China is located in two biggest earthquake activity belts of the world; therefore, it is indispensable to research geotechnical dynamic properties. Cyclic loading tests had been constructed by LoadTrac II dynamic triaxial equipment for Haikou red clay. The dynamic pore pressure curves of Haikou red clay were calculated by a practical pore pressure model and test results showed that they have the high correlation compared with calculation results.

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Large-scale sand boiling has occurred at Sawara dry riverbed in Chiba prefecture by Tohoku Region Pacific Coast Earthquake. Alluvial clay and sand layer, which is considered natural soil, are distributed at this site. In this study, the liquefaction characteristic of alluvial natural soil has been examined. The alluvial soft clay layer is distributed from earth surface to 3m in depth. The alluvial sand layer distributed below the soft clay is in loose condition. The grain size distribution curbs of sand layers are very steep and are not vary, the sand layers are almost uniformity. The content of fine-grained fraction is 20% from 5%, and water content is 40% from 30%. In addition, N value is 25 from 5. The cyclic triaxial test has been carried out using the samples obtained by GS sampler. The liquefaction resistance ratio ,R_L20, is in the range of 0.15 to 0.26, which is small value. The initial shear modulus, G₀, obtained by cyclic triaxial test and the one calculated by the result of PS logging are almost same. The sample quality obtained by GS sampler can be estimated good condition because G₀ calculated by PS logging is regarded the original in-situ initial shear modulus. It is considered that the thickness of non-liquefaction layer near surface ground is related whether the sand boiling will occur or not. According to ‘ Guidance of the Countermeasure for Liquefaction in City Area provided by Ministry of Land, Infrastructure, Transport and Tourism, as the thickness of non-liquefaction layer becomes thinner, the sand boiling is easily to occur. In this guideline, if the clay layer is very soft, whose N value is less than 2, and artificial soil, it is not able to count to the thickness of non-liquefaction layer. But, it is not commented that when the soft clay layer is natural soil, it is able to count to the thickness of non-liquefaction layer or not. It is very important issue to estimate the sand boiling phenomena of natural soil.

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Northeastern region of India is one of the six most seismically active regions of the world. Guwahati, the major city in the region is growing rapidly in every aspect. The 1897 great Assam earthquake and the 1950 Assam earthquake both of magnitude 8.7 are two of the many great earthquakes that had occurred in this region. There have been reports of extensive liquefaction occurring during these two earthquakes. These instances of liquefaction necessitate the need to evaluate liquefaction potential of the area. In the present study, an attempt has been made to predict the liquefaction susceptibility of Guwahati city based on corrected SPT values using deterministic as well as probabilistic performance based approach. The deterministic and probabilistic version of Toprak et al., Youd et.al, Idriss and Boulanger and Cetin, standard penetration test (SPT)- based liquefaction triggering correlations have been used. The results obtained in the probabilistic approach are then compared with their deterministic approach. Standard Penetration Test (SPT) N values, engineering properties of the soils and depth of water table were taken from a data base of 200 boreholes upto 30 meter depth covering an area of 262 km2 in Guwahati city. Liquefaction susceptibility from the methods is presented as maps showing zones of levels of risk of liquefaction. Comparison of the three methods in the deterministic approach have shown that there is a difference in the factors of safety in the same depth and comparison in the probabilistic approach have also shown a difference in the values of probabilities in the same depth. The SPT- based liquefaction evaluation procedures have been found to yield significantly different predictions. This study feels that the issues and uncertainties regarding the use of both the deterministic and probabilistic liquefaction triggering relationships in practice must be resolved so as to arrive at a common consensus to determine the same.

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The major problems associated with liquefaction-induced ground subsidence are tilting of houses, buckling of roads, lifelines cut off, etc. For the mitigation and preparedness over the liquefaction-induced damage, a detailed study on prediction of ground subsidence for future earthquake is important. On the 11th of March 2011, the Off the Pacific Coast of Tohoku Earthquake (MW=9) hit Japan and caused severe liquefaction in Urayasu City, Chiba Prefecture. In this study, in order to investigate the relationship between liquefaction potential, PL, and liquefaction-induced subsidence which occurred in the 2011 earthquake, liquefaction assessment is first carried out by using a number of boreholes and relevant soil test data from Urayasu city. Then, the liquefaction-induced road subsidence is extracted from a set of the Digital Surface Models (DSMs) from airborne LiDAR (Light Detection And Ranging) surveys before (2006) and after (2011) the earthquake. The extracted subsidence from the DSMs indicates that the liquefaction-induced road subsidence is larger for the residential roads than that of the main roads, thus the relationship between PL and road subsidence is different for each type of road. Finally, an attempt is made to apply the obtained PL and road subsidence relations to attain a unique hazard map for Urayasu city.

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The 2011 Tohoku Earthquake at the Pacific coast of Japan caused significant liquefaction-induced damage around Tokyo Bay where floated pipelines and manholes were widely observed. To protect existing underground lifelines from future earthquakes in some other regions, mitigation measures are urgently required. The conventional measures require considerable time and economic resources, which hinders the feasibility of these methods. In this regard, the authors previously proposed new mitigation measures: the vertical drain pipe method, connection with pavement by stiff bars (namely, horn structure method) and the chemical grouting method. The proposed measures can be executed with a partial excavation of backfill soil, resulting in less construction period and cost. Satisfactory performances of the proposed measures were demonstrated through 1-g shaking model tests by the authors. The present study aims to develop a framework for practical application with the proposed measures. To evaluate the performance of the proposed measures, challenges of developing a simple analytical method based on simple beam models were discussed. The proposed analytical models qualitatively captured the experimental results.

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This paper presents a three-dimensional numerical simulation method for the seismic response of piles in liquefiable soils using a unified plasticity model for large post-liquefaction shear deformation of sand. The unique constitutive model used is able to achieve unified description of the behavior of sand at different states under monotonic and cyclic loading during both pre- and post-liquefaction regimes. In the finite element analysis, soil is modelled through u-p form coupled brick elements and pile through second-order brick elements. Centrifuge shaking table experiments on single piles in level liquefiable ground, and on single piles in lateral spreading ground was simulated using the proposed finite element analysis method. Simulation results exhibits the method’s effectiveness in reproducing the dynamic response of both the ground and piles.

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Dynamic centrifugal model tests are carried out to confirm the effect that surface improvement using a high-permeability material has on reducing liquefaction damage to small structures. A gravel layer with a prototype thickness of 0.3–1.2m was laid under the model structure. Without improvement, the inclination of the model structure continued throughout the period of liquefaction, yielding a residual inclination of about 1/6.5. In cases with improvement by gravel, residual inclinations were 1/300 or less in all cases, even though most of the ground around the model suffered liquefaction.

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