Determination of Permissible Shear Stresses on Vegetation Mats by Soil Loss Evaluation

Abstract

By the activation of environment-friendly river works, application of vegetation mats is increasing, however, evaluation techniques for hydraulic stability of vegetation mats are not presented. This study is conducted to develop the objective test method for vegetation mats. Two kind of vegetation mats are tested by the real scale experiments, and hydraulic quantities are measured and analyzed to evaluate acting shear stresses. To evaluate soil loss, Terrestrial 3D LiDAR measurement is conducted and soil loss index are calculated from changes of bed elevation. Quantified evaluation for permissible shear stresses is conducted by graphical method for acting shear stresses and soil loss index. By the results of precision survey, changes of sub soil are limited to local range in stable cases and relatively large changes of sub soil which is similar to natural river bed are detected in unstable cases. From the study, evaluation of permissible shear stresses by ASTM D 6040 is avaliable in the failure mechanism and failure criteria by soil loss index.