Abstract

In geological disposal for high-level radioactive waste, bentonites are planned to be used as the buffer material surrounding radioactive waste in Japan. Bentonite-based buffer material requires low water permeation for delaying contact between groundwater and the waste. Because of the extremely long half-lives of radionuclides of the waste, several barriers including the buffer material are designed to maintain workability of the geological disposal facility for tens of thousands of years. However, in the disposal circumstances with high water pressure, high temperature and various groundwater chemistries, occurrence of cementation and consequently property changes of the bentonite in the buffer are concerned. Few studies are available to understand the effect of cementation on bentonite properties because of the difficulties of simulating long-term alteration process experimentally. From the viewpoint of natural analogues, cementation process of the buffer may be regarded as part of formation process of bentonite ore. Thus, in this study, permeability tests were conducted on three kinds of Na-type bentonite ores with different geological ages from respectively, Japan, USA, and China to see the influence of cementation on permeability of bentonites. For comparison, undisturbed and reconstituted specimens were prepared. The results show that difference of hydraulic conductivities of the undisturbed and reconstituted specimens for each ore is less than one order, and this difference seems not to correlate with the geological age of the ores. From these results, the influence of cementation on the hydraulic properties of bentonite buffer seems small. It may also be a counteracted result by cementation effects in terms of restriction of the swelling of montmorillonite and blockage of water flow paths.

With a newly developed swelling pressure apparatus, swelling pressure tests were conducted to elucidate initial water content and specimen preparation method effects on swelling pressures (swelling pressure evaluation curves and equilibrium swelling pressure) of Kunigel-V1 bentonite. X-ray diffraction (XRD) tests were conducted to investigate initial water content and specimen preparation method effects on basal spacing, including basal spacings of specimens before and after wetting. Experiments produced the following results. 1) The swelling pressure evaluation curve changed from a line with peak and valley to a line with early stage steady rise as increasing initial water content. 2) Initial water content and specimen preparation method exerted no apparent effect on the equilibrium swelling pressure. 3) Basal spacing of specimen before wetting was affected not only by the initial water content but also by specimen preparation method. 4) The initial water content did not influence basal spacing of specimen after wetting. It was only affected by the specimen preparation method. Based on the swelling pressure evaluation curve patterns, swelling mechanisms during saturation for specimens with different initial conditions were discussed. Initial water content and specimen preparation method effects on equilibrium swelling pressure were explained carefully with basal spacings.

A multi-ring and a newly developed swelling pressure apparatus were adopted for measuring swelling pressure during saturation of three low dry density bentonites (sodium type: MX-80 and Kunigel-V1; calcium type: Kunibond). Subsequently, slices from the multi-ring were observed using X-ray diffraction (XRD) tests to detect basal spacing changes. Distance between particles was calculated from basal spacing database. Relations between microstructural changes, including basal spacing and distance between particles, and swelling pressure are discussed. Results show that calcium type bentonite has greater swelling pressure than sodium type bentonites during saturation. When bentonites have the same cation type, lower montmorillonite content bentonite obtains smaller swelling pressures than those of high montmorillonite content ones. Basal spacing increases drastically first, then maintains a stable value during saturation. All three bentonites gradually reach 3 w state along with wetting (MX-80 and Kunigel-V1: 1-3 w; Kunibond: 2-3 w). The distance between particles increases with the saturation time. During saturation, swelling pressure generally rises with increasing basal spacing and increasing distance between particles. The mechanism for swelling pressure development is discussed.

This study starts from a question: how would initial water content (w_i) affect equilibrium swelling pressure (p_eq) of compacted bentonites in swelling pressure tests (p_s tests)? However, discussions, based on experiments of a bentonite, Kunigel V1 (K_V1), are extended to issues: 1) w_i effect on p_eq, 2) pore water density (ρ_pw), 3) co-existence of crystalline and osmotic swelling, and 4) relation between p_eq and compaction tests (p_c tests). It is revealed that w_i has insignificant effect on p_eq in general, though significant effect may appear for relatively high w_i and dry density (ρ_d) conditions. Two swelling types, crystalline swelling with basal spacing of montmorillonite (d₀₀₁= 1.0 nm - 1.9 nm) and osmotic swelling (d₀₀₁ ≥ ∼4.0 nm), co-exist in a w range from 36 to 65%. With the fact that ρ_pw of K_V1 may range from 1.1 to 1.2 Mg/m³, it is expected that crystalline swelling may mainly govern p_eq in p_s tests if the final dry density of a specimen (ρ_df) is larger than 1.46 Mg/m³, while osmotic swelling may mainly govern if ρ_df <1.05 Mg/m³. Together with results of p_c tests, the effect of w_i on p_eq are explained by the proposed conceptual model.

Sand-bentonite mixtures with bentonite content of 10-30% had been planned to handle low-level radioactive waste in Japan, because of its low permeability. Hydraulic conductivity of sand–bentonite mixture depends on the bentonite type, bentonite content, initial water content, and other factors. Given this background, falling head permeability tests were conducted on sand–bentonite mixture by varying the compaction energy for specimen preparation, initial water content (10–20%), and bentonite content (15– 30%). For these tests, the hydraulic gradient of 25-500 was set. Consequently, the hydraulic conductivities were 10^-8 – 10^-13 m/s for all tested conditions. Correlation between the hydraulic conductivity and the effective montmorillonite dry density (montmorillonite mass divided by the sum of montmorillonite, air, water volume), which is often used to correlate the hydraulic conductivity of bentonite, was found. Correlation was also found between the hydraulic conductivity and a new index designated as the effective montmorillonite wet density (sum of montmorillonite and water mass / sum of montmorillonite, air, water volume). Effective montmorillonite wet density reveals differences in the specimen structural distribution through consideration of the initial water content.

In Japanese project for disposal of high-level radioactive waste, the self-sealing capability of bentonite buffer material, which results from the swelling deformation to fill the gaps between waste container and wall of disposal pit, must be retained thousands of years. However, because of the effect of high pressures, occurrence of cementation and property changes of the buffer material are a concern. Few studies had examined cementation effects because of the difficulties for simulating long-term alteration process experimentally. In this paper, swelling properties of consolidated buffer are regarded as similar as those of naturally consolidated bentonite ore. Therefore, three kinds of bentonite ores were used for experiments to elucidate influences of cementation on self-sealing capabilities. Undisturbed and reconstituted specimens were prepared to assess their swelling pressures after filling a preset gap in a swelling pressure apparatus. Results show that for Japanese ores, the swelling pressure of undisturbed specimens is about half that of reconstituted specimens. For American and Chinese ores, the difference of swelling pressure is greater when the preset gap is smaller. Results imply that effects of cementation on self-sealing capability are smaller when swelling deformation is allowed.

