Ryukyu limestone formation belonging the Quaternary Era is wide spreadly distributed over Ryukyu archipelago. The sea shores constituted by Ryukyu limestone formation is generally steep and it often forms overhanging cliffs. It also contains many karstic caves. Overhanging cliffs and karstic caves cause engineering and social problems particularly in urbanized areas in addition to seashores and riversides. The authors are concerned with the stability of cliffs constituted by Ryukyu limestone formation along the seashores in Ryukyu Islands archipelago and they present some analytical methods and numerical analyses for the stability assessment of overhanging cliff subjected to gravitational and seismic loads. These methods are applied to some actual observations on seashore cliffs in several islands. They compared the case studies with estimations and discussed the possibility of estimating tensile strength of rock.

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  The present study reports the fundamental properties, compressive characteristics, and bearing capacity of lean-mixed granular polymer and cement treated soil. A trial mixture with slight admixture materials, such as polymer and cement, was conducted to make well-suited granular soil. In addition, a series of single particle strength test, one-dimensional compression test, and loading model test in a centrifugal acceleration field was carried out to investigate the strength, stiffness, and bearing capacity of granular cement treated soil. The test results showed that large quantities of polymer and cement was not needed to granulate cohesive soil and lean-mixed granular cement treated soil ensured strength, stiffness and bearing capacity.

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  Excavated slopes become safe only when they are either excavated to a safe slope angle or when protective measures are taken. During slope cutting work, slopes are at greater risk of failure. In many cases, slope failure suddenly occurs without any warning signs and the workers do not have time to escape and hence accidents take place. To prevent such accidents, the mechanism of slope failure caused by slope cutting work should be clarified. In this study, full-scale slope model tests and centrifuge model tests were conducted to examine the mechanism of slope failure during slope cutting works. It was found that local slope failure was observed before complete slope failure and this mechanism was consistent with previous slope failure accidents. The horizontal and vertical movements of the slope could be measured during excavation, so it may be possible to predict slope failure from the typical slope movement in order to prevent slope failure accidents in future.

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  This paper reported swelling property of undisturbed clay sample as related to geotechnical disaster such as heaving. In this study, an apparatus was newly developed to accurately measure one-dimensional swelling pressure of clay subjected to water infiltration. A series of tests was carried out on reconstituted bentonite, undisturbed mudstones, granite seam clay and rhyolite stiff clay. The test results showed that maximum swelling pressure correlated closely with specimen’s initial state index, and these tendencies were very similar to those of undisturbed samples. Especially it was shown that there exists a unique relationship between the maximum swelling pressure and the liquidity index for various soils. Swelling anisotropy was obviously recognized on the basis of test results on undisturbed samples.

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  It is common practice to cover railway embankment slopes with protective materials to prevent rain-induced slope failure. Although slope covering of this type is designed mainly for erosion control, it also has the effect of helping prevent the groundwater level rising through the embankment body in the event of heavy rain. First, this study investigates a time change of water-interception ratio of block-pitching work, which is one of slope covering, according to the results of sprinkling tests in laboratory and railway field. Next, it calculates groundwater level lowering effect of water-interception ratio of the block pitching work on the slope of a railway embankment made of sandy material, and the factor of safety of the slope that can be achieved by such slope covering. Finally, it discusses the effect of water-interception ratio and surface covering ratio on the rain-induced slope failure, and proposes a procedure for applying these results to a risk evaluation method based on critical rainfall.

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  Distinct Element Method (DEM) based on simple principles has been worthy of notice that it is able to simulate the deformation-stress behavior of granular materials. However, quantitative verifications have not been sufficiently done, although various qualitative results have been presented. It is a serious problem for DEM from the viewpoint of the quantitative prediction that is one of important tasks in geotechnical engineering field. Numerical experiments on biaxial isotropic compression have been investigated. It was found using global damping as Dynamic Relaxation Method (DR) that the simulated stress and strain smoothly and rapidly converge on the theoretical values for a regular composition model with one particle size, and that initial void ratios can be uniquely obtained depending on the frictional angle between particles for a composition model with different particle sizes.

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  In the DDA, the contact spring are introduced between the blocks contacting each other to prevent the penetration of the blocks but the dashpots are not usually introduced unlike DEM. However, it is well known that the numerical damping caused by numerical integration occurs during the simulations. In this study, the characteristics of numerical damping caused by Newmark β method in DDA was investigated using simple 1-D free oscillation problem. The 1-D collision problem was analysied using DDA with 3-D rigid sphere block and sensitivity analysis for the parameters related to Newmark β method was carried out. The effect of these parameters on the numerical stability and accuracy was also discussed. From the analytical results, in DDA, the calculation time step, Δt and natural frequency, T should satisfy the condition of Δt/T<0.05 to obtain the results with good accuracy. To evaluate the energy loss correctly when the two blocks collide each other, the effect of numerical damping and velocity ratio should be considered separately.

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  A series of centrifuge model tests was performed to investigate the characteristics of horizontal subgrade reaction of pile in liquefiable sand. Centrifuge model tests were performed by combining shaking test and the alternating load test immediately after shaking to examine the effect of depth, excess pore water pressure, lateral displacement and a thickness of non-liquefiable sand on the characteristics of lateral subgrade reaction. The data of alternating load tests were arranged and the experimental formula for the coefficient of horizontal subgrade reaction of pile is proposed. The proposed formula is also founded to be fairly comparable with previous formula obtained from a large-scale shaking table tests.

