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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 core of an earth dam is normally made of clayey base soils and protected by a sandy filter. Designing the filter can be very challenging considering the various criteria established today. This study commences with a review of three prominent criteria referred to in designing filters by the indirect method. No-erosion filter tests are then carried out involving 11 fine-grained, base soil samples with different properties; these are a highly dispersive soil, a soil with a medium to high degree of dispersion, a soil with a low-plasticity silt (ML) classification and a soil with a broad gradation curve. These tests represent the direct method. A comparison of results arising from the two methods shows that designing filters the indirect way, by following established criteria alone, is not always safe. Hence, it is proposed that such designs should be experimentally verified using no-erosion filter tests. Furthermore, instead of following the prevalent criteria in the indirect design method, the perfect filtering method for highly dispersive soils and the reduced particle size distribution method for broadly graded soils are proposed to be used, with merits given for each method. Finally, the paper recommends certain filter criteria from the literature for base soils with a moderate degree of dispersion and an ML classification respectively. [ABSTRACT FROM AUTHOR]

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

Helical screw piles are a popular solution for relatively low-capacity, removable or recyclable foundations supporting road and rail signage or similar light structures. When specifying a helical screw pile, a designer must choose the active length and the helical plate spacing ratio, which are governed by the number, spacing and size of the individual helices. This paper presents an investigation using transparent synthetic soil and particle image velocimetry to observe the failure of helical screw piles with helical plate spacing ratios of 1·5-3 and active lengths up to three times the diameter. For the geometries and properties examined, capacity is shown to be a function of active length and the dominant failure mechanism is characterised by the formation of a cylindrical failure surface. A simple analytical model is developed and used to assess the impact of different design methodologies on immediate displacements under loading. A traditional 'permissible stress' method is shown to be conservative, whereas modern 'partial factor' methods are more economical and lead to greater immediate displacements for a given design load. Designers using modern 'partial factor' approaches, such as Eurocode 7, might benefit from specifying a helical plate spacing ratio of less than 1·5 to maximise the stiffness of the response to axial loading and minimise the immediate displacements experienced upon application of working loads. [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.

A letter to the editor in response to the article "Ground heave induced by installing stone columns in clay soils" by B. McCabe and colleagues in a 2013 issue is presented.