Tephras of slightly-weathered nature are essentially silty-sand deposits with no to low plasticity. They can constitute variable gradations and geochemical compositions depending upon the type and extent of weathering of particles and minerals. Case histories of liquefaction events suggest that such sand and silty-sand deposits can liquefy and reliquefy by a succeeding seismic event. However, the liquefaction and reliquefaction characteristics of different compacted tephras for backfilling usage have not been largely investigated. This paper presents the results of a series of undrained cyclic triaxial tests on specimens of three tephras (two rhyolitic and one basalt-andesitic) sourced from the North Island of New Zealand. Specimens are compacted at 90 % degree of compaction, isotropically consolidated under 100 kPa effective confining stress and then subjected to the first cyclic loading phase until liquefaction is achieved. Following liquefaction, specimens are reconsolidated and reliquefied. The test results showed an increase in the degree of compaction after reconsolidation for the compacted tephra specimens. However, a non-unified change in the liquefaction resistance is observed for the tephra specimens, which is dependent on their geochemical composition (or degree of weathering value) affecting the stress level (CSR) required. The elementally identical rhyolitic Kaharoa ashes (White Kaharoa Ash – WKA – and Golden Kaharoa Ash – GKA) exhibited a decrease in the liquefaction resistance following the first series of loading cycles. Despite a similar reliquefaction response, the liquefaction resistance of GKA was significantly lower in comparison to WKA tephra due to its more weathered nature. On the other hand, the basalt andesitic Maungataketake Ash (MA) tephra, being the most weathered out of the three tephras, showcased an opposite trend of increase in cyclic resistance after initial liquefaction.

The Chiang Mai basin, including Chiang Mai City, is among the most economically influential regions in Northern Thailand. The basin lies in a shallow active seismic zone near the Mae Tha faults to the west. The basin's eastern boundaries are defined by north-to-south mountain ranges that align with the direction of river flow. The geological composition of the basin predominantly comprises sand and silt, a result of erosion and sedimentation processes. Following instances of liquefaction hazard in Northern Thailand in 2011 and 2014, researchers undertook assessments of liquefaction susceptibility within the Chiang Mai province. Examination of borehole data indicated the potential for liquefaction in certain Chiang Mai basin locations. This study seeks to utilize a geographic information system (GIS) to visually represent the various subsoil layers within the Chiang Mai basin. Data involving subsoil properties are soil type, geotechnical engineering characteristics, and water levels. In the analysis of liquefaction, surface peak ground acceleration data sourced from prior studies were integrated. The GIS information about Chiang Mai's subsoil layers can be used to formulate a map pinpointing liquefaction-prone area. This map can facilitate the development of proactive mitigation strategies aimed at mitigating the repercussions of earthquake-induced liquefaction hazards within this geographical zone.

The rising world demand for minerals and metals that can only be obtained through mining is increasing the number and size of tailings deposits, which may pose serious social, economic and environmental risks if unproperly managed. This is particularly true in seismically active regions, where the dynamic loading imposed to these structures may result in dramatic failures. In order to clarify the behaviour of these unconventional geotechnical materials under different loading conditions that may occur in situ, advanced geotechnical experiments must be carried out on representative samples. Because undisturbed samples are seldom available, reconstituted samples usually provide an appropriate mean to prepare comparable samples for testing. This paper discusses the effects of sample reconstitution procedures on the mechanical behaviour of iron ore tailings, with particular focus on the undrained cyclic behaviour. The reconstituted samples are prepared using a slurry-based method using different water content values representing possible field depositional conditions found in tailings dams, to assess the effect of the slurries’ water content on the characteristics and undrained mechanical behaviour of the samples. The behaviour of undisturbed samples from a Portuguese iron mine is used to evaluate if the behaviour of the reconstituted samples replicates, at least qualitatively, the real behaviour of the tailings. The research suggests that the characteristics and the undrained mechanical behaviour of reconstituted samples depend on the value of the slurry water content used in the reconstitution, larger water content values possibly promoting particle segregation during reconstitution and producing samples with mechanical behaviour which is less comparable to the behaviour shown by undisturbed samples.

