This study presents a controlled reconstitution method to develop artificially structured soils focusing on lightly cemented kaolin, aiming to replicate natural clay features for laboratory research. It systematically investigates the influence of light cementation, initial water content, curing time, and specimen orientation. Findings show that even 1% cement content significantly increases the yield stress, confirming soil structuration. Initial water content is a decisive factor, as higher values lead to a more open fabric, characterised by larger initial void ratios and pore sizes. Macrostructure tests reveal a brittle failure mode; strength and stiffness increase with cement and curing time, but decrease with higher initial water content. Anisotropy has only a minor influence on compressibility and mechanical properties, attributed to the low reconstitution pressure and early cement hydration ‘locking in’ a random particle fabric. Microstructural analyses, including SEM, mercury intrusion porosimetry (MIP) and X-ray diffraction (XRD), support these macroscopic observations. SEM images confirm ettringite formation and the progressive filling of inter-aggregate pores with increasing cement. MIP results indicate pore refinement, while XRD analysis indicates a reduction in kaolinite crystallinity due to chemical alteration. This research provides a methodological basis for standardising the preparation of artificially structured soils and advancing the understanding of lightly cemented clay behaviour.

Seismic events can severely impact earth-retaining structures near deep excavations, disrupting operations, especially in densely populated areas during emergencies and rescue efforts. Rapid assessment of seismic vulnerability is essential for these structures. Fragility curves are effective tools for evaluating earthquake-induced damage. This study focuses on developing fragility functions for embedded cantilever retaining walls. A key innovation of this research is identifying intensity measures (IMs) that strongly correlate with wall responses, addressing gaps in current seismic vulnerability assessments. The study employs an advanced approach by combining static simulations with two-dimensional (2D) dynamic analysis using Plaxis 2D software, allowing an accurate representation of the wall behaviour under earthquake. Thirty-one IMs were evaluated for norms such as efficiency, practicality, proficiency, and sufficiency, resulting in the selection of optimal IMs for the fragility functions. The response of the structure is characterised by a permanent lateral displacement at the top of the wall. Fragility functions were developed for the spectral acceleration, providing a unique tool for assessing the seismic vulnerability of embedded cantilever retaining walls. These proposed tools serve as valuable resources for emergency management and preparedness, aiding in the identification of priority actions and appropriate measures for mitigating seismic risk.

Studying the interaction between voids and retaining structures is vitally important, since the performance of such structures may negatively affected by nearby voids such as aqueducts, metro tunnels, and water collection tunnels in heavily urbanised areas. In this study, the impact of horizontal voids on a soil-nailed wall performance has been investigated. Horizontal deformations and ground surface settlements of a soil-nailed wall, which is close to a void, are analysed by simulation in ABAQUS. The results show that increasing the diameter of the voids leads to the exacerbation of horizontal deformation and vertical ground settlement. At a constant distance from the soil-nailed wall, the void closer to the surface of the ground had a greater destructive influence on wall performance. The worst state for the wall was occurred by a void, having 12 m diameter and situated at 16 m in depth from the surface. The acquired results were 34% and 350% increase for horizontal deformation and ground settlement, respectively.

Critical state theory evolved through various contributions relating to both sands and clays, but all were based on remoulded or reconstituted samples. This evolution has produced a perception that the theory applies only to ‘structureless’ soils, with the corollary of no relevance to natural soils which have developed structure and/or bonds through geological processes; residual soils are a particular example. A structured residual soil at the Cadia Northern Tailings Storage Facility displayed brittle undrained behaviour comparable to static liquefaction and contributed to a slump of the dam. The effect of structure is conventionally taken into account by expanding a soil’s yield surface but doing so leads to an increased elastic response whereas residual soils normally show plastic strains near immediately. Here we add ‘structure’ to the theory using two additional soil properties, one a true cohesion attributable to structure and the second characterising the rate of decay of that structure with distortion. This extended theory replicates the measured behaviour of the residual soil considered. The extended theory can be used with existing geotechnical modelling software to simulate progressive failure provided that the software includes user-defined routines (‘scripts’) to allow updating of the critical friction ratio as analysis proceeds.

