cases, good agreement between the results obtained from numerical simulations and laboratory experiments was observed. The results demonstrated that the geocell mattress redistributed the footing pressure over a wider area thereby improving the performance of the footing. The pressure-settlement responses corresponding to geocell-reinforced beds were found to be much stiffer in comparison with the unreinforced case indicating that a substantial reduction in footing settlement can be ascertained. The influence of rigid boundaries on the results of reinforced foundation beds in this study was found to be negligible. [ABSTRACT FROM AUTHOR]

The use of electrokinetic treatment to decrease the water content and increase the shear strength, preconsolidation pressure and axial load capacity of a laboratory-prepared soft clay soil was investigated. The tests were carried out in four identical electrokinetic cells. The cell has a volume capacity of 10 litres. A DC voltage of 10 V was applied in the tests investigating the water content, shear strength and preconsolidation pressure. A DC voltage of 5 V was used in the tests investigating the axial load capacity. The energy consumption for each test was 54 W h. The electrokinetic treatment decreased the water content across most of the cell with the lowest water content near the anode (32·8 ± 2% in comparison with 52·7 ± 2·7% in the control) and increased the undrained shear strength across the cell with the highest shear strength reported near the anode (62·5 ± 6·2 kPa in comparison with 6·3 ± 2·1 kPa in the control). Electrokinetic treatment increased the preconsolidation pressure across the cell with the maximum pseudo-preconsolidation pressure near the anode (91 kPa in comparison with pre-loaded surcharge pressure of 10 kPa). The axial load capacity of the foundation model after the treatment was 156 N when the foundation model was serving as the anode and 173 N when the model was not used as an electrode. The loss in the mass of the foundation model by corrosion was 4·7% for the former and 0·4% for the latter. [ABSTRACT FROM AUTHOR]

To examine the state of anisotropy of a natural (glaciated) clay sample lateral stress oedometer tests are carried out to determine the magnitude and direction of the principal stresses. Initially, this was done by assuming no slippage along the boundary, thus for a perfectly rough oedometric ring with uniform anisotropic stress state and zero in-plane deformation. Here the other extreme case, the perfectly smooth oedometric ring, is examined by accounting for the analytical solution of a circular cylindrical continuum for isotropic linear elasticity, using appropriate boundary conditions. After determining experimentally the frictional coefficient, this solution is used in a semi-empirical interpolation method for estimating the influence of the roughness of the oedometric ring. For the assumption of a rough oedometric ring for the investigated Potclay the anisotropy ratio decreases in the range 0·58 to 0·30 with increasing axial effective stress in the range 355 ≤ ≤ 1860 kPa. For the observed reduced wall roughness the anisotropy ratio is shown to increase to the range 0·70 to 0·40, which is a relative increase of 21% to 34%. The relative error in this estimated anisotropy ratio is estimated in the range ±9% to ±13%, increasing with increasing axial effective stress. The orientation of the in-plane anisotropy is shown to be independent of wall roughness. [ABSTRACT FROM AUTHOR]

This paper presents the effect of short, discrete, randomly oriented fibres (natural and synthetic) on the mechanical properties of clayey soils. The mechanical properties investigated include peak unconfined compressive strength, stiffness and ductility. Three types of clayey soil were obtained from the eastern part of Irbid city in northern Jordan. Two types of fibre were used in this study: nylon and palmyra fibres, with aspect ratios () equal to 75. The clayey soils were mixed with fibres at five different percentages by volume of solid soil particles: 1%, 2%, 3%, 4% and 5%. The results showed that the peak unconfined compressive strength, stiffness and ductility of the clay-fibre mixture increased with fibre content. The post-peak softening in compression resistance decreased with increasing fibre content. The relative unconfined compressive strength increased with fibre content. Palmyra fibre showed a higher increase in the relative unconfined compressive strength than nylon fibre when mixed with clayey soil, for all fibre contents. Furthermore, the clayey soil with a high activity index showed greater improvement when mixed with fibres than that with a low activity index. [ABSTRACT FROM AUTHOR]

