Case histories from more than 30 earthquakes worldwide have shown that liquefaction can occur in gravelly soils (both in natural deposits and manmade reclamations), resulting in large ground deformation and severe damage to civil infrastructure. However, evaluating the liquefaction potential and cyclic strain accumulation characteristics of gravelly soils remains a major challenge in geotechnical earthquake engineering. In this study, to provide new insights into this important topic, a series of stress-controlled undrained cyclic triaxial tests were performed, along with bender element shear wave velocity (VS) measurements, on reconstituted specimens of sand-gravel mixtures (SGM) with varying gravel contents (GC) and relative densities (Dr). The experimental results indicated that both GC and Dr have significant effects on the cyclic resistance ratio (CRR) and VS of SGMs, and both parameters should be considered jointly when evaluating the cyclic response, as similar macroscopic behavior can result from different combinations of density state and particle-size composition. Laboratory-based GC-specific CRR-VS correlations were also developed and found to be consistent with existing VS-based liquefaction triggering relationships derived from gravelly soil case histories.

Field observations from 32 documented liquefaction case histories indicate that gravelly soils within alluvial deposits are among the most liquefaction-susceptible geomaterials worldwide, yet the mechanisms governing their cyclic response remain poorly understood. This study investigates the liquefaction behavior of sand–gravel mixtures (SGMs) using stress-controlled undrained cyclic triaxial tests on specimens reconstituted with a newly developed water-sedimentation (WS) method, which enables the preparation of homogeneous specimens with minimal particle segregation. SGMs with gravel contents (Gc) up to 40

In this paper, the undrained simple shear behaviour of Toyoura sand specimens, isotropically consolidated at various initial effective mean stress levels (p0′ = 100 − 400 kPa) and void ratios (e0 = 0.884 − 0.667), was investigated using a large strain torsional shear apparatus (TSS). As anticipated loose sand showed fully contractive strain-softening behaviour which was followed by flow failure and extremely large shear deformation upon the instability state. Furthermore, medium dense sand exhibited only limited flow upon phase transformation (PT) state and at large shear stress (τ) levels the ultimate steady state (USS) of deformation was achieved. In contrast to previous studies, however, a peculiar behaviour was observed for dense sand, for which the predominant dilative strain-hardening response was characterised by a clear ultimate peak stress state (UPS) at failure. The data points at PT and USS (or UPS) plotted in terms of e–p′–τ relationships, indicated that (1) the stress-dependent PT lines obtained in this study from TSS are essentially consistent with that of previous studies; (2) yet, stress-dependent USS lines can be also established for sand, which is in contrast with finding from previous relevant studies.

Engineers must assess soil susceptibility to liquefaction, yet conventional evaluations are time‑consuming, costly, and affected by field-testing variability and semi‑empirical tools that introduce uncertainty. This study clarifies the importance of key parameters and proposes a streamlined machine‑learning approach using ensemble methods. A comprehensive reference dataset was compiled and used to train reliable machine‑learning models. Feature importance was examined with logistic regression and random forest, after which the data were split into training and test sets, predictors were scaled, and hyperparame0ters were tuned with GridSearchCV. Advanced models were then fitted, followed by ensemble approaches, including AdaBoost and voting classifiers. Based on feature importance results, the most influential features across all methods continue to be the Standard Penetration Test-derived parameters. The trained models were assessed, in which the AdaBoost provided the most accurate estimations by achieving precision, recall, F1_score, Jaccard index, and accuracy of 88

Shear wave velocity (VS) measurements are widely used to characterize geomaterials, evaluate small-strain stiffness, and develop indirect approaches for estimating the liquefaction resistance of various soil types. In this study, the bender element method was employed to investigate the VS characteristics of sand–gravel mixtures (SGMs), with the aim of clarifying the combined effect of key factors such as gravel content (GC), relative density (Dr), packing state, and soil fabric. Laboratory tests were performed on reconstituted specimens composed of two sandy soils and pea gravel with GC of 0, 10, 25, 40, 60, 80 and 100% and Dr of 20, 30, 45 and 60%. Specimens were prepared using wet tamping (WT) and air pluviation (AP) techniques. VS measurements were conducted under effective confining stresses (σ′0) of 50, 100, 150 and 200 kPa. The results show that the VS of SGMs increases with increasing Dr and p′0, whereas the influence of GC depends on the limiting and threshold sand contents. The effect of soil fabric was found to be marginal. Furthermore, the combined effects of GC and Dr on VS can be uniquely captured using the equivalent void ratio approach for SGMs with sand-dominated microstructures, while the skeleton void ratio approach is more appropriate for SGMs with gravel-dominated microstructures.

