Different definitions are used for the onset of liquefaction in engineering practice. For example, NCEER, JRA, and AIJ use γ =3 %, DA = 5 %, and γ = 5 %, respectively. The state where the excess porewater pressure becomes equal to the initial confining stress is used to identify the liquefaction in the field during earthquake and laboratory tests such as a shake table test. In addition, the number of cycles causing liquefaction, N_c is 15 in NCEER and AIJ whereas it is 20 in JRA. In total, 44 liquefaction strength tests of soils sampled from the natural deposits are used to evaluate the liquefaction strength under different definitions, and the relationships between various definitions are evaluated and discussed. The liquefaction strength at N_c = 15 is about 4 to 5 % larger than that at N_c = 20. The soil with large fines frequently does not become a zero confining stress state. The liquefaction strength of NCEER and JRA is nearly the same, and that of AIJ is about 7 % larger than them.

In reality, when seismic waves arrive, sites are shaken by multi-directional ground motions that are usually decomposed into three components: two perpendicular horizontal (E-W and N-S) and one vertical (UP). Numerous experimental and numerical studies have demonstrated that two horizontal (or bi-directional) motions can significantly aggravate the building and site responses compared to the scenario where only one horizontal motion is applied. However, 1D site response analysis (SRA) is still prevalent in quantifying site effects and responses due to its simplicity. Recently, we investigated the effect of bi-directional ground motions on site responses at potentially liquefiable sites. Results proved that bi-directional ground motions can intensify the site responses and increase the possibility of getting liquefied. In this study, we utilize a machine learning-based method to predict the soil liquefaction under four different excitation conditions, including 1D SRA using E-W, N-S and RotD100 motions, and 2D SRA subjected to bi-directional motions. Moreover, we evaluate the relative importance and correlations of a broad range of ground motion and soil parameters, i.e., peak ground acceleration (PGA), peak ground velocity (PGV), spectral acceleration, relative density, and V_{s, 30}, in evaluating the liquefaction hazards.

At the Okinawa Island, a construction project of large-scale jacket pier for large cruise ships is proceeding with the in-crease of cruise passengers from overseas. However, very loose coral pebble mixed soil was deposited thickly in the project site, and there was concern that liquefaction would occur in the coral pebble mixed soil. In order to evaluate the liquefaction characteristics of coral pebble mixed soil, it is necessary to collect samples with undisturbed condition, but it was predicted that it would be difficult to collect by conventional sampling method used in Japan. Therefore, we decided to apply a special sampling method called GS sampler. GS sampler is high-quality sampler for collecting loose sandy soil, gravel, fractured zone and waste matter which have been very difficult to obtain good samples with undisturbed condition. A total of eleven samples were recovered from coral pebble mixed soil layer with the thickness of about 15m to 20 m. When the sample collected by GS sampler was photographed with X-ray, it was confirmed that the sample was collected in a good condition without disturbance. Based on the undisturbed samples, the cyclic triaxial test was carried out, and it was found that the liquefaction strength, R_L20, of the coral pebble mixed soil was range of 0.22 to 0.27. Based on this result, as a result of evaluated the liquefaction, the input ground motion of level 1 earthquake, the liquefaction resistivity, F_L, was 1.6 to 3.4, and the result not liquefied was obtained. In this way, because of conducting a detailed liquefaction investigation by GS sampling and the cyclic triaxial test, it was unnecessary to initially improve the ground so that it was possible to greatly reduce the cost of the ground improvement.

Loess is an aeolian soil that covers approximately 10% of the South Island of New Zealand. In Canterbury, these materials typically have low plasticity (PI < 12), are silt-dominant (60-75% silt) and are widespread across slopes. Preliminary experimental research indicates that liquefaction of loess below the groundwater table may have been a contributing factor to slope deformation that occurred during the 2010 – 2011 Canterbury Earthquake Sequence. Indeed, cyclic liquefaction of loess has also been observed to be a contributing factor to slope failures that occurred during the 1920 Hauyuan and 1989 Tajikistan Earthquakes. To date the undrained cyclic properties (including pore water pressure generation and cyclic strain development) of loess in New Zealand has not been well understood. Given the region’s seismic environment, the potential for wetter slopes with future climatic change, and the extent of residential development on loess slopes in New Zealand, it is important to better understand the liquefaction resistance of loess and its contribution to future coseismic slope instability. This paper presents results from cyclic triaxial testing of reconstituted loess sampled from Akaroa Harbour, Banks Peninsula. A loess-specific liquefaction resistance curve (CSR-N_c) for reconstituted specimens is shown. Comparison with international data sets is also presented to better understand the liquefaction behavior of these aeolian soils.

