This research examined the effect of freeze-thaw actions on the bearing capacity of base course material C-40 by using our newly developed freeze-thaw CBR test apparatus. It was found that freeze-thaw history caused a decrease in the CBR of C-40 under various water content conditions. This is because the freeze action promotes to drain water absorbed into crushed stones. The increase in water on the surface of soil particles causes the decrease in interparticle friction and the change in soil skeleton structure, which resulted in the deterioration of bearing capacity. It was also found that while the decrease in CBR brought from the decrease of interparticle friction recovers over time, while that brought from the change of soil skeleton structure does not recover.

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Purpose of our research is to develop a sensor, nailing sensor focusing on the stability mechanism of the soil nailing, which measures the amount of displacement and at the same time resists in soil mass movement. Soil tank test in two different test conditions were done to measure the displacement of slope and the amount of underground moisture. From the measurement value the availability of installing nailing sensor had been proved in resistance to slope failure and measuring of displacement.

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Formulas to predict unconfined compression strength of the granular quicklime and the blast furnace cement-treated Ariake clay are proposed. In the proposed formula the strength of quicklime-treated Ariake clay is given by the amount of quicklime, the amount of oil, and the amount of quicklime-silica obtained from the physical-and-chemical analysis. And the strength of blast furnace cement-treated Ariake clay is given by the amount of blast furnace cement and the amount of blast furnace cement–silica.
In the case of the granular quicklime, multiple regression coefficient R of the proposed formula was 0.8693, and in the case of the blast furnace cement multiple regression coefficient R was 0.8787. The combination design method calculated from the regression line of survey strength and prediction strength was proposed.The strength prediction method of this research showed a possibility that the accessory role of an unconfined-compressive-strength examination could be achieved as a prediction method of strength of Ariake clay foundation improvement construction.

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In an embankment including culvert, sufficient examination on the earthquake resisting capacity in the culvert longitudinal direction was not carried out. This is because that principal body of culvert did not suffer major damages in the past earthquakes, and therefore it has been thought that just restoring collapsed bank is enough. In this study, the centrifuge model tests with arch culvert embankment are carried out by focusing on the structural designs of the culvert joints. As a result, it is confirmed that culvert joints and the configuration method of mine mouth affect the sectional force generated in culvert and displacement of wall. It becomes clear that the tension force generated in culvert has a major difference depending on the connection style of culvert’s jointing. Moreover, as the configuration method of mine mouth, when culvert is connected with the wall, large sectional force may occur locally due to the extrusion and tensile force by the wall.

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The seismic retrofit for embankment, which is one of the most important problems in Railway, has been carried out. In this study, a concept of earthquake performance for embankment based on the railway technical standard and its seismic retrofit are explained, and then the failure modes of 3 kinds of embankments during earthquake are verified through seismic centrifuge model test and soil-water coupled finite deformation analysis. The new findings are as follows; 1) As the height of embankment becomes tall and strength of clay ground becomes small, the failure mode changes from only embankment to both embankment and clay ground, and deformation level becomes higher. 2) Compared the Newmark method with experiment in the case of the failure of only embankment, the Newmark method can be a useful one in the design by considering the failure mode of the embankment.

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The purpose of this study is to duplicate the undrained shear characteristics of natural aged clays, which have structures formed by cementation in the sedimentation process. The reconstituted marine clay slurries being added a small amount of the portland cement were reconsolidated and cured. The cement contents of clays were smaller than that is necessary for mobilizing the unconfined compression strength by 1-3%. According to the series of triaxial CIU tests andK₀-consolidated compression and extension tests, the reconsolidated and cured clay samples show the strength and deformation characteristics similar to undisturbed clay samples having structures formed by the cementation.

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Although troubles of differential settlement and foundation of detached houses is not as common as that of the superstructure, repair costs of detached houses with foundation faults can be 10 times higher than that of ground reinforcement. The cause of differential settlement of the ground and foundation has not been much discussed. However, because of the frequent damage in the ground and foundation after a recent major earthquake, it is considered that there are some cases caused by a defect in the ground and foundation itself. It is important to organize the cause of differential settlement in foundation design and construction management. In this report, various dispute cases related to the ground and foundation were collected. With the results, we examined the difficulties in each case that were caused by method of design, construction and ground investigation.

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