The reuse of rubber inclusions obtained from End-of-Life Tires (ELTs) offers both environmental and technical benefits in civil engineering applications, reducing landfill disposal and enhancing the dynamic properties of geomaterials. The use of well-graded Gravel–Rubber Mixtures (wgGRMs), produced by blending well-graded gravel with granulated rubber, has been investigated for use in different geotechnical applications. The percentage of rubber inclusions included in wgGRMs significantly modifies the mechanical response of these mixtures, influencing stiffness, strength, dilatancy and dynamic properties. Due to the material heterogeneity (i.e., stiff gravel and soft rubber), the effective implementation of wgGRMs requires the development of constitutive models that can capture the non-linear stress–strain response of wgGRMs subjected to representative in situ loading conditions. In this study, a critical state-based generalized plasticity model is presented and tailored for wgGRMs. Calibration is performed using experimental data from isotropically consolidated drained triaxial tests on wgGRMs with different rubber contents. It is shown that the model accurately reproduces key features observed experimentally, including post-peak strain softening, peak strength variation, and volumetric changes across different confining pressure levels and rubber content fractions. This model represents a useful tool for predicting the behavior of wgGRMs in engineering practice, supporting the reuse of ELT-derived rubber.

The escalating environmental challenges posed by waste rubber tyres (WRTs) necessitate innovative solutions to address their detrimental effects on the geoenvironment. Thus, the knowledge about the recent advancements in material recovery from WRTs, emphasising their utilisation within the framework of the United Nations Sustainable Development Goals (SDGs) and the circular economy principles, is the need of the hour. Keeping this in mind, various techniques generally used for material recovery, viz., ambient, cryogenic, waterjet, and so on, which unveil innovative approaches to reclaiming valuable resources (viz., recycled rubber, textiles, steel wires, etc.) from WRTs and various devulcanisation techniques (viz., physical, chemical, and microbial) are elaborated in this paper. In parallel, the paper explores the utilisation of the WRTs and recovered materials, highlighting their application in geotechnical and geoenvironmental engineering development projects while addressing the necessary environmental precautions and associated environmental risks/concerns. This paper incorporates circular economy principles into WRTs utilisation and focuses on achieving SDGs by promoting resource efficiency and minimising their environmental impact.

Rubberized concrete (RuC), which incorporates recycled tire rubber aggregates in the matrix, offers a viable solution for managing waste tire disposal. Although adding rubber aggregates reduces the compressive strength of concrete, research suggests that in specific applications, such as flexure‐controlled members, this adverse effect can be minimized. However, detailed studies on the flexural performance of reinforced RuC members remain limited. This paper presents a comprehensive study to assess the flexural performance of RuC beams, providing detailed measurements of concrete strains, steel strains, neutral axis depth, and crack widths. The experimental program tested 12 reinforced concrete beams with varying rubber content (0%, 10%, and 20% of total aggregate volume), tension reinforcement ratios ( ρ = 1.13%–2.01%), and axial loads (0–0.1 A g ). The results indicated that beams containing 10% rubber experienced a decrease in moment capacity of up to 13%, along with a 10% reduction in cracked stiffness. In contrast, beams with 20% rubber exhibited more significant decreases, showing reductions of up to 19% in both capacity and stiffness. Additionally, the impact of axial load appeared to double these reductions for both rubber content levels. The findings confirmed that current modeling techniques can accurately predict this behavior when a modified stress–strain relationship for RuC is applied, considering the lower elastic modulus and strain at peak stress and crushing. The study concludes that 10% rubber content can be regarded as an optimal choice for flexure‐controlled elements subjected to low axial loads.

