Abstract
Vegetated soil’s shear strength has been usually assessed through direct shear tests and under triaxial compression stress paths while less is known about its behaviour under tensile stress. Tensile strength and shrinkage-induced cracking play a crucial role in the hydro-mechanical response of earth structures exposed to drying/wetting cycles. For this purpose, a new device for direct tensile tests has been designed and used to let plants grow in compacted soil samples. The equipment consists of two cylindrical moulds connected to each other by a soil bridge in which failure upon pulling is induced due to geometrical constraints. Different soil’s mechanical responses were observed depending on whether suction was low or high. Indeed, it was detected an increase of soil tensile strength and a more brittle behaviour as suction was increasing. However, at the same suction, vegetated soil’s response was more ductile than that of the corresponding bare soil. Results were analysed within a shear strength criterion for partially saturated soils. The analysis evidenced an increase in shear strength in the vegetated soil. A correlation was found between this increase and the roots’ mechanical and morphological features.
Highlights
Introduction and backgroundGlobal warming has led to more extended periods of drought and isolated heavy rainfalls
This paper presented results using a new apparatus that allowed testing a compacted partially saturated sandy soil under direct uniaxial tensile stress, with the facility of growing plants inside it
Soil matric suction was monitored throughout the tensile tests and the degree of saturation evaluated with a specific procedure at the end of each test
Summary
Global warming has led to more extended periods of drought and isolated heavy rainfalls These events are detrimental in fine-grained soils: very intense drying and wetting cycles generate cracks and alter their hydro-mechanical and structural properties [1,2]. Plant roots were found to enhance soil shear strength [6,7], but less is known about their effects on soil tensile behaviour and shrinkage-induced cracking. This lack of knowledge may lead to an incorrect prediction of the sliding surface of a landslide, as proved by recent research [8]
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