Slopes are often affected by slipping of the surface layer during the spring thaw through the continual cycle of frost heaving in winter and subsidence due to thawing in spring. When frost heave occurs, the ground is lifted to the same direction of heat flow, while during thawing, the force of gravity acts downward. This means that the direction of lifting due to frost heave and the direction of gravitational force acting during subsidence are different on a slope. Consequently, the ground moved by frost heave does not return to its original position, instead it is moved to a position further down the slope. This movement due to the repeated freeze-thaw process is believed to trigger the collapse of the slope.
In the present study, four experimental plots planted with different types of vegetation were set up on the slope of an embankment within the campus of the Kitami Institute of Technology and the behavior of these slopes during the freeze-thaw process was observed over five seasons. The following results were obtained; (1) the behavior characteristics of the surface of the slopes in the freeze-thaw process of seasonally frozen ground were measured; (2) it was shown that movement down the slope, which is believed to trigger collapse by slipping, occurred during the thaw period and that the amount of movement depended on the extent of the frost heave, the vegetation cultivation conditions and the presence of reinforcing vegetation.

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The biodegradable grouting pipe has been developed for environmental ground-improvement.This pipe for grouting and/or for soil remediation will be disintegrated into CO₂ and H₂O using biodegradable plastic, so that it can lessen environmental problems.This stronger, biodegradable pipe has been developed by adding recycled paper to the resin.
In this study, I hereby report on the property evaluation of these pipes concerning their quality for commercial use. They possess equivalent strength to that of vinyl chloride VP40, which being characterized by a smaller pull and break length, and biodegradable quality through the effect of hydrolysis by ground-water.

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Rope-net method is one of the methods against rock fall. To solve a problem about the maintenance of the Rope-net method, we carried out field investigations, tests of wire plating weight, and tensile testing of rusted wire ropes. Field investigations revealed that the Rope-net method rusts easily and that the wire rusts easily at the part where it touches the trees or the ground. Tests of wire plating weight show that the durability of wire ropes can be maintained for more than 100 years in a good forest environment. From the results of tensile testing of rusted wire ropes, we obtained a life curve for a wire rope. We discovered that parts of the wire rope that are easily prone to rust must be replaced 20 years after installation. From these results, it is clear that the life of the Rope-net method, which was believed to be only 30 years, can be extended considerably by replacing the rusted parts by appropriate maintenance.

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Waste plasterboard is generated in vast quantities as a byproduct of demolition of buildings and houses. If waste plasterboard can be effectively utilized as a construction material, the problems of waste plasterboard disposal and shortage of natural resources for construction may be solved. Bassanite is produced by heating gypsum obtained from waste plasterboard at 130°C or more. Engineering properties make bassanite obtained from waste plasterboard useful as an improver for soft soils. However, fluorine contents may exceed the approved value in the Japanese environmental quality standard. We thus have to investigate reduction in the solubility or mobility of fluorine, either physically and chemically. To overcome this problem, we developed a solidification technology for fluorine contaminated bassanite using coal ash and portland blast-furnace (B) cement. The concentration of fluorine decreases with increasing coal ash and portland blast-furnace (B) cement contents, and to values less than the Japanese environmental quality standard. In addition, concentrations of boron and hexavalent chromium also fell below the Japanese environmental quality standard value. This is due to concomitant increase in the production of ettringite.

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Totally 482 cyclic shear deformation characteristics test results are collected from 95 sites in the Kanto district. They are firstly classified into 26 categories based on geologic age and depositional environment. Geological age as well as sediment conditions, confining stress and plastic index affect the cyclic shear deformation characteristics. Younger soils are easily to become nonlinear than the older soils. For sandy soils, effect of confining pressure is the largest. For clayey soils, effect of plastic index is the largest, effect of geological age is larger than sandy soils, effect of confining pressure is predominant when plastic index is less than 30, but it becomes less effective when plastic index is greater than 30, and nonlinear behavior is more possible as plastic index becomes smaller. Finally, cyclic shear deformation characteristics are compiled considering the effects of confining pressure and plastic index.

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Centrifuge model tests generated accurate measurement in normal and tangential earth pressures and deformation of different types of sewer trunk culverts (arch-, box- and circular-types), when they were placed in a centrifugal acceleration field of 30 G (G: gravitational acceleration) and a surface load equivalent to a vehicle design load was applied at the center of the model ground. The tests quantified effects of the investigated factors, such as type of culvert, type of soil, density of ground, cover height and thickness of sand foundation, on the response of the culverts. The test results revealed that a current design specification for the circular-type culvert tends to overestimate markedly the bending moment and deflection of the circular-culvert.

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While a temporary structure is relatively simple to erect and remove, the fact that no particular measures such as pile installations or soil improvements are taken for its protection can mean that there is a risk of it collapsing in the event of an earthquake. This paper reports a numerical analysis of the seismic stability of a temporary structure erected on a foundation of alternating clay and sand layers in a case where the surface layer is sandy and clayey. It finds that the main cause for the structure’s collapse lies in 1) the increase in the amplitude of the tremors resulting from a coincidence of the predominant ground wave motion with the specific vibration of the structure, and 2) the decline in the bearing force and the consequent unevenness in the settlement of the structure as a result of liquefaction in the surface sand layer. One important prevention measure is to ensure that the specific vibration does not coincide with the predominant ground motion by making appropriate changes in the height and width of the structure; but another cheap but effective safeguard is to increase the area of contact between the structure and its foundation by laying a base immediately below the temporary structure.

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In pneumatic caisson foundation work, direct verification of bearing capacity of the foundation ground by performing plate loading test during construction work is very important to confirm bearing capacity and reliability of the caisson foundation. Since conventional plate loading test has been conducted manually under very high pressure condition, test must be done within very limited time, and loading duration must be short accordingly. However, remote control plate loading test method developed by us realizes un-manned operation of plate loading test by attaching the test equipment to the caisson excavation machinery. Since the method has no restriction on testing time, loading test can be conducted according to the required design load conditions of the bearing stratum. In this study we propose a method how the settlement values obtained by the loading test would be corrected, which is required when the test applies to pneumatic caisson foundation work. With this proposed method, measured settlement values can be corrected within a range of a few percent error.

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Cement-stabilized soil is generally used at shallow ground depths. For this reason, the pressure curing of specimens is not seen as an important part of the laboratory testing process. When cement-stabilized soil is used deep in the ground, however, an accurate appraisal of the compressive strength at the original depth is vital for the subsequent design and construction processes.
This study has evaluated the impact of curing and test methodologies on the compressive strength of cement-stabilized soil. Battery of tests on cement-stabilized soil under pressure curing conditions has been conducted. And it is clarified that when using laboratory tests to determine the compressive strength of cement-stabilized soil at deep original positions, it is important to maintain the pressure after the pressure curing.

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