A large amount of reclaimed ground along Tokyo bay suffered damage due to liquefaction during the 2011 Great East Japan Earthquake. The liquefied areas were mostly concentrated in newly reclaimed land. The aging effect is considered to be important for the susceptibility of ground to liquefaction. The liquefied soils contained a lot of fines and the fines content varied by place. In this study, in order to understand the dynamic deformation characteristics of the ground, a series of bender element tests and hollow cylindrical torsional tests were performed on sand and clay mixtures with various proportions of fines content. Furthermore, the water content of the mixed clay was varied between the liquid limit and two times the liquid limit. The variation of water content of the clay in the sand-clay mixtures was considered to represent the effect of aging. Test results show that the maximum shear stiffness decreased with increasing fines content and water content of the clay.

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Shirasu is a volcamic soil which is widely distributed in South Kyushu in Japan. It contains non plastic fines which was created by its fragment of coarse particles. In this study, a series of bender element tests on Shirasu was performed with varying its fines content. As a result, it was observed that the shear modulus of Shiarasu was decreased with increasing the fines content although void ratio decreased as fines content increased. However, it was found that there is a unique relationship between shear moduli of Shirasu and the equivalent granular void ratio, in which the proper contribution factor b for fines was assumed. Based on the findings in the study, an empirical formula to express the shear moduls of Shirasu with various fines content was developed as the function of the fines content, the equivalent granular void ratio and the effective confining stress.

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A newly developed direct shear apparatus for cyclic tests is, first, introduced. It is shown that liquefaction strength on Toyoura sand obtained using a newly developed direct shear apparatus and test procedure coincides well with that obtained from cyclic triaxial tests. Then, two series of cyclic direct shear tests were carried out on samples of sandy silt, which was excavated by a grab bucket at a construction site in Naruto City, Tokushima Prefecture. Therefore, considerable disturbance was expected. Results were compared with those from a series of cyclic triaxial tests on undisturbed samples by a triple-tube technique at the site. It was found that liquefaction strength from the direct shear tests coincided well with that obtained from cyclic triaxial tests. It is deduced that disturbance of a sample was well cured in the consolidation process, which is one of the advantages of the newly developed apparatus.

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Seismic liquefaction mitigation based on nanomaterial is a new method different from traditional chemical grouting, and its basic concept is that nanoparticles suspensions are slowly injected from the edge of the liquable site and transported through the groundwater flow into target position to improve the liquefaction resistance of liquable sand. The properties of the nanoparticles have important connections with the effects and mechanism of nanoparticles for liquefaction mitigation. Different from primary research on macroscopic geotechnical properties, this paper focuses on the microscopic characteristics of nanoparticles. The microscopic test, Transmission Electron Microscopy (TEM), was conducted to build up the microstructural characterization description of the nanoparticles for treating liquefiable soils, using laponite as representative nanoparticle. The morphology, size and internal microstructure of laponite particle in dry state were obtained by TEM test. Then the relationship between microscopic characteristics and seismic liquefaction mitigation are discussed. The specific objectives of the work are including providing the direct micrograph for the size and microstructure characteristics of laponite and analyzing the microscopic characteristics of nanoparticles related with liquefaction mitigation. This work can help establish structure characterization description of laponite applied to liquefaction mitigation and explore the microscopic nature of nanoparticles liquefaction resistance characteristics.

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Coarse-grained loose deposit, distributed widely in earthquake-prone area in southwestern China, is one of the challenging problematic geomaterials. The dynamic shear modulus G_d and the damping ratio D are two main parameters in seismic-hazard analysis and one of the principal influencing factors affect the dynamic parameters is initial conditions. This paper presents a study of the effects of initial stress ratio and moisture condition on dynamic shear modulus Gd and damping ratio D of loose deposit with large-scale dynamic triaxial tests. The experimental results show that, in the considered ranges of confining pressure (σ_c=100kPa-1000kPa) and stress ratio (K_c=1-3), the dry densities of the same prepared specimens after consolidation are well normalized with the mean effective stress σ_m. The maximum dynamic shear modulus G_dmax is calculated using σ_m and the influence of different consolidation stresses on initial void ratio has been considered. The test data demonstrate that the well-known Hardin’s equation underestimates the influence of stress ratio K_c on G_dmax. An improved empirical relation in consideration of the effect of stress ratio based on Hardin’s equation is proposed in the paper. It is also concluded that the curve of the dynamic shear modulus ratio G_d/G_dmax versus the normalized shear strain γ_dn under air-dried condition shows more obvious nonlinearity than the one under saturated condition. In addition, a case study using the proposed improved equation of G_dmax and the nonlinear relationships of G_d/G_dmax versus γ_dn is provided to illustrate the importance of considering stress ratio and moisture condition in the response spectrum analysis of ground.

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In this study, the effect of a slaking on a mechanical behavior of the crushed mudstone specimen is examined through laboratory test and interpreted based on the concept of soil skeleton structure through simulation using SYS Cam-clay model. Furthermore, seismic response on Makinohara highway embankment with slaking under soil-water finite deformation analysis code GEOASIA. The new findings are as follows, (1) After the early shear stage, the crushed mudstone aggregate specimens with a 100% compaction degree show hardening behavior with plastic expansion that follows the critical state line of the remolded sample. This behavior resembles overconsolidated soil. Additionally, a greater number of drying-immersion cycles correspond to a lower maximum deviator stress of crushed mudstone aggregate. Although this aggregate shows similar behavior at a 95% compaction degree, when compared at the same level of slaking progression, it shows an increase in maximum deviator stress with increasing compaction degree. (2) Employing elasto-plastic parameters for remolded samples and evolution rule parameters in calculations using a SYS Cam-clay model of an elasto-plastic constitutive model allowed us to reproduce the mechanical behavior of crushed mudstone aggregate with differing slaking progression levels and compaction degrees simply by changing the initial conditions. These calculations indicated that, given a constant compaction degree of the crushed mudstone aggregate, the structure decays and overconsolidation decreases as slaking progresses. (3) The behavior of the Makinohara Embankment failure was reproduced during an earthquake response analysis using GEOASIA. During the earthquake, large strain occurred at the mudstone–sand and gravel boundary, and at the sand and gravel–mudstone base boundary. After the earthquake, a very large circular arc slip failure occurred, bisecting the crown of the embankment. A typical element of the numerical model of the embankment was examined for behavior during the failure and showed the following. It shows softening behavior accompanying plastic compression and that the effective stress path approaches the point of origin. Simultaneously, there was a positive excess pore water pressure and strain grew to a high level. In a calculation assuming no slaking, there was little softening behavior during the earthquake, and so strain did not develop to high values and the embankment remained stable after the earthquake.

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