Effects of soil-plant-biochar interactions on water retention and slope stability under various rainfall patterns

Due to climate change, extreme rainfalls happen more frequently with different patterns. Biochar and plant roots can affect soil water retention curve (SWRC) and hence slope stability. Until now, no available SWRC model considers soil-plant-biochar interaction, which can also be used for slope stability analysis under extreme rainfalls with different patterns (i.e., advanced, bimodal, and delayed). This study proposes a new SWRC model for vegetated biochar-amended soil by considering the influence of soil-plant-biochar interaction on the void ratio and pore structure. A series of numerical analyses were conducted to investigate the significance of new SWRC model on slope stability under extreme rainfall patterns. Good agreements between laboratory measurements and the new SWRC model predictions were obtained. With an increase of biochar content from 0 to 10%, the number of soil micropores increased by 22%, which improved root volume ratio (R-v) by 130% and hence air entry value (AEV) of vegetated soil by 50%. Based on numerical analysis, the factor of safety (FOS) for vegetated slope under advanced and bimodal rainfall patterns was up to 53% lower than that under the delayed one during rainfall. The rainfall influence depth and FOS of vegetated slope without biochar was nearly 100% deeper and 60% lower than that with biochar, respectively. The lowest FOS was caused by advanced rainfall pattern, which is therefore suggested for slope design. The application of 10% biochar can better stabilize shallow slopes due to its substantial effects on plant root, soil pore structure, and SWRC.

Automated summary

This study proposes a new SWRC model considering the interaction of soil-plant-biochar, which significantly improves slope stability. Laboratory measurements and numerical analysis show that an increase in biochar content can enhance the safety factor of vegetated slopes, and advanced rainfall patterns have a significant impact on slope design.