It is well known that waste rubber disposal poses many serious environmental problems. Nevertheless, many researchers have utilized it for various geotechnical applications such as highway embankments, lightweight backfill materials, seismic isolation, and landfill leachate drainage material. Lately, the use of rubber sand mixture for liquefaction mitigation has started gaining attention. The literature indicates that the addition of rubber in the sand has the potential to increase liquefaction resistance even in a loose state. On the other hand, the theory of critical void ratio indicates that soils having a void ratio above the critical void ratio line should be liquefiable. The present study aims to evaluate the applicability of the critical void ratio theory for rubber sand mixtures. A series of consolidated drained tests has been carried out on the pure sand, rubber sand mixture and pure rubber to evaluate the critical void ratio of the material; then, the cyclic tests are carried out on specimens having a void ratio above the corresponding critical void ratio line. The results show that the critical void ratio reduces with the increase in rubber content. However, despite being highly contractive materials, rubber-sand mixtures develop lower excess pore water pressures during cyclic loading, thus contradicting the expected behaviour of granular soils and the role of the critical void ratio line, which does not play anymore a relevant role to predict the liquefaction potential.

The 2011 Great East Japan Earthquake caused long-duration earthquake ground motions in the eastern region of Japan, leading to ground liquefaction in many areas owing to its massive magnitude of M_W = 9.0. Subsequently, the authors (2014) conducted quantitative studies on the effect of the waveform shape of seismic waves on liquefaction strength and proposed a reasonable method for predicting liquefaction. This study discusses the liquefaction process of sandy soil under long-duration earthquake waveforms, based on the results of cyclic hollow torsional shear tests wherein shear stress is the driving force. The tests replicated the long-duration earthquake motions observed at K-NET Haramachi and K-NET Urayasu during the Great East Japan Earthquake while varying the density and fine-grain content. From the effective stress paths obtained for each seismic waveform, it was confirmed that the effective shear stress ratio, which is the historical maximum in the shear stress loading direction, was updated at the point where the excess pore pressure increased owing to the plastic deformation of the specimen. This point of change coincided with the yield surface indicated by Ishihara et al. (1975). Furthermore, the effective confining pressure decreased significantly when the effective shear stress ratio was updated when the shear stress history was subjected to a large number of irregular shear stress histories before updating the shear stress history. Therefore, owing to the higher number of cyclic waves, the seismic waveform of K-NET Haramachi was more prone to liquefaction than that of K-NET Urayasu. This characteristic is independent of the density or fine-grain content of the specimens.

As an alternative to the widely used simplified stress-based liquefaction triggering models, this paper presents an overview of a recent study by the authors wherein they propose a model where the imposed loading and ability of the soil to resist liquefaction are quantified in terms of normalized dissipated energy per unit volume of soil (ΔW/σ’_vo). The proposed energy-based model operates within a total stress framework, more directly accounts for factors influencing liquefaction triggering than stress-based models, and overcomes some of the limitations of many previously proposed energy-based triggering models. Energy-based triggering models unite concepts from both stress-based and strain-based procedures, and in its simplified form, the proposed model is implemented similarly to the simplified stress-based models. An updated field case history data base is used to develop probabilistic limit-state curves for the model. These limit-state curves express ΔW/σ’_vo required to trigger liquefaction as a function of corrected cone penetration test tip resistance (q_c1Ncs) for different probabilities of liquefaction (P_L).

Traditional liquefaction triggering evaluations using cone penetration test (CPT) data are generally conducted with simplified methods that employ the Soil Behavior Type Index (I_c) to differentiate between "sand-like" and "clay-like" materials. However, we observe that the commonly used I_c = 2.60 cutoff often misclassifies materials, particularly in cases where intermediate soils exhibit high friction ratios (F_r > 2-3%). This misclassification can result in overpredictions of liquefaction potential. To address these limitations, we propose using the Modified Soil Behavior Type Index (I_B) as an alternative for selecting "sand-like" materials for liquefaction evaluations. By applying a cutoff of I_B = 28 to paired CPT and laboratory classification data from sites in the San Francisco Bay Area, we achieve significantly improved material classifications, particularly for soils with high F_r values. Our findings suggest that the I_B parameter offers a more consistent and accurate material classification approach, ultimately enhancing the reliability of CPT-based liquefaction assessments.

Liquefaction has been often observed in sand deposits with fines particles during earthquakes. However, the effect of particle size ratio on the cyclic liquefaction of sand-fines mixtures is not extensively investigated. In this study, a series of undrained cyclic triaxial numerical tests were carried out emulating Toyoura sand mixed with non-plastic fines of different particle sizes using the discrete element method, to study the effects of fines content and particle size ratio on the cyclic liquefaction resistance of sand-fines binary mixtures at both the macroscopic and microscopic levels. The macroscopic behaviors, including the generation of excess pore water pressure and liquefaction resistance, and the microscopic behaviors, including the mechanical coordination number (MCN) and the mechanical redundancy index (I_R), were investigated. Results show that initial liquefaction occurs when MCN is smaller than 3.0 or I_R is smaller than 1.0. The liquefaction resistance decreases with the increase of fines content at a given void ratio. Both equivalent skeleton void ratio e* and initial mechanical coordination number (MCN₀) can well characterize the liquefaction resistance of sand-fines mixtures for various fines contents and particle size ratios, which demonstrates the applicability of macroscopic parameter e* in characterizing effective inter-particle contacts in sand-fines mixtures.