A testing procedure was proposed to study water movement in compacted bentonite and the development of swelling pressure (p(s)) when compacted bentonite specimens were wetted. In this procedure, a multi-ring mold was introduced for p(s) measurements, after which the specimen was sliced for X-ray diffraction to find movement of water in the interlayer space of montmorillonite. Results revealed a relation between four phases of ps development and evolution of four states of interlayer water molecule arrangement of montmorillonite (L): when ps reached its first peak in phase I, L moved from 1 row water arrangement (1w) to at least 2w; when p(s) decreased and re-increased in phases II or III, L moved from 2w to at least 3w; and when ps reached a steady state in phase IV, L = 3w. The w distribution in the compacted bentonite was also measured as water absorption time increased. Based on those results, the global water movement was estimated in terms of diffusivity (D) following a method employing Boltzmann transform. Results of comparisons implied that D calculated using this method matched experimental data well and the method was rather easily handled.

© Springer Nature Singapore Pte Ltd. 2019. In geological disposal of high level radioactive waste, it is essential to start considering consolidation accompanying cementation, taking into consideration high earth pressure and solution of groundwater. For engineering application of natural analogue, the authors thought consolidated buffer material will have similar physical properties to bentonite ore. In this study, we aimed to quantitatively evaluate the influence of cementation on swelling properties. In order to achieve this aim, we focused on swelling pressure and swelling strain of bentonite, using two kinds of bentonite ore whose generation dates are different respectively. As a result, swelling pressure was decreased by approximately one order of magnitude due to the influence of cementation. In addition, the swelling strain of younger bentonite ore did not decline, but those of older bentonite ore declined about half of original whether consolidation was retained or not. Therefore, there is a possibility that the swelling deformation of buffer will decline as cementation gets stronger over the course of time.

 The 2011 off-the Pacific coast of Tohoku earthquake affected Japan, wreaking severe damage to a nuclear power plant in Fukushima. During decommissioning, ensuring worker safety is important in relation to fuel debris retrieval. Given that background, the authors specifically examined the use of heavy bentonite-based slurry as a filling material in a nuclear reactor. Heavy slurry can shield gamma rays and neutron beams because of its high specific gravity and water contents. Also, soil materials are used for soil cover type storage facilities for radioactive waste without evaluation for shielding. This research was conducted to investigate and define the radiation shielding capability of soil materials for controlling nuclear accidents. To quantify the radiation shielding capability, the authors measured the transmitted radiation dose through soil materials under some conditions of pass length. Results show that the reduction of the gamma ray dose has a proportional relation with wet density of materials, and show that the reduction of the neutron beam dose is related with the volume water content of materials. The research described in this paper is a proposal for application to the design for construction using soils for decommissioning of the Fukushima Daiichi Nuclear Power Station.

This report presents carbon dioxide (CO2) fixation properties of an iron and steel slag containing calcium, in order to contribute to a geotechnical application for the formation of a sound material-cycle society and a low-carbon society. To investigate the properties of CO2 fixation, CO2 fixation tests with constant flow were conducted. Results show that when the CO2 concentration 4500 ?L- CO2/L was flowed in a specimen by 0.05 L/min, for a non-aged steelmaking slag, the amount of CO2 fixed was the maximum: 0.04 g- CO2/g-slag. The amount of CO2 fixed in the steelmaking slag resulted from about 20% of soluble calcium in the chemical reaction. Therefore, it is possible that the quantity of CO2 fixation can be evaluated from the viewpoint of the mechanism of CO2 fixation using the quantity of water-soluble calcium.

As for the low permeable layer, important functions are expected as an engineered barrier of radioactive waste disposal for low-level waste with comparatively high radiation levels. On examining the construction methods of this low permeable layer, it is important to confirm the possibility of the construction in the conditions similar to the actual constructed conditions with a true scale size. Therefore, the construction examination for the side part of the low permeable layer by bentonite and the performance check test of the low permeable layer were carried out. The result of the construction examination showed that the possibility of the construction were confirmed, and the result of performance check test showed that it was possible to ensure the required performance of the low permeable layer, such as hydraulic conductivity.

Bentonite-based buffer for high-level radioactive waste (HLW) disposal is expected to fill the interstitial spaces around buffer materials by its swelling deformation. This study performs one-dimensional model tests simulating the relation around the buffer and evaluates the self-sealing capability of the buffer quantitatively. It also investigates the applicability of the theoretical equations for evaluating the swelling characteristics of a bentonite-based buffer, first proposed by Komine and Ogata, to analysis of the self-sealing capability by comparing the calculated and experimentally obtained results. Furthermore, this study has shown the design flow for specifications of bentonite-based buffer from the viewpoint of self-sealing capability.

The 2011 off the Pacific coast of Tohoku earthquake has impacted Japan, and it made serious damage to nuclear power plant in Fukushima. At present, Japanese government and engineers proceed decommissioning of the power plant, and ensuring safety of workers is the most important matter especially in fuel debris retrieval. On these backgrounds, the authors focus on heavy bentonite based slurry for filling material of nuclear reactor. Heavy slurry is capable of shielding gamma ray and neutron beam from its high specific gravity and water content. The purpose of this research is to investigate and define the properties of heavy bentonite based slurry by soil mechanics experiment. That is, the research described in this paper is a proposal to use it for decommissioning of the Fukushima I nuclear power plant. For quantifying the radiation shielding properties, the authors measured the transmitted radiation dose through heavy slurry. The result shows the heavy slurry has definite radiation shielding properties. In conclusion, the heavy bentonite based slurry may be useful for radiation shielding, and save workers health in particular.

The paper proposes eco-friendly adaptive techniques using locally available materials and industrial by-products. Used automobile tires, as an industrial by-product, were combined with palm fibers to construct reinforced dyke systems as a multiple protective measure. The tires used with a mangrove plantation inside can work together with mangroves to protect against impacts from such severe climate events as storm surges. The addition of the palm fibers plays a role in increasing dyke stability, particularly when mixed with cement and dyke soils.

Fukushima residents have expressed strong concern about large areas contaminated by radionuclides from the Fukushima Daiichi Nuclear Power Plant Accident. During the more than four-year aftermath, decontamination has continued, but the use of radionuclide-contaminated soils from road maintenance is prohibited by law. Indeed, road maintenance cannot be conducted in Fukushima because no disposal method can be used for radionuclide-contaminated soils from road maintenance. Recent studies of radionuclide-contaminated soils show that silt and clay mainly adsorb radioactive cesium. Therefore, classification of silt and clay from radionuclide-contaminated soils can reduce the amounts of contaminated soil and radioactive wastes. This study investigates the applicability of a soil washing method to classify silt and clay from radionuclide-contaminated soils and to reduce radioactive concentrations of soils from road maintenance.

