Abstract
Direct shear tests on soil specimens including roots of Festuca rubra L. and Phalaris arundinacea L. based on the soil dressing seed spraying Engineering were conducted under the methods both of unconsolidated-undrained (UU) test and of constant pressure shear. Here, we discussed the relationships between the shear characteristics of soil specimen including roots of herbaceous plants and the soil cover thickness. When the soil specimen included the roots of herbaceous plants, the cohesion, c values increased, but the angle of shear resistance ,φ values stayed. Also, the c values tended to large with the thinner soil cover. The c values of P. arundinacea were larger than F. rubra with any soil cover thickness. However, the c values of F. rubra decreased to the cblank (1.1 kN/m2) including no roots with 1.5 cm or larger in the soil cover thickness. The root length density had a negative correlation with the soil cover thickness, had a positive correlation with the c values in both of F. rubra and P. arundinacea. Therefore, the c values were affected by growing condition of the roots in the soil specimens. F. rubra needed about 1.0 cm of the soil cover thickness to keep the strength of the c values. While P. arundinacea showed good growing condition and high c values with any soil cover thickness, and high applicability of the revegetation engineering for the slope conservation in the cold region with snowfall.
