Influence of grass plantation on the rainfall-induced instability of gentle loose fill slope

Abstract

The understanding of rainfall-induced landslides on gentle, loose-fill slopes is limited in comparison to steep slopes. Hence, two physical model tests were conducted on silty sand slopes under continuous rainfall: one on a bare slope and the other on a slope planted with ryegrass. The slope angle of 25° is much lower than the internal friction angle of slope material (34.3°), which makes the model test fall well into the category of gentle slope. For the initially unsaturated bare slope, a rainfall event with return period of 18 years could trigger a rapid and retrogressive global sliding, which differs from previous findings that gentle slopes would only experience shallow failure. A sudden increase in pore-water pressure was simultaneously observed, which might be generated by the wetting-induced collapse of unsaturated loose soil. On the other hand, the stability of the slope with grass plantation was significantly enhanced, and it was able to withstand rainfall event more severe than those with a return period of 100 years, with only minimal deformation. The results suggest that the gain in shear strength due to ryegrass roots surpasses the additional sliding force caused by the increased water retention capability. Additionally, it is found that the abrupt change in pore pressure was no longer indicative of slope failure in the case of the grass-reinforced slope.

Keywords

Gentle slope / Silty sand / Ryegrass / Rainfall / Failure pattern

CRediT authorship contribution statement

Pei Tai: Writing - review & editing, Writing - original draft, Methodology, Funding acquisition, Formal analysis, Data curation, Conceptualization. Fan Wu: Investigation, Formal analysis, Data curation. Bohan Bai: Investigation, Formal analysis, Data curation. Zhaofeng Li: Writing - review & editing, Writing - original draft, Software. Rui Chen: Writing - review & editing, Supervision, Resources, Project administration, Methodology, Funding acquisition, Formal analysis, Conceptualization. Lulu Zhang: Writing - review & editing, Project administration, Funding acquisition.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

All authors would like to thank the National Key R&D Program of China (2021YFC3001000), the National Natural Science Foundation of China (52239008, 52108311, and 52025094), and the Shenzhen Science and Technology Program (KQTD20210811090112003 and GXWD20231130125225001) for financial supports.

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