Although the key aim of soil classification systems for engineering purposes is to provide a standardised system for the identification and grouping of soils of similar composition and mechanical properties, there is no common consensus among different soil classification systems. Inconsistencies between different soil classification systems can lead to incorrect foundation and earthworks design and an increase in project time and cost. This paper presents a comparison of two chosen soil classification systems, the Unified Soil Classification System (USCS; ASTM D2487-17-reapproved 2025) and the Australian Soil Classification System (ASCS; AS1726: 2017), by way of extensive laboratory test results, the cone penetration test, and the critical state soil mechanics framework. A distinct difference in fine-grained soil classification has been identified between USCS and ASCS. It has been found that the threshold fines content (i.e. 35%), as adopted in ASCS to differentiate fine-grained soil from coarse-grained soil, is more appropriate compared with the threshold fines content (i.e. 50%) adopted in USCS. Furthermore, categorising soil plasticity into three groups (i.e. low, medium, and high) is assessed to be more practical in engineering practice. This review also highlights the need for a worldwide unified approach in defining organic soils due to their detrimental effect on soil mechanical behaviour.

Geotechnical Research is a Gold Open Access (OA) journal that applies an Article Processing Charge (APC) on accepted manuscripts. This model enables a streamlined peer-review process, facilitating faster publication timelines and accommodating longer manuscripts than usual. The journal is committed to broadening its impact by publishing high-quality research that advances both the theoretical and practical aspects of geotechnical engineering. In alignment with its mission to promote sustainable engineering practices, Geotechnical Research actively integrates the spirit of the United Nations Sustainable Development Goals into its published contents. APC waivers are considered on a case-by-case basis to support equitable access to publication, guided by the journal’s strategic priorities. This initiative particularly aims to reduce financial barriers for researchers from developing countries.This issue presents four articles themed broadly around the concept of ground improvement for airport and road pavements, deep excavation and instability of silty soils through sound laboratory processes, reliable numerical simulations and practical engineering knowledge and judgement.Zhang et al. (2025) conducted sensitivity analyses from two airport case studies involving 36 different aircraft models using the new Aircraft Classification Rating – Pavement Classification Rating (ACR-PCR) system, which replaces the globally adopted Aircraft Classification Number – Pavement Classification Number (ACN-PCN) system for airfield pavement rating. These rating systems are highly empirical, where ACN values indicate the relative impact of a specific aircraft type on the pavement structure, considering the aircraft’s weight and a specified standard subgrade strength. Conversely, the PCR was a unique number that represented the pavement’s load-bearing capacity and was independent of specific aircraft parameters or details of the pavement structure. The very broad findings indicate that the ACN-PCN method yields more moderate results compared to the ACR-PCR approach. Moreover, rigid pavement thickness has a more pronounced impact on PCN values than on PCR. These insights can support airport authorities in effectively managing the transition from the ACN-PCN system to the newer ACR-PCR framework.Senanayake et al. (2025) performed laboratory investigations into foamed bitumen stabilisation, typically used to improve pavement durability, moisture resistance, and reduce cracking. The research outcomes show that the combined use of recycled concrete aggregate + fine recycled glass + 3% foamed bitumen + 20% (Fly ash + granulated blast furnace slag) met local road authority requirements. In this instance, the field resilient modulus closely matches the soaked resilient modulus observed in the laboratory, confirming that 20% (Fly ash + granulated blast furnace slag) is suitable for use as a secondary binder.Lin et al. (2025) studied how the presence of anchor or ‘screen’ piles helped reduce the impact of detrimental vertical and horizontal movements on existing, adjacent tunnels during the pit-excavation process. Through laboratory tests and numerical simulations, their research output indicated that 2% cement content when applied to the surrounding disturbed soils during excavation would reduce the vertical and horizontal movements by 47% and 33%, respectively, thus providing effective protective measures to the adjacent tunnels.Baki et al. (2025) executed monotonic and cyclic triaxial tests that produced 166 critical state data points using Sydney sand with fines and pond ash to evaluate the effectiveness and reliability of some newly established sample preparation techniques, such as the modified moist tamping method and the liquid rubber sample preparation method. These reliable techniques improve testing conditions that eventually help measure and record instability behaviour of soils, thus improving the accuracy of estimation of state parameters through the development of a unique critical state line.Finally, sincere gratitude to our authors, reviewers, and editorial board members for their immense contributions to the development of our journal.

