Infrastructure in northern regions is increasingly threatened by climate change, mainly due to permafrost thaw. Prediction of permafrost stability is essential for assessing the long-term stability of such infrastructure. A key aspect of geotechnical problems subject to climate change is addressing the surface energy balance (SEB). In this study, we evaluated three methodologies for applying surface boundary conditions in longterm thermal geotechnical analyses, including SEB heat flux, n-factors, and machine learning (ML) models by using ERA5-Land climate reanalysis data until 2100. We aimed to determine the most effective approach for accurately predicting ground surface temperatures for climate-resilient design of northern infrastructure. The evaluation results indicated that the ML-based approach outperformed both the SEB heat flux and n-factors methods, demonstrating significantly lower prediction errors. The feasibility of long-term thermal analysis of geotechnical problems using ML-predicted ground surface temperatures was then demonstrated through a permafrost case study in the community of Salluit in northern Canada, for which the thickness of the active layer and talik were calculated under moderate and extreme climate scenarios by the end of the 21st century. Finally, we discussed the application and limitations of surface boundary condition methodologies, such as the limited applicability of the n-factors in long-term analysis and the sensitivity of the SEB heat flux to inputs and thermal imbalance. The findings highlight the importance of selecting suitable boundary condition methodologies in enhancing the reliability of thermal geotechnical analyses in cold regions.

The reasonable value of good gradation characteristic parameters is key in designing and optimising soil-rock mixed high fill embankment materials. Firstly, the DJSZ-150 dynamic-static large-scale triaxial testing instrument was used for triaxial compression shear tests on compacted skeleton structure soil-rock mixture standard specimens. The changes in strength and deformation indicators under different gradation parameters and confining pressure were analysed. Then, based on the Janbu empirical formula, relationships between parameters K, n, and (sigma 1-sigma 3)ult and the coefficient of uniformity Cu and coefficient of curvature Cc were explored. Empirical fitting formulas for Duncan-Chang model constants a and b were proposed, establishing an improved Duncan-Chang model for soil-rock mixtures considering gradation characteristics and stress states. Finally, based on significant differences in particle spatial distribution caused by gradation changes, three generalised models of matrix-block stone motion from different particle aggregation forms were proposed. Results indicate the standard specimen's strength and deformation indicators exhibit significant gradation effects and stress-state correlations. The improved Duncan-Chang model effectively simulates the stress-strain relationship curve under different gradations and confining pressure, with its characteristics explainable based on the matrix block stone motion generalised model.

Ensuring the accuracy of free-field inversion is crucial in determining seismic excitation for soil-structure interaction (SSI) systems. Due to the spherical and cylindrical diffusion properties of body waves and surface waves, the near-fault zone presents distinct free-field responses compared to the far-fault zone. Consequently, existing far-fault free-field inversion techniques are insufficient for providing accurate seismic excitation for SSI systems within the near-fault zone. To address this limitation, a tailored near-fault free-field inversion method based on a multi-objective optimization algorithm is proposed in this study. The proposed method establishes an inversion framework for both spherical body waves and cylindrical surface waves and then transforms the overdetermined problem in inversion process into an optimization problem. Within the multi-objective optimization model, objective functions are formulated by minimizing the three-component waveform differences between the observation point and the delayed reference point. Additionally, constraint conditions are determined based on the attenuation property of propagating seismic waves. The accuracy of the proposed method is then verified through near-fault wave motion characteristics and validated against real downhole recordings. Finally, the application of the proposed method is investigated, with emphasis on examining the impulsive property of underground motions and analyzing the seismic responses of SSI systems. The results show that the proposed method refines the theoretical framework of near-fault inversion and accurately restores the free-field characteristics, particularly the impulsive features of near-fault motions, thereby providing reliable excitation for seismic response assessments of SSI systems.

This study systematically investigated the pore structure response of kaolin and illite/smectite mixed-layer rich clay in a reconstituted state to one-dimensional (1D) compression by first performing oedometer tests on saturated clay slurries, followed by characterising their pore structure using multi-scale characterisation techniques, with the primary objective of advancing the current understanding of the microstructural mechanisms underlying the macroscopic deformation of such clays. Under 1D loading, the volume reduction observed at the macro level essentially represented the macroscopic manifestation of changes in inter-aggregate porosity at the pore scale. It was the inter-particle pores that were compressed, despite the interlayer pores remaining stable. Two distinct pore collapse mechanisms were identified: kaolin exhibited a progressive collapse of particular larger pore population in an ordered manner, whereas illite/smectite mixed-layer rich clay demonstrated overall compression of inter-aggregate pores. Accordingly, mathematical relationships between the porosity and compressibility parameters for these two soils were proposed, with the two exhibiting opposite trends arising from their distinct microstructural features. Approaching from the unique perspective of pore structure, quantitative analysis of pore orientation and morphology on the vertical and horizontal planes demonstrated some progressively increasing anisotropy during compression. These findings provide important insights into porescale mechanisms governing clay compression behaviour and enrich the limited microporosity database in soil mechanics.

