Recently, overflow due to the heavy rainfall causes the collapse of the river levee, as a result, serious flooding and damage. It is necessary to investigate the failure mechanism of the river levee due to the heavy rain and evaluate the stability of the river levee. According to the guideline for the design of the river levee, the seepage failure of the river levee is conventionally evaluated by the minimum safety factor of sliding, which is obtained from the circular arc calculation with the result of the seepage analysis. In this paper, the seepage failure caused by the overflow was mainly focused and simulated by newly developed coupled stress-water flow simulation code. In the numerical simulations, the seepage under saturated-unsaturated conditions considering rainfall, change of the water level, and overflow due to the heavy rain was solved and combined with the mechanical simulations. Stress and flow (seepage) were coupled only in the saturated zone and the coupled processes were not considered in the unsaturated zone. The simulation results clearly show the failure mechanism of the river levee by overflow.

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A newly designed direct shear apparatus was developed to prevent obstacle friction which occurs between the side wall of shear box and a sand sample during a shear test under a CD-test due to dilatancy behavior of a sample. A couple of independent air jacks with load cells were mounted on the upper counter plate. This system allows the upper shear box to move up and down without tilting during shearing, and, as a result, vertical stress, σ_N, can be measured correctly using the upper mounted load cells without influence of friction.

A series of CD-tests using the apparatus on Toyoura sand were conducted in order to compare shear properties including shear strength obtained using an ordinary type of direct shear apparatus (Mikasa's direct shear apparatus) and an ordinary triaxial compression apparatus. It was found that strength obtained using the new apparatus gives the same strength as that obtained by CD-tests using a triaxial apparatus and that obtained by CU-tests (φ') using Mikasa's direct shear apparatus. However, CD-tests using Mikasa's direct shear apparatus give 2 to 3 degrees of excessively higher strength. This shows that the developed new system for direct shear apparatus works effectively to prevent the influence of friction problem of CD-tests on sand samples.

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Recently the efficient/effective way to maintain the performance of the slopes along the roads has been required due to the limited budget for the construction. For the effective maintenance of the slopes, it is important to understand the failure mechanism of the slopes and to evaluate the middle/long term stability of the slopes properly. However, the following two points have not been clarified to make a decision systematically for the timing of the reinforcement of the slopes: 1) the factors and/or mechanisms which cause the decrease of performance and 2) which parameters should be used to evaluate the performance of the slopes. In this study, the significant decrease of the permeability at the toe of the slope and decrease of the strength caused by the cyclic wet/dry environment were assumed to be one of the main factors which cause the decrease of the performance of the slopes in the long term for the fill and cut land, respectively. Since the groundwater inside of the slope and slope stability are related closely, the coupled stress-flow simulations by FEM were performed to evaluate the long term stability and/or performance of the slopes. The proposed method in this study can be used for the health assessment and asset management of the slopes along the loads.

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It is very difficult to estimate transient freezing volume or completion time on artificial ground freezing (AGF), because the analysis depends on many thermal and physical conditions. The aim of this study is to establish the numerical model for the solidification or melting of water saturated soil and to clarify the effect of thermal and physical parameters, such as water content, initial and cooling temperature, on the artificial soil freezing. This numerical model can analyze the region which has multiple heat sources and sinks, diverse local thermal properties with/without ground water stream. From the numerical results, it was found that the initial water contents and cooling temperature affect the transient tendency of soil solidification. After connecting the solidified layers from each cooling tubes, the freezing rate decreases gradually. The knowledge obtained from this study will be useful to predict solid volume, decrease of necessary energy and minimize the influence to ambience on artificial ground freezing precisely.

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There are many dangerous slopes in Japan because of conditions such as geography, geology, weather, land-usage and so on. Due to the limitation of the budget for countermeasures for dangerous slopes, it is impossible to conduct countermeasures for all dangerous slopes. Therefore, it is necessary to propose an efficient screening technique, which can pick out high-risk slopes from large numbers of dangerous slopes. In this study, in order to make a database of friction angle of rock joints, tilting tests using specimens obtained from various areas in Gifu Prefecture are carried out firstly. Secondly, a stability analysis method for rock slope is modified using the results of the tilting tests. Finally, a framework of screening method for dangerous slopes is proposed utilizing the database Borehole sample.

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Compacted bentonite is planned for use as a buffer material in the geological disposal of the high-level radioactive waste. In the present paper, in order to study the failure behavior of the compacted bentonite under the unsaturated condition, a series of constant volume direct shear tests was performed using a newly developed high confining pressure direct shear testing apparatus. At the same time, shear bands were observed during direct shearing using an image processing system, which consists of a microscope and PIV digital image analysis. In addition, the insides of the sheared specimens were observed with a micro-focus X-ray CT scanner.
The over-consolidated unsaturated compacted bentonite specimen shows brittle failure behavior from an early stage of shearing. A shear band with a number of large cracks developed during shearing. By injecting water into the shear band, the cracks are gradually sealed by the swelling and expanding bentonite. On the other hand, according to the results of direct shear test for the saturated compacted benonite specimen, the shear resistance of the compacted bentonite decreases with increasing the swelling pressure and the pore water pressure. In addition, no shear bands or cracks were generated in the saturated specimen.

