Evaluation of effect of tree roots on shear strength of soil due to root water uptake

Abstract

Tree roots play a major role in ground and slope stabilization by increasing the strength and stiffness of the soil positively. When evaluating how vegetation affects ground improvement, tree roots are the primary factor because that they improve the strength of the soil with the help of their mechanical properties and provide the additional soil suction by the root water uptake. Previous studies, however, focused on the mechanical and hydraulic impacts of tree roots separately when evaluating the impact of vegetation, which failed to yield reliable results because suction influences on mechanical characteristics of tree roots. Recent laboratory research has shown that the mechanical interactions between roots and soil, such as root tensile strength and root cohesiveness, are suction-dependent. There are still significant gaps in knowledge regarding the effects of suction and root concentrations on root reinforcement despite these extensive previous research. This study investigated the influence of matric suction on root reinforcement of the Alstonia macrophylla with Sri Lankan Silty Sand using large-scaled direct shear tests. Cohesion due to root reinforcement of the Alstonia macrophylla should theoretically equal to the difference between the apparent cohesion of reinforced and unreinforced shear strength in saturated samples. This value was 2.99 kN/m2 when RAR, dry biomass of roots per unit volume of soil, and total leaf area of the plant were 6.22 x 10-3 %, 0.575 kg/m3 and 1195 cm2 respectively. However, the cohesion due to root reinforcement of the Alstonia macrophylla is slightly increased with the matric suction in the Sri Lankan Silty Sand as per the research outcomes