The reinforced soil method by vertical micro-piles which constructed from the top of slope enables the space-saving construction. The method can be utilized in the neighboring work and the maintenance work of infrastructure. While there are some precedents of micro-piles of such applications, the reinforcement mechanism has yet to be clarified. Therefore, to clarify the mechanical behaviour of the reinforced soil method by vertical micro-piles, the full-scale test embankment was conducted with the different pile angles and the pile spacing under the condition corresponding to the assumed slip line. The measured behaviour showed that the effect of suppressing the displacement was high in the case with raking pile on the front side. For the sectional force of micro-pile, the axial compressive force and the bending moment according to the deformation were measured. Regarding the overall behavior, the three dimensional FE analysis was carried out to evaluate the validity of measurement and the reinforcement effect.

In this paper, a simple cost-effective method for evaluating the stability of existing embankment is proposed. This proposed method would facilitate engineers to identify unstable embankments, and also to provide valuable information to select an appropriate countermeasure. This proposed method is comprised of surface geological exploration, dynamic cone penetration test, vibro-cone sampling, and simple stability analysis. Based on a couple of case studies, it is manifested that the proposed method provides a factor of safely, being slightly lower than that from the conventional method for detailed investigation, implying the adequacy when using the proposed method for screening aseismic stability of embankments. It is also suggested that the application of the proposed method would be greatly enhanced when the strength of fill material as well as the water level in the fill are both properly estimated.

In Japan, the Environmental Quality Standards for Soil Pollution of 1,4-dioxene was enforced in April 2017. In this study, the properties of 1,4-dioxane between three phases in soil were confirmed by batch tests and the volatility, infiltration and adsorption characteristics of 1,4-dioxane in soil, and groundwater were confirmed by three types soil column tests. The following conclusions were drawn from the results of these tests: The amount of 1,4-dioxane volatilized from unsaturated soil is relatively small, and most of volatilized 1,4-dioxane dissolves in soil pore water while it migrate and diffuses through the soil pore space. 1,4-dioxane quickly infiltrate downwards in unsaturated soil during rain infiltration, but shows no migration in unsaturated soil unless the rain infiltration occurs. There is a possibility that soil contamination occurs downgradient of groundwater flow when 1,4-dioxane contaminated groundwater continues to flow.

The purpose of this work was to evaluate locations with high risk of slope failure in an earthquake around transmission towers using desk analysis. To this end, a flowchart was constructed for extracting such locations. The flowchart has two stages, for a large area and middle area. In the large-area stage, the flowchart is implemented based on geologic and topographic maps after selecting the form of slope failure. The middle-area stage is implemented based on a digital elevation model (DEM). Basic factors calculated from the DEM and its threshold values are determined by a case history of slope failure during past upper-crustal earthquakes. The flowchart was applied to slope failure caused by the Mid Niigata Prefecture Earthquake in 2004, which showed that locations identified by the flowchart as dangerous and those with actual failure coincided well.

Since the ground surface above the damaged conduits might cave in, and it is difficult to estimate where and when it would occur because vast amounts of conduit are buried in the ground, it is useful to know priorities to the improvements based on the resistance characteristics of the soils. Concerned with this issue, the model tests to investigate the mechanisms and the searching technology for the existing caves were conducted and reported, but research from view point of soil characteristics related to the resistance against effluence is insufficient. In this paper, a series of model tests was conducted to cause soil particle effluence from an opening of the damaged pipe using several kinds of materials including either plastic or non-plastic fines in order to know the influence of both amount and plasticity index of fines on the resistance against effluence. It is proved that the combination of fine's content and plasticity index determine the resistance against effluence. Further, for the soil used in this study having a fine of rather large plasticity index, the resistance against effluence was larger when compacted under the condition of having a little more water content than the optimum water content.

The natural frequency of the bridge pier is used as an index to evaluate the soundness of pier foundation ground against scouring. It is difficult to obtain the natural frequency from microtremor in some cases, as the peak of the Fourier spectrum of the bridge piers from the microtremor does not appear clearly in many cases, unlikely that from the impact vibration test. Furthermore, conventional approaches based on microtremor require the natural frequency which is acquired recently from the impact vibration test. However, if the evaluation method based on microtremor could be put into practical use, it is advantageous in terms of cost, and suitable for constant monitoring. Therefore, we proposed a method that can automatically identify natural frequencies only from microtremor measurement results at both sides of the bridge piers, without requiring the latest result of the impact vibration test. Based on the results of measurements on the railway bridges, we showed that the natural frequency can be identified from microtremor measurement results by the proposed method.

Estimation of water level for the persistent situation or prior to earthquake is crucial for evaluation of seismic performance of road embankments. Numerical modeling studies and model experiments are conducted to investigate effects of condition of foundation on the water level in the embankment. Variations of rainfall intensity, rainfall duration, thickness of permeable foundation are considered. Parametric study and model experiments reveal that the thinner the foundation thickness or the smaller the foundation permeability, the higher the convergent water level and rise velocity and the lower the drop velocity of water level. This study also shows framework for evaluation of the water level by considering both the thickness of foundation and the permeability of foundation. In addition, the model experiments reveal that the shorter the rainfall duration, the lower the water level and rise velocity.