Reclaimed coastal areas are highly susceptible to uneven subsidence caused by the consolidation of soft marine deposits, which can induce differential settlement, structural deterioration, and systemic risks to urban infrastructure. Further, engineering activities, such as construction and loadings, exacerbate subsidence, impacting infrastructure stability. Therefore, monitoring the integrity and vulnerability of linear urban infrastructure after construction on reclaimed land is critical for understanding settlement dynamics, ensuring safe and reliable operation and minimizing cascading hazards. Subsequently, in the present study, to monitor deformation of the linear infrastructure constructed over decades-old reclaimed land in Mokpo city, South Korea (where 70% of urban and port infrastructure is built on reclaimed land), we analyzed 79 Sentinel-1A SLC ascending-orbit datasets (2017-2023) using the Persistent Scatterer Interferometry (PSInSAR) technique to quantify vertical land motion (VLM). Results reveal settlement rates ranging from -12.36 to 4.44 mm/year, with an average of -1.50 mm/year across 1869 persistent scatterers located along major roads and railways. To interpret the underlying causes of this deformation, Casagrande plasticity analysis of subsurface materials revealed that deep marine clays beneath the reclaimed zones have low permeability and high compressibility, leading to slow pore-pressure dissipation and prolonged consolidation under sustained loading. This geotechnical behavior accounts for the persistent and spatially variable subsidence observed through PSInSAR. Spatial pattern analysis using Anselin Local Moran's I further identified statistically significant clusters and outliers of VLM, delineating critical infrastructure segments where concentrated settlement poses heightened risks to transportation stability. A hyperbolic settlement model was also applied to anticipate nonlinear consolidation trends at vulnerable sites, predicting persistent subsidence through 2030. Proxy-based validation, integrating long-term groundwater variations, lithostratigraphy, effective shear-wave velocity (Vs30), and geomorphological conditions, exhibited the reliability of the InSAR-derived deformation fields. The findings highlight that Mokpo's decades-old reclamation fills remain geotechnically unstable, highlighting the urgent need for proactive monitoring, targeted soil improvement, structural reinforcement, and integrated InSAR-GNSS monitoring frameworks to ensure the structural integrity of road and railway infrastructure and to support sustainable urban development in reclaimed coastal cities worldwide.

Shallow cut-and-cover underground structures, such as subway stations, are traditionally designed as rigid boxes (moment-resisting connections between the main structural members), seeking internal hyperstaticity and high lateral (transverse) stiffness to achieve important seismic capacity. However, since seismic ground motions impose racking drifts, this proved rather prejudicial, with great structural damage and little resilience. Therefore, two previous papers proposed an opposite strategy seeking low lateral (transverse) stiffness by connecting the structural elements flexibly (hinging and sliding). Under severe seismic inputs, these structures would accommodate racking without significant damage; this behaviour is highly resilient. The seismic resilience of this solution was numerically demonstrated in the well-known Daikai station (Kobe, Japan) and a station located in Chengdu (China). This paper is a continuation of these studies; it aims to extend, deepen, and ground this conclusion by performing a numerical parametric study on these two stations in a wide and representative set of situations characterised by the soil type, overburden depth, engineering bedrock position, and high- and lowlateral-stiffness of the stations. The performance indices are the racking displacement and the structural damage (quantified through concrete damage variables). The findings of this study validate the previous remarks and provide new insights.

Underground structures may be buried in liquefiable sites, which can cause complex seismic response mechanisms depending on the extent and location of the liquefiable soil layer. This study investigates the seismic response of multi-story underground structures in sites with varying distributions of liquified soil employing an advanced three-dimensional nonlinear finite element model. The results indicate that the extent and location of liquefied soil layers affect the seismic response characteristics of underground structures and the distribution of their damage. When the lower story of the subway station is buried in liquefied interlayer site, the structure experiences the most serious damage. When the structure is located within a liquefiable interlayer site, the earthquake ground motion will induce greater inter-story deformation in the structure, resulting in larger structural residual displacement. When all or part of the underground structure is buried in the liquefiable soil layer, the structural failure mode should be assessed to ensure that the underground rail transit can quickly restore functionality after an earthquake. Meanwhile, permeability effects of liquefiable soil have a significant impact on the dynamic response of subway station in the liquefiable site.