Japan was severely impacted by the 2011 off the Pacific coast of Tohoku earthquake, and radiation from the subsequent accident at the nuclear power plant in Fukushima continues to pose problems for the region. This paper describes efforts that are underway to remediate the area based on civil engineering and environmental geotechnic principles. Specifically, this paper describes recommendations from a special task force that was organized by the Japanese Geotechnical Society (JGS) in response to the accident. The task force has identified several areas where new environmental geotechnic technologies are needed and has put forth ideas for educational initiatives that will be necessary to train future engineers to work on the project. Research efforts on behalf of the authors and collaborators to develop new radiation shielding geo-materials are also presented. Preliminary data show that heavy bentonite based bentonite based slurry has exceptional shielding properties, and this geo-material may be useful for radiation shielding near and inside of the nuclear reactors. Lastly, some ideas regarding the design of intermediary repositories for contaminated soil are presented. Such repositories will be used to store contaminated soil for a period of 30 years.

The literature contains limited information on variations in the factors of safety (FOS) of riverbank stability associated with river water level (RWL) fluctuations. This paper analyses a case study on the portion of the Red River flowing through Hanoi using the finite element method and extending the mechanics of saturated and unsaturated soils to understand how the riverbank's FOS varies with RWL fluctuations. The results show that hydrostatic force is one of the key parameters influencing the FOS when the soil's hydraulic conductivity is less than 10(-6) m/s. However, the pore-water pressure and rate of RWL change are the key parameters influencing the FOS when the hydraulic conductivity is greater than 10(-6) m/s. The study also indicates that a surcharge of 50 kPa or higher significantly weakens the riverbank stability and influences the FOS when the RWL rises. The construction of residential or other structures without taking special protection measures within 50 m of the lateral riverbank should be avoided for safety reasons. (C) 2014 Elsevier Ltd. All rights reserved.

This paper presents the CO₂ fixation properties of steel slag containing calcium, and proposes a geotechnical application for the formation of a sound material-cycle society and a low-carbon society. In order to investigate the properties of CO₂ fixation, CO₂ fixation test with vented constant flow was conducted. As a result, when the CO₂ concentration 4500μL_-CO2/L was vented in a specimen by 0.05 L/min, non-aging steelmaking slag amount of CO₂ fixed is the maximum, the value was 0.04 g_-CO2/g-slag. The amount of CO₂ that is fixed in the steelmaking slag was about 20% of water-soluble calcium. Therefore, a possibility that the quantity of CO₂ fixation could be evaluated was shown from the viewpoint of the mechanism of CO₂ fixation using the quantity of water-soluble calcium.

Reusing drinking water sludge discharged during water purification is anticipated for a good use of waste materials as geotechnical materials. So far, drinking water sludge engineering properties has been studied by laboratory tests. This study was conducted to inspect the results of laboratory tests were trial construction using drinking water sludge as a backfill material of water pipe construction. Used sample was mountain sand which was widely used as a backfill material of water pipe construction, two types of drinking water sludge difference from dewatering methods which is sun dry and pressure dehydration, and mixed soil of drinking water sludge mountain sand. The settlement of road surface was measured using surveying instrument during 19 months, and field density tests were conducted in trial construction. As a result, the settlement of road surface in the drinking water sludge and mountain sand were not a significantly differences despite degree of compaction is less than 90%. Finally, this study showed the flowchart about control method for quality of drinking water sludge for use as a subgrade material based on the laboratory CBR tests.

Drinking water sludge discharged during water purification contains a lot of organic matter. The generation process of drinking water sludge is quite different from that of general soils, so the influence of organic matter decomposition on the engineering properties is not interpreted enough. Therefore, it is important to investigate the decomposition characteristics of organic matter of drinking water sludge, and to discuss the relation between the organic matter decomposition and shear strength. First, this study isolated fulvic acid and humic acid, and observed the organic matter decomposition and soil respirations. The humic acid content of drinking water sludge was relatively high, and 44% of humic acid was decomposed during 6 month in aerobic condition. Second, triaxial compression tests were executed using the sludge that organic matter has been decomposed by hydroperoxide solutions. Approximately 1.38% of organic matter decomposition showed decrease in the internal friction angle from 39.7°-40.4° to around 37.9°.

Bentonite-based buffer materials for high-level radioactive waste (HLW) disposal are expected to fill up the space between buffer and a wall of the disposal pit, and/or between buffer and an waste-container called as overpack by its swelling deformation. That is called as self-sealing ability. This study performs the model tests simulated the relationship between buffer and space mentioned above. It also investigates the validity of the theoretical equations for evaluating the swelling characteristics of bentonite-based buffer and backfill material, which were proposed in Komine and Ogata (2003, 2004), by comparing the calculations and the experimental results.

The 2011 off the Pacific coast of Tohoku Earthquake of March 11, 2011, caused devastating geotechnical and geoenvironmental issues mainly in the coastal areas of the Tohoku and North-Kanto Regions, Japan. Through the earthquake and subsequent tsunami, approximately 22 million tons of disaster debris was generated. This report summarizes the current status on generation, clearance and temporary storage of disaster debris from geotechnical and geoenvironmental viewpoints. It also briefly introduces selected technical issues and their solutions in these processes.

On March 11, 2011, the Great East Japan Earthquake disaster, comprising a gigantic earthquake motion and a giant tsunami, caused huge geotechnical damage. The desalination of tsunami sediment and of salt-affected of soils has become necessary, but the enormous scale of materials over such a vast area presents severe difficulties. Nevertheless, tsunami sediment can be used as materials for renewal. Therefore, quantitative evaluation of desalinization of tsunami sediment by rainfall was conducted to assess the long-term influence of salinity. The necessary time for desalinization of tsunami sediment in affected areas can be predicted based on experimentally obtained results.

Some portions of levee in the Red River delta, located in north of Vietnam, have frequently been damaged by seepage failures. Therefore, a countermeasure of reinforcement for seepage failures are needed to be applied. The countermeasure using natural fiber material is considered to be effective in the Red River delta, because rice farms are flourishing and natural fiber material such as the straw is available at low cost. The purpose of this study is to evaluate the countermeasure of reinforcement by examining the resistance against seepage failure of short fiber mixture soil with natural material. Due to the shortage of soil material in the Red River delta, material was prepared under the simulation of grain size distribution in the Red River delta. The resistance against seepage failure of short fiber mixture soil and fiberless mixture soil are prepared ,respectively. As a result, reinforcement in soil material was confirmed to be effective when the percentage content of sand was over 68.

