Assessment of ground-anchored slope stability based on variation in residual tensile forces

The current maintenance process for ground-anchored slopes in Japan involves conducting lift-off tests to measure the residual tensile forces acting on the ground anchors of the slopes of interest. On highway slopes, at least 5% of the total number of anchors on a particular slope is measured once every five years. If a sufficient number of anchors is found to be under excessive tensile forces, additional lift-off tests are conducted to confirm the distribution of the residual tensile forces. Furthermore, if the collapse risk of the slope is estimated to be significant in these lift-off tests, additional surveys, which take measurements of the slope movement, borings, and so on, are carried out and necessary countermeasures are planned by technical committees. As the number of ground-anchored slopes in Japan is tremendous, however, the maintenance process could be time-consuming and costly. Therefore, the aim of this study is to develop a simple approach for identifying the dangerous ground-anchored slopes (that is, those requiring countermeasures) based only on the results of lift-off tests. This would allow maintenance engineers to significantly reduce the number of slopes that they submit to technical committees for further evaluation. This paper discusses comprehensive ground-anchored slope stability based on the variation in residual tensile forces. Firstly, the most significant parameter for judging dangerous slopes is identified through lift-off tests based on an examination of 45 ground-anchored slopes that had previously undergone maintenance, including additional surveys, slope stability evaluations, and countermeasure planning, as was necessary. Secondly, a probabilistic approach, using a simple circular slip analysis, is employed to confirm the relationship between the probability of slope failure and the parameter identified in the first step.