Boom clay, a stiff clay, has been selected as a potential host formation for the geological disposal of radioactive waste in Belgium. The underground research facility HADES has been constructed to enable various in situ experiments to be performed on Boom clay so as to study the feasibility of high-level radioactive waste disposal, and to provide reliable data on the performance of Boom clay as a host formation. Among the various laboratory studies performed on samples extracted from the HADES facility to investigate the thermo-hydro-mechanical behaviour of Boom clay, relatively few were devoted to the time-dependent behaviour, limiting any relevant analysis of the long-term behaviour of the disposal facility. The present work aims at investigating the time-dependent behaviour of Boom clay under both thermal and mechanical loading. High-pressure triaxial tests at controlled temperatures were carried out for this purpose. The tests started with constant-rate thermal and/or mechanical consolidation and ended with isobar heating and/or isothermal compression at a constant stress rate or by step loading. The results obtained confirmed the effect of the overconsolidation ratio (OCR) on the thermal volume changes (i.e. thermal dilation under high OCRs and thermal contraction with OCR close to unity). Significant effects of temperature as well as of compression and heating rates were also observed on the volume change behaviour. After being loaded to a stress lower than the preconsolidation pressure (5 MPa) at a low temperature of 25°C and at a rate lower than 0.2 kPa/min, the sample volume changes seemed to be quite small, suggesting a full dissipation of pore water pressure. By contrast, after being subjected to high loading and heating rates (including step loading or step heating), the volume changes appeared to be significant, particularly in the case of stresses much higher than the preconsolidation pressure. Because of its low permeability, full consolidation of Boom clay required a long period of time, and it was difficult to distinguish consolidation and creep from the total volume change with time. [ABSTRACT FROM AUTHOR]

Low-permeability clayey rocks, currently considered as suitable host rocks for high-level nuclear waste disposal, pose a challenge for the determination of thermal, hydraulic and mechanical properties. A thermo-hydraulic stainless steel cell, capable of testing undisturbed soil or rock cores 70 mm in diameter and 100 mm long, has been developed and used to identify thermal properties (conduction coefficient, heat capacity, thermal expansion), permeability (derived from gas and water tests) and swelling behaviour. The cell is operated in a constant-temperature bath. Miniature pore water pressure transducers and thermocouples are installed in different positions of the specimen. Strain gauges attached to a reduced-thickness ring section of the cell provide information for swelling pressure determinations. Temperature changes are applied by a thin heater centred in the axis of the specimen. A computer code was specifically written to perform and control experiments. Air permeability is determined by means of a pulse decay technique, whereas liquid permeability is directly interpreted at steady-state conditions. However, back-analysis of the complete measured response of the specimen (pore pressures, temperatures and swelling pressures) provides the best procedure for identifying properties. A testing protocol involving a sequence of undrained and drained heating tests has been developed to determine, in an ordered way, the thermal properties and the permeability. The procedure requires the concourse of a coupled thermo-hydro-mechanical code in order to simulate test results. The program CODE_BRIGHT, developed at UPC, was used for these purposes. The procedure was applied to the identification of the thermal properties of Opalinus clay shale. [ABSTRACT FROM AUTHOR]

Accurate determination of in situ shear strength using full-flow penetrometers (cylindrical T-bar and spherical ball) requires thorough investigation into soil characteristics such as strain rate dependency and strain softening, which have been shown to have a significant influence on the resistance factors relating penetration resistance to the soil shear strength measured in laboratory tests. In this paper, these effects have been quantified using a large deformation finite element technique, modelling both the strength enhancement owing to high strain rate and gradual degradation of soil during penetration disturbance. A parametric study confirmed that the separate factors quantifying effects of high strain rate and partial softening may be multiplied together to predict the combined effect, to derive a resistance factor for a given soil. Simple expressions are presented allowing the resistance factors for T-bar and ball penetrometers to be expressed as a function of rate and strain-softening parameters. By considering average strength conditions during penetration and extraction of these full-flow penetrometers, an approximate expression is derived that allows estimation of the hypothetical resistance factor with no strain-softening, and hence an initial estimate of the rate-dependency of the soil. [ABSTRACT FROM AUTHOR]