Some portions of levee in the Red River delta, located in north of Vietnam, have frequently been damaged by seepage failures. Therefore, a countermeasure of reinforcement for seepage failures are needed to be applied. The countermeasure using natural fiber material is considered to be effective in the Red River delta, because rice farms are flourishing and natural fiber material such as the straw is available at low cost. The purpose of this study is to evaluate the countermeasure of reinforcement by examining the resistance against seepage failure of short fiber mixture soil with natural material. Due to the shortage of soil material in the Red River delta, material was prepared under the simulation of grain size distribution in the Red River delta. The resistance against seepage failure of short fiber mixture soil and fiberless mixture soil are prepared ,respectively. As a result, reinforcement in soil material was confirmed to be effective when the percentage content of sand was over 68.

Engineered barrier made by bentonite is required to stand without settlement or lateral flow for long term in a repository of radioactive waste. Centrifuge tests which simulated radioactive disposal were executed for evaluating the bearing capacity. And actual deformation was predicted with considering centrifuge scale effect.<br> The result are as follows. Overpack settlement is predicted 8 mm (0.8% strain) after 55 years since the construction, if a repository is constructed with a condition that the highest overpack density is 3.4 Mg/m³ and the lowest engineered barrier density is 1.2 Mg/m³. The settlement is increasing according with overpack density. Siliceous sand mixed engineered barrier effects for reducing the overpack settlement.

Results of recent investigations suggest that climate change tends to exacerbate geo-disasters. Therefore, it is understood clearly that adaptation to climate change has rapidly become the most important and urgent issue for the future existence of human beings on Earth. These inferences form the background of this research. In comparison to those examining water disasters, few studies have examined climate-change-induced geo-disasters. This study aims at upgrading the methodology for estimating effects on geo-disasters of combined events, e.g., global warming with increased typhoon and rainfall severity or occurrence of great earthquakes. Such a methodology is expected to contribute to progress in the fields of natural disaster mitigation and land preservation, particularly near seacoasts and rivers. (C) 2011 Elsevier Ltd. All rights reserved.

The soil cement used for the cut-off wall is a brittleness material. Therefore, in the case of the soil cement cut-off wall, the problem of the water leak by generation on the shearing surface is feared. As the countermeasure against generating shearing surface, the tire chip mixture soil cement is proposed. In addition, under 10% of tire chip mixture ratio for the tire chip mixture soil cement is proposed as the measures, because the workability decreases as the mixed quantity of the tire chip increases. Then, the strength transformation characteristic of the tire chip mixture soil cement of the tire chip mixture rate under 10% was investigated. As a result, the tire chip mixture soil cement in the tire chip mixture ratio under 10% accompanied an increase at the tire chip mixture rate, strength showed the decreasing tendency, and the destruction strain showed the increasing tendency. Moreover, the improvement of toughness was remarkable in the tire chip mixture rate 5% or more.

Humanity faces an increasing possibility that unusual and extreme natural disasters will increase, compounded with climate change, including global warming. These compound events are designated as compounded natural hazards in this study. A methodology must be developed for predicting what events and risks will confront future societies, to propose countermeasures and adaptation strategies against these events, and to evaluate the influences of compound disasters on infrastructure which is particularly situated near coasts and rivers. Based on the above-stated background and demands, this study was undertaken with the intention of upgrading the methodology for estimating effects on infrastructure of compound events such as increased typhoon and rainfall severity caused by global warming occurring concurrently with a great earthquake in Japan. Such a methodology is expected to contribute to progress in the fields of natural disaster mitigation and land preservation, particularly benefiting coastal and river areas in Japan. Additionally in this study, risk and economic loss analyses for the possible occurrence of compound disasters for coastal infrastructure and foundations are produced for establishing environmental strategies at the governmental level. The authors further propose adaptation strategies and techniques as countermeasures against these events.

For environmental impact assessment, the Japanese leaching test (JLT) is frequently used in Japan. The grains in JLT are ordinarily smaller than 2.0 mm, but the grain size might be impractical. Therefore, this study investigated the influence of controlled clod size on the leaching characteristics of represented crushable waste
drinking water sludge (DWS). First, compaction tests were conducted using DWS. Second, batch and column leaching tests were performed using various clod size fractions of DWS. The Al concentration was analyzed to investigate the effect on plant growth. Consequently, 81 of DWS was crushed to less than 2.0 mm clod size by compaction, so the clod size in JLT is reasonable for environmental impact assessment of DWS utilization. Furthermore, results of batch leaching tests using clods smaller than 0.25 mm substituted for the maximum Al concentration in column leaching tests. © 2011 ASCE.

Liquefaction during earthquakes induces such damage of existing structures as uplift or settlement, depending on the weight of structure. It is important to mitigating damage occurring by liquefaction to take some countermeasures against harmful vertical displacement. This study specifically focuses on countermeasures against settlement induced by liquefaction of existing structures with sheet pile walls during earthquakes. For this purpose, the study considers the effects of sheet pile walls on decreasing liquefaction-induced settlement of existing structures using the model tests under normal gravity (1 g) conditions that simulate the situation of existing structures founded on sand deposits. Results show in the following: (1) The longer the sheet pile walls that are installed, the more markedly settlement of structures can be reduced. (2) Combined adaptation of sheet pile walls installation with a decrease in groundwater level engenders a great degree of reduction in the settlement of structures than with adaptation of the single technique of the sheet pile wall installation or dewatering of GWL. © 2011 ASCE.

This paper is an overview of the status in geo-environment research in the past, the present and the future in Japan as witnessed by the publications in "Soils and Foundations" over the years. The authors have paid special attention to the geotechnical researches concerning technologies of waste disposal, including radioactive waste disposal, the reuse and recycle of by-product and waste, the evaluation of the environmental impact of waste and by-product, and countermeasures and adaptations to the contamination of ground/groundwater. Some representative papers on the geo-environment published in "Soils and Foundations" have been drawn on heavily in this paper. The commentary provided by the authors is largely from a geo-environmental perspective. In addition, the authors have also paid attention to geotechnical issues in the research.

Reusing drinking water sludge discharged during water purification is anticipated as a good use of waste materials as a geotechnical material. Mixing is certainly effective to improve the amount of supply materials. However, the effects of mixing on environmental economics have not been discussed. Therefore, such mixture must be examined from environmental and economical perspectives. This study defined the environmental value of drinking water sludge, with emphasis on the final disposal amount and the loss of natural soil. The environmental cost was estimated in various mixture conditions. Results show the benefits for geotechnical works of using drinking water sludge alone or decreasing the amount of mixed natural soils.

This paper is an overview of the status in geo-environment research in the past, the present and the future in Japan as witnessed by the publications in “Soils and Foundations” over the years. The authors have paid special attention to the geotechnical researches concerning technologies of waste disposal, including radioactive waste disposal, the reuse and recycle of by-product and waste, the evaluation of the environmental impact of waste and by-product, and countermeasures and adaptations to the contamination of ground/groundwater. Some representative papers on the geo-environment published in “Soils and Foundations” have been drawn on heavily in this paper. The commentary provided by the authors is largely from a geoenvironmental perspective. In addition, the authors have also paid attention to geotechnical issues in the research. © 2010, The Japanese Geotechnical Society. All rights reserved.

