Observations were made of microtremors at 48 widely distributed sites in Miyazaki city to investigate the dynamic properties of surface soil layers. The relationship between the ground conditions and dynamic properties of the surface soil layers was investigated quantitatively, based on the results of the microtremor observation. Reasonable agreement has been obtained between measured and predicted values for the depth to engineering bedrock in the well-documented Miyazaki plain. From these results, a new equation has been developed to estimate the depth to engineering bedrock, based on the predominant periods of the ground. In addition, the engineering bedrock profiles obtained from the proposed equation to investigate its applicability were found to be reasonable in the preliminary design. To this end, microtremor measurements are recommended as a means of gaining a better understanding of earthquake damage and evaluation of the engineering bedrock. The method is relatively quick, and is also inexpensive. The applicability of the proposed equation to other areas requires further research.

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To improve the stability of a caisson type breakwater against wave force, it is effective to provide back-filling behind a caisson. To evaluate the effectiveness of the back-filling behind the caisson, it is necessary to clarify the interactive resistance of the caisson, the back-filling and the rubble foundation against wave force. However, it is thought that these effects are not clarified yet. Therefore, a series of the centrifuge model experiments has been carried out to clarify these effects. In these experiments, horizontal static load was applied to a model caisson with back-filling, and a sliding failure surface was evaluated from the deformation of back-filling and rubble foundation. Besides, the elasto-plastic FEM analysis was carried out to find out a sliding failure surface, and the stability of a caisson with back-filling was evaluated using the circular arc failure method considering the forces acting on back-filling and rubble foundation. As the results of the comparison between the experiment results and those calculated, both of the sliding failure surfaces fitted well, and it was conformed that the circular arc failure method is applicable as a design tool to evaluate the stability of the caisson with back-filling.

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Dynamic response analysis has been widely used in the seismic design of road bridges. However, static analysis is still used in the seismic design of foundation. To develop dynamic analysis method for bridges including the effect of nonlinear behavior of foundation, it is necessary to develop the modeling method of physical property of ground considering the effect of statistical variability of physical property of ground. This is because physical property of ground has wide variety, and this could affect the results of dynamic response seriously. In this research, a series of dynamic analysis for bridge columns with pile foundations were conducted, and the effect of the variability of physical property of ground was evaluated. The results show that the maximum shear stress of ground is one of the most important parameter to ensure certain accuracy in dynamic response analysis.

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It is generally said that the slope collapse occurs by decrease of the effective stress to be caused by increase in groundwater level in a slope with the rain penetration, while shear deformation progresses also in unsaturated slope. In order to predict the time when the rainfall-induced landslide occurs, it’s important to capture the prognostics of collapse, and, therefore, mechanism elucidation of shear deformation of unsaturated slope is necessary. In this study, relations of shear deformation and soil moisture in plural rain events were examined using observed data of suction, volumetric water content, shear deformation of slope and surface displacement at the natural slope for approximately two and a half years. As a result, we confirmed that shear deformation of unsaturated slope were greatly affected by moisture conditions before rainfall and changes of suction and volumetric water content in the rainfall.

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In this paper, the mechanism of embankment collapses due to rainfall after earthquakes was examined by means of the embankment model for shaking table test as well as the permeability test. The results suggest that, the amount of rainfall at deformed embankment decrease with increasing the displacement of the top of the slope due to vibration, and that the embankment model with the crack was observed increasing pore water pressure in locally. Additionally, the coefficient of permeability was seemingly unaffected by the shear history. Therefore, the mechanism of change of the infiltration characteristics on the embankment model could be relates with the crack in the embankment model.

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The authors conduct cyclic torsional shear tests to evaluate the effect of the long shaking on the occurrence of liquefaction. Silty sand taken from the boiled sand Urayasu City and Toyoura sand were tested under three densities, loose, medium dense and dense. Two types of shear wave were applied to specimen, i) sine wave of 20 cycles and ii) the seismic wave recorded during main shock and after shock of the 2011 Great East Japan Earthquake at Urayasu K-NET. Test results, showed that the influence of the long seismic wave on liquefaction strength was greater than the design standards shown to Japan Road Association. Moreover correction factor C_W according to the JRA standard increased with liquefaction strength. Based on the test results, safety factor against liquefaction F_L at Takasu Elementary School where liquefaction occurred during the Great East Japan Earthquake was estimated. The estimated F_L showed that reclaimed sand liquefied by the earthquake thought the maximum surface acceleration was not large.

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The complex response method is easy to understand and the responses are not significantly influenced by one’s level of experience. However, this method makes extensive use of superposition and thus is only applicable to linear systems. Therefore, when observing nonlinear effects, the equivalent linear method is more traditionally used.
Recent observations of extremely large earthquakes require engineers to consider the nonlinear effects on the ground materials. However, these huge nonlinear behaviors may not be appropriately analyzed using the equivalent linear method, as the accuracy of the responses in the high frequency region may be compromised.
In this paper, the equivalent linear method in the frequency domain and the nonlinear analysis in the time domain have been compared. The applicability of the equivalent linear method in analyzing large strain levels has also been examined.
The following improvements on the equivalent linear method to increase the accuracy on the responses in comparison to nonlinear analysis are suggested: 1) the use of strain dependent dynamic properties based on the least square method, 2) computation of stress by complex stiffness, 3) the use of effective strain coefficients as a function of input motions and 4) the introduction of the multi-equivalent linear method in order to improve the response at higher frequency regions.