A finite element model was developed to simulate the extraction of spudcans embedded in soft clay. The spudcan was assumed to be 'wished in place'. To simulate the effect of installation, assumptions were made to approximate the stress field and excess pore water pressure field in the soil above the spudcan, and for the effect of installation beneath the spudcan, load was applied on the spudcan until bearing failure of the soil was achieved. Thereafter, the maximum installation load (preload) was reduced to the maintained vertical load, and consolidation of the soil was allowed to occur to simulate the waiting (operational) period of the spudcan. In spite of the simplifying assumptions made in the finite element model, the results show an encouraging measure of agreement with the centrifuge tests results of Purwana et al. The significance of base suction in the extraction of the spudcan is further demonstrated. Parametric studies using marine clay properties show that the ratio of the difference between the breakout force and the top soil resistance at breakout over the maximum installation load depends largely on the soil properties and the waiting time after adjusting for the effect of the geometric size of the spudcan. Hence this may be a plausible way to estimate the force required for the extraction of spudcans embedded in soft clay. [ABSTRACT FROM AUTHOR]

The safe and economic use of mobile jack-up structures is still hindered by limited understanding of the installation of their large conical 'spudcan' footings in layered sand over clay sites. This paper addresses this by detailing experimentally observed bearing failure modes induced during the penetration of a spudcan through a layer of sand into underlying normally consolidated clay. Digital images were captured continuously by installing a half-spudcan against a transparent window, and analysed using a particle image velocimetry technique coupled with close-range photogrammetry correction. As the experiments were performed in a geotechnical centrifuge the observed mechanisms occurred in stress conditions of similar magnitude to the offshore case. The experimental evidence provides: (a) failure modes at different spudcan penetration depths; (b) the transitional failure mechanism at the event of peak bearing resistance; and (c) the changes in overall failure mechanism due to varying geometric and strength conditions of the layered soil. The results provide useful references for the development and validation of analytical or numerical solutions for this problem. [ABSTRACT FROM AUTHOR]

This study investigates the anisotropic behaviour of the shear strength of overconsolidated clayey soils. The results of the study will help engineers and scientists to predict the lateral shear strength of clayey soils from the ordinary vertical shear strength. The main objective of this paper is to investigate experimentally the effect of anisotropy on the shear strength properties of clayey soil. Fifteen types of clayey soil were obtained from various locations in the Irbid area, Jordan, and from different depths. Three undisturbed samples were obtained from each location at three different inclinations (horizontal, vertical, and inclined at 458 to the vertical). Unconfined compression tests were conducted on all soil samples. It was found that the unconfined compressive strength values were greater in the vertical direction than in the inclined and horizontal directions, and increased as the overconsolidated ratio increased. It was also noticed that the failure strain in the horizontal samples was smaller than in the vertical samples. The anisotropic behaviour of clayey soils almost disappeared at greater depth for both unconfined compressive strength and failure stain. [ABSTRACT FROM AUTHOR]

Geotechnical engineers often encounter problems in designing foundations of structures on soft clayey soil. There may be a need for ground treatment to improve the bearing capacity of the soil. In the case of mediumrise buildings in and around Kolkata, a common practice has been to provide closely spaced 150-200 mm diameter timber piles of 5-6 m length. These timber piles have helped the structures to stand on soft clayey soil with little or negligible distress over the years. The present investigation includes the study of bearing capacity and settlement behaviour of model footings resting on small-diameter timber piles. Model footings were tested on an artificially consolidated kaolin bed with small-diameter timber piles inserted into the clay bed. To supplement the results of laboratory model tests, prototype tests were also carried out in the field. In order to obtain a parametric study, the length and spacing of timber piles as well as the extent of piles around and below the footings were varied. The study shows that the use of small-diameter timber piles produced beneficial effects for pile lengths greater than the width of the footing. An appreciable effect on bearing capacity is observed when area ratio (i.e. pile area/soil influence area) becomes more than 10%. The extent of these timber piles beyond twice the width of the footing results in a marginal increase in the bearing capacity. Considerable reduction in settlement occurred when timber piles were used. A semi-empirical method of calculating settlement has been presented for foundations with small-diameter timber piles. [ABSTRACT FROM AUTHOR]