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Soilbag can be used as a measure of absorbing and isolating vibration in geotechnical engineering. Researches related to field tests and applications can be found in literatures. The numerical simulation for evaluating the mechanism of soilbag, however, is not so popular because of some difficulties in modeling the ground and the material used as bags. This paper tried to evaluate and investigate the vibration damping effect of soilbag by numerical simulation and its applicability is verified by field tests. A dynamic finite element analysis based on an elastoplastic constitutive model named as subloading tij model (Nakai and Hinokio,2004) was conducted to simulate the field test, and it is found that the simulated results were in good agreement with the experimental results.

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Waste tire derived rubber chip samples with average particle sizes of 2mm and 6mm are used to conduct triaxial compression tests and liquefaction tests for exploring their use as geomaterials. Results of triaxial compression tests show that for axial strain below 15%, shear between particles is not developed and different failure lines are obtained depending on drainage conditions. However, for axial strain above 15%, shear between particles causes volumetric strain to start developing, and at 25% axial strain, failure line assumes a single line irrespective of drainage conditions. For liquefaction tests, double amplitude axial strain (DA) reaches 5% level during the early stages of cycle numbers. The pore water pressure (Δu) become only about 30kPa though cycle numbers are increased, and the excess pore water pressure ratio (Δu/σ'c) is not reached above 0.9. Consequently, it may be concluded that the tire chips is not liquefiable materials in these test conditions.

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During the three stages of production, construction and demolition, approximately 1.5 million tons of waste plasterboard was generated in 2007. Bassanite is produced by heating gypsum obtained from waste plasterboard, under conditions of 130°C or more.
Engineering properties make bassanite obtained from waste plasterboard useful as an improver for soft soils. However, fluorine contents may exceed the approved value in the Japanese environmental quality standard. We have to investigate, therefore, reduction in the solubility or mobility of fluorine, physically and chemically. To overcome this, we developed a solidification technology for fluorine contaminated Bassanite using Portland blast-furnace (B) cement. The concentration of fluorine decreases with increasing curing time and bassanite content. The concentration of fluorine after treatment using Portland blast-furnace (B) cement became lower than the Japanese environmental quality standard value.

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This paper describes the effect of curing periods and bassanite content on strength-deformation characteristics of cement-stabilized soils mixed with bassanite obtained from waste plasterboard, and thus promotes waste plasterboard. The strengths of samples were determined by unconfined compression tests after 1, 3, 7, and 28 days of curing immediately following molding. The effects of curing periods and bassanite content on stress-strain behavior of cement-stabilized soils are quantified. Addition of 20 or 40 % bassanite to the soil increases the shear strength of cement-stabilized soil at short curing periods (1, 3, and 7 days), compared to cement-stabilized soil with no bassanite. This contribution of bassanite at an early stage of curing is significant for improvement of trafficability and the reduction of construction period for soft soil.

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Most of old earth dams were accumulated with a muddy soil in reservoir that caused the pollution and the shortage of reservoir capacity. This muddy soil is generally high-water-content and very soft clayey soil. In order to apply such a problematic soil as the embankment soil, we have developed a new type method to improve an old embankment by means of the cement-mixed muddy soil. It is noted by the past researches that the strength and strain behavior of the cement-mixed muddy soil is influenced considerably by the curing under pressure.
This paper represents the test results performed to investigate the effects of the curing under pressure on the unconfined strength of cement-mixed muddy soil in the improvement of old embankments. Test results showed that the strength of cement-mixed muddy soil increased with the increase of curing pressure.

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The flow of groundwater varies with time due to rainfall, atmospheric pressure change, tidal change, melting of snow during seasonal change, underground construction works etc. Therefore, to precisely assess in-situ groundwater flow characteristics, it is important to measure continuously the direction and velocity of the flow, in addition to obtaining accurate data for the afore mentioned environmental changes. The first part of this paper discusses the development of a new device for measuring the direction and velocity of groundwater flow. The device was composed of a unique floating sensor with a hinge end at the bottom, which enabled continuous measurement of groundwater flow using image data processing technique. In the second part of the paper, discussion is focused on the feasibility of adopting the new device in monitoring the direction and velocity of groundwater flow at low velocity range of less than 10^-2 m/s by analyzing the results of laboratory tests using a large water tank. Taking into considerations the data for different environmental changes, it is found that the new measurement device can monitor in a simple and continuous way the direction and velocity of groundwater flow in a borehole.

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Shear modulus of peat soil from Akita, Japan is evaluated and discussed in this paper. Bender element and triaxial cyclic loading tests are performed on disturbed and undisturbed specimens. Three techniques for travel time determination on bender element test proposed so far are applied on each specimen to discuss the resulting error on shear modulus evaluation. Estimated G-σ relationships show that the difference of shear modulus between cyclic loading and bender element tests is practically negligible and that the value of shear modulus is approximately 25% less than those from overseas or domestic reports. It is also described that structural anisotropy of peat soil caused by the fiber orientation has little influence on shear modulus in contrast with on shear strength.

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