Soil Reinforcement Modelling on a Hilly Slope with Vegetation of Five Species in the Area Prone to Landslide in Malang, Indonesia

Malang Indonesia is an area prone to landslides, resulting in the need to model soil reinforcement to determine the vegetation’s slope stability using the roots of five species. One of the methods to improve the stability of slopes prone to landslides is adequate vegetation preservation. Soil strengthening with vegetation roots is environmentally friendly and an inexpensive alternative to reduce the vulnerability of slopes along mountainous slopes and the risk of shallow erosions. Therefore, this study aims to evaluate the vegetation arrangement on the slopes in Malang Regency, Indonesia, with a view of geotechnical engineering on the role of its root characteristics. Slope stability was analyzed by modeling the distribution of vegetation roots as an equivalent cohesion approach, where the factor of safety (FoS) is calculated using the PLAXIS-2D version 86 software. Soil and root parameters were obtained through direct shear testing and examining five plant species’ tensile strength. The results showed that the highest stability is achieved when the position of the vegetation on the slope’s surface is compared to the top. The factor of safety (FoS) increased from 23% to 30% and from 28% to 31% for slopes with uniform and combined species. Of the five plant species, P. merkusii demonstrated some advantages in maintaining stability because it has better root mechanical properties, among others. However, the combined species, such as C. arabica, had better performance because they possess vertical and lateral root systems, which act as an anchor in penetrating and griping the soil. This means combining vegetation species is a preferable preventive measure to increase slope stability. The analysis results also demonstrated the significance of vegetation on slope stability. The results show that the FoS decreases when the slope angle increases and reaches its maximum when the species are combined. The mechanical effect of the plant root matrix system can increase the shear strength of the soil, thereby raising the slope stability. The density of roots in the soil mass and the tensile strength contribute to the soil’s ability to withstand shear stresses.