Influence of root fractal dimension on soil shear strength with 3D printing method

The rapid development of expressway provide convenience for our life. But during the construction and operation, the slope instability is a serious ecological problems which can threat the normal use of the expressway. As slope protection is essential, the ecological slope protection is an environmental friendly method to reinforce the slope stability as the root can make contribution to the soil shear strength. From the macro perspective, the soil reinforced ability of root system is greatly affected by the structure and distribution morphology of plant root system. So it is crucial to study the influence of root distribution characteristics on the soil shear strength. As the structure of plant root has typical fractal feature, fractal dimension which is the most important quantitative parameter is chosen to establish the relationship with the soil strength. Because the structure of the plant roots is very complex and no two roots are identical, it is difficult to find the same root to conduct contrast tests. But at least four tests with different cell pressures are essential to obtain the cohesion and internal friction angel. Thus 3d printing method is a superior choice to ensure each test condition is as same as possible. The purpose of this study is to explore the relationship between the root fractal dimension and soil cohesion, and internal friction angel. In order to reduce the influence of root difference on the triaxial compression test, 3D printing method is applied to make simulative plant roots which can maintain the fractal dimension. So single variable experiment could be guaranteed, the general rule between fractal dimension of root system and soil reinforced ability can be revealed. Four roots of Cynodon dactylon with different fractal dimension were chosen to establish 3D printing model. Corresponding to each fractal dimension, four triaxial compression test were conducted with four cell pressure. The results indicate that both of the cohesion and internal friction rise with the increasing of the fractal dimension, but the influence of fractal dimension on cohesion is slight compared with the influence on the internal friction. That is to say, the root with larger fractal dimension possess better reinforced effect on slope soil by increasing the the internal friction.