Numerical And Experimental Research Of Limit Loads Of Soil-root Composites

The vegetation roots play a very important role in reducing soil erosion by means of being embedded in, entangled in and enwrapped in soil. The vegetation have been used to improve shallow slope stability and reduce geological disasters for several hundreds years. However, the mechanical mechanism of the soil-roots composite is still not very clear today. In Loess Plateau, Qinghai Province, China, the roots of vegetation grow unidirectional and arrange periodically, so the soil and the roots can be considered as a kind of homogeneous long fiber reinforced composites. In this dissertation, the mechanical mechanism of soil-roots composites is studied through numerical simulation and experimental study.Based on the homogenization theory and generalized plane strain assumption, a kind of numerical method to analysis the homogeneous long fiber reinforced composite is established. A representative volume cell is chosen to reflect the microstructure of a periodic composite. By introducing the macroscopic and microscopic scale, the generalized plane strain element is constructed based on microscopic fluctuation displacement. The corresponding elas-plastic incremental finite element equation is established. In the state of generalized plane strain, a kind of interface element is developed based on microscopic fluctuation displacement to simulate the weak interface between the matrix and the fiber. And the corresponding numerical method is established.The properties of soil-root composites were obtained in experiments conducted in Qinghai Province. A kind of experimental method for the limit load of the soil-root composites was proposed. The sample preparation process was modified for the soil-roots composites. In the experiment, two soil-root composites specimens with the root fraction of 0.5% and 1%, respectively, were submitted to triaxial test. The limit loads and failure mode were obtained. In addition, the basic properties of the roots and the natural soil were measured from experimental tests for the numerical simulation. The finite element models of the representative volume cell are established based on the numerical method proposed in this dissertation. The numerical limit loads of soil-root composites are obtained and compared with the experimental values. Good agreement of limit loads has been achieved between the numerical and the experimental results. The relationship between limit loads and the angle of load is obtained. And the effects of material parameters on limit loads are also studied.