Earthquake-induced soil liquefaction (liquefaction) is a leading cause of earthquake damage worldwide. Liquefaction is often described in the literature as the phenomena of seismic generation of excess porewater pressures and consequent softening of granular soils. Many regions in the United States have been witness to liquefaction and its consequences, not just those in the west that people associate with earthquake hazards. Past damage and destruction caused by liquefaction underline the importance of accurate assessments of where liquefaction is likely and of what the consequences of liquefaction may be. Such assessments are needed to protect life and safety and to mitigate economic, environmental, and societal impacts of liquefaction in a cost-effective manner. Assessment methods exist, but methods to assess the potential for liquefaction triggering are more mature than are those to predict liquefaction consequences, and the earthquake engineering community wrestles with the differences among the various assessment methods for both liquefaction triggering and consequences. State of the Art and Practice in the Assessment of Earthquake-Induced Soil Liquefaction and Its Consequences evaluates these various methods, focusing on those developed within the past 20 years, and recommends strategies to minimize uncertainties in the short term and to develop improved methods to assess liquefaction and its consequences in the long term. This report represents a first attempt within the geotechnical earthquake engineering community to consider, in such a manner, the various methods to assess liquefaction consequences.

Soil Liquefaction during Recent Large-Scale Earthquakes contains selected papers presented at the New Zealand – Japan Workshop on Soil Liquefaction during Recent Large-Scale Earthquakes (Auckland, New Zealand, 2-3 December 2013). The 2010-2011 Canterbury earthquakes in New Zealand and the 2011 off the Pacific Coast of Tohoku Earthquake in Japan have caused significant damage to many residential houses due to varying degrees of soil liquefaction over a very wide extent of urban areas unseen in past destructive earthquakes. While soil liquefaction occurred in naturally-sedimented soil formations in Christchurch, most of the areas which liquefied in Tokyo Bay area were reclaimed soil and artificial fill deposits, thus providing researchers with a wide range of soil deposits to characterize soil and site response to large-scale earthquake shaking. Although these earthquakes in New Zealand and Japan caused extensive damage to life and property, they also serve as an opportunity to understand better the response of soil and building foundations to such large-scale earthquake shaking. With the wealth of information obtained in the aftermath of both earthquakes, information-sharing and knowledge-exchange are vital in arriving at liquefaction-proof urban areas in both countries. Data regarding the observed damage to residential houses as well as the lessons learnt are essential for the rebuilding efforts in the coming years and in mitigating buildings located in regions with high liquefaction potential. As part of the MBIE-JSPS collaborative research programme, the Geomechanics Group of the University of Auckland and the Geotechnical Engineering Laboratory of the University of Tokyo co-hosted the workshop to bring together researchers to review the findings and observations from recent large-scale earthquakes related to soil liquefaction and discuss possible measures to mitigate future damage. Soil Liquefaction during Recent Large-Scale Earthquakes will be of great interest to researchers, academics, industry practitioners and other professionals involved in Earthquake Geotechnical Engineering, Foundation Engineering, Earthquake Engineering and Structural Dynamics.