Foamed bitumen stabilisation (FBS) is widely used to enhance durability, moisture resistance, and road flexibility while reducing cracking. Addressing knowledge gaps in its application with recycled materials can expand their usage in road construction. This study focused on stabilising mixes of 50% recycled concrete aggregate (RCA) and 50% fine recycled glass (RG) using foamed bitumen (FB). Recycled toner aggregate (RTA) and geopolymers derived from ground granulated blast furnace slag (S) and fly ash (FA) were evaluated as potential alternatives to conventional secondary binders, such as Portland cement for FBS of recycled material blends. To assess the performance of RTA, a fixed 3% FB dosage was combined with varying RTA amounts (1%–4%). Geopolymers including FA, S, and (FA + S) at dosages of 10%, 20%, and 30% by mass of RCA and RG blend were tested alongside 3% FB for their stabilising effectiveness. FB-stabilised samples with RTA initially failed the indirect tensile modulus tests, but their performance improved significantly after extended curing. The blend incorporating geopolymers, RCA + RG + 3% FB + 20% (FA + S), met local road authority standards. These results demonstrate the potential of sustainable secondary binders for the stabilisation of RCA and RG mixtures in road construction.

Triaxial apparatus is a commonly adopted testing device for understanding the mechanical behaviours of soils from laboratory tests. The uniform distribution of stress–strain inside the specimen till a large strain close to a steady state is a challenge. Over nearly three decades, research at the University of New South Wales, Canberra, has led to notable improvements in triaxial testing techniques. This article reviews both standard and advanced triaxial testing techniques. These include the ability of the triaxial testing device to measure and record instability behaviour, specimen preparation techniques, enlarged platens with free ends, and its effects, accuracy, and errors involved in the different measurements/calculations. A total of 166 critical state data points of Sydney sand with fines and pond ash prepared under different specimen methods and testing conditions have been included to evaluate the effectiveness and reliability of the abovementioned techniques. Representative monotonic and cyclic test results have been presented to further validate the techniques. The results demonstrate that a unique critical state line can be reliably established, enabling the accurate estimation of state parameters to predict instability behaviour using the critical state soil mechanics framework under both static and cyclic loading conditions.

This paper analyses the impact of construction disturbances on the effectiveness of anchor pile protection measures for metro tunnels through laboratory experiments and numerical simulations. Artificially disturbed soil was prepared by incorporating salt grains and varying amounts of cement into remoulded silty clay from Ningbo. One-dimensional compression and triaxial tests were conducted to study the engineering properties of both undisturbed and disturbed soils. The relationship between cement content and disturbance degree was established based on compressibility, shear strength, and structural yield stress, providing parameters for the hardening soil model with small-strain stiffness. Disturbance zones were classified using the unloading ratio and field disturbance tests conducted at the Gaotangqiao metro station excavation site. Using PLAXIS 3D, the study analysed the effects of pit excavation–induced and anchor pile construction–induced disturbances on tunnel displacement. The results indicate that at 2% cement content, disturbed soil properties were essentially equivalent to those of undisturbed soil. Pit excavation–induced disturbances increased the tunnel’s maximum vertical displacement by 18.3%. The maximum uplift and horizontal displacements of the tunnel increased by 18% and 17%, respectively, due to anchor pile construction–induced disturbances. Despite these construction disturbances, the anchor pile construction effectively controlled tunnel displacement compared with unmitigated excavation.