This paper proposes a simple method for estimating the horizontal effective stress in clay soils, from which the mean effective stress can be determined. It is shown that the method is applicable to a wide range of clay soils with varying stress histories, including normally consolidated and heavily overconsolidated clays. Although this paper is expected to be of use to many practitioners in the field of geotechnical engineering, it also has a particular relevance with respect to the effects of moisture abstraction on shrinkable clay soils by vegetation, or simply by seasonal variations. While the effects are well known, the methods for identifying clay desiccation and for calculating heave potential are often relatively expensive, and the results can be inconclusive. Using the proposed method, this paper describes a simple and low-cost alternative method for estimating the in situ mean effective stress in desiccated clay soils. This information can be used to confirm the likely depth of clay desiccation, and provides a means of calculating a further estimate of heave potential. [ABSTRACT FROM AUTHOR]

The article focuses on a study that explores the proper modeling of embankments used on weak clay reinforced with sand columns. The study applied a numerical simulation on the embankment on weak clay reinforced with sand columns and was analyzed using equivalent critical state parameters of the composite ground. According to the results of the numerical analyses, improvement in vertical as well as lateral displacement of the embankment depends on the location and extent of the sand columns.

In this paper a new anisotropic model for time-dependent behaviour of soft soils is presented. The formulation is based on a previously developed isotropic creep model, assuming rotated Modified Cam Clay ellipses as` contours of volumetric creep strain rates. A rotational hardening law is adopted to account for changes in anisotropy due to viscous strains. Although this will introduce some new soil parameters, they do not need calibration as they can be expressed as functions of basic soil parameters through simple analytical expressions. To start with, the one-dimensional response of the model is discussed, making it possible to explore how the model is capable of capturing key features of viscous soft soil behaviour. Subsequently, the three-dimensional generalisation of the model is presented, followed by comparison with experimental data, showing good agreement in both triaxial undrained compression and extension. In the authors' opinion, the simple formulation of the model makes it attractive for use in engineering practice. [ABSTRACT FROM AUTHOR]

The paper examines the influence of soil strength and stiffness on the end resistance mobilised by a cone or displacement pile in a two-layered soil profile (i.e. strong soil overlying or underlying weak soil). The investigation involved a series of numerical analyses that idealise pile/ cone penetration assuming the spherical cavity expansion analogue. It is shown how the end resistance mobilised by a penetrometer in a dense sand (i.e. strong soil) varies with the number of penetrometer diameters (D) from a weak soil (assumed here to be either a loose sand or soft clay), and depends on the ratio of the steady-state penetration resistances of the strong and weak layers. The penetrometer resistance in the weak soil is not affected by an adjacent strong layer at penetrations greater than 2D. A design procedure based on a numerical parametric study is proposed, and this is subsequently shown to compare well with centrifuge test data and with previous numerical research. [ABSTRACT FROM AUTHOR]

The results of an experimental investigation to explore the effectiveness of coir geotextile vertical drains for ground improvement are reported. The time settlement behaviour of clayey soil, as influenced by coir geotextile drains, is summarised and the construction and installation details are also discussed. Two types of coir drains, a circular type and a rectangular type, using two varieties of coir geotextiles were tested in three configurations, namely a single drain and triangular and rectangular patterns. It was observed that the time for consolidation was very much reduced due to the installation of coir drains irrespective of the type of coir geotextile used, type of coir drain and the layout of the drains. Furthermore, in addition to ease of construction these drains are eco-friendly and will not pose any environmental problems. [ABSTRACT FROM AUTHOR]

The article presents the summaries of papers of the Institution of Civil Engineers (ICE) proceedings in 2007. It includes "Reducing differential settlements of approach embankments" case history of approach road remedy project in Japan. "Volume loss experience on open-face London clay tunnels" describes ground movement in the building of Jubilee Line Extension. "Embankment supported on piles with biaxial geogrids" case study of pile embankment made at soft organic clay layer 10 meter deep.