Based on the boring database, soil distribution, N-value and various engineering properties were revealed in alluvial subsurface layers of Niigata City. In northern area of the city, soft fine-grained soils and organic soils are contained in the shallow layer between dune deposits. In the depth of about 10-40 m, coarse-grained soil layers with average N-value over 30 are dominantly. These layers are composed of fine or medium sands with average fines content F_c under 10% in shallow, while F_c tends to increase at the depth of more than 20m. In the southern back mash area, subsurface layers contain fine-grained soils and coarse-grained soils in same degree from shallow layers to deep deposits and average N-values are smaller than in the northern area. As F_c is higher in coarse-grained soil, and as clay content is higher in fine-grained soil, the layer indicates smaller wet density, larger void ratio and natural water content. Fine-grained soils have about 70% average liquid limit and most of them are distributed near the A line of the plasticity chart. Unconfined compression strength and consolidation yield stress increase with depth, and they tend to be overconsolidation in shallow layers, while they are close to normal consolidation in deeper 30m.

A variety of types of grouting models have been proposed. We propose the parallel plates radial flow model with limited geometrical parameters. The model is considered to be useful to the intelligent construction for grouting. Also, the model is applicable mainly to a developed fractured rock mass in which turbulent and laminar flow condition coexists. Therefore the critical Reynolds number is very important to the model, which is related to the transfer condition between laminar and turbulent flow. Thus we conducted laboratory tests in use of single rock fissure and in-situ permeability tests with highly viscous fluid in several dam sights. Moreover, we conducted grouting simulations with the model under consideration on the viscous property of a grout as non-Newtonian fluid. This analysis researched for injection conditions in order to adjust a turbulent-laminar transfer radius to a target grouting radius under a low critical Reynolds number. The result indicates that the condition is available on limited injection pressure, flow rate and grout mix corresponding to each hydraulic fracture-aperture.

In order to investigate the effects of the specimen preparation method on liquefaction properties of sandy soil, a series of undrained cyclic triaxial test and image analysis were performed. Test specimens were prepared by using Toyoura sand under different conditions in terms of compaction thickness and initial water content. As a result, the liquefaction resistance depended on the compaction thickness, and the liquefaction resistance curve moved upward slightly with a decrease of compaction thickness. In addition, the liquefaction resistance changed by approximately 20% with a change in the initial water content by only 1.5%. The distributions of the local axial strain obtained by the image analysis showed different tendencies depending on the compaction thickness. In particular, significant effects of local density distribution in the vertical direction could be inferred from the local axial strains of the specimen with 4 layers of compaction.

Damage of house such as settlement or tilting by ground liquefaction has been reported every time earthquake occurs. In order to prevent from these damage, some liquefaction countermeasures have been proposed and proved these effect. However, the verification of effect haven’t been enough in the case of building houses already or for the method of reducing and suppressing damage to houses by liquefaction. Therefore, in this study, 1G model shaking table test and simplified analysis were conducted to confirm the effect of countermeasure using artificial drain pipe for existing housing ground and to establish its design method. As the result, it was possible to confirm the damaging suppression effect of the countermeasure from the model experiment, and by numerical analysis it was possible to reproduce the relative housing settlement suppression effect of liquefaction countermeasure.

Torrential rainfall occurred around Hiroshima City, in August 2014, leading to large scale debris flows that traveled via mountain streams. The weathered granitic rock in the Hiroshima region is likely to erode further during heavy rainfall, causing similar sediment disasters. Believing that it is important to elucidate the frequency and impact of previous disasters, and to assess the probability of future ones, we conducted a field survey. We observed multiple layers of paleo debris flow deposits along streams in this area and used radiocarbon dating techniques on carbonized materials in the deposits to determine when the debris flow occurred. We found evidence of at least 7 debris flow events based on the results of dating and historical documents. The occurrence cycle of debris flow is estimated at 150-400 years．

The paper proposes the method of measuring groundwater levels through variations of the earth resistance. The earth resistance varied by two to forty times between above and below the groundwater level. Therefore, the groundwater level can be revealed regardless of permeability of soil from variations of the earth resistance continuously measured with electrodes installed into the ground. The proposed method has the following advantages over conventional methods of measuring groundwater levels. 1. A water standpipe is not required. 2. The groundwater level can be measured without waiting time even in cohesive soils. 3. The method can be adopted alone as well as along with the soil investigation. The groundwater level can be economically measured in a short time by the proposed method regardless of soil types compared with the conventional methods.

For the design of pipe foundation of large-span bridge, in-situ loading test on the deep Pleistocene clay layer was carried out.　The loading plate, the diameter of which was 250mm, was placed on the Pleistocene clay layer at 70 m depth utilizing the bore hole.　The settlement was observed for 9 months, in which the step loading was given by the hydraulic jack. Measured settlement showed the periodic fluctuations related with the tidal change, and the settlement continued with time and the tendency of convergence was not shown within the 9 months. The compression strain of Pleistocene clay calculated from the measured settlement was almost same as that predicted from the consolidation yield stress and coefficient of secondary compression obtained from laboratory test of undisturbed samples. The settlement-time relationship of in-situ loading test was explained by the numerical analysis in which Cam-Clay model was used for the Pleistocene clay layer.