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 great care during the tunnel construction. 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 ground behavior. This paper firstly describes the field measurement results of slope behavior due to tunnel excavations. Then, numerical simulations are conducted to understand the mechanism of the displacement behavior due to the excavations.
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. To establish a design for both the construction method of tunnels and the countermeasures required for such unstable conditions, it is important to reveal the mechanism of the ground behavior.
This paper is divided into two parts. Firstly, field measurement results are shown in order to investigate the real slope behavior due to tunnel excavations. The measurements were conducted at parallel expressway road tunnels constructed in a landslide area of Central Japan. Inclinometers and the GPS (Global Positioning System) displacement monitoring system were used to monitor the displacements of the slope. The measured displacements indicated that the slope above the tunnel moved down to the toe along the slip surface. It is clear that these displacements occurred in the landslide block above the slip surface due to the tunnel excavations.
Secondly, a numerical simulation is conducted in order to discuss and understand the mechanism of the real slope 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 still difficult to express the real behavior of the ground with these methods. Therefore, an appropriate numerical procedure that can express the separation and the sliding of the ground materials is required. A numerical modeling is proposed using DEM, and the mechanism of the behavior is discussed.