The pile designer in a seismically active region will generally need to estimate the maximum seismically induced internal moment and shear of the pile in order to provide adequate strength to maintain the structural integrity of the pile. In this paper an effort has been made to provide a simple means of carrying out such an estimation for a single pile embedded in a homogeneous clay layer. The results have been presented in the form of design charts that can be used directly by designers with no or little computational effort. The variables in the design charts include the length and diameter of the pile, the Young's modulus of the pile material, the strength and stiffness of the soil, and the factor of safety against axial failure of the pile. The charts have been obtained from a time domain analysis of pile-soil interaction, and are based on the response of the piles to a range of earthquakes recorded in North America and Australia. [ABSTRACT FROM AUTHOR]

The ‘delayed collapse’ of cuttings in stiff high-plasticity clay is known to be significantly affected by long-term recovery of pore pressures and progressive failure resulting from brittle material behaviour. Limit equilibrium methods are not well equipped to model these effects, but the increasing use of numerical modelling offers new potential to improve understanding of these failure mechanisms. A series of numerical analyses incorporating brittle material behaviour has been undertaken, specifically considering deep-seated first-time failure of cuttings in weathered London Clay. Because of progressive failure, the average mobilised strength is between the peak bulk strength and the residual strength. In current practice, parameter selection is often based on Chandler and Skempton's back-analysis of several deep-seated failures in the ‘brown’ weathered London Clay. This paper considers variation of the critical (minimum) height for delayed deep-seated failure in cuttings in weathered London Clay with slope angle, and variation of mobilised strength with cutting height. [ABSTRACT FROM AUTHOR]

The article describes a process developed to create samples of overconsolidated sedimented clay in the laboratory. It highlights a study which investigated the differences in samples made by sedimentation and made in the conventional manner by reconstitution and compression from a slurry. According to the author, the laboratory samples were sedimented through salt water.

The article cites a study which presents a possibility for assessing the initial moduli G0(ij)of Boom clay material at a very small strains by measuring Gvh , Ghh, and Ghv on the same sample at any stress state with independent control of vertical and horizontal stresses. The study utilized a triaxial apparatus to measure shear wave velocity. Several graphs are presented depicting the methods employed in the study and the results of the study.

The article presents a study which investigates the suction effects in deep Boom Clay block samples through characterization of the water retention and swelling properties of the clay. It also examines the relationship between suction and stress changes during loading and unloading sequences. Furthermore, it evaluates the effect of suction release under an isotropic stress close to the estimated suction.

The research and development programme on geological disposal for high-level and long-lived waste (HLW) in Belgium was initiated in 1974. A deep tertiary clay formation, the Boom Clay, present under the Mol-Dessel nuclear site, was selected as a reference host formation for experimental purposes. The construction of the underground laboratory HADES (at a depth of 223 m, initiated in 1980 and extended in 2002) allowed the building of a valuable geotechnical database, and led to the development of improved excavation techniques that significantly reduce the excavation-damaged zone (EDZ). Since the operational start of HADES about 25 years ago, many geotechnical measurements have been performed around excavations. Comparison between in situ measurements and modelling results allowed a continuous improvement of our knowledge on the Boom Clay behaviour. Important issues for interpreting the measurements correctly are good control of the excavation parameters and the boundary conditions. An extensive characterisation of the hydromechanical response of Boom Clay around an excavation for short- and long-term conditions has been performed. One important finding was the occurrence of measurable hydraulic effects at a distance of about 60 m (12.5 tunnel diameters) ahead of the tunnel excavation. [ABSTRACT FROM AUTHOR]

