THE INFLUENCE OF VEGETATION ROOTS ON SLOPE STABILITY IN LANDSLIDE SUSCEPTIBLE AREAS

Slope protection against shallow landslides using vegetation has been widely applied in civil and environmental engineering throughout the world, but its root role in slope stability has not been studied in Indonesia. This paper provides an indication of the mechanical strength parameters of several species of vegetation roots in the productive forest area on the hillside of Pujon, Malang Regency, East Java, Indonesia. Laboratory tests were conducted to evaluate the physical properties and shear strength of roots with roots and roots without roots [control]. The contribution of root strengthening to soil shear strength with respect to slope stability has been investigated by finite element analysis using Plaxis 2D software. This approach allows quantification of the effect of mechanical root strengthening on slope safety factors and assessment of the sensitivity of slope stability to variations in the cohesion and depth of the root zone, Hr [1 and 2m] and slope [α] between 15o and 45o with numerical simulations. This study showed that roots have shown to increase soil strength. The highest cohesion of the root-soil system was found in P. merkusii (12.03 kN /m2 ), followed by A. dammara (10.24 kN / m2 ) and T. ciliata (8.34 kN /m2 ), the lowest was found in Eucalyptus sp. (8.02 kN /m2 ). Compared to the control those values were 66.8 to 100 times higher, and the average internal friction angle [] decreased by 43% compared to rootless soil. The analysis showed that the effect of root reinforcement on the FOS has increased 14 to 21% for both depths compare to the control. While that of 2 m depth increased 19 to 27% compare to the 1 m. The results also showed that P. merkusii had the strongest roots, followed by A. dammara, T. ciliata, C. arabica and Eucalyptus sp.