Amorpha f ruticosa

Leapedeza and Cynodon dactylon

as well as their root-soil composites

were used as the research objects

a comparative analysis was made for the effects of different root contents and plant roots on the shear strength of root-soil composite through laboratory shear tests. Results showed that the shear strength was enhanced by roots and increased with the increased root amount.However

if root amount reached a certain value

the shear strength of root-soil composite did not increase obviously

i.e.

there is an optimum range of root amount.Compared with the cohesion of soil without roots

there was no significant change in the internal friction angle of root-soil composite

but the cohesion was greatly increased.The increased percentages of cohesion for Amorpha fruticosa

Leapedeza and Cynodon dactylon were 47.5%

39.2% and 38.9%

respectively.The effects of the rootsoil composites of Amorpha fruticosa

Leapedeza and Cynodon dactylon on the shear strength were different.This implies that planting shrub species could effectively increase slope stability and efficiently reduce soil erosion in the regions suffering from soil and water loss.