This paper examines an appropriate interval measuring surface displacement and elapsed time to a slope failure using data measured in a large sandy slope under artificial rainfall. We compared the reproducibility by comparing a time-displacement curve of original data with that of thinned out data in different time and/or displacement. When intervals measuring surface displacement make less than 5% of total surface displacement to the slope failure, the reproducibility of original data becomes high. Similarly, high reproducibility is provided by making time intervals measuring the slope failure time less than 5% of total time to slope failure. These results imply that the adequate measurement accuracy depends on the displacement amount and time until failure and it is necessary to choose a monitoring device corresponding to the measurement accuracy.

Generally, the performance of reinforced soil retaining walls against earthquake is known as higher than other non-reinforced soil structures. Some of the structures are suffered from the decreased efficiency of drainage facilities due to insufficient designs or constructions. The reinforced soil structures were often damaged during earthquakes due to the effects of seepage induced by rainfalls. In order to clarify the mechanism of the damage, it is necessary to examine seismic behavior of reinforced soil walls under the infiltrated rainfall. In this study, a series of centrifuge model tests on the multi-anchored reinforced soil retaining wall were conducted to investigate the deformation mechanism due to earthquake. As a results, high seismic performance of reinforced retaining soil walls was recognized even during seepage flow. In the case of the reinforced soils retaining walls with very loose compaction of backfill, however, the large deformation leading to ultimate critical state occurred. The test result also shows the unique behavior of reinforced region that moved integrally. This implies that the reinforced region has been behaved as if it became one mass, and this behavior make this structure increase seismic performance. It was clarified that design and construction of the backfill equipped with drainage facilities are important to maintain the stability of the soil retaining walls during earth quake with high ground water level.

A permeability evaluation method of micro-particles was introduced in this study to establish efficient micro-particles permeation methods for liquefaction countermeasure. Since permeability of micro-particles is closely related to that of soil, a pore strongly contributing to permeability of soil was defined as “representative pore diameter”. First, effectiveness and problems of the Creager equation were discussed through the results of permeability tests with mixed sand and matrix-void ratio, where “representative pore diameter” is assessed by distribution of particle sizes. Next, an estimation method to obtain “representative pore diameter” from permeability coefficients was suggested and the estimated “representative pore diameter” was defined as “pore index”. Its applicability was verified from the result of permeability test with variously mixed sand. Finally, permeation tests using micro-particles were carried out and an evaluation to determine the permeability by the pore indexes and the uniformity coefficients was proposed.

This study aims to analyze damage caused by typhoon No.10 that attacked at the end of August in 2016. Heavy rain induced by the typhoon caused extensive damage in Tohoku area and Hokkaido. The damage caused in Iwate prefecture, the most severely affected prefecture in Tohoku area, is mainly studied. The damage of slope disaster and flood are analyzed from viewpoints of geotechnical engineering and river engineering, respectively. Regarding to flood, the most serious damage occurred in Omoto area, and the damage is mainly investigated in this study. Based on the analyzed results, current issues for heavy rain disaster mitigation are discussed.

The Hokkaido heavy rainfalls due to Typhoon 7th, 11th, 9th and 10th in 2016 caused floods of rivers, slope failure and debris flow. In particular, serious geotechnical damages were induced in Hidaka district, for example collapses of road embankments and cut slopes and road facilities. This paper describes geotechnical characteristics of decomposed granite and periglacial soils sampled from the Nissho mountain pass and Hokkaido Odan Express-way (Do-to-do). A series of site investigation and laboratory tests for physical mechanical properties were performed on the soils materials. In consideration of test results, it was found that soil layers of weathering residual granite soils specified into problematic soils were observed in disaster areas and that the mechanical behavior was changed depending on the degree of weathering (environmental conditions). In order to evaluate geotechnical evaluation of soil materials having particle breakage, the mechanical behavior of the decomposed granite soils was compared with those of volcanic coarse grained soils with particle breakage. Based on the results, a geotechnical evaluation method was also discussed in this study.