Early warning system for landslide of gentle Piedmont slope based on displacement velocity, factor of safety, and effective rainfall threshold

Owing to extremely heavy rainfall caused by EI Niño and human activities, landslides have increased significantly on gentle Piedmont slopes in the Ningzhen area in recent years. These gentle Piedmont slopes comprise fillings or clay on the surface, gravel in the middle, and bedrock at the bottom. Landslides occurred during or after heavy rainfall, and the monitored displacements of the slope surface indicated that sliding did not stop after a long period of continuous rainfall, which is a creeping landslide. To effectively predict this type of landslide, we first derived a stability equation for calculating the factor of safety (FOS) of gentle Piedmont slopes combined with the sliding mechanism of these landslides. Second, early warning thresholds, including displacement velocity, FOS, and effective rainfall early warning indicators, were determined using different prediction methods for landslides and specific landslide data. Finally, an early warning and forecasting system suitable for the instability of gentle Piedmont slopes in the Ningzhen area was developed and verified by integrating early warning indicators. The research results provide important theoretical and technical guidance for the early warning prediction of landslides on gentle Piedmont slopes.