Embankment erosion due to overflow is the number one cause of embankment failures. The purpose of this paper is to reveal erosion characteristics of compacted soils used for embankment materials. Samples of compacted silty sands containing 22% fines by weight were prepared. An experimental apparatus using an open channel has been built and applied to measure the erosion rate of the compacted soil. Water flows the channel and erodes the soil samples fixed at the bottom of the channel. The rates at which the samples erode were measured and the shear stresses imposed on the samples were calculated. The relationship between erosion rates and shear stresses are the primary results of the tests. The erosion process of the compaction layers and the dependency of erosion rates on the dry density have been investigated. It was found that the erosion rate increased linearly with the increase of shear stress and that the erosion rate decreased linearly with the increase of dry density. The obtained experimental results about the erosion rate and the critical shear stress were modeled.

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The stability of the repository of high-level radioactive waste (HLW) disposal was discussed. To examine the effect of the degradation of crystalline rock on the behavior of near field of the repository, the damage exapansion model was applied with the varying boundary conditions for one million years. The elastic model, the constant degradation model and the hypothetical progressive degradation models were examined. It was observed from the analyzed results that the damage would be developed locally at the spring line and crown of repository tunnel. At about one hundred years after closure of repository, the damage evolution would be finished even if the degradation progressed so long.

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The uncertainties of the boundary conditions, the elastic modulus and Poisson's ratio on the mechanical behavior at near field of high level radioactive waste repository were examined. The method used to examine the error propagation was the first order second moment method. The reliability of the maximum principal stress, maximum shear stress at crown of the tunnel and the minimum principal stress at spring line was examined for one million years. For elastic model, the reliability of the maximum shear stress gradually decreased while that of the maximum principle stress increased. That of the minimum principal stress was relatively low for one million years. This tendency was similar to that from the damage model.

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From our previous studies, it has reported that the brittle behaviors of cement treated clay was improved to ductility by adding some tire chips in unconfined compressive test and tri-axial compressive test. Because tire chips are elastic material, it has been expected that it was prevented from generating and growing cracks by elastic reaction which generated from tire chips during compressive shearing.
In this study, it was investigated and experimented that the relation between deformation and changing in permeability of cement treated clay with added tire chips under deformation. Because it was paid attentions to a low permeability of cement treated clay at no-deformation, and the effect of improving ductility by adding tire chips. From these studies, it was obtained that, during deformation, the permeability of cement treated clay without adding tire chips was changed to high, but also, in the case of adding tire chips, the changing permeability was very small.

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To analyse the seismic behaviour of a fill dam that was actually damaged during a recent earthquake, a series of triaxial tests were performed on gravel including fines retrieved from the site. To understand different performances of the downstream and upstream slopes of the rock shell, saturated specimens were subjected to monotonic and cyclic loading histories under undrained conditions, while specimens that were moist as in the field under drained conditions. With undrained saturated specimens and drained moist specimens, the effects of cyclic loading conditions on the peak strength when subsequently subjected to monotonic loading were evaluated. In all the test conditions, the effects of compacted dry density on the strength and deformation properties were evaluated. The following was found. The residual strain by cyclic loading is much larger with the undrained saturated specimens than with the drained moist specimens. The increase in the strength with an increase in the compacted dry density is significant in both cases. The effects of cyclic loading on the subsequent compressive strength are negligible with drained moist specimens, while the strength may decrease significantly by cyclic loading with undrained saturated loose specimens.

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Cement-treated soil is expected of high durability for a long time. However it is reported that cement-treated soil deteriorates due to Ca leaching. In addition, it is confirmed that the influence of Cl^- contained in outer environment on Ca leaching from cement-treated soil is large in previous studies. In this study, the numerical prediction method for strength deterioration due to Ca leaching from cement-treated soil considering the influence of Cl^- was established. This method consists of ion migration model, Ca adsorption model, carbonation model, Ca leachimg model considering Cl^- and strength deterioration model. The validity of the method was verified with comparing the result of exposure test and the prediction result.

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Vertical hydraulic conductivity generally differs from horizontal one in sedimentary rocks, however, there seems to be no simple methods to measure it. Therefore, this study aims to develop a new method to estimate vertical hydraulic conductivity from responses of pore pressure to atmospheric loading. First, formulation is extended from isotropic materials to transverse isotropic materials more relevant to sedimentary rocks. Next, in order to increase information available to estimation and remove the parameter describing attenuation of atmospheric pressure fluctuation in unsaturated zones, it is proposed that pore pressures should be measured at multiple depths. Finally, vertical hydraulic conductivity in the Tertiary sandy tuff formation is estimated from the data obtained at multiple depth intervals and effectiveness of this method is also discussed.

