Hydraulic hysteresis of natural pyroclastic soils in partially saturated conditions: experimental investigation and modelling

Abstract

In many geotechnical applications, especially in the study of weather-induced landslides, a reliable soil hydraulic characterization in unsaturated conditions is required. Currently, the experimental techniques that neglect the hydraulic hysteresis represent the greatest limitation to landslide forecasting. In this paper, a procedure to obtain an unsaturated soil hydraulic characterization on natural pyroclastic samples is proposed and verified. The approach enables the evaluation of the soil hydraulic properties along the main drying path and wetting/drying cycles to fully quantify the effects of the hydraulic hysteresis. Pyroclastic soil samples collected at a test site at Mount Faito in the Campania region (southern Italy) were tested. The experimental investigation consisted of a sequence of testing phases: a constant-head hydraulic conductivity test, a forced evaporation test followed by several wetting–drying cycles, and a drying test in a pressure plate apparatus. The hysteretic model proposed by Parker and Lenhard (1987) was adopted to fit the data, while inverse modelling of the forced evaporation tests allowed to derive the model parameters. Therefore, the main drying and wetting branches and the soil response to drying and wetting cycles from any reversal point were reproduced with the model, which suitably described the hysteretic behaviour of the pyroclastic soil under all conditions and along all paths.

Soil water retention curves of a silty clayey sand compacted at different dry density

“…The fact that the dry density after compaction is the predominant parameter affecting wetting-induced deformations under vertical stress is also confirmed by [17] and [19]. After saturation, the soil water retention curve (SWRC) of the mixture along the main drying branch was determined by using in series a ku-pF (Umwelt-Geräte-Technik GmbH) commercial apparatus and a Richards plate described in [7,13,[20][21][22]. In the ku-pF apparatus the saturated specimen is subjected to a drying process during which the water content (by weight) and suction up to 80 kPa (by small tip tensiometers) are measured and recorded.…”

Analytical and numerical modelling of air trapping during wetting of unsaturated soils

“…Wen et al, 2020) and the calibration of water retention constitutive models (e.g. Dias et al, 2021) for use in numerical analyses. Appropriate understanding of the true values of the pore gas and liquid pressures, and hence suction, is also significant for the representation of mechanical behaviour by unsaturated mechanical constitutive models (e.g.…”

Calibration of a granular matrix sensor for suction measurements in partially saturated pyroclastic soil

“…From 2015 to 2019, the Mount Faito test site, located in the municipality of Castellammare di Stabia (Naples), was extensively investigated through boreholes to collect undisturbed soil samples for laboratory testing [14,15] and trenches to reconstruct the stratigraphic setting [16]. To monitor matric suction and volumetric water content in the pyroclastic cover, two parcels were selected to install equipment.…”

“…In this regard, several test fields have been set up in Campania region (southern Italy) [10,11]. In particular, field matric suctions were measured by both conventional jet-fill tensiometers and granular matrix sensors (Watermark, Irrometer®) at different depths over two years (from 2017 to 2019) at the test site of Mount Faito, located at the Lattari Mountains, southeast of Naples [12,13,14,15,16].…”