(1. Key Laboratory of Geological Hazards on Three Gorges Reservoir Area of Ministry of Education，China Three Gorges University，Yichang，Hubei 443002，China；2. College of Civil Engineering and Architecture，China Three Gorges University，
Yichang，Hubei 443002，China)
Abstract：In biotechnical slope protection engineering，the spatial distribution of plant roots exerts an important impact on the strength of root-soil reinforced composite. Two common plants，i.e. medicago sativa and cynodon dactylon，were planted in containers. Till the roots penetrating the whole soil (referring to base material of vegetation-growing concrete)，direct shear tests along the soil depth on the undisturbed soil and root-soil composite system are conducted respectively，and the fractal characteristics of roots are analyzed. The relationship between cohesive strength added value and the fractal characteristics of vegetation roots is to be studied by contrast. The results show that：(1) The shear strength of soil increases evidently after roots distributing in soil，especially the added value of cohesive strength increases obviously，but the increasing amplitudes of medicago sativa and cynodon dactylon manifest very significant difference. (2) The roots of the two plants both have fractal structure，the more biomass and well-distributed of roots in soil，the fractal dimension is comparatively larger. (3) The cohesive strength added value of soil is significantly positively correlated with the fractal dimension of the vegetation roots.
2011, Vol. 30 
