A Comprehensive Study on Young Roots of Acacia mangium Willd. Species for Soil Bioengineering

Soil bioengineering has been leveraged for controlling shallow landslides and soil erosion. Acacia mangium Willd. species is widely used for soil bioengineering, but its root properties have not been extensively investigated. This study aimed to measure the various properties (i.e., morphological traits, biomechanical properties, chemical composition and root reinforcement) for establishing roots of A. mangium Willd. species through a series of laboratory experiments (i.e., rhizobox observation, uniaxial tensile test, direct shear and volumetric water content and suction monitoring). The results underscored the rapid growth (i.e., 0.43 +/- 0.01 cm/day) and highlighted variations in "side" root area ratios of A. mangium Willd. species with depth. Root orientation also demonstrated a significant correlation with root diameter following a linear model (p < 0.05, R-2 = 0.39). At the early-stage establishment (28 weeks), A. mangium Willd. roots exhibited the tensile strength, Young's modulus and mechanical reinforcement of 10.18 +/- 0.62 MPa, 325.18 +/- 21.72 MPa and 3.15 kPa, respectively. The presence of roots was found to increase the soil suction, air-entry value and saturated water content of lateritic soil by improving the soil-water characteristic curve. This work elucidated the root properties of A. mangium Willd. during the early-stage establishment, raising caution for the design of slope-stabilisation projects using soil bioengineering, especially during the initial phase of projects.