The paper presents an interpretation of an in situ heating test carried out on Opalinus clay in the Mont Terri underground laboratory. Opalinus clay is a stiff, strongly bedded, Mesozoic clay of marine origin. When subjected to thermal loading, saturated stiff clays exhibit a strong pore pressure response that significantly affects the hydraulic and mechanical behaviour of the material. The observations gathered in the in situ test have provided an opportunity to examine the integrated thermo-hydro-mechanical (THM) response of this sedimentary clay. Coupled THM numerical analyses have been carried out to provide a structured framework for interpretation, and to enhance understanding of THM clay behaviour. Numerical analyses have been based on a coupled theoretical formulation that incorporates a constitutive law especially developed for this type of material. The law includes degradation of bonding by damage. By performing three-dimensional computations, it has been possible to incorporate anisotropy of material parameters and of in situ stresses. The 3D simulation has proved able to furnish a satisfactory representation of the development of the in situ test and of the main observed patterns of behaviour. A sensitivity analysis has also been carried out to examine the potential effect of various key or uncertain parameters. The critical examination of test observations and the results of the numerical analyses have allowed the classification, by differing degrees of significance, of the various coupled phenomena present in the problem. [ABSTRACT FROM AUTHOR]

The design and construction of a contiguous bored pile propped retained cut on the approaches to Ashford International Station raised some challenging design issues. Design problems associated with under-drainage and groundwater control (including the performance of semi-permeable propped retaining walls) and the effects of wall installation and movement on in situ stresses were compounded by the relatively limited geotechnical engineering experience of the Atherfield and Weald Clay formations. Differences in the permeabilities of these two strata were expected, but the impact of these on the design was only fully established at the start of construction. Some aspects of the engineering behaviour of the Atherfield and Weald Clays are discussed with reference to an instrumented section of the propped retained cut. The changes in total horizontal stress and pore water pressures measured during and over a six-year period following construction of the retained cut are presented, and their significance is discussed. [ABSTRACT FROM AUTHOR]

The paper discusses the intrinsic properties, geological history, natural structure and mechanical behaviour of stiff Italian clays, part of the sub-Apennine Blue Clay formation, which are located at different sites within the marine basin where the clay formation was deposited in the early Pleistocene. For all the clay deposits being considered, diagenesis, unloading due to erosion, and weathering of the top strata represent the main stages of the geological history. However, the clays have undergone different levels of unloading, and have developed different levels of structure due to their different locations in the basin. These differences are accounted for in the analysis of their current states and behaviour. Based upon a large experimental database, the structure and mechanical behaviour of the clay samples from the different sites are compared and related to the clay history. In particular, the soil structure is characterised based upon SEM analysis results and compression-swelling test results. The comparison of the response to compression-swelling cycles of the natural clay with that of the same clay when reconstituted leads to the evaluation of parameters such as the stress sensitivity Sσ and the swell sensitivity C*s/Cs, which are used to assess the structural strength of the natural clay with respect to that of the reconstituted clay. The stress-strain behaviour of the different clays along different constant stress-ratio compression paths and shear paths (from low to high pressures) is discussed in detail. The variations in stress-strain response of samples subjected to different pre-shear consolidation paths are outlined. The corresponding trends of the plastic strain increment ratios are investigated. As a result of the analysis, the features of the gross yield curves of the different clay horizons are also assessed. Finally, the study provides elements for the characterisation of the hardening properties of stiff clays, and therefore of the evolution of the material anisotropy during plastic deformation. [ABSTRACT FROM AUTHOR]

In recent years, fundamental research has been carried out into the properties of some natural stiff clays and the corresponding reconstituted materials, highlighting the role of microstructural features in the observed differences. In this paper the results of an experimental investigation into the mechanical behaviour of an Italian stiff clay of marine origin are presented. Medium-pressure and high-pressure stress-controlled triaxial cells were used in which natural samples underwent isotropic and anisotropic compression and swelling before drained or undrained shearing. Comparison of soil behaviour observed after different compression histories up to different values of maximum effective stress allowed the following aspects to be discussed: the effects of the initially structured state on the medium to large strain response and shear strength characteristics of the soil; the relevance of volumetric and deviatoric plastic strain to the structure degradation; the role and implications of the imposed non-isotropic stress histories; the permanent differences between reconstituted samples and fully destructured natural samples; and the uniqueness of the critical state condition. [ABSTRACT FROM AUTHOR]

