Due to basemat uplift and yielding of foundation soils during earthquakes, stress induced upon bridge structures that have shallow foundations may reduce. This paper studies the effects of basemat uplift and soil yielding on the reduction of section force induced in bridge piers by using a macro-element model developed by PWRI so that it can deal with basemat uplift. Attention is paid especially to the effects of frequency characteristics of input motions on degree of stress reduction in the structure. As a result, it was found that degree of stress reduction effects vary depending on frequency characteristics as well as amplitude of the input motions in a complicated manner reflecting the complexity of nonlinear soil-structure interaction. To gain insight of such complicated mechanisms, they are further discussed taking into account flow of energy (i.e. how the given energy is transformed to kinetic and potential energy and how they are dissipated etc.) with regard to the SSI system and ground motion shaking.

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In the restoration from the Eastern-Japan Great Earthquake and the following accident of Fukushima-Daiichi nuclear power plant, the treatment and disposal of a large amount of wastes and excavated soils is one of the most important problems. In this study, the feasibility of barrier materials of coastal disposal facility for wastes and soils contaminated by radio-active cesium is discussed. Assuming the initial concentration of radioactive contaminants 100,000 Bq/l, 4 m thick clay barrier was designed and analysed. The analyses revealed that the hydraulic conductivity of the clay barrier needs to be kept below 5.0×10^-10 m/s to avoid the leachate of contaminants below the environmental safe limits. Therefore, a series of laboratory experiments was conducted on Tokuyama marine clay mixed with different proportions of bentonite to examine the engineering characteristics. The results of laboratory experiments showed that the hydraulic conductivity decreases with the addition of bentonite in the soil mixture. The performance on adsorption of clay mixture was measured by batch test and permeability test. The permeability test results showed that the adsorption properties were achieved by adding the bentonite to the Tokuyama marine clay.

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At the soft ground, the earthquakes generate large ground deformations. The large ground deformations displace the pile foundations, and induce the large pile forces at deep location. But it is not clear about the behavior of damaged piles, therefore, piles are generally designed not to be damaged by kinematic and inertial forces. In consequence, piles at soft ground have large diameter and it is difficult to cut off of the longitudinal bars in case of reinforced concrete piles at shallow location. The aim of this paper is to propose the economic seismic design code of pile foundations, and we make a study on the effect of cutting off of longitudinal bars reinforced concrete pile on lateral resistance under kinematic and inertial interactions by model tests and numerical simulations. The results of model loading tests confirmed that the damage at stepped rebar arrangement by ground deformation had no effect on lateral resistance, if the piles are not damaged by inertial forces. And it was possible to simulate the experimentally results by the static nonlinear analysis procedure with seismic displacement method. As a result, it indicated possibility of design considering the damage by ground deformations.

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In the radioactive waste disposal facility, sodium-type bentonite will be used as an artificial barrier material. They are expected to delay the infiltration of groundwater and fill the crack with the surrounding ground because they have high swelling performance. However, during the tens of thousands of years, the bentonite can be deteriorated and dissolved by the alkaline solution leached from the surrounding cement-based materials. Then, swelling performance of the bentonite may be lowered. In order to solve this problem, we proposed a method to mix inorganic materials such as fly ash, silica fume, sodium carbonate and ground granulated blast-furnace slag. In this study, we investigated the effect of the mixing on the degradation of swelling performance of the bentonite by using specimens immersed in the saturated aqueous solution of Ca(OH)₂ or the distilled water. The experimental results revealed that the maximum swelling strain of the bentonite immersed in the saturated Ca(OH)₂ solution was improved by mixing of fly ash, silica fume, or sodium carbonate. On the other hand, the mixing of ground granulated blast-furnace slag reduced the maximum swelling strain because the specimens were not saturated by the solution.

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We investigated properties relating to long-term stability under environmental exposure of soils improved by magnesium oxide addition, in laboratory experiments with a mixed solidifier composed of magnesium oxide and blast-furnace slag in varying ratios, with the ultimate objectives of reduced materials cost and an expanded range of applicable soils. A mixed solidifier with a magnesium oxide content of 0% to 100% was added to four types of soil to obtain improved soil having a solidifier content of 10%, and the uniaxial compressive strength and pH of the improved soil were measured. The results showed that the strength of the mixed solidifier slurry and the improved soil is substantially higher than when magnesium oxide alone is used as a solidifier. The uniaxial compressive strength of the mixed solidifier slurry was five to six times that of the magnesium oxide slurry. The strength of the mixed solidifier slurry and the improved soil varied with the mixing ratio of magnesium oxide and blast-furnace slag powder, and was highest for magnesium oxide mixing ratios of 30% or under. The strength of the improved soil under repeated submergence in water, rather than declining, tended to increase with age, much as in wet curing. The pH of the improved soil under repeated water submersion initially fell substantially but thereafter remained nearly constant.