Mixtures of sand and bentonite will be used as bentonite-based backfill materials for high-level radioactive waste repositories. They are also used in Japan as artificial barriers in disposal facilities for low-level radioactive waste. Very low hydraulic conductivity of the sand-bentonite mixture is expected to keep wastes separated from the surrounding environment. Some researchers have investigated hydraulic conductivities of sand-bentonite materials at different dry densities and at different mass ratios of sand and bentonite to design and develop specifications of the materials described above.
However, the function of low permeability of those materials is degraded by the altered hydraulic conductivity of sand-bentonite mixtures after swelling deformation. This study investigates experimentally hydraulic conductivity changes before and after swelling for sand-bentonite materials. Furthermore, results confirm the applicability of theoretical equations for evaluating the hydraulic conductivity of compacted bentonites and sand-bentonite mixtures, which have already been proposed in Komine (2008), by comparing calculated results and experimental results. (C) 2010 Elsevier B.V. All rights reserved.

It is presently anticipated for reusing drinking water sludge which is discharged during water purification as geotechnical material. However, drinking water sludge contains flocculating agent, poly-aluminum chloride, and it is expected that aluminum leaches and influences to plant growth. Therefore, this study assessed the environmental impact of drinking water sludge, focusing on aluminum leaching. Japanese leaching test, column leaching test, pH-dependant test, and serial batch test were executed, and aluminum leaching characteristics and the applicability to geotechnical works were discussed. Finally, this study showed the flowchart of environmental impact assessment of drinking water sludge.

Recently, impact to society by global warming is attracting greater attention in all the world. It is afraid that the global warming is bringing sea-level rising and increases of heavy raining and storm. The IPCC prefigures that the maximum amount of rising sea-level due to global warming will be 59 cm. It is also prefigured that brackish-region in rivers will expand by running of seawater to the upside of rivers. If the above phenomenon will appear, it is afraid that levees and riverbanks made by soil material are affected by seawater. From the background, it is required to evaluate vulnerability of levees and riverbanks as infrastructures in Japan. This study investigates changes of properties of soil materials, which is used to construct levees and riverbanks, by water chemistry in laboratory. The laboratory experiments use the distilled water assuming fresh-water, and the artificial seawater assuming brine-water and brackish-water. From the laboratory experiments, this study evaluates vulnerability of levees and riverbanks as infrastructures by sea-level rising due to global warming.

The purpose of this study is to assess the influence of dual impacts of sea-level rise due to global warming and land subsidence on inundation area in Chao Phraya delta. The future situation of land subsidence in 2100 has been predicted by using a method of reliable land subsidence mapping based on the observations of settlements proposed by Murakami, S. et al. (2005). The future elevation model in the objective regions has been made by using the present elevation model and the predicted land subsidence by using GIS. For investigating the influence of dual impacts of both 59cm sea-level rise and land subsidence on inundation area in Chao Phraya delta, a hazard map of the inundation area has been represented. The hazard map shows that the inundation area caused by dual impacts of 59cm sea-level rise and land subsidence will be approximately 1000km^2. The result shows that it is important for inundation area in Mega Deltas, where land subsidence has taken place, to consider not only sea-level rise but also land subsidence in the future.

Recently, we have had so many disasters and accidents such as damages of levees at large rivers, which are caused by torrential rainfall in Japan. In this study, the authors have conducted the water retentitivity tests in drainage process of some kinds of soils, which will be used as river-levee and bank materials. It has investigated the water retentivity and one-dimensional deformation characteristics of some soils from the soil water characteristic curve and the change of void ratio of soils. From the experimental results, this study has proposed the simplified evaluation on vulnerability of river levee and bank by torrential rainfall.

Recently, we have had so many disasters and accidents such as damages of levees at large rivers, which are caused by torrential rainfall in Japan. In this study, the authors have conducted the water retentitivity tests in drainage process of some kinds of soils, which will be used as river-levee and bank materials. It has investigated the water retentivity and one-dimensional deformation characteristics of some soils from the soil water characteristic curve and the change of void ratio of soils. From the experimental results, this study has proposed the simplified evaluation on vulnerability of river levee and bank by torrential rainfall.

In high-level radioactive wastes geological disposal, an engineered barrier by bentonite which is called buffer around a waste package is built. When the buffer suffers high temperature by generation of heat from wastes for long term, the heat may deteriorate barrier performance of the buffer material. In order to evaluate suitable heat influence for design of the repository, behavior of buffer under high temperature needs to be clarified. In this research, dry shrinkage examinations of bentonite-based buffer were carried out, and the tendency of the relations between specification of buffer, temperature and water ratio depression, dry shrinkage were clarified.

Bentonite is currently designated for use as a buffer material for the repository of high-level radioactive waste because such a material requires swelling characteristics to seal the waste. A high-level radioactive waste disposal facility may be built in a coastal area of Japan because transportation of this waste by ships is feasible. Therefore, it is important to investigate the effects of seawater on a bentonite-based buffer. This study is intended to investigate the influence of seawater on the swelling pressure and swelling deformation characteristics of five common types of bentonite. The experiments described herein clarify the relations between the influence of seawater grade and compaction density, type of exchangeable cation, montmorillonite content of the bentonite, and vertical pressure condition. Based on experimental results, suitable specifications have been defined for a bentonite-based buffer that can withstand the effects of seawater.

A high-level radioactive waste disposal facility might be built in a coastal area of Japan to facilitate transportation of radioactive waste. This study investigates the influence of seawater on the self-sealing capability of a bentonite-based buffer. It also investigates the change of compositions of exchangeable cations such as Na + and Ca 2+ in a bentonite-based buffer before and after self-sealing to clarify infiltration/filtration mechanisms of seawater cations into bentonite. © 2009 IOS Press.

Inundation analyses based on an unstructured mesh model were performed. The method gives detailed consideration to the geometrical shape of the geography and composition. Using other analytical results obtained before and after land subsidence that took place in the region, a comparison was carried out to show the influence of land subsidence on inundation damage. Results indicate the necessity for evaluating inundation damage in consideration of the future land subsidence. In addition, the current study presents a GIS-aided procedure for inundation analyses using an unstructured mesh model that facilitates production of information used for inundation analysis for sites that have undergone land subsidence over a long period.

Eco Frontier Kasama is a public-operated waste management facility which consists of incinerators, fusion reactors, and a leachate-monitored land fill. Until August 2005 of its inauguration, communication with the local people has been repeatedly carried out and is being held thereafter. In this report, an actual example of the way how they activate information disclosure and motivate environment learning at Eco Frontier Kasama is introduced and a risk communication experience is also described.

