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.
Highlights
Several geotechnical problems in unsaturated soils require an in-depth understanding and modelling of the hydraulic relation between matric suction and water content, which is known as the water retention curve (WRC) [36]
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
With respect to previous studies on the hydraulic hysteresis of pyroclastic soils performed on site, we present a complete laboratory procedure of experimental techniques devoted to calibrate a hysteretic model
Summary
Several geotechnical problems in unsaturated soils require an in-depth understanding and modelling of the hydraulic relation between matric suction and water content, which is known as the water retention curve (WRC) [36]. These curves play an important role in the assessment of unsaturated soil property functions such as the hydraulic conductivity, volume change and shear strength [70, 73]. The analysis of the phenomena governing landslide triggering requires both (i) monitoring of hydrological and meteorological processes [45, 55] and (ii) hydraulic and mechanical characterization of natural soils [39, 40, 66]. Representative testing sites of different regional geological contexts were instrumented to monitor the weather conditions, soil matric suction, and soil water content to investigate the field hydraulic properties of pyroclastic soils [12, 13, 15, 21, 33, 45, 48,49,50,51,52,53,54]
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