Monitoring of a Full-Scale Embankment Experiment Regarding Soil–Vegetation–Atmosphere Interactions

Abstract

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.

Multi-scale effects on the hydraulic behaviour of a root-permeated and compacted soil

“…Main drying results using tensiometer for bare and root permeated soils. Comparison of results obtained for this study and by [14] for the same soil.…”

“…Laboratory studies were performed on a silty sand retrieved at the Llobregat river's delta in Barcelona. Its physical properties are summarised in Table 1 and further detailed in [14]. The same low-plasticity soil was used to build a full-scale embankment currently under monitoring for investigating soil-vegetation-atmosphere interactions [14].…”

“…Its physical properties are summarised in Table 1 and further detailed in [14]. The same low-plasticity soil was used to build a full-scale embankment currently under monitoring for investigating soil-vegetation-atmosphere interactions [14]. For this study, the retrieved soil has been sieved at 9.5 mm.…”

“…For this study, the retrieved soil has been sieved at 9.5 mm. [14] Eight cylindrical specimens (150 mm in diameter and 70 mm in height) were statically compacted in PVC pots at a water content of w = 15%, matric suction s = 40 kPa and dry density 1.60 Mg/m 3 (point 'A' in Fig. 1).…”

Overview of Landslide Hydrology

“…These factors influence the timing of landslides with respect to precipitation inputs and antecedent soil moisture [14][15][16][17], the mass and mode of failure [18], and the extent of runout or transformation of landslides into debris flows [19].Both the infiltration of rainwater and snowmelt and bedrock exfiltration provide the local trigger of these landslides, while drainage and evapotranspiration tend to stabilize hillslopes by rerouting and removing subsurface water. Subsurface hydrology is strongly affected by preferential flow within the soil, substrate topography, and exfiltration from fractures in bedrock [2,13,18,[20][21][22]; the overall regolith moisture regime and recharge rates are influenced by evapotranspiration, soil development processes, soil water-groundwater interactions, and landform aspect and shape [14,16,[23][24][25]. The dynamic behavior amongst these interacting hydro-eco-geomorphic components evolves across spatial and temporal domains creating the conditions for landslide initiation.…”