عنوان مقاله [English]
Planar failure is one of the most common types of riverbank destruction worldwide. Annually, it destroys much fertile soil and leads to the collapse of nearby infrastructure. The angle of riverbanks after failure plays an important role in defining the geometry of a failed block when analyzing the stability of this type of failure. Studies published thus far estimate the angle of the riverbanks after planar mass failure, but they fall short because they only can be used for homogeneous bank material. No relation has been introduced to estimate the angle of different layers in a multi-layered river bank. This research used a physical model in a laboratory consisting of two layers of soil and measured the angle of failure of the bank for different soil layers. Two relationships to estimate the amount of upper and lower bank failure angles are introduced using two-thirds of the measured values for each layer. Evaluating these relationships using one-third of the measured values results in a mean relative error of 0.14 and 0.015 for the upper and lower bank layers, respectively. Another relationship is introduced and its results compared with those obtained from available relationships using the mean of physical and mechanical specifications of the banks and by imaging a homogenous river bank. The results show that the river bank angle of failure after planar mass failure is better estimated using the new relationship and it can be used to estimate the angle of the river bank for both multilayered and homogenous river banks.