Newsletter Volume 10, Issue 3 September 2025

 

Professor, Departement of Civil & Environmental Engineering
University of Auckland, New Zealand

 

Introduction

Established in 2016, the New Zealand Centre for Earthquake Resilience (QuakeCoRE) is one of the Centers of Research Excellence (CoRE) funded by the Tertiary Education Commission and the Royal Society of New Zealand. Its main objective is to revolutionize the earthquake resilience of communities and society through cutting-edge research, education of emerging professionals, and strong domestic and global collaborations, utilizing Aotearoa New Zealand as a natural seismic laboratory.

Functioning as a national consortium of top-tier New Zealand earthquake resilience researchers, QuakeCoRE’s research programs seek to enhance both the scientific understanding and practical implementation of seismic resilience. This is achieved through a systems-based approach involving seamless collaboration across physical sciences, engineering, and social science disciplines, and with partner institutions. The current framework is structured around Disciplinary Themes (DTs), Interdisciplinary Programs (IPs), and the Coordination Mechanisms of Technology Megatrend (TM) Capability Areas and Regional Network (RN) Areas (see Fig. 1).
 

Fig. 1. Structure of QuakeCoRE’s research programs (https://quakecore.nz/)

 
Geotechnical hazards are crucial to earthquake resilience, making Disciplinary Theme 1 (DT1: Integrated Seismic Geohazards) a fundamental area within QuakeCoRE. A primary research strand under DT1 focuses on soil liquefaction by developing innovative approaches and methodologies to evaluate its effects on land and infrastructure, grounded in a deep understanding of its initiation and impacts, and to quantify and mitigate the risks associated with liquefaction. Research in this area leverages insights from the 2010-2011 Canterbury earthquake sequence (CES) [1-5] and the 2016 Kaikōura earthquake [6-8], and involves the use of advanced field, laboratory, and numerical tools tailored to NZ-specific soil conditions. A schematic of this research strand is provided in Fig. 2, highlighting efforts to extend liquefaction assessment beyond current industry practices.
 
 

Fig. 2. Overview of QuakeCoRE’s soil liquefaction research under DT1

This paper provides a concise overview of selected QuakeCoRE research projects focused on soil liquefaction. Further technical details of each project are available in the cited references.

Liquefaction evaluation of gravel-sand-silt mixtures

Gravelly soils have traditionally been regarded as less prone to liquefaction than clean sands due to their higher permeability. Consequently, existing semi-empirical liquefaction methods seldom account for these soils, leading to questions about the applicability of sand-based evaluation methods to gravel-rich deposits. Following the 2016 Kaikōura earthquake, significant liquefaction damage was reported at the Port of Wellington (CentrePort), where reclaimed land composed of gravel and sandy hydraulic fills experienced widespread failure, damaging wharves and port facilities, as shown in Fig. 3 [7, 8].

To explore the validity of standard liquefaction assessment methods for this gravelly fill, 121 Cone Penetration Tests (CPTs) were conducted. Liquefaction triggering and post-event settlement predictions were made using conventional CPT-based procedures and then compared with actual ground performance.
 
A representative east-west cross-section of the gravelly fill, based on CPT data, is shown in Fig. 4. Cone tip resistance (q_c) values typically ranged between 6.5-8.0 MPa, generally remaining below 10 MPa. These relatively low values indicate a loose fill state, consistent with the construction approach that involved dumping soils into the sea and allowing deposition without compaction [7].
 

Fig. 3. Post-earthquake liquefaction effects at CentrePort following the 2016 Kaikōura earthquake [7,8]

 
 

Fig. 4. East-west cross-section through the gravelly fill of Thorndon reclamation showing CPT qc traces and summary of representative qc and lc values for various soil units [9]

 
The CPT results also indicated soil behavior type index values (l_c) of 2.1-2.2, suggesting sand-silt characteristics. Thus, the CPT data appear to reflect primarily the sand-silt matrix, with gravel effects noted only as q_c spikes. This interpretation aligns with grain-size distributions and observed site behavior during the earthquake, which mirrored liquefaction patterns typical of sand-silt mixtures [9].
 
Dhakal et al. [10-12] used the collected CPT data to evaluate liquefaction triggering using simplified liquefaction assessment procedures for a free-field level ground condition [13], while the Zhang et al. [14] procedure was used to estimate post-liquefaction reconsolidation settlement. Key analytical considerations included the dominance of the sand-silt fraction and the need for careful interpretation of empirical data, particularly in terms of material and in-situ state characterization [9-12].
 

Fig. 5. Results of the simplified CPT-based triggering analysis for the 2016 Kaikōura earthquake [10]

Results demonstrated that simplified CPT-based procedures successfully predicted liquefaction across most of the site for the 2016 event (see Fig. 5). The CPTs captured the behavior of the fine-grained matrix, enabling accurate triggering predictions. Estimated post-liquefaction settlements were slightly underestimated in free-field zones but aligned well with observed performance. Observed vertical ground movements increased in the areas of lateral spreading, but these effects are beyond the scope of settlement estimates based on the simplified liquefaction evaluation procedure.
 
Liquefaction of crushable volcanic soils

Pumice sands, common in the central North Island of New Zealand, are composed of low-density, vesicular particles that are highly crushable and compressible (Fig. 6). Their unusual characteristics complicate geotechnical evaluation, and there is uncertainty about the applicability of empirical models developed for more conventional, hard-grained soils [15]. This issue has long been noted by practitioners working with these natural pumiceous (NP) deposits.


   
To address this, laboratory testing, including triaxial and bender element tests, was performed on both reconstituted and high-quality undisturbed NP samples from the Waikato Basin and the Bay of Plenty region in NZ [18-20]. These studies revealed distinct behavior when compared to typical normal (hard-grained) sands, such as Toyoura sand. Fig. 7 illustrates the undrained cyclic behavior in terms of double amplitude axial strain (ε_DA) and the maximum pore pressure ratio (r_u) at the end of each cycle of loading, showing clear differences from hard-grained sands under similar conditions.
   