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  In order to validate the three-dimensional nonlinear elastic constitutive model for the original ground and the multiscale analysis method for partially improved grounds, both of which have been developed by the authors in the previous report, we compare the results of the static load-settlement experiments under centrifuge gravity and those of singlescale and multi-scale numerical analyses. The surface settlements calculated by the proposed model and analysis method are in good agreement with the experimental results that show that the resulting surface settlement is uniform in load-surface area on non-improved sandy ground and non-uniform (larger on center position) on improved sandy ground. To verify the practical applicability of the method, we also apply it to the in-situ load-settlement problem whose site is partially piled with 250 piles. The analysis results agree with the in-situ measured data.

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  In the Maizuru-Wakasa expressway construction, the soft ground composed of the cohesive soil and humus soil is also thick 40m or more and piles up. In the test embankment executed for this soft ground measures, a very big settlement was generated, and a large deformation as for the surrounding ground was caused. In addition, a special tendency to concentrate only on the one side of the embankment was seen as for the deformation of the surrounding ground. The check boring and FEM analysis were executed to examine such a deforming behavior factor in this thesis. As a result, the possibility that a local slipping in the humus layer are caused, and it was guessed that this humus layer moved along a basic inclination. Moreover, it has been understood to be able to expect an enough effect as a deformation control measures against the surrounding ground by promoting the consolidation of this humus layer.

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  Since water inflow into a tunnel significantly impacts construction costs and schedules, it is important to estimate the impact on these factors quantitatively based on prior information about hydrogeological properties. A simplified formula is proposed in order to estimate water inflow volume into tunnel. This formula enables us to calculate water inflow risk more quickly than DFN model. Monte Carlo simulation and sensitivity analysis about water inflow risk are performed by using this formula. Then relationships between water inflow risk and amount of information about fracture properties are obtained based on the the sensitivity analysis.

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  This study investigated the mechanism of liquefaction-induced ground displacement caused by the collapse of a quay wall. The investigation was based on case studies of past earthquakes, 1G tests, and centrifuge tests using a ground model. The ground displacement in the area of the collapsed quay wall was five to ten times greater than the thickness of the liquefied soil layer. The displacement ultimately extended 200∼300 meters from the quay wall, which centrifuge tests showed was due to the inclination of the land surface. This was verified through re-analyses of the ground slope measurements and case studies of the 1995 Kobe earthquake. The results of these tests and case study analyses were used to quantitatively measure the attenuation characteristics of the horizontal displacement of the liquefied soil behind the quay wall.

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  Some sedimentation test on small scale sandy deposits were carried out and the shear resistance of sand layers before and after sedimentation were measured. The experimental result showed that the thickness of sand deposits showing lower shear resistance increases with increasing the vertical distance of possible sedimentation, which indicates the disturbed soil fabric during sedimentaiton. The disturbed soil fabrics formed during the sedimentation of soil particles which moved with the upward flow of water after liquefaction is thus believed to be one of the mechnisms leading to the occurence of re-liquefaction.

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  It is well known that NAPL is trapped in soil when NAPL infiltrates into unsaturated soil and that NAPL residual saturation influences the distribution of NAPL. However any paper hasn’t conducted the numerical simulation for air-NAPL-water multi-phase flow with NAPL residual saturation, until now. Therefore the this paper conducted the simulations for air-water-NAPL multi-phase flow with NAPL residual saturation and compared the results of the simuations and the results of experiments with a chamber for NAPL infiltration. As a result, it was found in this paper that the distrubtion of NAPL saturation could almost simulate with the NAPL rediual saturation.

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  Underpass structures for a public road and a airport service pass were constructed under the south taxiways in the second manmade island of Kansai International Airport. Two major issues in this construction were studied. One was prediction of large and uneven settlement of manmade-island under the structures, and the other was the design method of the structures in such a condition.
  In this paper, the design methods of underpass structures under uneven settlement of manmade-island were proposed after analyzing the site measurement and observation.

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  Recently, there have been accidents in which the drill rig has toppled over. In this study, to clarify the mechanism which makes the drill rig unstable when it is self-propelled, real-scale experiment and centrifuge model tests were pereformed. The behavior of the real-scale and the model of a drill rig were measured by putting accelerometers in three places. As a result, it was understood that long periodic shakes in both real-scale and a 1/25 scale model of a drill rig occur during self-porpelling. It was clarified that the ground contact pressure that acted during self-propelled was larger than the value used to design.

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  Centrifuge shaking table test with 30G of the acceleration of gravity is conducted in order to clarify the failure mechanism of the earth structure under the unsaturated condition. A soil structure model composed of an embankment with sandy soil, a foundation ground, and a base layer. Four earth structures models are tested, in which moisture condition in the embankment and liquefaction of the foundation ground are chosen as test parameters. The observed record at the river dike during the 2003 Northern Miyagi Prefecture earthquake was used as an input wave. It is found that slope failure occurred in the unsaturated embankment because of excess pore water pressure generation, whereas it does not occur in the dry embankment. The process of excess pore water pressure generation depends on the permeability of the foundation ground.

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