Study on the behavior of debris flow into reservoirs and establishment of flood control technology by utilizing abandoned reservoirs

In Japan, many reservoirs for agricultural use are located around valleys and streams, and there have been an increasing number of cases of serious damage due to debris flows into reservoirs caused by heavy rainfall. In order to prevent accidents caused by the failure of reservoirs, construction work is rapidly underway to cut open and remove unused reservoir embankments. We are conducting experiments to clarify the behavior of debris flows into reservoirs and to verify the effectiveness of the abandoned reservoirs in damming up debris flows, with the aim of establishing flood control technology.

Study on mechanical behavior of buried pipelines during sheet pile extraction

Agricultural pipelines are constructed by the proceadure of excavating the ground, retaining the ground with steel sheet piles, laying the pipe, backfilling the soil, and extracting the sheet piles. Extraction of the sheet piles causes the change in the earth pressure around the pipe, which can cause deformation of the pipe. However, the current design standards are not based on mechanical evidence. The laboratory aims to establish a design method based on mechanical evidence by conducting laboratory model experiments using a large soil-container to reproduce the sheet pile extraction.

Development of flexible structural precast concrete conduits for earth dams

At the bottom of the embankment, conduits (drains) are installed to intake water from the reservoir and convey it to an irrigation channel or to drain it to empty the reservoir. Since conduits have a rigid structure consisting of concrete blocks connected by bolts, it cannot follow a ground settlement, which may cause cracks and water leakage. Through model experiments and large-scale shaking-table tests that reproduce ground settlement using conduits without bolts, we are contributing to the development of flexible conduit structures that can follow ground settlement and the proposal of a new construction methods.

Model experiments for mechanical behavior of polyethylene pipes with joints under soft ground

In Japan, irrigation pipelines have often been damaged due to local ground settlement under soft ground such as peat ground, and it costs a lot for repair. In order to prevent the damage, high density polyethylene pipe (PE pipe) is used under the soft ground. Especially, damage is often occurred in the vicinity of pipe joints. However, there are few studies on PE pipe under the soft ground and the design method has not established. We are conducting the model experiments to reproduce the ground settlement and the field experiments on peat ground in order to examine the mechanical behavior of the PE pipe and its joints.

Study on structural design of coastal dike considering tsunami overflow

One of the themes of this laboratory is to review the structure of actual coastal dikes and consider better design methods to reduce the damage to human life and social infrastructure caused by tsunami attacks. Following the Great East Japan Earthquake of 11 March 2011, massive tsunami caused serious damage to coastal dikes. Since massive tsunami caused by a huge earthquake such as the Nankai Trough are expected in the near future, there is a need for an update to coastal dikes considering massive tsunami, that is, tsunami overflow. In this laboratory, we examine methods of 1) suppressing the scour at the ground behind coastal dikes against the tsunami overflow, 2) reducing tsunami velocity at the back of coastal dikes, and 3) reducing the quantity of the tsunami overflow.

Research and development of flexible thrust restraint design for pressure pipe bends

Agricultural pipelines deliver water by applying water pressure inside. Pipelines have many bends, and thrust force is generated at the bends. To resist thrust force, concrete blocks are usually used in pipe bends. However, the blocks move significantly during earthquakes, causing damage to the pipe joints. The laboratory aims for the practical application of a method to resist thrust force by wrapping pipes and gravels with geogrids.

Study on mechanical behaviour of small earth dams with GCLs.

In Japan, there are approximately two hundred thousand small earth dams. Since nearly 70 % of them were constructed before the middle of the 19th century, it is urgently necessary to repair the aging embankments. Embankments of small earth dams are constructed by filling soil materials. In the repairing works, to ensure the water storage function, impervious cohesive soils are usually used in the upstream side of embankments. In the cases that such soils are not available near the dam site, geosynthetic clay liners can be installed in the embankments as the water barrier materials. However, the design guideline of the small earth dams using GCLs has not established yet. In our laboratory, to establish it, the following tests are conducted: 1)Direct shear tests on the interfaces between GCLs and soil materials, 2)Shaking table tests of embankment model.

Centrifuge modeling for sand erosion from a composite breakwater with wave-dissipating concrete blocks

One of the problems of a model experiment is the influence due to the difference in size between actual structures and models (scale effect). In order to solve this problem the centrifuge modeling test is performed by applying centrifugal force to the model. This method is used to elucidate problems of geotechnical engineering, but the current situation is that few studies focusing on the sand erosion of a coastal structure foundation and the sand scouring. In this study, we focus on the sand erosion in the foundation ground of a composite breakwater with wave-dissipating concrete blocks in problems of a coastal structure. We conduct the wave experiment in the centrifugal force field using a drum centrifuge equipment. In addition, we evaluate the effectiveness of centrifuge modeling by comparing with the previous research.

Research for the effect of pipe thickness on the behavior of buried pipes and for the establishment of design technique

When designing a pipeline for Japanese agricultural water, we multiply the pipeline thickness by the cube of the stiffness of materials,and this value is regarded as the strength of a pipeline. This means that the strength of the thick pipeline made with soft materials is approximately the same level of that of the thin pipeline made with hard materials. However, in late years a lot of unexpected accidents came to occur in thin and hard pipes. In response to this, there are increasing opinions that we should reconsider the standard of a pipeline design. Then in our laboratory, by experiments and analyses we make a detailed investigation how the pipeline thickness affects the pipeline strength.

Research for the effect on buried structures by shear deformation

In late years, giant earthquakes, including such as Great Hanshin Earthquake and Great East Japan Earthquake, frequently occured. The destruction of underground structures at the time of the earthquake causes the expansion of damage and the great hindrances for the later restoration work. We study the behavior of the important underground structure pipeline at the time of the earthquake. For the study, we conduct both the model experiments using the aluminum bars and the analyses using a two-dimensional distinct element method (DEM).

Research for the buried pipe behavior on uneven ground

The ground around buried pipes sometimes becomes non-uniform by the outflow of the ground by earthquakes and torrential rains, inadequate backfill during construction and so on. However, the deformation behavior of the buried pipes is not adequately considered. Currently most of the internal behavior in the middle section of a pipe is not examined when this nonuniformity occured in a pipe axial different section. In our study, we reproduce the heterogeneous ground in a soil tank and examine the heteromorphic behavior of a pipe and it's internal behavior. We also push examinations forword with three-dimensional FEM analysis　and model experiments.

Research for the rehabilitation technique of aging pipes

Recently, most irrigation facilities for agriculture, which were built during the era of high economic growth, are aging. As for the pipeline for agriculture alike, various problems such as the strength degradation of pipes and invation of the groundwater occured. From now on it is important to repair and rehabilitate these pipelines economically and systematically. It is the pipeline rehabilitation method that we consider as repairing aging pipes. In brief, with this method we construct new pipes inside aging pipes and don't need to dig the ground. Therefore there are less noise, vibration and traffic congestion caused by construction work and it makes us possible to minimize influence on local residents' lives. In our laboratory we carried out numerical analyses and construction experiments in order to clarify mechanisms in applying this method and to reveal force that influenced the pipes.

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