A relation for accelerating deformation of sandy soil and its application to predict the time to failure of a sandy model slope under repeated rainfall

The measurement of groundwater level and surface displacement in a sandy model slope under repeated rainfall was conducted to examine the effect of repeated pore pressure loading and unloading on the slope deformation. The velocity increased with small fluctuation even immediately before failure. Positive and negative accelerations occurred due to fluctuations in the velocity. The velocity increased with a considerable rise in the groundwater level and approached its ultimate value immediately before failure. The surface displacement increased not only with the rise in the groundwater level but also with the fall of the groundwater level and under a constant groundwater level. The relationships between the velocity and the absolute value of the acceleration derived from the surface displacement were linear on a logarithmic scale and unique for each stage with increasing and decreasing velocities due to the rise and lowering in the groundwater level. While the relationship was different during the stage of creep during failure. The relationship had been recognized to be applicable only during an increase in velocity; in this paper, a new relationship was established for any velocity trend and the method for predicting the time of failure was proposed based on the relationship between the velocity and acceleration. The time remaining to failure, which was defined as the difference between the predicted failure time and present time, could approach zero at the actual failure time when the constant alpha in the equation was greater than 1.4, and the determining factor in regression analysis for deriving the constant was high under different periods of measurement before the final event. The time remaining to failure approaching zero might be an indicator for predicting failure time.

Automated summary

This study measured groundwater level and surface displacement in a sandy model slope under repeated rainfall to examine the effect of repeated pore pressure loading and unloading on slope deformation. The velocity had small fluctuations even immediately before failure, and positive and negative accelerations occurred due to velocity fluctuations. The velocity increased with a rise in groundwater level and approached its ultimate value before failure. Surface displacement increased with both rising and falling groundwater levels, as well as under a constant groundwater level. The relationship between velocity and acceleration derived from surface displacement was linear on a logarithmic scale and unique for each stage with increasing and decreasing velocities due to groundwater level changes. A new relationship was established in this study for any velocity trend and a method for predicting the time of failure was proposed based on the velocity-acceleration relationship.