Rock slope, which have not clearly slide before, sometimes bring about deep-seated landslide owing to external force (e.g. heavy rain fall). In the inner part of such a rock slope, the rock bridges are certainly confirmed on the actual cases of a deep-seated landslide. In this study, two cases of centrifuge model tests assuming two actual landslides were conducted to evaluate deformation mechanisms of a deep-seated landslide. The deformation behaviors due to monotonous centrifugal loading demonstrated that local deformations are concentrated around inner rock bridge, and different deformation behaviors are clearly obtained due to the location of rock bridge. Swelling behaviors on the middle of slopes are locally observed in both two cases.

The purpose of this study is to evaluate the influence of the spatial heterogeneity of the geotechnical materials on the uncertainty of the factor of safety(Fs) of slope. Monte Carlo Simulation(MCS) based on slope stability analysis with using shear strength reduction FEM was performed. As the results of MCS against for each parameter controlling the spatial heterogeneity in materials, it is shown that the average values of the probability density distribution of Fs obtained by MCS are always below the results of analyses assuming the homogeneity in materials. Given this fact, it is possible that the assumption that the materials are homogeneous leads to overestimate the durability of the structure. Furthermore, based on the results of MCS, the overdesign factors commonly used to secure the safety of the structure was calculated. The overdesign factors tended to increase exponentially as the coefficient of variation of probability density distribution obtained from MCS increased.

The water retention tests in this study were conducted using wettable and water repellent soils to investigate its water retention characteristics. For this, a newly established water retention testing system which uses continuous pressurization method was utilized, and the water repellent sand was artificially prepared by the silanization process. As a result, it was confirmed that the testing time for the drying and wetting processes in the soil water characteristic curve was remarkably shortened. The air entry value of the water repellent soil is similar to that of the wettable soil, while the water entry value and water infiltration value of the water repellent soil are smaller than the wettable soil. Even with a limited data, this indicates that the effect of the repellent state on soils has a larger hysteretic behavior than the wettable state on soils due to material characteristics.

In snowy areas, slope failure triggered by snowmelt water (hereinafter referred to as snowmelt disasters) have occasionally occurred. In this paper, we analyzed 45 cases of snowmelt disasters that occurred along the railway slope. In embankment cases, there was a tendency to cause snowmelt disasters frequently in expanded or embankments under cutting slope with the height of about 3m or more, and in cutting slope of terrace cliff. In addition, as an extracting method of the dangerous location concerning snowmelt disasters, we focus on the risk assessment criteria of rainfall for the slope failure that is used in Japanese railway and compared the evaluation points of that criteria between the snowmelt disaster cases and the no-disaster cases. As the result of comparison, the tendency of the evaluation point of disaster cases to be lowered and it is confirmed that the proposed extracting method of dangerous location can be effective.

Bioremediation is a low-cost, environmentally friendly technique that uses the degradation capability of microorganisms. To accelerate biodegradation process in practice, it is necessary to incorporate with injection of enhancement agent. The injection of an enhancement agent into a low-permeability stratum, however, is not easy, because mass transport within such stratum is mainly controlled by diffusion in most cases. In this study, derivation of theoretical solutions to and parametric studies on diffusion in three different systems were performed. The three types of diffusion were planar diffusion, hollow cylindric diffusion and hollow spherical diffusion which correspond to three approaches potentially being used in practice, respectively: utilization of an aquifer or a slit created by water jet, utilization of a borehole, and utilization of the bottom of a borehole. The results of theoretical examination illustrated that planar diffusion that can be realized through cutting slits by water jet is the most effective way for the injection of an enhancement agent in engineering practice.

Injection of hydrogen release compound can enhance bioremediation process of chloroethylenes in situ. In the case of remediating low-permeable formations, difficulties can be induced due to hard permeation of enhancement agent for injection method or dissolution of formation into mud for stirring method. To overcome these difficulties, we proposed an approach that injects hydrogen release compound into slits cut by waterjet with a curtain interval considering the advantage of using planar diffusion based on the theoretical examination. In situ demonstration tests were performed at two contaminated sites with a slit interval of 0.3m. The results demonstrated that for low concentration contamination, the site could be almost completely remediated within 8.5 months, and for high concentration contamination with the maximum PCE concentration of 75mg/L, it could be degraded to below the environmental standard (0.01mg/L) within 2 years. The effectiveness of using waterjet for injecting bioremediation enhancement agent based on planar diffusion was verified through the in situ demonstration tests.

