Research results

Detecting the movement of a sliding mass
Observation devices that can be used in special landslide environments


Photo A: Condition of landslide beginning to move


Photo B: Condition 3 days later
Photo 1: A long-traveling landslide after fluidization (Photos taken by the Okinawa General Bureau)

Fig. 1 IT ground tiltmeter system


Fig. 2 Overturningtype soil mass arrival detection system


Fig. 3 Vibration device-type soil mass arrival detection system

A phenomenon in which a slope slowly moves downward, in whole or in part, due to the effects of groundwater and gravity is called a "landslide."
At landslide sites, judgment based on measurement data that captures the movement of a soil mass is regarded as an important factor in reviewing warning, evacuation, and emergency measures. However, since landslides of which sites are difficult to access, landslides with large movements of earth and landslides where sliding soil mass is muddy and fluidized and the range of arrival thereof is difficult to predict are special, no technique for appropriate and swift measurement has been established.
We have developed six kinds of observation devices that can be used in such special landslide environments. In this article, we would like to introduce devices that detect the gradient or movement of a sliding mass.

1. System to measure the gradient of ground moved by a landslide

IT ground tiltmeter system
One method to detect the movement of a landslide is the measurement of the ground tilt.
Conventional measurement devices have several problems, including a long setup time and a functional limit in which the range of measurement is exceeded in a short period of time, if the sloping movement of a landslide is very large.
As a solution, we developed a system ensuring continuous measurement at a sloping movement range of ± 20°. The installation procedure is very simple: a single cylinder is driven into the ground, and a sensor is inserted into it and fixed there. (Fig. 1)
This system allows us to swiftly measure the sloping movement of even those landslides with a large sloping movement.

2. System to detect the arrival of a sliding soil mass
2.1 Overturning-type soil mass arrival detection system
When the movement of a sliding soil mass is monitored at a landslide site that is difficult to access, one problem is that the measurement equipment cannot be safety installed.
As a solution, we developed a warning device that is simple to install. The device is composed of many sensors, each of which is simply thrown onto the soil mass so that many sensors can be safety and quickly installed over a wide area. As those sensors are moved by the sliding soil mass, the tilt formed by the moving sensors is detected by the measuring device, which transmits the information to an observation station safely away from the landslide site (Fig. 2).
With this system, we can quickly detect the area in which a sliding soil mass should arrive by throwing the sensors over the end of the soil mass.
2.2 Vibration device-type soil mass arrival detection system
To date, there was no system to detect the arrival of a sliding soil mass at a landslide site with high-speed fluidized mass movement.
To overcome this problem, we developed a warning device that detects the arrival (contact) of a sliding soil mass (water and sediment) from the frequency characteristics of the materials in contact with the sensor (Fig. 3).
By installing this detection system at the end of a sliding soil mass, we can detect the area of arrival of collapsed sediments or a muddy and fluidized moving soil mass.
The next issue outlines a device that measures landslide movement.



(Contact: Landslide Research Team)