How the toe loading suppresses the movements of an instable slope: Mechanisms revealed from triaxial compression tests under varied strain rate condition

• The displacement rate of a slope with a volume of over 2 × 106 m3 was 35 mm/day.
• The displacement rate decreased to 15 mm/day due to the toe loading.
• In TC tests, the strain rate decreased by 90% with a reduced stress level by 1.9–5.6%.
• The remediation effect of toe loading was explained on the basis of the strain rate effect.

Series of triaxial compression (TC) test on in situ retrieved soils were performed to reveal mechanisms of a toe loading. Due to toe excavation, an existing failed slope was reactivated with a sliding mass of over 2 × 106 m3 and the maximum displacement rate of 35 mm/day. As an emergency countermeasure, 7000 m3 of soil packed in bags was loaded at the toe of the slope, and led to a decrement of the displacement rate of more than 57%. TC test results showed a significant strain rate effect and stress relaxation at residual state. Quantitative analysis of the strain rate effect on the residual strength showed that if the stress is reduced by 1.9–5.6%, the displacement rate decreases by 90%. Based on the field investigation results and the experimental results, the range of the displacement rate decrement due to the toe loading was evaluated to be 46 to 84%. Comparison of the range of the evaluated decrement in the displacement rate and the measured decrement in the displacement rate verified that the strain rate effect may explain the significant remediation effect of toe loading on the sliding of the slope. This research provides a rough method of evaluating the remediation effect of toe loading.