Shredded rubber from waste tyres has progressively been adopted in civil engineering due to its mechanical properties, transforming it from a troublesome waste into a valuable and low-cost resource within an eco-sustainable and circular economy. Granular soils mixed with shredded rubber can be used for lightweight backfills, liquefaction mitigation, and geotechnical dynamic isolation. Most studies have focused on sand-rubber mixtures. In contrast, few studies have been conducted on gravel-rubber mixtures (GRMs), primarily involving poorly-graded gravel. Poorly-graded gravel necessitates selecting grains of specific sizes; therefore, from a practical standpoint, it is of significant interest to examine the behaviour of well-graded gravel and shredded rubber mixtures (wgGRMs). This paper deals with wgGRMs. The results of drained triaxial compression tests on wgGRMs are analysed and compared with those on GRMs. Stress-strain paths toward the critical state and energy absorption properties are evaluated. The tested wgGRMs exhibit good shear strength and remarkable energy absorption properties; thus, they can be effectively utilised in several geotechnical applications.

The influence of rubber aggregate stiffness on the cyclic performance of concrete columns exhibiting flexure-shear interaction remains unclear. It is also uncertain whether existing design provisions can be applied effectively to rubberized concrete columns with these properties. This study examines the cyclic behavior of six circular columns designed for flexure-shear interaction at two ductility levels: limited (LD, mu <= 2) and moderate (MD, 2

Soil–rubber mixtures have been proposed as cost-effective seismic and dynamic risk mitigation techniques. The granulated rubber used for these mixtures is obtained from end-of-life tires, allowing for stockpiles of waste rubber tires to be recycled. To date, most of the research has focused on the mechanical properties of sand–rubber mixtures, while limited studies have been performed on gravel–rubber mixtures (GRMs). In particular, GRMs with well-graded gravel (wgGRMs), which are of significant practical interest due to their availability, have only been poorly characterised. As part of a wider investigation aimed at facilitating the use of wgGRMs as geotechnical dynamic isolation systems, this paper presents bender element and small-strain cyclic triaxial test results performed on mixtures with 25%, 40%, and 55% volumetric rubber content. It is found that, thanks to their excellent energy absorption properties, wgGRMs can be efficiently adopted as geotechnical dynamic isolation to mitigate seismic risk of and anthropically induced vibrations on existing and new structures/infrastructures. Their easy implementation, low-cost, and widespread availability further facilitate their use.

From a geotechnical engineering viewpoint, recycling and reuse of crushed glass and tire rubber can significantly help reduce the demand for natural resources (i.e., sand and gravel aggregates). Following an earlier study by the authors aimed at characterizing gravel–rubber mixtures (GRM), this paper focuses on the geotechnical assessment of gravel–glass–rubber mixtures (GGRM) made of recycled crushed green glass bottles and recycled granulated tire rubber. Specifically, the compaction, one-dimensional compressibility, and shear strength characteristics of GGRM prepared at 40% and 55% rubber content by volume (RB) with varying glass content by volume (GL) are investigated. It is found that compacted GGRM possesses high strength (i.e., friction angle ≥ 30°) and adequate compressibility, making it a suitable general and structural fill material for use in eco-friendly geotechnical applications.

Volcanic ash air-fall or tephra deposits comprise nearly 31% of the North Island of New Zealand. For those belonging to slightly weathered or negligible to little cohesionless nature (silty sands to sandy silts), the compressibility and collapsibility features of compacted tephras have not been largely investigated. Correspondingly, the compressibility and collapse potential (CP) of compacted airfall tephras (at 90% and 100% degrees of compaction) were evaluated. At vertical stresses up to 200 kPa, the consolidation coefficient cv and permeability coefficient k were in the range of 10-5-10-8 m2/s and 10-6-10-8 m/s. Interestingly, for feldspar-silica type cohesionless tephras, it was possible to correlate the weathering degree and mineralogy to the compressibility. The results of the CP tests showed that the CP increased with the decrease in degree of compaction and increase in vertical stress; with values ranging from 0% to 5% indicating low-to-moderate collapsibility of the tephras upon properly compacted placement condition. The compacted tephras, as such, could be considered suitable structural fills for typical geotechnical applications owing to features such as low compressibility, low permeability and low-to-moderate CP.

