Abstract. Rapid mass movements (RMM) pose a substantial risk to people and infrastructure. Reliable and cost-efficient measures have to be taken to reduce this risk. One of these measures includes establishing and advancing the state of practice in the application of early warning systems (EWSs). EWSs have been developed during the past decades and are rapidly increasing. In this paper, we focus on the technical part of EWSs, i.e., the prediction and timely recognition of imminent hazards, as well as on monitoring slopes at risk and released mass movements. Recent innovations in assessing spatial precipitation, monitoring and precursors of the triggering and deformation of RMM offer new opportunities for next-generation EWSs. However, technical advancement can only be transferred into more reliable, operational EWSs with an adequate well-instructed dedicated staff. To this end, an intense dialog between scientists, engineers and those in charge of warning, as well as further experience with new comprehensive prototype systems jointly operated by scientists and practitioners, will be essential.
MX-80 bentonite used in engineered barrier systems would be subjected to wetting and drying cycles. To assess the response of the material under such circumstances, a comprehensive experimental characterisation of the water retention behaviour of compacted MX-80 granular bentonite was performed in this study. A new methodology is proposed to investigate this behaviour under a constant volume condition for specimens prepared at different dry densities. The material was subjected to different hydraulic paths, including cyclic variations of the water content. As a result, an irreversible modification of the retention behaviour was observed when the material approached a fully saturated state during the first main wetting, and a new hydraulic domain was consequently created. The water retention capacity of the material increased as a result of such modification. Microstructural observations were performed at different stages of the hydraulic paths to relate the permanent change in the retention behaviour to the evolution of the fabric during the wetting and drying cycles. A clear transition from a double-structured to a single-structured fabric, followed by a permanent change of the microfabric, was found following the first wetting. Available data on the hydration of smectite particles were used to relate the microstructural evolution to the change in the water retention properties. This correlation shows the evolution of the active porosity at the particle level within the microstructure, which consequently affects the macroscopic response of the bentonite in terms of its water retention behaviour
SUMMARYThis paper presents a dynamic fully coupled formulation for saturated and unsaturated soils that undergo large deformations based on material point method. Governing equations are applied to porous material while considering it as a continuum in which the pores of the solid skeleton are filled with water and air. The accuracy of the developed method is tested with available experimental and numerical results. The developed method has been applied to investigate the failure and post-failure behaviour of rapid landslides in unsaturated slopes subjected to rainfall infiltration using two different bedrock geometries that lie below the top soil. The models show different failure and post-failure mechanisms depending on the bedrock geometry and highlight the negative effects of continuous rain infiltrations.
Behaviour of the pile–soil interface is important to correctly predict the response of floating piles in terms of displacement and lateral friction. Regarding energy piles, which couple the structural roles of deep foundations with the principle of shallow geothermal energy, the response of pile–soil interfaces is influenced by seasonal and daily cyclic thermal variations. Accordingly, the goal of this paper is to experimentally investigate the response of the pile–soil interface at different temperatures. This experimental campaign aims to analyse (i) the cyclic mobilization of the shear strength of the soil–pile interface that is induced by thermal deformation of the pile and (ii) the direct influence of temperature variations on the soil and soil–pile interface behaviour. In this study, a direct shear device was developed and calibrated for nonisothermal soil–structure interface testing. It appears that the sand–concrete interface was affected by cyclic degradation but not affected directly by temperature. Conversely, the response of the clay–concrete interface changed at different temperatures, showing an increase of strength with increasing temperature, presumably due to the effects of temperature on clay deformation.
a b s t r a c tShales are among the most commonly considered geomaterials in current energy-related geomechanical investigations, as they are involved in engineering applications such as the extraction of natural gas, CO 2 sequestration and nuclear waste storage. A deep understanding of their behaviour with regard to variations in the degree of saturation is of significance for such applications. With the aim to establish a sound protocol for shale retention behaviour analysis, this paper presents an experimental methodology that takes into account the specificities of shales such as small pore size dimensions and the large variations in water potential to be applied to induce significant changes in the degree of saturation. The technique involves the direct control of the shale water content and the subsequent measurement of the suction at equilibrium by a psychrometer. A fluid displacement technique with a non-polar liquid is also used to assess the volume changes of the shale and to compute the degree of saturation. Selected test results are presented for various shale samples that have been cored at different depths. The results indicate that important features of the retention behaviour of geomaterials are fundamental aspects to be considered when analysing the retention behaviour of shales, such as the existence of main wetting and drying paths, the hysteresis domain, and the dependency of the air entry value on the void ratio.
Abstract:The paper presents an experimental and modelling approach for the soil-water retention behaviour of two deformable soils. The objective is to investigate the physical mechanisms that govern the soil-water retention properties and to propose a constitutive framework for the soil-water retention curve accounting for the initial state of compaction and deformability of soils. A granular soil and a clayey soil were subjected to drying over a wide range of suctions so that the residual state of saturation could be attained. Different initial densities were tested for each material. The soil-water retention curves (SWRCs) obtained are synthesized and compared in terms of water content, void ratio, and degree of saturation, and are expressed as a function of the total suction. The studies enable assessment of the effect of the past and present soil deformation on the shape of the curves. The void ratio exerts a clear influence on the air-entry value, revealing that the breakthrough of air into the pores of the soil is more arduous in denser states. In the plane of water content versus suction, the experimental results highlight the fact that from a certain value of suction, the retention curves corresponding to different densities of the same soil are convergent. The observed features of behaviour are conceptualized into a modelling framework expressing the evolution of the degree of saturation as a function of suction. The proposed retention model makes use of the theory of elastoplasticity and can thus be generalized into a hysteretic model applicable to drying-wetting cycles. The calibration of the model requires the experimental retention data for two initial void ratios. The prediction of tests for further ranges of void ratios proves to be accurate, which supports the adequacy of formulated concepts.Key words: soil-water retention curve, unsaturated soils, deformable media, constitutive modelling. Mots-clés : courbe de rétention d'eau du sol, sols non saturés, médium déformable, modèle constitutif.
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