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The effects of compaction conditions in terms of dry density, water content and compaction energy on the strength and deformation properties of backfill were evaluated by performing triaxial compression test and plane strain compression tests on six types of sand/gravel backfill materials. The results of these laboratory stress-strain tests revealed that the compressive strength was controlled rather uniquely by compacted dry density irrespective of water content during compaction. However, the pre-peak stiffness, creep deformation and dilatancy characteristics were controlled not only by compacted dry density but also water content during compaction as well as compaction energy on granular materials. The effects of the degree of compaction D_c on the strength and stiffness of all backfill materials for D_c higher than 90% were significant while the material was very weak and soft when D_c was 90%. Furthermore, rational compaction control method of backfill discussed based on the results of laboratory stress-strain tests in the present study.

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Clay ground improved by Sand Compaction Pile (SCP) method is a composite of compacted sand piles and a soft clay layer. This type of composite ground shows complicated deformation and failure patterns under backfill loading because of the component materials with different characteristics. In the present study, centrifuge model tests were conducted to investigate the ultimate state of SCP improved ground. Results of model tests showed that fixed-type improved ground failed with bending mode and that floating-type improved ground failed with sliding mode. The model tests were also simulated by circular slip analyses in order to evaluate the calculation accuracy.

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In order to estimate the bearing capacity of two types of foundation of the pre-cast arch culvert, two-dimenstional loading test using the aluminum rods modeling ground has been carried out. Through the experimental results and their image analyses, the bearing capacity and the embedded depth in each foundation type have been discussed. As a result, the effect of the embedded depth is defferent as depending on the foundation types. In case of the footing foundation, the bearing capacity is affected by the ground depth located on the inside of culvert. In case of invert type foundation, it is also confirmed that the bearing capacity can be estimated as the embedded depth of the height of the embankment.

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The bending tests of the composite beams which includes frozen soil and two steel pipes under increasing and constant loads are performed for safety evaluation of adfreeze along the interface between frozen soil and steel pipes. As a result, it is showed that the influences of temperature, strain rate and grain size on the failure load of adfreeze is small. It is explained that the creep failure of frozen soil does not occur as far as adfreeze is maintained. Additionally, some guidelines to manage pipe roofing for maintaining adfreeze between frozen soil and steel pipes are proposed using the analysis result on site scale model.

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Twenty percent of slope surface soils show a very acidity below pH 4.9. There is a possibility of a gradually decreasing performance in slope protection work in such an acid ground. In this paper, sodding and a retaining wall deteriorated by soil acidification were reported in terms of damage circumstance, cause and countermeasures. Especially, a sample in which an acidic substance dissolved while causing slaking was investigated. The acidification speed changed uniquely with the grain size of the sample. The decrease in strength with soaking was independent of the pH of the pore water. The effects of the carbonationprocessing of the sample on compaction and strength properties were apparently recognized.

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Earthquake research at Niigata and South Hyogo areas revealed that, structures with pneumatic caisson foundations showed small degree of liquefaction damage. The general assumption is that liquefaction strength increases with increase in unsaturated condition. In order to validate this assumption, researchers have conducted cyclic undrained triaxial tests on soil samples from the earthquake areas. Results from the tests confirm the assumption on the liquefaction strength increasing with unsaturation. It is therefore important to ensure or maintain unsaturated condition around the foundations of structures. However, the issue has been how to reduce saturation.
The objective of this paper is to discuss proposed methods of un-saturating the soil/ground in order to increase the liquefaction strength of structures during earthquake disasters by injecting water with dissolved air and only air into the ground.
Soil samples were taken from the earthquake areas and injected with water with dissolved air, and air only to convert saturated condition to unsaturated condition. Firstly, one dimensional (1-D) column experiments were conducted. Based on the experimental results, a 2-D column experiment was carried out using only air injection method. The 2-D experiments were conducted under confined and unconfined conditions.
During the experiments, moisture content and the duration of air particles within the soil sample pores were measured. The results show that injecting only air to cause un-saturation is effective and is applicable in both confined and unconfined conditions.

