In humid temperate region, Landslide is one of the most important processes of slope formation. But usual landform classifications of landslide area were uncertain and even the name of each landform units was not consistant. In this report the authors tried to set up the landform units composing of landslide area on the bases of usual studies and investigations of some Landslides occuring in the Tertiary of Tohoku district, from the point of view that each landform was not only an index of landslide area but also some reflextions of the process or structure of the Landslide.
The results obtained are summarized as follows.
1. ‘Topographical height’ is subdivided into four landform units. BLOCK is the height which is not crushed in the process of mass movement and is formed by tension stress. PRESSURE-RIDGE is formed by compression stress towards the movement direction, so it's structure is remarkably clushed. DEBRIS-FLOW-RIDGE and DEBRIS-FLOW-CONE are formed in the process of consumption of the end of landslide area by flow and composed of debris.
2. ‘Scarp’ is subdivided into two types. SLIDING SCARP is formed by slumping and SEPARATING SCARP is by glock-glide. They are generally divided by topographical feature and pattern of landform arrangement.
3. ‘Crack’ is subdivided into TENSION CRACK and COMPRESSION CRACK. Tension crack mostly grow at right angle to the movement direction.
4. ‘Hollow’ which is formed by block-glide and exposes slip surface can be recognized by topographical feature and we call it DITCH-LIKE-HOLLOW.
Consequently it become evident that each landslide area is composed of the conbination of above nine landform units.

View full abstract

In the previous two papers, Parts I and II, the authors have described the fundamental concept of the newly proposed inverse calculation method of c and φ along a given slip surface and a calculation procedure based on the ordinary method of slices (Fellenius Method). This paper is concerned with an extension of the method to the situation in which the Bishop Method is used to calculate the factors of safety. The factors of safety equation in the Bishop Method is rather complicated in comparison with that of the Fellenius Method. A way to determine the c-tanφ relationship, therefore, is first described for the Bishop Method. The strength parameters c and φ to be obtained must lie on the c-tanφ curve. In addition to this requirement, a complete inverse calculation method must satisfy the condition that the factor of safety along the given slip surface is a minimum of all the possible adjacent slip surfaces. An approach to satisfy these two conditions is then developed, thereby giving an extremely limited range within which the unknown parameters, c and φ, should exist. Finally, a graphical solution is shown to determine c and φ uniquely and efficiently with the aid of a digital computer. Applications of this method to three fictitious problems indicate that it is of much practical use due to its accuracy and reasonable computer time.

View full abstract

This paper deals with the results of the continuous measurement of the behavior of C. I. P. concrete piles placed in the sliding slope for four years at K-section in Kobe group of the tertiary system.
The results obtained were as follows:
1) Delayed with rainfall, the groundwater level changed in a minute range in the lower part of the slope. There was no relation between the G. W. L. and rainfall.
2) No relation between the change of stress of piles in a line, strain of the intermediate pile, earth pressure, pore water pressure at the measuring point and the change of the G. W. L. was recognized.
3) Difference in the behavior of a pile owing to small difference in the condition of φ and C was small.
4) Bending moment came to a maximum value near the fixed point and the distribution of it showed a damping wave over plus and minus territories.
5) Safety factors of piles to the bending moment and to the shearing force showed large values which were more than F_s=1.2.
6) The results of the continuous measurement for four years showed that no piles was destroyed.

View full abstract

The large-scale landslide landforms, wish source areas wider than 1 km were mapped by air-photograph interpretation in the Tohoku district between latitude 38°N and latitude 42°N. On the basis of the mapping, characteristics of the distribution of those large-scale landslide landforms are discussed from geomorphological and geological points of view.
Six regions are recognized as those of concentration in the central part of the Ou Mountains, the Shirakami Mountains, the Hinotodake-Kamura Mountains and the northern part of the Asahi Mountains. Those regions mostly coincide with the areas of the maximum uplift during the Quaternary time in the Tohoku district. Those are also underlain by the zones of the Lower and Middle Miocene sedimentary rocks and submarine volcanic rocks, commonly called “Green Tuff”, and the Quaternary volcanic rocks. The topography in those zones are characterized by cap rock structures.
The large-scale landslide landforms of the Quaternary volcanic areas are dominantly found in the old and/or dormant volcanoes, and are roughly divided into three types from the main contributing factors of landsliding, the volume in source area, morphology and so on.
(1) Type 1 is a catastrophic landslide or collapse of a volcanic cone associated with volcanic activity. Its tophographic and structural feature is composed of the so-called the collapse caldera of the source area and hummocky relief of the deposition area. The latter is a typical topographic feature of volcanic dry avala nche deposits composed of megablocks and interstitial fine material. The volume of the source area is the largest of the three types. Examples can be seen in Iwate volcano, Iwaki volcano, Gassan volcano, Cheikai volcano, Zao volcano and Shirataka volcano.
(2) Type 2 shows a typical landslide landform associated with a gentle arc-shaped main scarp and a moving mass. Main scarp of this type is found on the slope of a thick lava flow near the top of the volcano.
The activity of the volcanoes, where the landslides of this type occurred, ceased in the late Pleistocene and seems to be almost dormant at present.
The contributing factor to the landsliding may be a large quantity of water supply related to the late Quaternary climatic change.
Water are prepared in the form of the perennial snow patches and are supplied by the rapid melting of the perennial snow patches with the rising air temperature. The formative age of the perennial snow patches ranges from the late Pleistocene to the eariest Holocene (period about 18, 000y. B. P. to 8, 000y. B. P.).
Because the sea level of this period is lower than that of the present, mountains were vigorously dissected. Then the stability of the mountain slopes rapidly deteriorated and a number of large-scale landslides occured.
Those landslides are found in Hachimantai volcano, Yakeishi volcano, Kurikoma volcano, Funakata volcano, Gassan volcano and Zao volcano.
(3) Type 3 is recognized along the dissected vally wall in the pyroclastic deposits and pumice fall deposits. Type of movement is mostly rotational. The volume in source area is smaller than that of the type 2. However, the same contributing factor may be important for the landslides of type 3 as the type 2.

View full abstract

The writers plotted a location of active mass movennent on a 30“×45” mesh map.It depends on an observation of a stereoscopic pair of aerophotos and surficial survey. Mass movement lies on the elevated side of thrust fault, an anticlinal axis of active folding and the margin of a tectonic basin. Such statistics are shown in this paper.
Itoigawa-Shizuoka tectonic line is a greatest thrust fault which has been identified with a boundary line between Eurasian and North American plates since the Central Japan Sea earthquake 1983.
The division of creep movement and landfall depends on the facies of layer. Clayey soil introduces creep movement and sandy one an accidental fall by heavy stormy rain or the earthquake. Ancient or fossil mass movement marks are found independent of present crustal movement. Artificial land development may lead slope disasters. They may issue from fossil landslides.
Deposits of dam sites-Miwa, Koshibu, Yasuoka and Hiraoka-are very large along the Tenryu river, which flows through an upheaval district. An occasional mud flow takes its rise at Mt. Hieda along the Ura river, Nagano prefecture.

View full abstract