In order to study deformation characteristics of humic soils deposited under railway embankment during earthquakes, a series of in-situ tests, laboratory tests and numerical analyses were conducted. In the laboratory, undrained cyclic triaxial tests were performed on undisturbed samples to evaluate their strain level dependency of shear modulus and hysteresis damping. Based on results from the in-situ and laboratory tests, seismic response analyses were executed to compute the amplification characteristics of the humic soil layer. In addition, effects of cyclic loading history on the strength properties under monotonic loading were investigated experimentally.

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Significant amount of boiled sand was observed in the area of liquefied ground after the Great East Japan earthquake. In this study, a series of model tests was conducted in order to understand the mechanism of sand eruption through the gap of pavement when liquefaction occurs. Liquefaction and sand boiling was simulated in the model test. Sand grains initially moved horizontally and then vertically, causing disturbance and loosening in the ground. Velocity of the water is the most important factor for the sand eruption. It was found that the hydraulic gradient for the sand boiling was larger than the critical hydraulic gradient.

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A new type of disk transducer with the size of 80 mm diameter has been developed successfully by assembling 4 numbers of p-type piezo ceramic element and 4 numbers of s-type piezo ceramic element, in order to carry out the elastic wave study of small to large g rain size geomaterials on single apparatus. Properties of fine to medium sand measured by proposed disk transducer method were compared with previous research and the stiffness found to be fallen in similar range within allowable scatters. It was also confirmed that the large disk transducer can be applicable to gravel having mean diameter of 12mm.

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A method to detect the sand boiling by using RapidEye satellite image was proposed in this study. The ground truth data through the field investigation were collected, and used in the procedure of the decision tree classification process to detect the sand boiling. The results of the detection classified into 4 levels based on the similarity index which was defined in the study. The outcome of the study is comprehensible and consistent with the existing research reported by the professionals.

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Currently, the N value or shear wave velocity is generally used to estimate the liquefaction resistance. However the correlation between theses was not always good. Therefore, in order to investigate the correlation between relative density, dynamic shear modulus and liquefaction strength of sandy soils. A series of drained compression test and liquefaction test were conducted on Toyoura sand by using triaxial apparatus. And we measured the shear wave velocity during the test to calculate the dynamic shear modulus of specimen. It was found that the dynamic shear modulus was increased as the number of drained vertical cyclic loadings increases, which may indicate that the interlocking effect was enhanced by the drained vertical cyclic loading history. On the other hand, from the results of drained compression test and liquefaction test, the effect of changes in the microscopic structure of sandy soils due to drained vertical cyclic loading history on the drained compression strength and liquefaction strength became clear.

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In order to investigate the seismic performance of retaining wall, RW, reinforced by a square-shaped geocell embedded in sandy and gravelly backfills, a series of shaking table model tests was carried out. For a comparison purpose, the tests on RW models without reinforcement and those reinforced by a conventional geogrid were also performed. It was found that the RW models reinforced by the square-shaped geocell exhibited higher seismic performance than non-reinforced RW models as well as those reinforced by the geogrid, which was evaluated based on the residual sliding displacement and overturning angle of the wall facings, settlement of the backfills and response acceleration of the wall facings.

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In order to investigate the possible change in liquefaction properties during multiple events, a series of tests was conducted using a newly-developed stacked-ring simple shear apparatus. A combination of cyclic shear tests under constant volume condition and one-dimensional compression tests were executed repeatedly on a single specimen of Toyoura sand. The specimen was gradually densified with the multiple liquefaction history, while its liquefaction properties were different from those of the reference specimen that liquefied for the first time under similar density. Such change in liquefaction properties was found to depend on the shear strain amplitude that the specimen underwent during the previous liquefaction events.

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As of the last big earthquakes, masonry structures have demonstrated its seismic vulnerability, especially for un-reinforced （URM） walls. Many casualties occurred due to the collapse of URM walls, not due to the earthquakes itself. Regarding this condition, there is a need to strengthen masonry houses by retrofitting with specific material. Although some retrofitting materials, such as fiber reinforced polymer, steel fiber-reinforced polymer and glass fiber-reinforced polymer, etc., have been investigated, these synthetic materials are expensive and not available in many parts of the world. Therefore, a natural fiber called abaca fiber is used in this study, which is locally available and high tensile strength mixed in mortar as reinforcement. The final objective of the study is to investigate the seismic behavior of masonry houses retrofitted by the proposed system and assess the feasibility of the system. The axial tension test and the in-plane diagonal compression test using brick masonry wallets are conducted in this research. Based on the experimental results, cement mortar reinforced by abaca fiber increase strength and deformation capacity of masonry wallets.

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About sixty percent of the total population of the world still live in masonry structures, and there have been heavy casualties in the past earthquakes due to their structural collapses. To improve seismic capacity of these weak structures, many retrofit methods have been developed. However, most of them are time-consuming and labor-intensive and can only be applied for new construction, which slows down the spread of these methods. In our research, a much easier new method applicable for both new and existing constructions was developed. The material used in this method is called ‘SG2000’, paint reinforced with glass fiber. There are two merits to use it. Firstly, it needs much less time and labor to retrofit. Secondly, it has endurance to UV-ray, water, and fluctuation of temperature. An experimental study has been conducted to evaluate the performance of SG-2000 as a masonry retrofit material, and to find the best way to paint on the wall. It has been proved that the wallette coated with SG-2000 has about 14 times and 16 times larger deformation capacities in inplane and out-of-plane tests, respectively, than that of the unreinforced masonry wallette. We have also found some efficient ways to coat masonry walls.

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In order to investigate the effects of the segregated soil structure that the reclaimed ground using dredged sandy soils would exhibit, a series of undrained cyclic triaxial tests were conducted on two types of specimens which were re-constituted using sandy soils that actually liquefied during a past earthquake. The liquefaction resistance of segregated specimens prepared by pluviation through water was higher than that of uniform specimens prepared by moist-tamping. The interface silty soil layers of the segregated specimens underwent larger local deformation than the underlying sandy soil layers.

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In order to investigate the liquefaction properties of iron ore fines and sandy soils under saturated and unsaturated conditions, a series of cyclic triaxial tests was conducted. Their liquefaction resistances under unsaturated condition were higher than those under saturated condition. The ratio of liquefaction resistance under unsaturated condition to that under saturated condition increased with the decrease in the degree of saturation, or with the increase in the volumetric strain due to compression of pore air, while their relationships for iron ore fines and Inagi sand were quantitatively different from those for Toyoura sand. By considering swelling potential due to reduction in effective stress, a new parameter called volumetric strain ratio was introduced, and more unique relationships could be obtained with the ratio of liquefaction resistance.

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The observed visual damage such as crack width and crack length is not the same for the specimens with different scale ratio. In this paper, the conversion procedure to full scale specimen from small scale specimen of visual damage is proposed. For the verification of this procedure, a series of experiments including a full scale and several small scaled specimens were conducted. As a result, the proposed method shows good agreement with experimental results.

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