In Japan, landslides and slope failures are frequently attributable to characteristic environmental conditions and additionally human interferences to ground. As a result of Japan's experience with disasters caused by mass movement, considerable progress has been made here in techniques for investigating and analyzing these phenomena, as well as in the fields of design techniques to control them.
For three years, Working Group on Slope Engineering in JSCE have been reviewing these techniques and recent developments in slope engineering on soft and weak rock in Japan. This paper is concerned with these findings of this working group. In addition, objectives for further study of the outlook for technology applied to sliding movement are outlined.
Distribution of landslides in Japan Japan has a long history of landslide disasters. There remains a historical record from the 12th century that tells of a pile driving project to prevent landslides undertaken by farmers. In this way, landslide disasters have been closely related to agricultural production for hundreds of years.
Since about a hundred years ago, with the start of industrialization, landslide disasters increased sharply. At first, railway construction projects were the main causes. However, in the last 25 years, with the remarkable growth of the Japanese economy, development projects in mountainous districts became widespread, with a resulting increase in instances of landslides caused by human intervention. Positive measures have been required to cope with the situation.
In 1958, the Landslide Prevention Law was promulgated. From that time, landslids control works came to be widely practiced.
An investigation of dangerous potential landslide sites was undertaken on a nationwide scale. As shown in Fig. 1, more than 10,000 areas were. registered as "designated landslide areas". Investigations and control works for these areas are under way(JSL1972).
As can be seen from Fig. 1, the landslide areas tend to be clustered in specific districts. It shows that the distribution of landslides is closely related with lithologic character and geologic structure. Landslides in Japan are often characterized according to the three landslide types proposed by Koide(1955) or the five landslide types proposed by Nakamura(1946).
Koide proposed the following landslide types:
Tertiary,
fracture zone and
hydrothermal types.
Nakamura's classifications are:
Tertiary,
Mesozoic,
Paleozoic,
metamorphic and
volcanic type landslides.
Tertiary type landslides refer to those found in regions of Tertiary strata, including green tuff areas, composed of weakly consolidated rocks and regions contained coal-bearing Tertiary strata. Tertiary type landslides are densely distributed in the northeast of Hokkaido, the northern part of the main island of Honshu and a belt zone along the Sea of Japan.
The fracture zone type landslides cited by Koide and the Mesozoic, Paleozoic and metamorphic type landslides cited by Nakamura occur mainly in areas where rocks are shattered along a tectonic or fault line. There is a large fracture zone, running north-south through the center of Honshu, called the Fossa Magna. The west boudary of this zone is the Itoigawa-Shizuoka line.
(Figure in full paper)
