Abstract
Abstract. In the last decades, in Campania (southern Italy), steep slopes mantled by loose air-fall pyroclastic soils have been the seat of shallow, fast, rainfall-induced landslides. The occurrence of such events has been the result of the combination of critical rainstorms and of unfavourable initial conditions determined by antecedent infiltration, evaporation, and drainage processes. In order to understand the nature of the phenomena at hand and to clarify the role of all influencing factors, an automatic monitoring station has been installed in an area already subject to a recent killer flowslide (December, 1999). The paper reports data collected in 2011 about volumetric water content and suction (used to investigate the soil water retention features) and rainfall depth and temperature (providing the boundary conditions). In particular, the installation at the same depths of tensiometers and time domain reflectometry (TDR) sensors allowed us to recognise the hysteretic nature of the wetting and drying soil response to weather forcing and its influence on the slope stability conditions. The data reported in the paper are freely available at https://doi.org/10.5281/zenodo.4281166 (Comegna et al., 2020).
Highlights
The hydraulic response of unsaturated soils subjected to infiltration and/or evaporation phenomena is usually modelled through the well-known Soil Water Retention Curve, SWRC, correlating matric suction, s, with volumetric water content, θ
Even though the relationship between measured volumetric water content and suction values has to be carefully considered and has to account for all the factors which can adversely affect its validity, monitoring provided useful information about the hydrological soil response
Collected data highlight the influence of the initial conditions, which depend on the antecedent wetting and drying history and on the weather-induced hydraulic paths
Summary
The hydraulic response of unsaturated soils subjected to infiltration and/or evaporation phenomena is usually modelled through the well-known Soil Water Retention Curve, SWRC, correlating matric suction, s, with volumetric water content, θ. Experimental evidence and theoretical considerations (e.g., Mualem, 1976; Pham, 2002; Wheeler et al, 2003; Tami et al, 2004; Li, 2005; Tarantino, 2009; Yang et al, 2012; Pirone et al, 2014; Comegna et al, 2016c; Chen et al, 2017, 2019; Rianna et al, 2019) indicate that the SWRC is not univocal but may depend on soil initial conditions and on the induced wetting or drying paths This soil response, known as hydraulic hysteresis, may be related to microscopic phenomena affecting the energy state of water at pore scale (i.e. variations in contact angle during solid particle wetting and drying or bottlenecks differently affecting filling and emptying of pores), as well as macroscopic phenomena depending on the boundary conditions and on the rate of the specific transient wetting and drying process (e.g. air entrapment). In some cases, if the wetting process is very slow, it may occur that θs,w ∼= θs,d
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