The Loess plateau located in the Northwestern China is an area of intense seismic activity and where many disastrous earthquake-induced landslides have occurred. For example, the Haiyuan earthquake (M=8. 5) of Dec. 16, 1920 occurred in Ninxia Province, China, triggered many large-scale landslides and resulted in more than 100, 000 casualties.
We sampled Loess soil from these landslide areas and performed laboratory tests to examine the mechanism of the landslides, using the cyclic loading ring shear apparatus and the cyclic triaxial compression apparatus. From these tests, the following results were obtained.
1) The cyclic triaxial shear tests could not reproduce the sliding surface, and it is unsuitable for the research of landslides triggered by earthquakes because the shear deformation after failure did not correspond with the landslide phenomenon.
2) In the undrained cyclic ring shear test of saturated Loess samples, pore pressure was accumulated cycle by cycle when the cyclic shear stress was added and a large excess pore pressure was generated instantaneously after the sample failed. The sample was sheared continually after failure. From this test, it could be concluded that the occurrence mechanism of Loess landslide with high mobility during earthquakes is the result of the increase of excess pore pressure induced by cyclic shear stress under the undrained state.
3) In the cuylic ring shear test with dry Loess soil, the shear displacement stopped at the end of the loading of cyclic shear stress because the shear strength did not decrease below the initial shear stress. It can explain why the slope consisted of layer with lower degree of saturation degree can not form a landslide with high mobility of long distance and its displacement just occurred while the seismic force worked on it.

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Concrete facilities suffer damage from acid river flow in volcanic area. Therefore, the reinforcing durability of concrete against acid solution is a important subject. And then, the reinforcing can make the construction and maintenance of concrete facilities easier.
In a purpose of obtaining the basic data for the durability of concrete against acid solution, the experiments that cement mortal prisms mixed with some mixtures soaked in sulfuric acid solution and hydrochloric acid solution have been carried out, In the experiments, a fly ash, a blast-furnace slag and a high performance AE water reducing agent were used for the mixtures.
These effects of the mixtures against the both acid solution were recognized. But, they showed different effects for the each acid solution, and for researched items. The change in quality of prisms in sulfuric acid solution were remarkably. The effects of fly ash was recognized to be significant and the ratio of 30% in weight was appropriate for mixing.

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The data of water discharge and sediment yield monitored since 1986 at the outlet of the Kurabone basin which is a headwater of Chikuma river system were examined from the viewpoint of the passing of a sediment wave at a point of the stream. As a result, the passing process of a sediment wave was demonstrated by revealing temporal changes in response of sediment yield to peak discharge. In the last of its process, pools temporarily filled with sediment and some of boulders creating steps were moved. As a result of analysis of hydraulic conditions for the flood which caused the deformation of step-pool bedforms, it was considered that a superior mobility of the mixed sediment, which is caused by such effects of mixing as smoothing, exposure and collision, played an important role for moving the boulders creating steps.
Therefore, the passing of a sediment wave caused by a large amount of heterogeneous sediment supplied from the upstream is an important factor in deforming step-pool bedforms.

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Approximately 200 million cubic meters of debris have deposited due to pyroclastic flow activity in the surrounding area of Unzendake between May 1991 and February 1995. One extremely good way of using this debris is to mix it with cement to make soil cement for use as an ordinary building construction material.
So, in order to clarify the properties of soil cement made with the pyroclastic flow debris, its usability as a construction material, and the economic feasibility of its use, on-site test construction were carried out. The test construction were done for three mixing methods: plant mixing, back hoe mixing with cement milk at place, and back hoe mixing with cement powder at place.
The results reveal that if the cement is about 8 %, compressive strength between 5 × 10⁶Pa and 8 × 10⁶Pa is obtained. The results also demonstrate that the back hoe mixing with cement powder at place is suitable for fast small-scale work and the plant mixing method is appropriate for preparing large quantities of high quality soil cement.

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The heavy rainfall caused by a front attacked the north Nagano prefecture and the south-west Niigata prefecture, in July, 1995.
It caused gigantic sediment movement in Hime-kawa drainage area, and gave severe damage to the houses, road, railroad and many other infrastructures. Although there occured lots of debris-flows and landslides, no one was killed in this disaster.
Therefore, in the interest of disaster prevention planning, we carried out a questionnaire on the action taken by the inhabitants to evacuate from the sediment-related disasters, and grasped the actual state of debrisflow warning and evacuation at that time.

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We found some paleograph in the Edo Era. And they consequently inform us of the sediment-related disaster.
Then, we investigated the actual conditions of the sedimentrelated disaster, by analysis of the paleograph.
They inform us of scale of the sediment-related disaster, and they indicate how to cope with the sediment-related disaster.
In 1707, the Mt. Fuji erupted. and did a great deal of damage to all villages on the east foot, that covered about 40, 000ha by thick ash.
If the paleographies are correct, we are able to plan to keep from danger of the sediment-related disaster, now.
We report results of the survey, in case of more than 150 cm at depth, the paleographies are expect to the plan for keep from danger of the sediment-related disaster.

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