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The influence of the inherent fabric anisotropy of sand and its evolution on the footing bearing capacity and failure mechanism has been modelled and analysed with a multiscale approach that couples the finite-element method (FEM) and the discrete-element method (DEM). In this approach, the material constitutive responses are captured by DEM simulations on representative volume elements (RVEs) assigned to the FEM Gauss points. The inherent fabric anisotropy of sand is reflected by the bedding plane angle α of the RVEs composed of elliptic particles, where α measures the average angle between the long axes of the particles and the horizontal direction. The bearing capacity is found to decrease with an increasing α and the reduction can reach as high as 25%. Asymmetric deformation has been observed in the α other than 0° or 90° cases, which is mainly attributable to the different relative principal directions between the stress and the fabric at the two sides of the domain. Further multiscale analyses reveal that the load-bearing structure of the material expressed by the contact-normal-based fabric tensor is more fragile under the footing loading at one side of the domain and in larger α cases, which offers a micromechanical explanation to the observation of the asymmetric deformation and the decreased bearing capacity with increased α.

In practical engineering, natural soil deposits often sustain an initial driving force prior to cyclic shear, owing to earthquakes, traffic and waves; such asymmetrical loading conditions may significantly affect the liquefaction susceptibility and failure mechanism of sand. To understand the typical cyclic liquefaction responses, comprehensive asymmetrical cyclic loading tests were conducted on sand samples subjected to either compressional or extensional static stress. The results indicated that different stress conditions can result in three distinct failure mechanisms: flow liquefaction, cyclic mobility and residual deformation accumulation. According to the experimental observations, an anisotropic sand model was developed within the framework of the anisotropic critical state theory. The model employed a fabric-dependent dilatancy, and accounted for the effects of the fabric evolution and accumulated loading index on the plastic hardening, in order to better reflect the cyclic degradation of the plastic modulus. The predictive capacity of the model was confirmed through undrained monotonic test results for samples with different densities. Comparisons between the model responses and experimental results indicated the excellent capabilities of the developed model in terms of capturing the typical deformation, strength and fabric characteristics of different cyclic failure mechanisms of sand under either symmetrical or asymmetrical loading conditions.

Approximately 25% of China's 120 000 km of expressway, as well as many new metro lines and airports, rest on soft clay deposits. However, service settlements are proving larger than expected, especially in southeast China. This note describes laboratory experiments on K0-consolidated intact samples of soft clay taken near Wenzhou, south-east China, that explore whether cyclic traffic wheel loading contributes significantly to the observed settlement trends. Cyclic triaxial (CT) tests are reported together with cyclic hollow cylinder (CHCA) experiments that imposed cardioid-shaped 2τzθ − (Δσz − Δσθ) stress paths. Cyclic principal stress axis rotation is shown to have an important influence on vertical straining. Once a certain threshold has been exceeded, the resilient and permanent strains developed in the CHCA tests become progressively larger than their counterparts in CT tests conducted at the same vertical cyclic stress ratio, with trends that diverge progressively as vertical cyclic stress ratio increases. Critical cyclic stress ratios can be defined that divide the response into (a) stable, (b) metastable and (c) unstable cyclic ranges. The novel experimental approach and high-quality data reported should aid practitioners and modellers in developing new analyses to address this economically significant geotechnical problem.

The axial capacities of piles driven in silica sands are known to grow over the months that follow installation, long after all driving-induced pore pressures have dissipated. However, there is uncertainty over the processes that govern the observed set-up and how they may vary from case to case. This paper evaluates three hypotheses against evidence from updated field test databases and laboratory investigations with highly instrumented and pressurised model piles. Potential influential factors are considered including: pile and sand particle sizes, installation style, access to free water, test conditions and external stress change cycles. Laboratory local stress measurements support the hypothesis that moderation, over time, of the extreme stress distributions developed during installation is a key contributor to capacity growth, while field tests confirm the action of enhanced dilation near the shaft. However, field and laboratory piles show paradoxically different ageing trends. The paper proposes that the fractured but compacted sand shear zone that forms around pile shafts during installation leads to set-up being far more significant with large field driven piles than in model tests.

This paper describes an integrated study of the effects of fabric anisotropy on granular soil response, in which the microscopic measurements are properly linked with the macroscopic modelling. Using an image-analysis-based technique and an appropriate mathematical approach, the inherent fabrics of sand specimens prepared in the laboratory using different sample preparation methods were measured, quantified and compared at a microscale level. It was found that the specimen prepared by the dry deposition method had a more anisotropic microstructure than the specimen prepared using the moist tamping method, which is considered directly associated with the experimental observation that different sample preparation methods produce samples with distinctive responses under otherwise identical conditions. An existing platform model was then extended so that the combined effects of initial fabric and shear mode dependence were accounted for in a simple yet rational manner. To calibrate and verify the model, a series of laboratory tests was conducted for Toyoura sand under various combinations of loading and sample preparation conditions. It is shown that the model is capable of simulating in a unified manner the experimental results reflecting the combined effects of sample preparation methods, loading paths, soil densities and confining pressures.

The impact of fabric anisotropy on the behaviour of granular soil remains a subject of great interest. In particular, the effects of principal stress rotation on the undrained response of saturated sand are not fully understood. This paper describes an experimental investigation conducted in an automated hollow cylinder apparatus into the undrained anisotropic behaviour of saturated sand in rotational shear, which is defined as a class of non-proportional loading with a continuous rotation of the principal stress directions but a constant deviatoric stress. Special attention in this investigation was placed on the influence of the relative magnitude of the intermediate principal stress, characterised by the parameter b = (σ2 − σ3)/(σ1 − σ3), on the pore pressure response and deformation characteristics. The experimental observations indicate that soil specimens, even in very dense state, were weakened by the build-up of pore water pressure in rotational shear. The intermediate principal stress parameter b was not a negligible factor for the behaviour of saturated sand in the rotation shear, but had significant impact. Under otherwise identical conditions, the soil specimen rotationally sheared under the condition b = 0 exhibited a much stronger resistance to pore pressure build-up and a less dramatic stiffness degradation than that sheared under the condition b = 1·0. This observation is considered to be directly associated with the soil fabric anisotropy.