The stability and erosion of natural and man-made slopes is influenced by soil-vegetation-atmosphere interactions and the thermo-hydro-mechanical slope conditions. Understanding such interactions at the source of slope mass-wasting is important to develop land-use planning strategy and to promote environmentally adapted mitigation strategies, such as the use of vegetation to stabilize slopes and control erosion. Monitoring is essential for calibrating and validating models and for better comprehending the physical mechanisms of soil-vegetation-atmosphere interactions. We approached this complex problem by means of an experimental work in a full-scale monitored embankment, which is divided into four instrumented partitions. These partitions are North or South-faced and present a bare and vegetation cover at each orientation. Our main findings show that vegetation enhances rainfall infiltration and decreases runoff, which reduces slope stability and surficial erosion, while plant transpiration induces higher suctions and hence slope stability. Concerning thermal aspects, vegetation reduces the incidence of net solar radiation and consequently heat flux. Thus, daily temperature fluctuations and evaporation decreases. However, the effect of vegetation in the development of dryer soil conditions is more significant than the orientation effect, presenting higher drying rates and states at the North-vegetated slope compared to the South-bare slope.

Slope mass-wasting like shallow slides are mostly triggered by climate effects, such as rainfall, and soil–vegetation–atmosphere (SVA) interactions play a key role. SVA interactions are studied by a full-scale embankment with different orientations (North and South) and vegetation covers (bare and vegetated) in the framework of the prediction of climate change effects on slope stability in the Pyrenees. A clayey sand from the Llobregat river delta was used for the construction of the embankment and laboratory tests showed the importance of suction on the strength and hydraulic conductivity. Sixty sensors, which are mostly installed at the upper soil layer of the embankment, registered 122 variables at four vertical profiles and the meteorological station with a 5 min scan rate. Regarding temperature, daily temperature fluctuation at the shallow soil layer disappeared at a depth of about 0.5 m. There was great influence of orientation with much higher values at the South-facing slope (up to 55 °C at −1 cm depth) due to solar radiation. Regarding rainfall infiltration, only long duration rainfalls produced an important increase of soil moisture and pore water pressure, while short duration rainfalls did not trigger significant variations. However, these changes mostly affected the surface soil layer and decreased with depth.

An attractive approach to reduce the carbon dioxide footprint of deep soil mixing (DSM) is to replace Portland cement-based binders by geopolymers based on metakaolin. Safe design requires a good understanding of the mechanical and hydraulic properties of the improved ground, but very little is known about metakaolin–soil mixtures. For instance, shrinkage during curing is a significant issue for metakaolin-based concretes but has not been previously studied in soilcretes. In this work the permeability and strength of sand- and silty sand-based metakaolin soilcretes are studied under different curing conditions. The development of microcracks induced by geopolymer shrinkage is confirmed through a microstructural study using mercury intrusion porosimetry, scanning electron microscopy and X-ray computed tomography. The influence of microporosity and binder filling on permeability and strength is clarified adapting well-established soil models. A modified Kozeny–Carman formulation is proposed for permeability. A mixture ratio model is calibrated to represent strength. In general, the metakaolin-stabilised materials present excellent mechanical and hydraulic properties, although these are very sensitive to curing conditions.

As society moves towards decarbonisation, it is important to assess the hydromechanical behaviour of binders that could offer a low-carbon alternative to Portland cement in ground improvement technologies. This work considers two such alternatives: one still largely unexplored (metakaolin-based geopolymers) and a better known one (colloidal silica). Results from unconfined compressive strength, permeability tests, undrained monotonic and cyclic triaxial tests on granular soils (sand and silty sand) treated with those two binders are presented and discussed, emphasizing similarities and differences with the response of similar soils treated with other conventional and unconventional binders. Effects of silt content, curing conditions and soil/binder ratios are examined. Both colloidal silica and metakaolin-based geopolymer significantly improve the mechanical properties of the treated soils, although the geopolymer results in a stronger and stiffer material. Both treatments reduce much the permeability of the treated soil, but the reduction achieved with colloidal silica is larger.

Literature studies are presenting counterposed effects of vegetation on soil hydraulic behaviour. Besides, root impacts at the micro-scale are rarely correlated to phenomenological observations due to the complexity of adopting up-scaling factors. In this study, the microstructural causes behind observed changes in vegetated compacted clayey sand’s hydraulic and volume change behaviour were explored. Laboratory experiments were carried out on compacted samples seeded with Cynodon dactylon. Significant changes in soil water-saturated permeability, water retention and shrinkage upon drying were observed after root growth. Laboratory measurements were complemented by the quantification of root morphological features and observations at the micro-scale for different soil hydraulic states. X-ray scans and mercury intrusion porosimetry allowed to cover seven orders of magnitude of pore sizes, shedding light on soil fabric changes at the soil–root interface and the clay aggregate scale. The effects of roots on the soil pore size distribution consisted of Multiphysics phenomena: fissure generation, void clogging and soil aggregation due to roots’ chemical interaction. Furthermore, a good correlation was found between the normalised volume of roots and the micro-pores volume. This new expression was included in a framework to predict soil water retention behaviour considering the aggregated structure and soil–root hydro-chemical interactions.