This paper introduces the activities of the technical committee on environmental risk in geotechnical reuse and recycling of waste materials, which was held from 2005 to 2007 year. This paper describes compositions and members of the technical committee, the activities in the JGS annual conferences, site visits and technical seminars cooperated with the other academic societies such as the Japan Society of Civil Engineers and the Japan Society of Waste Management Experts.

Compacted bentonite and sand-bentonite mixtures are sought as buffer and backfill materials for high-level radioactive waste disposal facilities because they have very low permeability. To establish specifications such as the dry density and sand-bentonite mass ratio for buffer and backfill materials, we must quantitatively evaluate a material's hydraulic conductivities. This study presents theoretical new equations for evaluating the hydraulic conductivity of compacted bentonites and sand-bentonite mixtures. New equations are proposed for evaluating the flow velocity of interlayer water between two montmorillonite parallel-plate layers considering the swelling behaviors of montmorillonite. Furthermore, a prediction method for hydraulic conductivity of compacted bentonite and sand-bentonite mixtures is presented by combining new equations with previous equations for evaluating swelling behavior of montmorillonite in bentonite. The applicability of this method is clarified by comparing predicted results with experimental data reported by previous research on hydraulic conductivities of compacted bentonites and sand-bentonite mixtures.

We have developed a new construction technique called Hybrid Sandwiched Reinforcement (HBS) method in which thin sand layers are placed above and beneath the geosynthetic fabric to increase the mechanical potential of cohesive soil embankment and foundations. This reinforcement method offers advantages of reinforcement improvement and maintenance of hydraulic conductivity. Successive to the authors' previous works, this paper describes small-scale model tests on embankments with and without reinforcement and a sand layer. Results from model tests are interpreted with emphasis on improved toughness of HBS-reinforced embankments. Results clarified that HBS not only controls embankment deformation; it also improves the toughness using placement of geosynthetics in an embankment comprising cohesive soils such as Kanto loam of volcanicash origin. As an important finding related to toughness improvement of HBS earth structures, the model test results show that the improved toughness of foundations and embankments are independent of the sand layer thickness, which implies that the sand thickness in sandwich-type earth structures is sufficient for maintaining the HBS structures' hydraulic conductivity and avoiding clogging of the geosynthetics.

The increasing infrastructure instability is an important issue in relation to the influences of global climate change in urban areas. A serious issue pertaining to this is the dual nature of damage triggered by events combined with climate change and natural hazards. For example, catastrophic damage could result from the combination of global warming with a great earthquake, which is a worst-case scenario. Although this worst-case scenario has rarely occurred and presents a low probability of occurrence, countermeasures must be prepared in advance based on an appropriate response and adaptation strategies. After an overview of possible infrastructural instabilities caused by global warming, methodologies are proposed placing emphasis on the increasing probability of infrastructural instability triggered by natural hazards resulting from groundwater-level (GWL) variations. These effects are expected to be particularly serious in coastal regions because of the influence of the rising sea level resulting from global warming. The influence of sea-level rises (SLR) will become apparent along with land subsidence because groundwater abstraction will become severe in coastal regions. Additionally, the probability of earthquake liquefaction increases if GWL rises in accompaniment with SLR. Using case histories, we examined the possible occurrence of these natural hazards as a result of global warming. Finally, possible countermeasures and adaptation strategies for reducing and mitigating infrastructure damage accelerated by global warming are described for each case in specific regions. In particular, special attention should be paid to adaptation strategies in coastal lowlands, which particularly suffer from the effects of land subsidence.

This paper describes a spatial interpolation procedure for settlements to increase the reliability of subsidence mapping. For this study, a spatial interpolation method based on the ordinary Kriging method was investigated for applicability to a land subsidence area in the northern Kanto plain. First, the spatial variability of settlements using a semivariogrant was investigated in detail. For a short distance, the semivariogram of settlements increases. However, after the maximum value at about 35 km, the semivariogram decreases because settlement observation locations are typically arranged around an area in the center of a severe land subsidence zone. Therefore, the semivariogram is only useful up to that maximum value for investigating spatial variability of settlements in a land subsidence area. A spatial interpolation procedure based on Kriging method is proposed. Applicability of that procedure is investigated through comparison of estimations with observations. Drawing both estimations and standard deviations of those estimations represents a reliable land subsidence map. Moreover, to improve the map's accuracy, new allocation for monitoring settlements is undertaken by installation in areas where the estimation standard deviation is greatest. The effect can be investigated using simulated results in the distribution change of the estimated standard deviation.

As one of promising field techniques for earth reinforcement, the hybrid sandwich earth structures reinforced with geosynthetics have been developed. The reinforcement in this technique is attained by enhancement of interaction between geosynthetics and thin sand layers which are placed above and beneath geosynthetics. This technique is usually adopted for reinforcing and improving soft or marginal soils which are not usually suitable for banking, backfill and foundation geomaterials. Among the advantageous aspects of sandwich-type reinforced earth structures combined with geocomposites and sand mat, toughness improvement as well as hydraulic conductivity improvement is highlighted in this paper.

Bentonite has been examined recently in some countries as candidates for buffer materials in highlevel radioactive waste repositories. Granular bentonites are anticipated as the raw materials for constructing bentonite-based buffer materials by in-situ compaction methods. For that reason, it is important to understand the influence of grain size distribution and physicochemical properties of bentonite ore on compaction and hydraulic properties of granular bentonites. In this study, compaction and hydraulic conductivity tests of some kinds of granular bentonite with different sources and grain size range were performed. As a conclusion, compaction and hydraulic properties of granular bentonites can be evaluated by plastic limit and montmorillonite content of bentonite ore used as raw materials.

The effects of gravel drains on the mitigation of earthquake-induced lateral flow deformation of saturated Toyoura sand were investigated in 1g laboratory model tests. Earthquake-induced dynamic loading was simulated by using lateral impact loads generated by a pendulum typehammer on the side of the testing equipment. An emphasis was placed on the applicability of a recycled material, tyre-chips, instead of gravel, to accelerating the drainage in sand deposits. The results of the model tests showed that the tyre-chip drain exhibited almost the same effects as conventional gravel drains and in particular : (1) a tyre-chip drain installed in an inclined slope of medium dense sand reduced the excess pore pressure generation, and subsequent lateral flow deformation and post-cyclic settlement and (2) even if liquefaction occurred in sand deposits with tyre-chip drains, the lateral deformations and vertical settlements were reduced.

Geotechnical engineering is very significant science for mainly civil engineering, architecture, and agriculture. It has greatly contributed to constructions for infrastructure and living space, protection against large earthquake and countermeasure against natural disasters such as landslide and debris avalanche. Recently, it also is developing new science, i.e., Environmental Geotechnics contributing to solve environmental problems around humanity, e.g. industrial waste problem and global warming. This paper introduces a part of Environmental Geotechnics and discusses future development of geotechnical engineering for sustainable development in the world.

