Abstract: To explore the effect of compaction and vegetation root content on the shear strength of the modified expansive soil, The root-soil composite samples of the modified expansive soil were prepared, and the direct shear tests were performed. The test results showed that the shear strength behavior of the remolded root-soil composite samples conform to the Coulomb equation. The shear strength of composite samples increases with the increase of the degree of compaction as well as the root content. With the increase of the degree of compaction, the cohesion and the internal friction angle increase, but the increase of the cohesion is greater than that of the internal friction angle. There is a positive correlation between the root content and the cohesion, c, while the internal friction angle, φ, has little relation with the root content; the m value of reshaped soil samples with roots is between 1.31 and 2.31, and the bermudagrass root-soil composite is at the low positive. It is more effective to improve the strength of the soil under the lower stress than the higher stress. The bermudagrass root system has a better effect on the shallow reinforcement of the slope; the plant root system has a good reinforcement effect on the modified expansive soil which significantly enhances the shear strength of the base material. Compared with the remolded soil, the binding force between the root and the soil of the undisturbed soil is larger, and the root system has a more obvious strengthening effect on the strength of the root-soil composite.

Key words: Modified Expansive Soil, Root-Soil Composite, Shear Strength Parameters, Degree of Compaction