Abstract: The spatial distribution of the root system has a significant effect on the shear strength of the composite soil. In recent years, the rapid development of the transparent soil test technology provides suitable technical support for visual observation of plant root distribution. Based on the transparent clay manufactured by Carbopol Ultrez 10, the distribution patterns of two plant root systems (tall fescue and vetiver) were visually observed in the growing processes. The growth of rhizomes in natural sand and natural clay was also carried out for comparative analysis. Based on the vane shear test method, the strengths of tall fescue root reinforced composite soil with different spatial distributions (such as vertical, inclined, intersect and mixed) were measured in detail. The optimum root content, root enhancement effect coefficient, and surface reinforcement effect were also discussed. The results show that the optimal root content in the transparent clay material is about 0.35%, and the root enhancement effect coefficient of the mixed root system is the largest, about 1.4-1.5 under this experimental condition.

Key words: vegetation, transparent clay, root compound soil, vane shear test