Influence of slope inclination on the triggering and distal reach of hydraulically-induced flow slides

• Influence of slope inclination on mobility is dependent on groundwater conditions.
• Water storage in gently inclined slopes increases flow liquefaction susceptibility.
• Conditions can permit landslides on 20° slopes to travel further than on 30° slopes.

In the absence of water, a dry granular landslide mass released on an incline will experience greater acceleration than an otherwise identical mass released on a plane of lower inclination. However, when water is introduced to the system, the outcome is more complicated. While it requires less water pressure to trigger a landslide on a steep slope, the additional saturated soil in a gentle slope can make it more susceptible to flow liquefaction, which in turn can make it the slope of greater risk in terms of the landslide velocity and distal reach. Results from seven geotechnical centrifuge tests were evaluated to compare the behavior of flow slides triggered in a loose granular soil layer inclined at 20° and 30°. The results indicate that the influence of slope inclination on mobility is highly dependent on antecedent groundwater conditions. In low antecedent groundwater scenarios, the mobility of the failures triggered in the 20° and 30° were similar. However, in a high antecedent groundwater scenario, a flow slide triggered on the 20° slope was observed to travel twice the distance, and reaching nearly twice the maximum velocity than a flow slide triggered on the steeper 30° slope. These results provide experimental data documenting the complex interaction between slope inclination and antecedent groundwater conditions to control the triggering and distal reach of hydraulically-induced flow slides.