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The authors have proposed a reliability analysis method for long continuous structures considering investigation sites to counter liquefaction failure. This method is characterized by continuously calculating the failure probability caused by liquefaction at an arbitrary point and quantifying the uncertainty concerning the investigation site and quantity. The purpose of this study is to verify its effectiveness based on application to an actual river dike that suffered liquefaction failure due to the 2011 Earthquake off the Pacific coast of Tohoku.

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This paper described the estimation of the groundwater flow system based on the principal component analysis of the dissolved major ions data of groundwater and the non-hierarchical cluster analysis of the principal components scores. In Nagara river alluvial fan on Nobi basin, the characterization of groundwater quality was represented by only two principal components. And then, the cluster analysis produced four groups in the relationship between the first and the second principal component scores. When the groups of sampling locations were examined, it was recognized that the groundwater flow could be divided into four systems. The groundwater systems was in good agreement with the one evaluated from groundwater level distribution. Furthermore, the flow system of groundwater recharged from the Nagara river water was specified based on the resemblance of the ions data between the groundwater and the river water.

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A lot of development housing sites in Sendai city had been damaged during the Great East Japan Earthquake. Authors conducted seismic damage survey from April, 2011 to July, 2011 on five development housing sites with a gently-sloping of ground surface in Sendai city. In this paper, housing damages, open crack of ground, differential settlement, water pipe damage, and block wall damage were analyzed by using the result of seismic damage survey, and the damage rate of each area of housing site (filled-valley area, cut area, and boundary area) and the change of damage rate according to a development age were studied As a result, the following knowledge was shown quantitatively. A filled-valley area and a boundary area has high possibility of damage generating compared with a cutting ground area. Most complete-or-half-destruction damage of houses was caused by the ground deformations like the open crack of ground and the differential settlement. The damage rate became so large that the development age is old.

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In the past, the concepts of “error” or “accuracy” were used to express the reliability of measurement. However, the practical application of these concepts widely varied, depending on the fields of technology and countries. “Uncertainty” is a newly developed scale to convey the reliability of measurement data and has been used since in 1990s. It is now used in various technical and academic documents in which the reliability of measurement data play a significant role. But, it is not widely applied in geotechnical engineering.
In this study, the authors research the evaluation method of the reliability of the soil particle size distribution test results and make clear the effective factors on the uncertainty of test results. Then by the proposed expressing method of uncertainty of soil particle distribution curve, it is easy to evaluate the uncertainty of grain size distribution indexes such as 50% size, effective size, uniformity coefficient, fine grain content, clay content and so on.

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This paper discusses applicability of Isotache Model to the peaty ground, which is extensively distributed in Hokkaido, Japan. The conventional oedometer test with constant incremental loading was carried out for peat samples collected at two sites in Hokkaido. Isotache parameters were obtained from this test and compared with those of usual clayey soils. In addition, these characteristics are compared with the rate dependency calculated from settlement measured at fields, such as embankments and reclamations. It is concluded that the applicability of Isotache model to the peaty ground is confirmed and the strain rate dependency in the peaty ground is more significant than that in clayey ground.

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Recently, the landslide disaster caused by the torrential rain or a typhoon is increasing. And the importance of the quantitive and long-term maintenance management of a reinforcement soil is increasing in the viewpoint of disaster prevention. Therefore, authors focused on digital photogrammetry that has been used to measure slopes in express way due to its relative low cost and ease of measurement, and try to maintain reinforcement soil. From two years of measurement to terre armee reinforcement soil wall by digital photogrammetry, it was found that wall displacement during two years is minute compared with deformation of as-built. Moreover, it was shown that long-term observation of reinforcement soil by digital photogrammetry is sufficiently possible.

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Swedish weight sounding test (thereafter, called WSW test) is widely used as a research method to evaluate the residential sites. Advantage of SWS test is possible to evaluate the bearing capacity of residential sites. In particular, by continuous measurement, it is relatively easy to capture boundary formation. On the other hand, a disadvantage of SWS test is to determine the soil and groundwater level. The determination of the soil is based on the experience of the operator. Only information obtained from the results of the SWS test is insufficient to evaluate the residential ground. Suppose that if it is possible to incorporate the determination method of the soil by electrical resistivity using SWS test holes, a lot of information will be gained. As an ideal way, the electrical logging method by the electrode to the SWS test hole, is effective. As a basic research, the authors attempted to clarify the evaluation method of soil fine fraction content by using the electrical resistivity using a sample soil of 56 types of laboratory experiments. We also revealed the size effect of the measurement hole provided in the soil gives to the electrode diameter. Further, as situ testing by filling the pores of the natural ground potassium chloride solution was to verify the validity of the estimate equation by the electrical resistivity.

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