This paper introduces a concept of maintenance and management of infrastructures damaged by a wide land subsidence. The present situation and future trend of land subsidence caused by groundwater fluctuation in the northern Kanto plain have been represented as maps using Geographical Information System (GIS). The future trend map has been represented by using results of settlements predicted by the authors' proposed observational prediction method based on one-dimensional consolidation theory. The performance reductions of piled foundation and river dike due to land subsidence in the region have been evaluated and this paper has mentioned it is important to consider future land subsidence. GIS-aided groundwater monitoring system for maintenance and management of infrastructures in wide land subsidence area has been proposed.

A high level radioactive waste disposal facility may be built on a coastal area. Therefore, it is important to investigate the influence of seawater on bentonite buffer material. The purpose of this study is to investigate the influence of seawater on the swelling pressure and swelling deformation characteristics of five typical kinds of bentonites. This experimental work clarified the relations between the influence grade of seawater and compaction density, type of exchangeable-cation, montmorillonite content of the bentonite, and vertical pressure condition. Based on experimental results, a specification for the buffer material which can overcome the influence of seawater was defined.

A high level radioactive waste disposal facility may be built on a coastal area. Therefore, it is important to investigate the influence of seawater on bentonite buffer material. The purpose of this study is to investigate the influence of seawater on the swelling pressure and swelling deformation characteristics of five typical kinds of bentonites. This experimental work clarified the relations between the influence grade of seawater and compaction density, type of exchangeable-cation, montmorillonite content of the bentonite, and vertical pressure condition. Based on experimental results, a specification for the buffer material which can overcome the influence of seawater was defined.

This paper presents an experimental investigation of the ultrasonic removal of clogging of six commercially available geotextiles. The clogged specimens were exhumed from two fine-grained soils, which were previously consolidated from slurry stage under a consolidation pressure of 400kPa. The mechanism of ultrasound and formation of micro-bubbles in a sort of "cold boiling" or "cavitation" within liquid medium have been explained. The in-plane and cross-plane flow capacities of the clogged geotextile specimen have been evaluated before and after ultrasonic cleaning and results are presented in a design chart signifying the beneficial effect of ultrasonic cleaning. With increasing confining pressure clogging caused more reduction in the cross-plane flow capacity than the in-plane flow capacity. Ultrasonic cleaning efficiency for all clogged geotextiles was more than 80% @ 5 minutes washing time. The thinnest (2.2mm) geotextile was severely affected by clogging, however, after ultrasonic cleaning the clogging potential reduced to unity, which was not affected by increasing normal pressure.

An in-situ compaction with inner mold system is one of the methods of buffer construction technology. The method is examined in this study by carrying out compaction tests, and validated with real-size disposal pit made of concrete and semi-automatic compaction machine designed for work with remote controlled system. In this study, basic performance of in-situ compaction machine with inner mold was confirmed as mechanically feasibility, and it was also confirmed that compaction buffer has an appropriate dry density of more than 1.6Mg/m³ toward a required specification of engineered barrier system. Finally, it is concluded that the technology is prospective for actual construction of buffer material.

In order to build up the construction technology of buffer for geological disposal of radioactive waste, it is necessary to investigate the compaction characteristics of mixture material of bentonite and silica sand. From the results of static compaction experiment, relation between specifications of buffer and compaction characteristic was investigated. And the particle action mechanism during compaction was investigated by comparison between dynamic compaction and static compaction, and by microscopic observation. As results, the influence factors on compaction characteristics of buffer material are shown from the viewpoint of particle action mechanism.

In the design for buffer and backfill materials for repositories of high-level nuclear waste, we must choose the adequate bentonite among many kinds of bentonite in the world. To select the adequate bentonite, we have to get the fundamental properties such as seepage and swelling of many kind of bentonite. To solve this problem, the study proposed the new simplified experimentation using measuring cylinder and new analysis method for seepage and swelling properties. We investigate the validity of new method by the laboratory tests using five kinds of bentonite. Furthermore, this study describes the influences of water-chemistry to the seepage and swelling properties of bentonites on the basis of the experimental data obtained by new method.

Bentonite is currently planned for use as a buffer and backfill material for repositories of high-level nuclear waste because these materials must have swelling characteristics to seal the waste. However, it is necessary to choose the appropriate bentonite from among many kinds of bentonite in the design of buffer and backfill materials. To do this, the writers have proposed a new prediction method for swelling characteristics of bentonite-based buffer material. This prediction method comprises some equations that were previously developed for repulsive and attractive forces between two montmorillonite layers; others included in the method are the writers' previously proposed equations for (1) the swelling volumetric strain of montmorillonite (Komine and Ogata 1999), and (2) the influence of pore water chemistry and specific surface of bentonite (Komine and Ogata 1996a). However, the applicability of this prediction method to swelling characteristics of some bentonites remains unclarified. This study clarifies the applicability of the prediction method by comparing predicted results with experimental data for five kinds of bentonite produced in Japan and the United States.

The purpose of this study is to investigate the influence of initial static shear stress (ISSS) on cyclic softening of non-plastic silt using volume decrease potential. Through comparing results from cyclic direct simple shear (DSS) tests, it was known for non-plastic silt that (1) although cyclic strength was smaller, cyclic softening of strength was faster, (2) maximum stiffness of non-plastic silt was not smaller than others, but decrement of stiffness with increasing the number of load cycles was more eminent, and the influence of ISSS on stiffness degradation was the largest among them, and (3) liquefaction feasibility of silty soils was explained in terms of the volume decrease potential as well as relative density.

Buffer material as a part of an engineered barrier system for high-level waste disposal is expected to seal the initial gaps between the buffer material and the surrounding rock during the resaturation process. Since the self-sealing ability represents the swelling characteristics of the buffer material, it is very important to estimate the swelling behavior during the resaturation process. This paper expands the theoretical model for evaluating the swelling characteristics of saturated buffer material proposed by Komine to deal with unsaturated media, and it is applied to the coupled thermal, hydraulic and mechanical (THM) model used in Japan. The new model is validated by comparison with a series of laboratory experiments quoted from the literature. © 2004 Elsevier Ltd. All rights reserved.

The first purpose of this report is to exhibit organized ta- bles concerning the contents and methods for evaluating performance quality of landfill liners by brainstorming among some research engineers. This report can clarify the contents of performance quality which the landfill liner should be required, and the methods for investigating the property values. The organized tables exhibited in this report can provide the available information concerning the landfill liners for matriculates of the Japanese Geotechnical Society and engineers who construct waste disposal facilities.

