Analysis of soil shear strength of tropical plants with direct shear test and simple perpendicular model

Eight trees of similar age of Acacia mangium and Macaranga tanarius were selected along East-West Highway, Malaysia. To analyze the effect of tree roots on soil shear strength, the direct shear tests were used by manually pushing the cylindrical shear box in rooted soil with known volume (63.4 mm diameter * 20 mm height), simultaneously, the root area ratio and root tensile strength analyzed by digging the soil 70 cm in depth and 50 cm in width. Direct shear test machine were used to calculate the soil cohesion of rooted soil and also Wu/Waldron model were used to calculate the additional soil cohesion due to roots. The results of both analysis showed that the cohesion of M. tanarius soil-root syetem is more than that of A. mangium.