Bioengineering in slope stabilization: experimental evaluation of grass rugs as a Nature-based Solution for Sustainable Management

Slope stabilization is essential for hazard management and plays a crucial role in preventing landslide events while also contributing to environmental protection. Effective protection of slopes is vital, as it not only ensures the safety of structures but also helps maintain the ecological balance in the surrounding areas. To address the challenges posed by steep slopes, soil bioengineering techniques are employed to mitigate surface water erosion and control the movement of soil masses. These techniques are particularly important in areas where the risk of erosion and landslides is heightened.

The present study aimed to evaluate the effectiveness of emerald grass rugs (Zoysia japonica) as Green Infraestructure (GI) in providing protection and stabilization for slopes based on investigation in experimental plots. The research was conducted on a steep 60% slope located at the Federal Rural University of Pernambuco State in Recife, Brazil. The experimental plots were designed with an area of 10.35 m², featuring dimensions of 3.0 × 3.45 m, and were bordered by masonry walls to control the experimental conditions. At the lowest point of each experimental unit, a 100 mm drainage pipe was installed to collect runoff and sediments, ensuring proper storage in 500-liter PVC tanks. An automatic rainfall gauge was set up on-site, providing critical data for the study.

Several treatments were implemented during the experiment: the first involved the installation of grass rugs with four replicates; the second treatment consisted of grass rugs with an underlying application of coconut powder as a bioretention layer, which had two replicates; and the final treatment served as a control, consisting of bare soil. The parameters evaluated throughout the study included rainfall, runoff, sediment loss, and erosion rates. The results indicated that for all rainfall events, the control plot exhibited a Runoff Coefficient of approximately 60%. In contrast, the grass rugs demonstrated a significantly lower coefficient of around 28%, while the grass rugs with coconut powder showed an impressive reduction to about 16%.

When examining erosion specifically, the grass rugs proved to be highly effective, exhibiting approximately 500 times less soil loss compared to the bare soil control plot. Moreover, the addition of coconut powder beneath the grass rugs further enhanced their protective capabilities, resulting in nearly 1000 times less soil loss when compared to conditions of bare soil. These findings clearly highlight that vegetation cover associated to a bioretention layer plays a vital role in maintaining the integrity of soil structure. Among the treatments tested, the arrangement of grass rugs combined with the underlying application of coconut powder was identified as the most efficient Nature-based Solution NbS method for slope stabilization and erosion control, demonstrating the potential benefits of integrating bioengineering practices into construction and environmental management strategies.