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Soils including disaster waste and tsunami deposition soils were generated in large quantities. In order not to induce a new environmental impact, it is important for restoration and revival work to use these soils effectively as an engineered fill materials for construction. Organic matters, such as wood waste, are contained in these soils in large quantities, and in order to use as an engineered fill material for construction, it is necessary to evaluate the soil mechanical properties and to use for suitable purpose at suitable place. Moreover, depending on the case, the soil improvement is needed. In this study firstly, soil specimen was prepared through the same separation treatment as that conducting at the actual waste treatment site. Using the specimen with different wood waste percentage, the availability of soils as a construction material was evaluated. The result showed that these soils can be available as a construction material with appropriate treatment method. Moreover, the cost when the recycled soil is used for restoration and revival works was also examined, and the decrease of social cost by utilization of the recycled soil was shown.

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The measurement of pore-water pressure using tensiometers has been carried out to clarify seepage behavior in the ground until now. The value of measurement using tensiometers includes the influence of pore water pressure and pore air pressure. However, since it is assumed that pore air pressure is at 0 kPa of gauge pressure, effect of pore air pressure is not considered. Several studies have proved that increase of pore air pressure in the ground have influence on slope failure, rainfall infiltration, and so on. In this paper, we have measured the pore air pressure in the ground to investigate behavior of pore air pressure under different rainfall intensity and boundary conditions during rainfall infiltration. As a result of the experiments, increase of pore air pressure is observed under flood conditions at surface of the ground, and the necessity of measurement pore air pressure is shown.

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The ground layers of a section from Nanyo-Takahata IC to Yamagata-Kamiyama IC in the Tohoku Chuo Expressway is very soft includes mainly organic soil layers. Therefore, surrounding ground deformation and long term settlement by road embankment construction were predicted. To reduce these deformation and settlement, vacuum consolidation method was examined as a countermeasure, and trial embankment was carried out to confirm the improvement effect of this method.
This paper describes the study on the two-dimensional soil-water coupled FEM analysis result and 20 years long term settlement estimation for this trial embankment.

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Sinkhole accidents and depressions in urban areas are mainly caused by soil outflow through the breakage of sewer pipes. Underground cavities and loosened zones around those cavities are generated due to such soil outflow. However, some types of cavities are found to have developed close to underground structures, even though there has been no clear breakage in the structures. In this study, the influence of buried structures on the generation of cavities was investigated. A series of permeability tests was conducted to examine the local permeability of the soil at the boundary between the soil and a structure. It was suggested that the boundary between the soil and the structure had higher hydraulic conductivity than that of the ground. Model tests were also carried out to investigate the effects of buried structures on the expansion of cavities and ground deformation. It was revealed that the position of the underground structures strongly affects the generation of ground cavities. It was also observed that ground deformation expands before the expansion of cavities in sandy materials.

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A new technology has been introduced to recycle glass bottles into granular materials to be used as geo-materials. One of these granular materials has diameters in the range of 5 to 10 mm. In order to use of this material as backfill material of underground pipes, the validity of use of this material against earthquake-induced uplift of underground pipes, compaction technique on this material, and deformation characteristics of this material under cyclic loading was studied. A series of centrifugal model tests revealed that this material would not liquefy during earthquakes since this material has a high permeability. A series of compaction tests using large scale mold revealed that insertion of geogrids on the compaction of this material is effective. One-dimensional cyclic loading tests and cyclic triaxial tests revealed that residual strain of this material under cyclic loading is about 0.2%. These experimental results ensured that this material can be used as a backfill material of underground pipes for preventing them from earthquake-induced uplift and for preventing the settlement of ground surface.

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The restraint effect of ground displacement by reinforcement of the sheet pile, the sheet pile combined with the tie rod, and the sheet pile combined with the nailing are investigated by model tests and corresponding finite element analyses. An elastoplastic model, subloading t_ij model, is used in the analyses. Two loading conditions which are the simple vertical loading to the footing and cyclic loading associated with repeated shear deformation to the ground are applied to both series of the model test and finite element analysis. It is revealed that when the bearing capacity of the ground increases, the lateral and vertical displacements are restrained. The reinforcement by the sheet pile combined with the nailing is equal or more effective compared with the sheet pile combined with the tie rod.

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We reveal the relationship between the occurrence of shallow landslides triggered by heavy rainfall and the amount of effective rainfall using an equation involving the saturated seepage flow. The relational expression of the saturated seepage flow is expressed by an equation of continuity considering the amount of rainwater that infiltrates the soil layer, bedrock and the amount of water drained from the bedrock. Based on a tank model analysis, the amount of pore water included in the seepage flow within the soil is used to explain the amount of effective rainfall (D) and to obtain the previously mentioned effective rainfall equation. The coefficient of the amount of effective rainfall is linear to regional precipitation, which is unique to every region.

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In this study, the geotechnical data obtained from the boring logs and geotechnical tests in Myanmar were compared to those of Japanese data. The distributions of the particle density and the activity of both clays were almost similar. The compressibility indexes of Myanmar clays at the same liquid limit were about half of those of Japanese clays. The coefficients of consolidation of Myanmar clays at the same liquid limit were much smaller than those of Japanese clays. The average strength increment ratios, which were obtained from the relation between unconfined compressive strength and the effective overburden stress in the normally consolidated ground, were 0.225 two third of Japanese clays.

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