A comprehensive investigation into the stress-strain behavior of rubberized concrete columns is presented. Twenty-three uniaxial compression tests were conducted, including seventeen on circular columns and six on square columns. The circular columns had a diameter of 500 mm, while the square columns had a side length of 450 mm. Additionally, eighteen compression tests were performed on medium-scale plain cylinders with a diameter of 300 mm. Two rubber contents, 10% and 20% by total volume were investigated. The study evaluated the effects of the volumetric reinforcement ratio, strain rate, and cross-sectional shape on the compressive response of each rubber content level. The results suggest that columns with 10% rubber content, having unconfined compressive strength similar to that of conventional concrete, are likely to exhibit comparable stress-strain behavior, with a slightly higher strength enhancement for the RuC columns, attributed to the quicker action of lateral confinement. Increasing the rubber content to 20% resulted in more pronounced strength and maximum strain improvements, which were linked to an increased lateral stress-to-unconfined compressive strength ratio, particularly due to a decrease in unconfined compressive strength in columns with 20% rubber content. Such results challenge the conventional understanding that higher rubber content directly correlates with increases in ultimate compressive concrete strain, translating in larger ductility displacement capacity. The study also evaluated existing confinement models and introduced new expressions for estimating strength and ductility enhancements in RuC members that significantly improved the accuracy of predictions.

The North Island of New Zealand is a region of high volcanic activity, with significant eruptions over the past. Analogous to past events, future volcanic eruptions would produce a considerable volume of ash and granular soils, covering widespread areas and raising concerns for their disposal and storage. Such deposits, primarily airfall tephra, could be potentially used in geotechnical engineering applications such as foundations, roadway embankments and land reclamations. However, before their use as structural fills can be recommended, detailed laboratory investigations of their physical, chemical, compaction, and geotechnical engineering properties (strength, compressibility, collapsibility, liquefaction potential, etc.) must be conducted. Different tephra deposits can be products of different eruptions, so chemical composition analyses can be combined with the physical, compaction, and engineering properties to characterize such deposits. Accordingly, this paper provides useful insights from physical (grain size, specific gravity, and morphology), chemical (elemental and mineralogy using X-ray fluorescence and X-ray diffraction), and compaction tests (maximum dry density, optimum water content, and particle breakage) for eleven selected volcanic tephra samples sourced from the North Island of New Zealand in the Rotorua, Taupo, and Auckland regions.

At least 32 case histories have shown that liquefaction can occur in gravelly soils (both natural deposits and manmade reclamations) during severe earthquakes, causing large ground deformations and severe damage to civil infrastructures. Gravelly soils, however, pose major challenges in geotechnical earthquake engineering in terms of assessing their deformation characteristics and potential for liquefaction. In this study, aimed at providing valuable insights into this important topic, a series of isotropically consolidated undrained cyclic triaxial tests were carried out on selected sand–gravel mixtures (SGMs) with varying degrees of gravel content (Gc) and relative density (Dr). The pore water pressure generation and liquefaction resistance were examined and then further scrutinized using an energy-based method (EBM) for liquefaction assessment. It is shown that the rate of pore water pressure development is influenced by the cyclic resistance ratio (CSR), Gc and Dr of SGMs. However, a unique correlation exists between the pore water pressure ratio and cumulative normalized dissipated energy during liquefaction. Furthermore, the cumulative normalized energy is a promising parameter to describe the cyclic resistance ratio (CRR) of gravelly soils at various post-liquefaction axial strain levels, considering the combined effects of Gc and Dr on the liquefaction resistance.

The use of weathered airfall tephra deposits for geotechnical applications such as backfilling in embankments or foundations requires investigation. As a part of an experimental laboratory investigation addressing this issue, this paper focuses on the monotonic shear strength evaluation under drained and undrained shearing conditions of three airfall tephra deposits—namely Kaharoa (white–grey and golden brown) and Maungataketake (black-grey) ashes belonging to New Zealand. The shear strength results include tephra samples compacted at 90