Microstructural and mineralogical observations of clay-stones reveal the presence of clay aggregates bonded by a skeleton of inert minerals such as calcium carbonate. The behaviour of these natural materials evolves from a rock-like behaviour, when undisturbed, to clay-like soil when weathered or when subjected to straining. A model has been developed to simulate the constitutive behaviour of these transitional materials. Following the proposal made by Vaunat & Gens, the material is conceived as a composite medium made of a clay matrix and a quasibrittle bonding microstructure. The basic model has been modified and extended to reproduce the expansive behaviour of the clay matrix, a fundamental aspect to simulate weathering effects, induced largely by drying-wetting cycles. The clay matrix reacts to stress and suction changes, whereas the bond component is not affected by suction changes. An elasto-plastic double-structure model for expansive clay soils describes the clay matrix. The bonding structure follows a damage model. The interaction between the two constitutive models derives from strain compatibility conditions and energy considerations. The model performance is first illustrated by means of a sensitive analysis that explores the effect of initial bond strength, bond damage rate, bonding concentration, and wetting-drying cycles. Simple stress paths (uniaxial deformation; triaxial compression) are used to highlight the features of the formulation and the role of significant parameters. Some published tests are also reproduced with the model. They have been selected to show some relevant features of evolving soft clay rocks: stiffness and strength degradation during loading and enhanced rebound during unloading, and the effect of drying-wetting cycles on subsequent stiffness and strength degradation. [ABSTRACT FROM AUTHOR]

The peak strength of overconsolidated clay soil is conventionally related to the effective stress by a linear Mohr-Coulomb criterion in which the parameters c′p and Ø′p depend on the nature of the soil grains, on the water content, and on the range of stress over which measurements are made. For soils that have zero or very small interparticle bonding the failure line must pass through or close to the point τ = 0 and σ′ = 0, and it must meet the critical state line, so a linear Mohr-Coulomb criterion cannot satisfactorily describe the peak strength of soil except over relatively small ranges of effective stress. The paper reports the results of special triaxial tests in which the peak strengths of samples of stiff clays from southeast England were measured at small effective stresses and large overconsolidation ratios. For each soil the peak strength, with a suitable normalising parameter to take account of water content, was related to the effective stress by a non-linear power law criterion similar to that familiar in rock mechanics. In addition, the peak stress ratios were linked to a state parameter through a relationship similar to that for ordinary Cam clay. For each clay tested the material parameters that describe the peak strength were found to be only loosely related to their plasticity. [ABSTRACT FROM AUTHOR]

This paper presents a detailed field study of a soft clayey silt stratum improved in situ with preloading combined with prefabricated vertical band drains (PVDs). The clayey silt stratum was to support a warehouse in a chemical plant. As the bearing capacity of the soil was much lower than the load it was to support, the subsoil condition was improved by installing PVDs in combination with preloading. Thus the rate of consolidation of the clay stratum was increased. The band drains were installed up to a depth of 14·2 m at a spacing of 1·6 m. The intensity of preloading applied was 52 kPa. For preloading, the surcharge fill was placed up to a height of 3·10 m from the natural ground level. The area of both preloading and band drains was 15% greater than that of the floor of the warehouse for more effective improvement of the ground. Preloading was done for 60 days. Settlements were monitored using settlement gauges. The settlements observed across the entire area indicated that the preloading operation was uniform all through. The amount of settlement was large up to the point of filling the surcharge, but thereafter it did not show a significant increase. [ABSTRACT FROM AUTHOR]

