Abstract

When a tunnel is constructed in a landslide area, the excavations may induce the instability of nearby slopes. However, it is not clear how tunnel excavations actually affect landslide behavior. In order to establish a design for both the construction method of the tunnels and the countermeasures required for such unstable conditions, it is important to reveal the mechanism of the behavior.

The objectives of this study are to simulate the displacement behavior of a landslide slope due to tunnel excavations, using the proposed model, and to discuss the mechanism of the landslide behavior and the effects of countermeasures applied to prevent landslides.

1. Introduction

When a tunnel is constructed in a landslide area, the excavations may induce the instability of nearby slopes. The tunnel entrance is one part that requires particularly great care during the tunnel construction. However, it is not clear how tunnel excavations actually affect landslide behavior.

In this paper, firstly, the results of field measurements obtained at a tunnel constructed under a landslide area are shown to indicate the real landslide behavior due to tunnel excavations.

Secondly, numerical simulations are conducted to understand and to discuss the mechanism of the behavior. The Finite Element Method (FEM) and the Distinct Element Method (DEM) are usually used for the numerical analysis of tunnel excavations. However, it is difficult to simulate the displacement behavior of a landslide slope due to tunnel excavations with either of these methods. Therefore, an appropriate numerical model that can express the sliding and separation behavior of the ground materials, proposed by Shimizu et al. (2015) and Amafuji et al. (2017), is used here. The Particle Flow Code (PFC) is employed for the modeling. An unstable area, corresponding to a landslide block, is assumed to exist as a limit state area, since a landslide has already occurred before the tunnel excavations. The limit state condition continues to develop, due to the decrease in strength of the contact bonds, until the slope collapses.

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