In recent years, landslides caused by heavy rainfall have been occurring frequently, and there is concern that landslides caused by heavy rainfall may become more serious. It has been suggested that one of the causes of landslides due to heavy rainfall is the effect of surface water erosion on the ground surface. In this paper, the erosion of the land surface is evaluated based on the water level of surface water predicted by the code TAG_FLOW developed by Nguyen et al. The code was applied to the case of a landslide in Tomioka City, Gunma Prefecture, Japan which was severely damaged by Typhoon Hagibis in 2019. The results of the analysis showed that the method can qualitatively represent the actual disaster phenomena to some extent, although there are some issues to be improved in the modeling of erosion, suggesting the possibility of future application of the method.

It is important to predict the deformation of the temporary earth-retaining wall and the surrounding ground when performing large-scale excavation near existing structures. However, the lateral pressure applied in the current design of excavation earth retaining work is calculated from various values of the ground based on the results of field measurements and laboratory tests uniformly regardless of the excavation step. It is rarely conducted to measure the lateral pressure and to compare the measured values with the value used in the designs. In this study, in order to clarify the relationship between the earth pressure distributions acting on the earth retaining wall and the amount of displacement, series of centrifugal excavation experiments were carried out using a centrifugal model experimental device which could consider the process of excavation in real construction works. As a result, it was confirmed that the earth pressure at the beginning of the excavation step is larger than the active side pressure applied by the current design method, and this value tends to decrease shallower than the excavation surface as the excavation work progresses.

The relationship of permeability and shear properties to soil compaction curves is well known, but the mechanism has not been clearly explained. This is because it has been difficult to accurately evaluate PSD (pore size distribution). This paper clarifies the physical basis of PSD obtained from SWCC (soil water characteristic curve) and enables quantitative evaluation of the soil structure using PSD obtained from high-precision tests and SWCC. This enables quantitative evaluation of changes in soil pore structure depending on the water content during soil compaction, and clarifies the mechanism of compaction curves and hydraulic conductivities. When unsaturated sandy soil is compacted and tested after saturation, the results suggest that the water content during compaction affects the results.

Strength and permeability characteristics of waste ground mixed with plastic, debris, etc. at inert waste landfill sites and illegal dumping sites were investigated using in-situ strength tests, boring investigations, and large column tests conducted at 27 waste ground sites (49 locations) in Japan and overseas. Waste ground mixed with long plastic and other materials has high shear resistance and also has high slope stability due to its unique tensile resistance. On the other hand, for collapses that occur domestically and internationally due to heavy rainfall and in which the deposited waste layer slides on the sloping subgrade, the slip resistance of the subgrade, which generally has low shear resistance, becomes dominant. The slope stability evaluation should take into account the long-term storage of rainwater on the upper surface of the sheet-like materials in the waste layer. The slope failure patterns that are mainly assumed based on the strength and infiltration characteristics are also shown.

In this study, we discussed the calibration curves (experimental, theoretical, and approximate) for the refractive index of aqueous glycerol solution. Next, the results (refractive index) of the water content test using the glycerol method, which has been conducted on commercially available reagent gypsum that imitates recycled gypsum derived from waste gypsum board, were applied to three different calibration curves (experimental, theoretical, and approximate) and calculations were made to determine how much the different calibration curves used affect the water content value. The obtained results showed that the difference between the water content obtained by the glycerol method and the set water content increases as the set water content increases, and at a set water content of 300%, the difference between the water content obtained by the glycerol method and the set water content was 8.4% for the experimental method, 50.8% for the theoretical method, and 296.6% for the approximate method, and therefore, it was clear that the water content obtained by the experimental equation was sufficiently accurate.