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To establish the protective design for underground structures, the characteristics of ground shock pressure should be estimated properly. In this study, the effects of soil properties on the ground shock pressure are examined by small-scale underground explosion tests with the different kinds of soil, and then a quantitative evaluation of ground shock pressure is presented. A charge was exploded in the subsurface soil specimen, and the pressure in soil due to explosion was measured. From test results, it is found that the effect of the degree of saturation on the properties of ground shock pressure is remarkable. Then, ground shock pressure and impulse are formulated as a function of degree of saturation. To validate the proposed formulae, the formulae are compared with the past data, and they agree well with the larger scale test data.

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In order to prevent and mitigate disaster due to earthquake-induced slope failures, it is important to make clear the effect of topographic conditions and depth of surface soil layer on the seismic response property on mountain slopes quantitatively. In this study, we evaluated the effect of them on the response property of maximum response acceleration and maximum shear strain by using the past and added result of seismic response analysis. The results of the evaluation were as follows. 1) Maximum response acceleration was amplified as altitude becomes higher. In addition, it was amplified at points where depth of surface soil layer was thick and where surface showed a convex shape. 2) Maximum shear strain increased at points where depth of surface layer was thicker. Furthermore, it showed a tendency to become larger at those points where shape of slope was convex.

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Authors proposed a sheet-pile foundation that combined sheet piles with footing. Sheet-pile foundation can be expected the reinforcement effect of constraint of the ground. Because sheet piles reinforce the inside ground of sheet piles, the sheet-pile foundation has higher seismic resistance than footing foundation.
In this research, a series of lateral static loading tests of sheet-pile foundation and footing foundation were conducted. The pressures of the bottom of the footing were measured, and the ground displacement was calculated by image processing system. It was found from these results that sheet-pile foundation had the improved effect of seismic resistance and settlement, and that the improved effect was demonstrated by vertical resistance of sheet piles.

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In order to examine the influence of void ratio on the shear strength and volumetric change of unsaturated sandy soil, unsaturated conventional triaxial compression test with specimens of different initial void ratio was implemented. The test results are as follows. At failure state, relation between net mean principle stress and deviator stress, and between net mean principle stress and void ratio are independent for different initial void ratio. But at critical state, those relations aren't affected by initial void ratio. The difference of deviater stress between at failure and at critical state is linear with the difference of viod ratio between at failure and at critical state, and this relation isn't affected by suction.

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This paper shows a construction example of a large excavation slope in Kobe, Japan. According to previous landslide cases and geological investigations near the construction site, we thought that there were three layer-parallel fracture zones which formed landslide surfaces. And there was no geotechnical information about the lowest landslide surface. So we carried out additional geological investigations, and the result implied that there was an unstable, dip slope structured block separated by several faults. Based on these geotechnical and geological knowledge, we specified the most important issues in designing the slope were as follows; When the excavation work executed, how large the displacement range would be by the release of in-situ stress, How strong the sliding surface would be. To solve these issues, we constructed a test excavation slope and carried out field observations. Based on the field observation results, we could estimate the displacement range and the strength of the sliding surface, so we designed and constructed the countermeasures against landslide. We carried out field observation during the construction too, and we confirmed the stability of the large excavation slope up to the completion.

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The development of H-jointed steel pipe sheet piles and H-H joints commenced in 2000 as one of the steel pipe sheet pile (SPSP) technologies. H-jointed SPSPs are a building material in which two steel pipes and an H-steel are integrated by welding them beforehand in a factory, and H-H joints are a joint section in which two H-steels with different sizes are combined together. In this research, we conducted field installation and permeability tests for H-jointed SPSPs with H-H joints as their first application in the field; this was conducted in December 2006. In a series of field installation and permeability tests, we verified the factors considered in the construction field when using SPSP methods. In this paper, the field installation and water interception performance of H-jointed SPSPs with H-H joints are reported based on the results obtained from the field installation and permeability tests. In the field installation of H-jointed SPSPs with H-H joints, we observed that rotating breaks did not occur. Therefore, a highly accurate installation was possible for H-jointed SPSPs with H-H joints in the field.

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Three kind of marine clays with various plasticity and silica sand were mixed at different proportions, and specimens were prepared either by water sedimentation or by pre-consolidation. A series of undrained triaxial compression tests was performed on the specimens under various confining stresses. Thus, soil samples with wide grain size distribution, i.e. ranging from sand to clay, were formed and, based on the test results, a unified method to evaluate the friction angle of sand-clay mixtures was proposed. When the fines content is low, phase transformation point appeared before reaching failure during undrained shear. On the other hand, the phase transformation point disappeared when the fines content exceeded F_c=30% in the case that fines were constituted of plastic clayey soils while it appeared at any fines content in the case of non-plastic fines.

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