Bentonite is attracting greater attention as buffer and backfill materials for repositories of high-level nuclear waste because these materials must have high swelling property and low permeability. To contribute the design of buffer and backfill materials, this study investigated the swelling properties of sand-bentonite mixtures, of which bentonite contents are within 5-100%, and four typical kinds of bentonite produced in Japan and the USA. The experimental works clarified the influence of bentonite-content, dry density, montmorillonite-content of bentonite and excangeable-cation-compositions upon the swelling characteristics of materials. Moreover, it was found that the authors' parameter &ldquo;Swelling volumetric strain of montmorillonite&rdquo; can easily evaluate the maximum swelling pressure and the maximum swelling strain of sand-bentonite mixtures and various kinds of bentonite at various dry densities and bentonite contents.

This study reported the experimental data of the hydraulic conductivity of bentonite liner at different bentonite-content and dry density. From the experimental data, it is found that the impermeability of bentonite liner is caused by the filling of the void space by swelling of bentonite. On the basis of the above results and considerations, the author has proposed the evaluation of hydraulic conductivity of bentonite liners using the parameter "Swelling volumetric strain of montmorillonite". Based on this evaluation procedure, one can obtain the hydraulic conductivity of bentonite liner at various dry densities and bentonite-contents.

The potential benefits of geo-composites in reinforced foundation beds are investigated. Dry Toyoura sand at three different densities (Dr=32%, Dr=70%, Dr=89%) has been used for the investigation. Medium size model box along with loading frame are fabricated to carry out tests on a 10cm wide (B) strip footing. One geo-composite layer was used centrally below the footing at different depths and lengths. From the test results, optimum length (L) of reinforcement was found to vary between 2B to 3B and placement depth (U) was between 0.25B to 0.5B. Same trend has been observed for three different densities. Moreover, at medium density load and settlement response showed significant improvement.

In chemical grouting, it is difficult to evaluate the improved region. To solve this problem, author proposed the evaluation method of improved region by resistivity tomography. For a practical application of this method, this study shows the validity of proposed evaluation by chemical grouting test in field. The sodium-silicate grout was used in this test. The field test result showed that improved regions, which were evaluated by the proposed method using resistivity tomography, almost agreed with the solidified regions of boring samples. The test results ascertain the availability of the evaluation method of improved region by resistivity tomography in practical fields.

Compacted bentonites are attracting greater attention as back-filling (buffer) materials for high-level nuclear waste repositories. For this purpose, it is very important to quantitatively evaluate the swelling characteristics of compacted bentonite. New equations for evaluating the relationship between the swelling deformation of compacted bentonite and the distance between two montmorillonite layers are derived. New equations for evaluating the ion concentration of pore water and the specific surface of bentonite, which significantly influence the swelling characteristics of compacted bentonite, are proposed. Furthermore, a prediction method for the swelling characteristics of compacted bentonite is presented by combining the new equations with the well-known theoretical equations of repulsive and attractive forces between two montmorillonite layers. The applicability of this method was investigated by comparing the predicted results with laboratory test results on the swelling deformation and swelling pressure of compacted bentonites.

Compacted bentonites are attracting greater attention as back-filling (buffer) materials for repositories of high-level nuclear waste. However, since there are few studies about the swelling characteristics of compacted bentonites, it is first necessary to clarify the fundamental swelling characteristics in detail. For this purpose, various laboratory tests on the swelling deformation and swelling pressure of compacted bentonites were performed and the results analyzed. The following conclusions were drawn from the study. (i) The curve of swelling deformation Versus time is strongly dependent on the initial dry density, vertical pressure, and initial water content. The maximum swelling deformation, however, is almost independent of initial water content, and the maximum swelling deformation increases in proportion to the initial dry density. (ii) The maximum swelling pressure increases exponentially with increasing initial dry density, whereas the maximum swelling pressure is almost independent of initial water content. (iii) The swelling mechanism of compacted bentonite was considered on the basis of the swelling behavior of swelling clay particles such as montmorillonite. Furthermore, a model of the swelling characteristics and a new parameter (swelling volumetric strain of montmorillonite), which were able to evaluate the swelling characteristics of compacted bentonite, were proposed.

Bentonite/Sand Mixture is expected to be an effective component of barriers for radioactive waste facilities. Several effective characteristics of Bentonite/Sand Mixture are 1) low permeability, 2) self-healing, 3) long-term durability. Low-permeable mixture can be obtained through enrichment of bentonite content of the mixture. But the data of relation between bentonite content and permeability have been taken in few kinds of sand, therefore we cannot estimate the appropriate arrangement of mixture in case of using another kind sand. On the other hand there is no guiding principle regarding which sand is better for making low-permeable mixture. Compaction tests and permeability tests were executed in order to research the method how to choose the better sand and to decide the appropriate bentonite content. First we made many kinds of Bentonite/Sand Mixture using 3 kinds of sand in 3 or 5 cases of varied bentonite content, and measured the permeability in laboratory. The difference of permeability between 3 kinds of sand was not negligible in spite of same bentonite contents, especially in condition of poor bentonite content. Then we examined the relation between permeability and effective void ratio which is calculated from bentonite content and density of the mixture. The effective void ratio is useful parameter for choosing better sand and for deciding optimum mixture. We propose the following procedure for designing the Bentonite/Sand Mixture. 1) To examine the conditions of maximum dry density through compaction test using few kinds of candidate sand and varied bentonite content. 2) To calculate effective void ratio from maximum dry density and plot the relationship between bentonite content and effective void ratio of each candidate sand. 3) To decide the optimum effective void ratio for the target permeability according to the relation between permeability and effective void ratio. 4) To decide the optimum bentonite content of each candidate sand according to the relation curve between bentonite content and effective void ratio. 5) To choose several cases of potential mixture design. 6) To examine not only permeability but also mechanical properties of the chosen mixture design. 7) To choose the best mixture design.

Expansive soils have recently attracted increasing attention as back filling (buffer) materials for repositories of high-level nuclear waste. However, since very little has been known concerning the physical and mechanical characteristics of such materials, it is necessary to clarify the swelling and compaction characteristics of expansive soils.<br>For this purpose, various kinds of index tests and a series of static compaction tests were performed using several kinds of swelling soils in order to investigate the relationship between the fundamental physical properties and the compaction characteristics.

In the chemical grouting for the improvement of the cohesive soils, the hydrofracture occurs in all cases. The object of this study is to investigate the mechanism of strength increase of cohesive soils by grouting. The increase of strength by grouting depends upon the formation of solidified grout, the consolidation by the injection pressure and moreover the cementing action between the cohesive soil and the liquid dehydrated from the solidified grout. These factors are influenced by the grout itself and the ground condition, such as the strength of cohesive soils before grouting, the exchangeable cation, and the buffer capacity of soil.