Abstract: Effective ecological slope protection can be achieved by planting ecological plants on slope reinforced by geogrid.The mechanical mechanism of composite reinforced soil consisting plant root system and geogrid is investigated via triaxial consolidation undrained tests on plain soil,root-reinforced soil,grid-reinforced soil,and root-grid composite reinforced soil with the ecological slope protection project of Guangxi Guilong Expressway as the research background.The mechanical properties of the three reinforced soils are also compared.Results demonstrate that both plant roots and geogrids can increase the strength of reinforced soil,while the composite reinforcement combining roots and geogrids has the best effect.Root-geogrid reinforced soil sees an increase by 265.0%,101.0%,and 33.2% in its cohesion,respectively,compared with plain soil,root-reinforced soil,and geogrid-reinforced soil.Under the optimum geogrid layout,the cohesion of root-geogrid reinforced soil first increases and then reduces with the rising of root content,and reaches its maximum when root content is 0.5%.Analysis on the triaxial test curves of the reinforced soils reveal that the stress-strain relationship of the three reinforced soils is in accordance with the Duncan-Chang model,and the Duncan-Chang model parameters of the reinforced soils are obtained and verified through test data.

Key words: ecological slope protection, plant root, composite reinforced soil, mechanical properties, root content, Duncan-Chang model