Effect of Oriental beech root reinforcement on slope stability (Hyrcanian Forest, Iran)

Abstract

Vegetation significantly affects hillslope mechanical properties related to shallow landslides and slope stability. The objective of this study was to investigate and quantify the effect of Oriental beech root reinforcement on slope stability. A part of Hyrcanian forest in northern Iran was selected for the study area. To do the research, the Wu model (WM) was used and data related to the distribution and tensile strength of Oriental beech roots were collected. Root distribution was assessed using the concept of the root area ratio and trenching method. Laboratory tensile tests were conducted on fresh roots for strength characteristics. The factor of safety was calculated for two different soil thicknesses (1 and 2 m) and slope gradients between 10 and 45°. The results showed that the root distribution generally decreased with increasing soil depth and the mean root strength value was 38.23 ± 1.19 MPa for 0.35–5.60 mm diameter range. The results verified a power relationship between tensile strength and root diameter. The reinforcement effect (C_r) decreased with depth and the strongest reinforcement effect was in the second soil layer (10–20 cm) which showed a shear strength increase of 1.47 kPa. The increased factor of safety due to the presence of roots in one- and two-metre soil thicknesses was 27–44% and 15–26%, respectively. The improvement effect of roots was increased with increasing slope gradient and shallower soil thicknesses.