Liquefaction of foundation soil attributes significant damage to infrastructures. The sand compaction pile method is one of the countermeasures against liquefaction to densify the ground by installing dense sand piles. In recent years, an innovative method has been developed to install the sand piles at various geometric form into the ground. However, the effects of the geometric forms on the response and deformation behavior of the improved ground are not well understood. The authors have studied the effect of SCP improved ground geometry on the seismic behavior of embankment by physical modeling and numerical analyses. The centrifuge model test results were reported already. In the analyses, a series of dynamic FEM analyses is carried out to investigate the behavior of unimproved ground and SCP improved grounds with vertical geometry and inclined geometry. From the analyses, the unimproved ground is liquefied during shaking and the foundation ground is experienced large lateral deformation, which induces significant settlement of embankment. For SCP improved grounds, although liquefaction is not prevented, the significant reduction in foundation ground deformation and embankment settlement can be observed. The inclined SCP improved ground shows the larger reduction of the embankment settlement than the vertical improved ground.

The authors focused on the excellent reinforcing effect of the reinforced wall method which is widely used in land construction, and proposed a reinforced sheet-pile quay wall structure that applies geogrid as a reinforcing material behind the sheet-pile. This study attempted to solve the problems in the practical use of the new structure via pull-out tests, large-scale loading model tests, and centrifuge model tests. As a result, irrespective of differences in air / water or pulling out during static / seismic condition, the authors confirmed the generation of a shear resistance force for geogrids even in loose rubble ground, and the proposed structure was effective at both static and dynamic situations. Numerical analyses showed that it was necessary to sufficiently fix the geogrid to the land side of the active failure surface and particularly the length of the lowest geogrid had a huge influence on the overall external stability. A design method for the new structure was also proposed, based on the aforesaid investigation.

In this paper, we propose a calculation method of pore size distribution which formed by soil having various soil particle sizes, assuming that soil particles and the pore between the soil particles are spherical. The pore spheres formed between the soil particles are defined as spheres that are inside four mutually contacting soil particle spheres and circumscribe all four soil particle spheres. The size distribution of the pore sphere is obtained from the probability of taking out 4 soil particle spheres based on the type and quantity of the soil particle sphere present. In addition, a calculation example of the pore radius distribution of the pore sphere formed by soil particle spheres having a particle size distribution similar to actual sandy soil is shown. By this method, it is expected that the suction stress acting between the soil particles of the unsaturated ground can be quantitatively evaluated and the suction stress in the unsaturated soil can be reflected in the design.

Severe liquefaction disaster, caused by the Great East Japan Earthquake, occurred at the residential area of 200ha in Hinode district, Itako city, Ibaraki prefecture, in March 11 2011. Itako city aimed to restrain recurrence of liquefaction, and began project countermeasure against liquefaction in urban area used “the Great East Japan Earthquake disaster reconstruction subsidy” in February 2012. In this project, we focused on the development history of Hinode district, and considered that the “groundwater level drop method” is suitable for this area. We also verified its feasibility. After the verification, the countermeasure work against liquefaction was carried out. In April 2018, the liquefaction measures review committee confirmed drop of groundwater level, the work which was unprecedented as countermeasure against liquefaction in the existing urban area was completed. The series of circumstances were referred, in decision of “the guidance for countermeasures against liquefaction in urban area”, which is the guideline of the Japanese government. The guidance is used as a guide in followed other cases. This report reports the process of these series of projects.

For a large unstable rock mass on the slope close to road, countermeasures such as fixing by steel wires, rock bonding method and removal after crushing small have been often carried out. A long period of traffic regulation by countermeasure treatment of mountainous road which connect local communities imposes a great deal of inconvenience to the local community. The target of this case is a large unstable rock mass sitting on the slope with the falling energy of about 8,000 kJ. The details of circumstances of rock removal by the national highway agency are described including the process of thinking for risk avoidance, preliminary survey, design, and the validation of field treatment. The knowledge obtained in this study will serve as a reference measures of risk management of road and rockfall mitigation in the future.