The application of prefabricated assembly technology in underground structures has increasingly garnered attention due to its potential for urban low-carbon development. However, given the vulnerability of such structures subjected to unexpected seismic events, a resilient prefabricated underground structure is deemed preferable for mitigating seismic responses and facilitating rapid recovery. This study proposes a resilient slip-friction connection-enhanced self-centering column (RSFC-SCC) for prefabricated underground structures to promote the multi-level self-centering benefits against multi-intensity earthquakes. The RSFC-SCC is composed of an SCC with two sub-columns and a series of multi-arranged replaceable RSFCs, intended to substitute the fragile central column. The mechanical model and practical manufacturing approach are elucidated, emphasizing its potential multi-level self-centering benefits and working mechanism. Given the established simulation model of RSFC-SCC-equipped prefabricated underground structures, the seismic response characteristics and mitigation capacity are investigated for a typical underground structure, involving robustness against various earthquakes. A multi-level self-centering capacity-oriented design with suggested parameter selection criteria is proposed for the RSFC-SCC to ensure that prefabricated underground structures achieve the desired vibration mitigation performance. The results show that the SCC with multi-arranged replaceable RSFCs exhibits a significant vibration isolating effect and enhanced self-centering capacity for the entire prefabricated underground structure. Benefiting from the multi-level self-centering process, the RSFC-SCC illustrates a robust capacity that adapts to varying intensities of earthquakes. The multi-level self-centering capacity-oriented design effectively facilitates the target seismic response control for the prefabricated underground structures. The energy dissipation burden and residual deformation of primary structures are mitigated within the target performance framework. Given the replacement ease of RSFCs and SCC, a rapid recovery of the prefabricated underground structure after an earthquake is ensured.

The Arctic has been warming much faster than the global average, known as Arctic amplification. The active layer is seasonally frozen in winter and thaws in summer. In the 2017 Arctic Boreal Vulnerability Experiment (ABoVE) airborne campaign, airborne L- and P- band synthetic aperture radar (SAR) was used to acquire a dataset of active layer thickness (ALT) and vertical soil moisture profile, at 30 m resolution for 51 swaths across the ABoVE domain. Using a thawing degree day (TDD) model, ALT=K root TDD, we estimated ALT along the ABoVE swaths employing the 2-m air temperature from ERA5. The coefficient (K) calibrated has an R2=0.9783. We also obtained an excellent fit between ALT and K root(TDD/theta) where theta is the soil moisture from ERA5 (R2=0.9719). Output based on shared-social economic pathway (SSP) climate scenarios SSP 1-2.6, SSP 2-4.5, and SSP 5-8.5 from seven global climate models (GCMs), statistically downscaled to 25-km resolution, was used to project the impacts of climate warming on ALT. Assuming ALT=K root TDD, the projections of UKESM1-0-LL GCM resulted in the largest projected ALT, up to about 0.7 m in 2080s under SSP5-8.5. Given that the mean observed ALT of the study sites is about 0.482 m, this implies that ALT will increase by 0.074 to 0.217 m (15% and 45%) in 2080s. This will have substantial impacts on Arctic infrastructure. The projected settlement Iset (cm) of 1 to 7 cm will also impact the infrastructure, especially by differential settlement due to the high spatial variability of ALT and soil moisture, given at local scale the actual thawing will partly depend on thaw sensitivity of the material and potential thaw strain, which could vary widely from location to location.

Permafrost thaw and thermokarst development pose urgent challenges to Arctic communities, threatening infrastructure and essential services. This study examines the reciprocal impacts of permafrost degradation and infrastructure in Point Lay (Kali), Alaska, drawing on field data from similar to 60 boreholes, measured and modeled ground temperature records, remote sensing analysis, and community interviews. Field campaigns from 2022-2024 reveal widespread thermokarst development and ground subsidence driven by the thaw of ice-rich permafrost. Borehole analysis confirms excess-ice contents averaging similar to 40%, with syngenetic ice wedges extending over 12 m deep. Measured and modeled ground temperature data indicate a warming trend, with increasing mean annual ground temperatures and active layer thickness (ALT). Since 1949, modeled ALTs have generally deepened, with a marked shift toward consistently thicker ALTs in the 21st century. Remote sensing shows ice wedge thermokarst expanded from 60% in developed areas by 2019, with thaw rates increasing tenfold between 1974 and 2019. In contrast, adjacent, undisturbed tundra exhibited more consistent thermokarst expansion (similar to 0.2% yr(-1)), underscoring the amplifying role of infrastructure, surface disturbance, and climate change. Community interviews reveal the lived consequences of permafrost degradation, including structural damage to homes, failing utilities, and growing dependence on alternative water and wastewater strategies. Engineering recommendations include deeper pile foundations, targeted ice wedge stabilization, aboveground utilities, enhanced snow management strategies, and improved drainage to mitigate ongoing infrastructure issues. As climate change accelerates permafrost thaw across the Arctic, this study highlights the need for integrated, community-driven adaptation strategies that blend geocryological research, engineering solutions, and local and Indigenous knowledge.