Experimental study on the stability of vegetated earthen slopes under intense rainfall

Soil bioengineering using vegetation is an environmentally friendly solution to maintain the stability of shallow earthen slopes. To explore the microscopic mechanical reinforcement mechanism of plant roots on slope stabilization, the stabilities of three soil slopes covered by live grasses in different root morphologies under intense rainfall were examined extensively by both experimental tests and numerical simulations. Highly-bionic root morphological models were developed and validated to simulate the changes in root morphologies and root axes contact-forces. It was revealed that the roots in a uniform morphology effectively strengthened the slope toe through strong shear resistance in the middle and anchoring force at the end of root system; the roots in an upside-down triangular morphology maintained the stability of upper soil slope through its wide upper roots, which extended deeply into the slope interior and hence gave full play to tensile force. Compared with the previous two, the roots in a fusiform morphology had the weakest soil reinforcement and the slope experienced a series of retrogressive failures until the upper residual slope soil collapsed eventually. The significant increase in shear strength of root-soil composites derived primarily from the increase in cohesion. The root axis with the strongest contact-force during slope failure was not necessarily the longest taproot in the middle of root system but a single-root on one side.