Fig. 8. Vs-based liquefaction resistance chart comparing NP and normal sands [20]. CRRField corresponds to the CRR under field conditions, while Vs1 is the normalized shear wave velocity.

NP specimens showed immediate deformation under cyclic loading, with rapid r_u buildup. With continued cyclic loading, axial strains increased steadily while r_u development slowed, indicating a highly contractive initial response due to particle crushing, followed by dilative behavior likely driven by particle rearrangement and densification.
 
Additional tests confirmed that NP sands possess lower small-strain shear stiffness (G_max) and shear wave velocity (V_s), and greater cyclic resistance (CRR) when compared to normal sands at equivalent packing levels. These laboratory findings, combined with field data, were used to develop a V_s-based liquefaction resistance chart tailored to NP soils (Fig. 8), offering valuable guidance to engineers.
 
Consideration of system response in liquefaction assessment
 
Following the 2010-2011 Canterbury earthquake sequence, discrepancies between simplified liquefaction models and actual field observations prompted a detailed evaluation of these methods. While simplified procedures generally identified broad trends, they often failed to predict liquefaction occurrence or severity accurately in certain zones [21, 22]. A notable example was the absence of observed liquefaction damage in southern Christchurch suburbs during the 4 September 2010 Darfield earthquake, despite predictions of moderate to severe effects.

A detailed investigation across 55 case history sites, ranging from no damage to severe manifestation, was undertaken using seismic effective stress analysis [21]. These response history models explicitly simulated key features of the soil response and liquefaction process, such as pore pressure development, stiffness degradation, and water migration, offering a complete picture of liquefaction behavior under seismic loading.
 

Fig. 9. Schematic illustration of liquefaction assessment using simplified approach: (a) layer-specific FS, γmax, and εv calculated separately; (b) cumulative damage index is calculated for the deposit (site) by superposition of individual effects from each layer [21]

The study revealed a major limitation in the simplified approach, with each soil layer assessed in isolation, ignoring interlayer dynamics. Factors of safety (FS), shear strains (γ_max), and volumetric strains (ε_v) are estimated per layer (Fig. 9a), and damage indices, like LSN [23] and LPI [24], are derived via weighted summation (Fig. 9b). This method overlooks the critical role of dynamic interactions and pore pressure migration.
 
Fig. 10 shows a schematic of the system-response mechanisms, where the effective stress modeling identified three key mechanisms at sites that experienced surface liquefaction: (1) early and rapid liquefaction of the shallow critical layer (defined as the layer that is the most likely to trigger and manifest liquefaction at the ground surface); (2) additional disturbance of the liquefied critical layer due to substantial inflow of water from the underlying layers that did not liquefy but generated high excess pore water pressures; and, (3) seepage-induced liquefaction in shallow soils above the water table [21]. Conversely, sites that remained unaffected had features, such as non-liquefiable surface crusts and deep liquefiable layers that created ‘base-isolation’ effects and inhibited upward pressure transmission.  

These insights from seismic effective stress analyses may explain the system response effects on both sites that manifest severe liquefaction and no liquefaction following the CES. For the former, the system response effects increase the severity and consequences of liquefaction (Fig. 10a), whereas for the latter, the interaction mechanisms mitigate liquefaction manifestation at the ground surface (Fig. 10b). In both cases, there are important cross-interactions between layers and different parts of the deposit through the dynamic response and water flow that substantially influence the development of liquefaction and even govern its manifestation at the ground surface. These findings underscore the importance of system response in governing liquefaction manifestation and call for its incorporation into assessment protocols. Current efforts are focused on integrating these effects through comprehensive effective stress analyses [25, 26].
 

(a)	(b)
Fig. 10. System response effects: (a) amplification of surface liquefaction manifestation; (b) suppression of surface manifestation through ‘base-isolation’ effects [21]

 
 
 

Concluding Remarks 

In addition to the work discussed, the QuakeCoRE’s liquefaction strand continues to explore other important topics, including the behavior of other problematic NZ soils, sustainable liquefaction countermeasure techniques, soil-structure interaction effects, and the use of big data and machine learning in liquefaction studies. Collectively, this research represents leading-edge developments in the field and is expected to significantly advance the understanding, assessment, and management of liquefaction hazards at both local and regional scales.
 
Acknowledgments
 
The author would like to acknowledge all his co-researchers who have contributed to past and ongoing liquefaction research under Te Hiranga Rū QuakeCoRE, an Aotearoa New Zealand Tertiary Education Commission-funded Centre.This is QuakeCoRE Publication Number 1085.
 
References
 
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[24] Iwasaki, T., Tatsuoka, F., Tokida, K., & Yasuda, S. (1978). A practical method for assessing soil liquefaction potential based on case studies at various sites in Japan. Proc. 2nd International Conference on Microzonation for Safer Construction Research and Application, San Francisco, 885-896.
 
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A brief CV of Prof. Rolando P. Orense
 
Rolando P. Orense is a Professor of Geotechnical Engineering at the Department of Civil & Environmental Engineering, University of Auckland. He received his BSCE (cum laude) and MSCE degrees in Civil Engineering from the University of the Philippines and a Doctor of Engineering degree from the University of Tokyo (Japan). His research and professional practice focus primarily on geotechnical earthquake engineering, liquefaction-associated problems, and site/soil characterization. He currently leads the “Soil Liquefaction” Strand of Disciplinary Theme 1 (DT1: Integrated Seismic Geohazards) of the New Zealand Centre for Earthquake Resilience (QuakeCoRE).