With the advent of modern microstructural testing techniques and microstructure based constitutive models the microstructural characterisation of soils is gaining prominence. This paper reviews the history of microstructure investigation in unsaturated soils and discusses the engineering significance of this research to date. After a brief overview of the main microstructural techniques, the paper focuses on the evaluation of the current state of use and the development of two widely used techniques to study the microstructure of partially saturated soils, namely mercury intrusion porosimetry and the environmental scanning electron microscopy. The details of these techniques, their advantages and limitations, are first covered, followed by the presentation of selected test results. These results highlight the use of these techniques for understanding different hydro-mechanical behavioural features observed at macroscopic scale. Specifically, the paper shows the use of these techniques to explore the fundamental properties of water retention characteristics, water permeability, and micro and macrostructural interactions along different hydro-mechanical paths.

Microstructure Investigation in Unsaturated Soils: A Review with Special Attention to Contribution of Mercury Intrusion Porosimetry and Environmental Scanning Electron Microscopy

https://hal-enpc.archives-ouvertes.fr/hal-00629665/document

Desiccation and cracking behaviour of clay layer from slurry state under wetting-drying cycles

Impact of cyclic wetting–drying on swelling behavior of lime-stabilized soil

Rainfall-triggered landslides are among the most widespread hazards in the world. The hydrology in and around a landslide area is key to pore pressure buildup in the soil skeleton which reduces shear strength due to the buoyancy force exerted by water in a saturated soil and to soil suction in an unsaturated soil. Extraordinary precipitation events trigger most of the landslides, but, at the same time, the vast majority of slopes do not fail. The intriguing question is: ‘When and where exactly can a slope become triggered to slide and flow downwards?’ The objective of this article is to present and discuss landslide hydrology at three scales—pore, hillslope, and catchment—which, taken together, give an overview of this interdisciplinary science. We argue that ‘filling, storing, and draining’ of water are all equally relevant to understand and to quantify landslide behavior. Furthermore, by addressing landslide hydrology from both earth sciences and soil mechanics perspectives, we aim to manifest the hydrological processes in hillslopes and their influence on behavior and triggering of landslides and vice versa. The challenge of landslide hydrological research is matching, at hillslope scale, causal hydrological processes with detailed physics of triggering mechanisms. At the same time, mass movements initiate changes in the hydraulic character of the soil which are important for better understanding short- and long-term hydrogeomorphic responses of soil and hillslope. Interdisciplinarity is key in advancing our knowledge on water flows in (un)stable slopes.



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Landslide hydrology: from hydrology to pore pressure

https://hal.archives-ouvertes.fr/hal-00418913/document

An experimental study of the water transfer through confined compacted GMZ bentonite

Expansive bentonite-sand mixtures in cyclic controlled-suction drying and wetting

Granular mixtures made of high-density pellets of bentonite are being evaluated as an alternative buffer material for waste isolation. Ease of handling is an often-mentioned advantage. The paper described the experimental program performed to characterize the hydromechanical behaviour of compacted pellet’s mixtures used in the engineered barrier (EB) experiment. The material tested in the laboratory was based in the pellet’s mixtures actually used for the emplacement of the EB in situ experiment. Grain size distribution was adjusted to a maximum pellet size compatible with the specimen’s dimensions. Dry densities of statically compacted specimens varied in most of the cases in the range: 1.3–1.5 Mg/m 3 . Pellets had a very high dry density, close to 2 Mg/m 3 . The outstanding characteristic of these mixtures is its discontinuous porosity. Pore sizes of the compacted pellets vary around 10 nm. However the inter-pellet size of the pores is four to five orders of magnitude higher. This double porosity and the highly expansive nature of the pellets controlled all the hydraulic and mechanical properties of the mixture. Tests performed include infiltration tests using different water injection rates and mechanisms of water transfer (in liquid and vapour phases), suction controlled oedometer tests and swelling pressure tests. The interpretation of some of the tests performed required backanalysis procedures using a hydro-mechanical (HM) computer code. Material response was studied within the framework of the elastoplastic constitutive model proposed by Alonso et al. [Alonso, E.E.,

https://upcommons.upc.edu/bitstream/handle/2117/2225/69.pdf;sequence=1

Hydro-mechanical behaviour of bentonite pellet mixtures

Compacted granular mixtures of high-density bentonite pellets have been evaluated as an alternative buffer material to fill the empty space around nuclear waste disposal canisters in horizontal drifts. Despite the obvious benefits of these compacted mixtures (the backfilling operation becomes easier and the gaps between the host rock and the buffer are minimised), there are several aspects of concern such as the effective blockage of the large inter-pellet pores due to granule swelling – this blockage improves the water permeability properties – and the tendency to develop initial collapses before reaching an adequate swelling pressure. Selected test results of a comprehensive laboratory experimental programme are presented to gain insight into the hydromechanical response of this multi-porosity compacted material. To improve the information on local transient behaviour, simulation-assisted techniques using a double-structure constitutive model are used. The paper presents a physically based one-dimension...

C. Hoffmann

Papers

Expansive bentonite-sand mixtures in cyclic controlled-suction drying and wetting

Hydro-mechanical behaviour of bentonite pellet mixtures

Hydromechanical behaviour of compacted granular expansive mixtures: experimental and constitutive study

Gb-SAR interferometry displacement measurements during dewatering in construction works. Case of La Sagrera railway station in Barcelona, Spain

Combining different controlled-suction techniques to study expansive clays