Effect Of Herb Roots On Shearing Strength In Vegetation-Growing Concrete Matrix

Plant roots are playing an important role in slope shallow protection and plants are widely used in slope ecological restoration projects. With strong roots system and fast growing speed, roots of herb plants could form three dimensional space structures in a short time. It would be reasonable to believe that herb plants play far more important role than trees and shrubs in slope ecological prophase protection.In this paper, two commom herb plants Alfalfa and Cynodon Dactylon were planted in vegetation concrete base material and take the blank plot of vegetation concrete base material as CK, roots structures characteristics and shearing strength characteristics in varied periods and varied depths, the relationshilp between roots structures characteristics and shearing strength were analysed. What's more, shearing strength values calculated by mechanics models were compared with the anti-shear strength values of the experiment. The field sampling method could maintain the roots distribution characteristics in natural state. The main conclusions are as follows:1)Plant root fractal dimensions increased with growing period which means that plant roots grew more branching roots and lateral roots, showing better filled capacity. The root fractal dimensions of Alfalfa and Cynodon Dactylon in different depths varied, and both had a tendency of increased first and then decreased. With more branching roots and lateral roots, root fractal dimensions increased while for the decrease of roots contents and roots diameter with soil depth, root fractal dimensions decreased.2) The shear strength of all the three plots satisfied the Mohr - Coulomb criterion. The shear strength of the blank control plots changed lightly over time for the blank control plots was unvaried in substrate with time and depth if neglect the effect of water and the dead weight of soil. While that of Alfalfa and Cynodon Dactylon plots had a growing tendency with time for plants roots grew stronger ang form better 3D space structures.3) Compared with the blank control plots, it indicated that contribution to soil shear strength of root-soil composite was substantial. The soil cohesion added values caused by root-soil composite were big, the growth rate of soil cohesion caused by Cynodon Dactylon reached as high as 128%, while that of Alfalfa was 157%. The minimum amplification of soil cohesion caused by Cynodon Dactylon and Alfalfa were 48% and 18%, respectively. The influence over soil internal friction angle of roots was small. 4) The results suggested that soil shearing strength amplification may be related to root fractal dimension, the amplification of shearing strength increased first and then decreased with root fractal dimensions. Bigger root fractal dimension, better coordination of roots-soil composite leading to greater anti-shear strength. When root fractal dimension was too big, the shearing strength decreased for the shear dilatation behavior as there were too many roots in soil.5) The shearing strength of root-soil composite calculated by mechanical models validated the results of the experiments. The shearing strength amplifications calculated by mechanical models were bigger than those values measured by test. This might because that the mechanical models considered all roots broke at the same time which was not the same as the experinment. What's more, shear plane in the experiment was not the feeblest surface, sometimes.In this paper, take the vegetation concrete base material and two commonly used herb plants as the base material of the three test plots to analyse the added value of root-soil composite shearing strength and the relationship between soil shearing strength amplification and root fractal dimensions has a special significance in the further research, ecological benefit evaluation and its application of vegetation concrete base material ecological protection technology.