Liquefaction damage from the 2010-2011 Canterbury earthquake sequence devastated parts of Christchurch, New Zealand. There were many sites where state-of-practice liquefaction assessment procedures indicated liquefaction would be expected to occur, and surface manifestations of liquefaction were observed. However, there were also numerous sites, which were predominantly silty soil sites, where state-of-practice liquefaction assessment procedures indicated that liquefaction would be expected to occur, but no surface manifestations of liquefaction were observed. This discrepancy between state-of-practice liquefaction assessments and post-earthquake liquefaction observations led to the development of the research program presented in this dissertation. Several silty soil sites were selected for investigation to further our understanding of fine-grained soil liquefaction response and to evaluate potential limitations in the current state-of-practice liquefaction assessment procedures, which are based primarily on case histories and laboratory testing of sands. This dissertation investigates the liquefaction response of silty soil sites through no-liquefaction case histories from the Canterbury earthquake sequence, evaluating depositional environment effects on observed liquefaction performance, site characterization of silty soil deposits, and laboratory testing to characterize element-scale cyclic response. Depositional environment effects are evaluated through regional CPT-based analyses and site-specific comparisons. Stratified silty soil swamp deposits are shown to have mitigating effects on the manifestation of liquefaction beyond what can be captured by simplified liquefaction assessment procedures in Christchurch. Differing surficial geology and depositional environments are found through examining historical documents to explain in part the limitations of current liquefaction assessment procedures in the swamps of southwest Christchurch, which contain stratified silt/sand deposits or thick silt layers. Consideration of depositional environment distinguishes between liquefaction performances that could not be differentiated through the CPT-based assessment alone. CPT resolution is not sufficient to capture the thin layering at these stratified sites, and the simplified liquefaction assessment methods do not take into account the effects of the stratification on pore water pressure movement within a soil profile. Continuous sampling and careful logging of high-quality samples provides important insights on in-situ stratification at these silty soil swamp sites, discerning differences in stratigraphy resulting from differences in depositional environment. Site investigation techniques are evaluated at the silty soil case history sites to discern their capability to characterize thin layers and groundwater table fluctuation, two potential causes for the discrepancies between state-of-practice liquefaction assessments and post-earthquake liquefaction observations. CPT, mini-CPT, sonic borings, and high-quality sampling are critiqued in terms of their ability to capture thin layer stratigraphy, which is of importance for liquefaction assessment. Piezometers, sonic borings, high-quality sampling, crosshole testing, and regional groundwater maps are evaluated to assess their ability to capture groundwater table fluctuation. CPT, mini-CPT, and conventional sonic borings offer important information for site characterization, but they do not capture full details of thin layering at silty soil sites. Detailed logging of high-quality samples captures the actual in-situ layering that helps explain limitations of simplified liquefaction assessment procedures. Use of multiple groundwater measurement methods more fully illuminate fluctuating groundwater conditions. Subsurface investigation programs should utilize tools that characterize features impacting liquefaction potential in adequate detail for the intended engineering purpose. Use of multiple, complementary investigation techniques provides the most robust assessment. A field investigation and advanced laboratory testing program was conducted in Christchurch. High-quality samples were obtained using a Dames & Moore hydraulic fixed-piston thin-walled sampler for cyclic triaxial testing to characterize the liquefaction response of silty soils at the no-liquefaction sites in southwest Christchurch. These natural silty soil specimens contained heterogeneity and variability that should be considered and is difficult, if not impossible, to replicated with laboratory-prepared specimens. Test results for stress-strain response and axial strain accumulation indicate a nuanced range of transitional responses for these intermediate soils. Post-liquefaction reconsolidation testing shows clear differences in specimen response, ranging from "sand-like" immediate reconsolidation to time-dependent reconsolidation. Simplified liquefaction assessment procedures estimate significant liquefaction at these case history sites and yet no liquefaction manifestations were observed during the Canterbury earthquake sequence. Laboratory estimates of cyclic resistance (CRR) are consistent with estimates from the simplified procedures, and both estimates of CRR are well below simplified procedure estimates of seismic demand (CSR). Depositional characteristics such as thin-layering of fine sand and silt may be why manifestations of liquefaction were not observed at these sites. Post-liquefaction reconsolidation testing provides insight that water and ejecta may not accumulate in these stratified silty soils as they would accumulate in thick deposits of liquefiable clean sands. Additional mitigating factors may also contribute to the discrepancy between simplified procedure estimates of liquefaction and the lack of liquefaction observed at these sites. The interaction of several factors contributing to observed liquefaction response at these silty soil sites indicates that in-situ "system" response should be considered and that further research on silty soils is warranted.

This text was compiled by the Japanese Geotechnical Society. It describes everything about the remedial measures against liquefaction currently used in Japan following research projects after the Niigata earthquake of 1964.