Abstract
Shallow landslides, either on bare or vegetated slopes, can be triggered after a rainfall event due to loss of suction. An extensive laboratory programme was performed in this study to assess the relationships between water content, plant-induced suction, root biomass and shear strength parameters. Root-permeated soils, planted with combinations of different species, were tested in an inclinable large-scale direct shear apparatus. The effects of mycorrhizal fungi were also investigated with inoculated specimens. The results suggested that the root biomass, as well as root/shoot ratio, was an indicator of plant-induced suction and shear strength of root-permeated soils tested under laboratory conditions. Longer plant growth duration and more species yielded higher mean values of matric suction and normalised shear stress. Mycorrhizal fungi were found to be beneficial in improving the plant functions related to water uptake.
Highlights
The Van Genuchten (1980) closed-form equation establishes a link between the water content and the matric suction – that is, matric suction decreases with increasing water content in partially saturated soils
Mean dry weights of total and non-woody above-ground biomass (AGB) were highest in PLPLM12, while that of woody AGB was observed in PLPHM6
PLPLM12 contained the highest amount of mean root biomass, while PLPLM6 had the lowest
Summary
The Van Genuchten (1980) closed-form equation establishes a link between the water content and the matric suction – that is, matric suction decreases with increasing water content in partially saturated soils. Increase in saturation degree of a slope by water, in the form of rainfall, snowmelt or rising groundwater, can cause loss of suction, which is considered to be the primary triggering effect of landslides (Highland and Bobrowsky, 2008), since a decrease in suction causes a reduction in shear strength (Vanapalli et al, 1996). Interception due to AGB reduces the infiltration, indirectly induces matric suction and delays the saturation process during rainfall (Leung et al, 2015a; Ng et al, 2016a). Vegetation is known to alter soil-water retention characteristics (Leung et al, 2015b) and the soil permeability (Vergani and Graf, 2016)
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