Over the past years, prior research has shown that bidirectional horizontal shaking can increase seismic settlements in dry sand, the buildup of excess pore water pressures in saturated granular soils, and the liquefied depth. However, the state of practice for either simplified liquefaction triggering procedures or numerical/experimental seismic simulation is typically for one-dimensional (1D) conditions, without considering the impact of bidirectional horizontal shaking on soil deposits with stratigraphic variabilities. In this paper, three-dimensional (3D), fully-coupled, nonlinear finite element analyses are used to evaluate how bidirectional horizontal shaking affects the seismic response of layered liquefiable soil deposits. The two horizontal components of each selected motion were rotated to find the maximum rotated (RotD100) peak ground acceleration (PGA). The two horizontal components and the RotD100 component were subjected to the base of each 3D soil column model, to represent the site response analysis under bidirectional (BD) and 1D shaking, respectively. The numerical results showed that the BD shaking and pore water pressure migration increased the excess pore water pressure (EPWP) buildup in soils, particularly for medium-dense and dense soils. This led to an increase in liquefied depth when the soil deposits were under moderate-intensity shaking, as compared to the model under 1D shaking or evaluated by the simplified liquefaction triggering procedure. For the case considered, the BD shaking amplified the maximum excess pore water pressure ratio by about 1.3 times on average (with a standard deviation of 0.3) compared to that under 1D shaking, particularly for PGA ranging from 0.002~0.3g. However, the impacts of BD shaking on the EPWP generation became minor when PGA was greater than 0.3_g. These results indicated that the impact of bidirectional shaking on the seismic response of porous media must be considered with extreme care when assessing the risk of liquefaction.

Events like the 2010–2011 Canterbury Earthquake Sequence demonstrated the impacts of liquefaction and lateral spreading across New Zealand infrastructure networks. Statistical liquefaction models based on geospatial data can be used to rapidly calculate the probability of liquefaction (manifestation) for large-scale networks. Using the simulated ground shaking intensity of 478 earthquake scenarios, the liquefaction probability is estimated across the New Zealand State Highway network. The overall exposure is measured by the number of events (NoE) that are expected to cause liquefaction manifestation along a road section. Compared to the assessment of a specific earthquake scenario or a specific return period, the multi-scenario approach helps to identify State Highways that might be affected by liquefaction manifestation during a range of different earthquakes, therefore, might lead to a recurrent disruption of transport services. The results are presented in a hazard map, highlighting State Highway sections with increased NoE, indicating that they might repeatedly experience liquefaction manifestation during seismic events. Limitations arise from the fact that the geospatial model does not account for subsurface soil characteristics and that vulnerability aspects of the State Highways are not considered in the assessment. Future research should also investigate combining the exposure results with indicators for network criticality (e.g., number of vehicles, or freight value) to better quantify the impact of liquefaction manifestation. The framework is adaptable to other infrastructure networks and can be used to support decision making processes regarding hazard mitigation or preparedness for future earthquakes.

Historically, liquefaction triggering methodologies have relied on the use of cyclic resistance curves to predict the initiation of liquefaction. These curves are informed by the undrained hypothesis which assumes that loading during an earthquake occurs too quickly for void redistribution to occur. However, recent research challenges the validity of this assumption, especially in layered soil deposits with varying permeability characteristics, where partially drained conditions are more appropriate. In parallel, the current body of earthquake case histories contains only data from shallow depths and relies on empirical correlations to extrapolate to greater depths. This is of concern for structures such as dams, levees, and embankments, which impart much greater effective overburden stresses than are accounted for by current simplified methodologies. Additionally, many such structures have historically been constructed with little consideration on the liquefaction potential of their foundation soil stratigraphy, where partially drained conditions can lead to localised volumetric strains. In this study, loose (D_R= 30%) Hostun sand specimens were subjected to both undrained and partially drained triaxial cyclic loading. Undrained experiments were used to create a baseline cyclic resistance curve. Partially drained tests at varying volumetric strain rates revealed the sensitivity of liquefaction resistance to volumetric strain. Volume contraction was associated with increased cyclic resistance, even at very small strain rates, while volume expansion resulted in decreased cyclic resistance. Effects were more pronounced under higher overburden stresses.

Continuous monitoring of ground acceleration and pore water pressure took place at a site susceptible to liquefaction in the reclaimed land of the Tokyo Bay waterfront area. This location experienced extensive liquefaction during the 2011 off the Pacific Coast of Tohoku Earthquake. A survey of the site revealed a soil profile up to a depth of 17m. The installation site for the pore water pressure gauges and accelerometers exhibits a high content of fine particles, not only comprising sand but also significant quantities of silt and clay. Hollow torsional shear tests were conducted on the extracted soil to assess its resistance to liquefaction. Using these and other soil test outcomes, a three- dimensional dynamic response analysis using one- dimensional column model was performed based on the measured wave data. In the results of the element tests conducted in this study, it was found that the silty sand collected from the field site exhibits a significantly low liquefaction resistance. The analysis revealed that the excess pore water pressure tends to increase to some extent.