Comparing roots mechanical characteristics of hornbeam trees in different diameter at breast height classes

Quantifying the mechanical properties of roots is one of the most important issues in stabilizing slopes and modeling soil reinforcement. The aim of this study was to estimate the mechanical properties of hornbeam trees in three stem diameter classes include small, medium, and large trees in Patom district of Kheyrud forest. For this purpose, number of five trees in small (7.5-32.5 cm), medium (32.5-57.5 cm) and large (57.5-82.5 cm) diameter classes were selected and roots on both up and down sides (slope of 20-30 percent) of the trees were collected, then placed between two jaws of the Instron machine. Tensile strength test and tensile force were performed. The results showed that there is a positive power relationship between root diameter and tensile force. In all stem diameter classes at both sides of trees, tensile strength decreases by increasing root diameter based on negative power function. The results of covariance analysis showed that tensile force and tensile strength were significantly different among three stem diameter classes. Tensile force was higher in medium and small trees at up and down sides, respectively. While, in large trees tensile force in downside was more than upside. In medium trees, tensile strength were significantly higher in upside and downside (F=12.9, P<0.05) than small and large trees. Covariate factor (root diameter) was significant in all cases. The results of this study showed that stem diameter of trees and up and down sides of the trees affect the tensile force and tensile strength of hornbeam trees and it is possible to change the amount of tensile strength with age. Therefore, it is necessary to investigate changes in roots mechanical properties in different ages of trees in order to modeling the slope stability.