In order to verify the stability evaluation flow of slopes with prevention piles installed, a model test of a slope was conducted. Prevention piles were designed to be installed on a slope with a distribution of successive weak layers, ensuring the safety factor of 1.2 for the design maximum seismic coefficient (KH) equal to 0.6, based on past stability evaluation flows. A slope model installed with prevention piles based on the design was created and a dynamic centrifugal force model experiment was conducted. As a result, it was confirmed that the prevention piles functioned even when the maximum horizontal acceleration (6.31 m/s2) equivalent to the designed seismic coefficient worked, and that no noticeable change occurred on the slope. Based on these facts, the validity of the existing stability evaluation flow was demonstrated.
In order to improve the seismic resistance of slopes around important structures, countermeasure construction is sometimes carried out (Nuclear Standards Committee of JEA 2016). The use of prevention piles is one effective measure. An earthquake stability evaluation method has been proposed for slopes with prevention piles (Toda et al. 2013). However, the effectiveness of the flow of stability evaluation has not been sufficiently verified, since it is difficult to ascertain the behavior of the actual slopes with the prevention piles installed at the time of the collapse. In order to verify the flow, a dynamic centrifugal model experiment was carried out on a model slope reinforced with prevention piles (Kobayakawa et al. 2017). In this paper, the effectiveness of the proposed stability evaluation flow is demonstrated from the results of the dynamic centrifugal model experiment.
The proposed flow is shown in Figure 1. Prevention piles for landslides are usually designed according to the guidelines for the steel pipe pile for landslide (Board of directors of the guidelines for the steel pipe pile for landslide 2013). In this guideline, the concept of design differs depending on the pile deterrence mechanism. However, since the stress state of the piles and the surrounding ground during the earthquake is complicated, it is difficult to presume the deterrence mechanism in advance. Therefore, in this flow, the specifications of the prevention piles were decided based on the section force of the piles and the destruction state of the surrounding ground by a parameter study of dynamic equivalent linear analysis. Specifically, the section force of the piles was set so as to be within the elastic limit. With respect to the destruction of the ground around the piles, we checked the slip safety ratio of the ground surrounding the piles and determined the setting of the piles so as to secure an allowable safety factor of 1.2.