Alessandro Tarantino

Alessandro Tarantino 
University of Strathclyde, Glasgow, Scotland (UK)

Alessandro Tarantino is Professor of Experimental Geomechanics at the University of Strathclyde in Glasgow, Scotland. His current research interests include the direct measurement of water tension in soils and plants, micromechanical behaviour of saturated and unsaturated clays, soil-plant-atmosphere interaction, and stability of natural and engineered slopes subjected to rainwater and floodwater infiltration. 
He has led major European consortium research projects including the Marie Curie European Training Network 'TERRE (’Training Engineers and Researchers to Rethink geotechnical Engineering for a low carbon future, 2015-2019). He is co-editor of the books ‘Advanced Experimental Unsaturated Soil Mechanics’ (2005) and ‘Laboratory and Field Testing of Unsaturated Soils’ (2009).
He has been keynote/theme lecturer at numerous International Conferences (the 16th IACMAG Conference 2022 the most recent one) and will deliver the next  ICE Géotechnique Lecture (October 2023).

Themed Lecture

Plant-based hydrological reinforcement of slopes

Plants represent a potential Nature Based Solution to improve stability of natural and engineered slopes. Plants can reinforce slopes hydrologically by removing soil water via transpiration to generate stabilising suction. In turn, the depletion of soil water content reduces the hydraulic conductivity of the shallow layers, and this hinders rainwater infiltration during the wet period possibly preserving suction in the deeper layers susceptible to failure. Plant-based hydrological reinforcement is key to reinforce slopes for the very frequent case of failure surfaces developing below the root zone (where root mechanical reinforcement obviously plays no role).
Evapotranspiration occurs in two different regimes, ‘energy-limited’ and ‘water-limited’ respectively. Energy-limited (potential) evapotranspiration occurs when the soil-plant system can supply the water demanded by the atmosphere. When the degree of saturation and, hence, the hydraulic conductivity of the soil declines, the soil-plant system is not able to accommodate the evaporative demand of the atmosphere and the evapotranspiration reduces (water-limited regime). A very convenient and widely adopted empirical approach to model water uptake by vegetation in these two regimes is to multiply the potential evapotranspiration PET by a reduction factor assumed to be a function of soil suction in the root zone (e.g., Feddes function). This approach is convenient in geotechnical numerical modelling because only requires information about the suction in the root zone without the need to address the complex interaction between the soil, the plant, and the atmosphere. However, this simplicity is only apparent because the complexity of such an interaction is hidden in the ‘empirical’ choice of the parameters of the reduction function.
To improve upon vegetation-based hydrological stabilising technique, it is vital to develop physically-based transpiration models that account for the hydraulic characteristics of the soil, the plant (below- and above-ground), and the atmosphere in order to guide the choice of suitable plant functional traits. This presentation i) discusses the conceptual, practical, and experimental limitations of ‘routine’ evapotranspiration reduction functions, ii) revisits the plant science literature to identify the bottlenecks generating the decline in evapotranspiration in the water-limited regime, iii) presents the development of a closed-form transpiration reduction function built upon the concept of Soil-Plant-Atmosphere Continuum (SPAC), and iv) illustrates the application of the High-Capacity Tensiometer to the measurement of xylem water potential to underpin the experimental characterisation of the SPAC-based reduction function.