Assessment of shear strength increment and measurement of direct shear test on rooted soil sites

This study performed the field direct shear tests on soil samples after on-site soil preparation, digging, and production. The direct shear tests were proceeded and the relationship between the shear strength and the lateral displacement was established simultaneously. After the test, the number of roots on the shear plane was counted and then the plant roots around the samples were extracted to measure the roots diameter and length and conduct direct tensile tests. According to the data obtained from experiments, the statistical analysis was performed to obtain the parameters for the root strength modelstudy. Because the field plants exist in the poor-drained sandy and non-uniform grained soils, the roots of the plants on the field soils appear to be more complicated. It is not easy to evaluate, the shear strength increment of the soil using the model analysis with simple assumptions. Hence, this study used shear zone thickness and average root-soil bond strength as variables to explore the influences of these variables on the shear strength increment of rooted soils. By comparing with the result of the model analysis and the on-site test, it was found that, as the lateral displacement of the soil increased, the shear zone thickness increased and the average root-soil bond strength decreased.