In temperate European climates, the season of peak water demand by vegetation (summer) is out of phase with the season of greatest rainfall (winter). This results in seasonal fluctuations in soil water content and, in clay soils, associated problems of shrinking and swelling that can in turn contribute to strain-softening and progressive slope failure. This paper presents field measurements of seasonal moisture content and pore water pressure changes within the surface drying zone of a cut slope in the London Clay at Newbury, Berkshire, UK. A climate station was installed at the site to measure the parameters needed to determine specific plant evapotranspiration. This information was used to carry out a water balance calculation to estimate the year-round soil moisture deficit caused by the vegetation. The calculated soil moisture deficit matches reasonably closely the field measurements of soil drying. The field measurements of seasonal changes in pore water pressure and suction are linked quantitatively to the measured changes in water content using the soil water characteristic curve for the London Clay. The suctions generated by the light vegetation cover at Newbury were found not to persist into the winter and early spring. [ABSTRACT FROM AUTHOR]

Limited guidance on usage and methodology is currently available to engineers for the most common rapid load pile test, known as Statnamic. In order to improve the analysis of Statnamic testing in clay soils a full-scale instrumented auger bored pile was installed and tested in glacial lodgement till. As a result, improvements have been suggested in the test methodology and analysis. The inclusion of an accelerometer at the pile head would allow direct measurement of acceleration and verification of displacement measurements and velocity calculations. High-precision optical levelling of the pile before and after test cycles would allow multiple loading cycles to be considered cumulatively with greater confidence. The separation of the laser reference source from the test pile should be sufficient to avoid surface wave disturbance. [ABSTRACT FROM AUTHOR]

The article analyzes the behavior of pore water pressure on clay-infilled joints sheared in undrained, triaxial conditions. The test demonstrated that asperity interference influences the stress-strain behavior of the joints. It also shows that in the absence of asperity interference, it shows the shear behavior of normally consolidated clay.

Dynamic experiments in lateral mode were carried out on model aluminium single piles in a simulated elastic half-space filled with clay soil to determine dynamic constants of the soil-pile system and to study the bending behaviour of piles. Model piles with various lengths were subjected to steady state harmonic vibrations with different magnitudes of force of 7-30 N applied over a wide range of frequencies from 2 Hz to 50 Hz. The load transferred to the pile, pile head displacement and strain gauge readings at different locations on the pile were measured. It is observed consistently that the magnitude of the applied force and the pile length significantly affect the natural frequency of the soil-pile system. It is found that rigid piles behave linearly even at the higher magnitudes of applied force, but that flexible piles behave non-linearly as the magnitude of the applied force increases, which leads to a substantial reduction of the lateral stiffness of the soil-pile system. Damping of the soil-pile system is found to increase with an increase in pile length and magnitude of the applied force, owing to the occurrence of radiation and hysteretic damping. Based on experiments carried out on model piles embedded in clay at low confining pressure, it is found that the maximum dynamic bending moment of long flexible piles is about four times higher than that of short rigid piles. The maximum bending moment under dynamic loads occurs at deeper depth than the corresponding depth for static loads, which indicates an increase of the active length of piles under dynamic load. [ABSTRACT FROM AUTHOR]

The paper presents compression and triaxial tests conducted under controlled suction in horizons B and C of a residual soil gneissic rock profile from south-east Brazil. Horizon B, found at the surface, consists of a 2 m thick reddish lateritic clayey soil layer, whereas horizon C is a saprolitic soil layer that reaches great depths. The block samples representing horizons B and C were manually taken from depths of I m and 5 m respectively. The test programme carried out consisted of isotropic and anisotropic compression tests as well as drained and constant water content triaxial tests. Tests were performed under saturated and unsaturated conditions at controlled suction. Strength parameters c and φ were shown to increase with matric suction. The critical state parameters were shown to vary with suction, which also expanded the yield curve. Data obtained may be useful for the development of soil constitutive models for unsaturated soils. [ABSTRACT FROM AUTHOR]

This article reports that geotechnical engineers are normally not very well trained in the application of statistics in soil mechanics. Incorrect conclusions are therefore often made from graphical plots of soil data owing to inappropriate choice of variables in correlating different soil properties. It is informed that the plasticity chart proposed by A. Casagrande can be used as a tool for the classification of soils. In the plasticity chart, the plasticity index is plotted against the liquid limit. Different types of clayey or silty soils tend to take up different zones in the plasticity chart.