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Atmospheric phenomena such as rainfall and evapotranspiration contribute to slope movements in unsaturated soils, the study of which requires fully coupled numerical methods, combined with realistic boundary conditions and appropriate mechanical and hydraulic soil properties. This paper focuses on the effect of the hydraulic behaviour, and in particular of the modelling of the soil-water retention curve and the permeability on slope movements, with the aim of identifying which model parameters are critical and, therefore, require careful experimental identification.

The stability of cut slopes is greatly influenced by seasonal pore-water pressure variations under the combined effect of rainfall and vegetation. However, predicting soil–atmosphere interaction is not straightforward, due to the complexity of both the boundary conditions involved and the hydromechanical behaviour of soils, which is coupled and highly nonlinear, rendering the use of numerical tools, such as finite element analysis, necessary. This paper discusses the numerical modelling of soil–atmosphere interaction and presents the analysis of a slope cut in London clay in a highly vegetated area. The whole life cycle of the slope is considered with phases of low and high water demand vegetation and vegetation clearance. The analysis results indicate that dense vegetation is associated with high factors of safety, but may induce large differential displacements, which are likely to affect the serviceability of the slope. Vegetation clearance, however, may initiate instability, highlighting the need for effective vegetation management to achieve a balance between serviceability and ultimate limit states. Although the case considered is representative of southeast England, it introduces the necessary tools for realistic numerical analysis of soil–atmosphere interaction.

A temperature rise in soils is usually accompanied by an increase in excess pore fluid pressure due to the differential thermal expansion coefficients of the pore fluid and the soil particles. To model the transient behaviour of this thermally induced excess pore fluid pressure in geotechnical problems, a coupled THM formulation was employed in this study, which accounts for the non-linear temperature-dependent behaviour of both the soil permeability and the thermal expansion coefficient of the pore fluid. Numerical analyses of validation exercises (where there is an analytical solution), as well as of existing triaxial and centrifuge heating tests on Kaolin clay, were carried out in the current paper. The obtained numerical results exhibited good agreement with the analytical solution and experimental measurements respectively, demonstrating good capabilities of the applied numerical facilities and providing insight into the mechanism behind the observed evolution of the thermally induced pore fluid pressure. The numerical results further highlighted the importance of accounting for the temperature-dependent nature of the soil permeability and the thermal expansion coefficient of the pore fluid, commonly ignored in geotechnical numerical analysis.

In this paper, 2-dimensional, hydro-mechanically coupled finite element analyses are performed to assess the performance of an engineered barrier aimed at reducing flood risk in urban environments. The barrier consists of an unsaturated compacted soil layer and a drainage layer of a coarse granular material, constructed on top of the natural soil, in this case London clay. The barrier is vegetated so that its water storage capacity is renewed after each rainfall event. Sophisticated boundary conditions are used to simulate the effect of precipitation and evapotranspiration. The rainfall water infiltration and the initiation of water run-off during intense precipitation events are simulated. The effect of the hydraulic properties of the unsaturated soil layer on the performance of the system is investigated by means of parametric analyses. The effect of precipitation rate and geometry of the barrier is also discussed. Design recommendations for the properties of the compacted layer and the dimensions of the system are given at the end of the paper.

The structural testing and finite element (FE) analysis described in this paper were part of a major research project undertaken at Imperial College London to investigate the deformation of bolted segmental grey cast iron (GCI) tunnel linings. A key aim was to quantify how joints influence the behaviour of the lining, through a three-path approach comprising physical experiments, finite element modelling, and field instrumentation. The laboratory results have been used to assess the validity of the tunnel assessment methods used by industry. This study examined joint articulation under the serviceability limit state in the absence of hoop force focussing on factors such as applied bolt preload, the loading direction and the freedom of the circumferential flange to deflect. Two half-scale GCI lining segments were bolted together at the longitudinal flanges to form a bolted arch in a similar fashion to the tests performed by Thomas (1977). Modern instrumentation was implemented to gain detailed measurements quantifying changes in global displacements of the two segments, bolt forces and joint opening under applied loading. For the first time, the physical experiments were conducted contemporaneously with the development of a three-dimensional FE model of the joint. The experimental data and the results from the FE analysis indicate a reduction in joint stiffness as the joint articulates under applied load. It is shown that the presence of a joint has far greater influence on the behaviour of the ‘arch’ than the level of preload applied to the bolts in the joint. The FE analysis allowed the deformation behaviour of the joint under positive and negative bending to be investigated: its response under the two modes differs significantly.

Buffer materials for nuclear waste disposal applications generally consist of blocks made of highly expansive compacted clay. However, high-density pellets of bentonite are being evaluated as an alternative buffer material for waste isolation. The material response of pellet-based buffers may be quite different from that of compacted buffers, because of the peculiar discontinuous porosity presented. An overview of the literature available on pellet-based buffers is presented and, in particular, two main topics are discussed: firstly, the characteristics of the fabric of the pellets that can be observed through techniques of micro-structural investigation, secondly, the most important behavioural features that can be seen during material testing. Additionally, the constitutive frameworks that have already been developed specifically for pellets are also reviewed. The overall objective of the paper is to highlight the differences between compacted and pellet-based bentonite buffers, in order to propose suitable assumptions to start developing a constitutive model for the latter.

The paper presents the Finite Element formulation of the equations proposed by Tsiampousi et al. (2016) for coupled consolidation in unsaturated soils. Their coupling is discussed in relation to a conceptual model which divides soil behaviour into zones ranging from fully saturated to dry states. The numerical simulation of a laboratory experiment involving drainage of water from a vertical column of sand is used to validate the equations. Finally, the example of rainfall infiltration into a cut slope highlights how aspects of the conceptual model are reflected in the numerical analysis of boundary value problems involving unsaturated soils.

The equations governing coupled consolidation in unsaturated soils are known to contain additional parameters when compared to the equations for saturated soils. Nonetheless, the variation of these parameters with suction or degree of saturation is not generally agreed upon. The paper introduces a novel approach to deriving general equations for each of these parameters and their variation, and explains that, for consistency with the constitutive and soil-water retention curve models adopted, these general equations need to be transformed into case-specific expressions. Finally, a conceptual model is presented highlighting how the behaviour of unsaturated soil reflects aspects of its water content.

Deep and slow landslide processes are frequently observed in clay slopes located along the Southern Apennines (Italy). A case study representative of these processes, named Pisciolo case study, is discussed in the paper. The geo-hydro-mechanical characteristics of the materials involved in the instability phenomena are initially discussed. Pluviometric, piezometric, inclinometric and GPS monitoring data are subsequently presented, suggesting that rainfall infiltration constitutes the main factor inducing slope movements. The connection between formation of landslide bodies and slope-atmosphere interaction has been demonstrated through a hydro-mechanical finite element analysis, whose results are finally reported in the work. This analysis has been conducted employing a constitutive model that is capable of simulating both saturated and unsaturated soil behaviour, as well as a boundary condition able to simulate the effects of the soil-vegetation-atmosphere interaction.