Limit analysis is a convenient approach for the estimation of the ultimate collapse state of geotechnical constructions, including pipes, tunnels and retaining walls. A soil-filled masonry arch bridge is a combined geotechnical/masonry structure where rapid limit analysis can play a valuable role in assessing the ultimate load-carrying capacity for multiple load cases. However, currently available rapid analysis techniques for masonry arches only model masonry elements directly, with the soil backfill indirectly modelled, leading to reduced clarity in the predictions of the bridge load-carrying capacity. To address this, a soil backfill model based on lower-bound stress field theory is proposed in this paper. The results, compared with upper-bound solutions obtained using the discontinuity layout optimisation (DLO) numerical limit analysis procedure, show good matches of upper and lower bounds typically to within 10%. The proposed methodology has applications beyond that of arch bridges, such as to tunnels and buried pipes.
Vibro-installation of monopiles is an attractive alternative compared to the traditional impact-hammered installation. The advantages include low noise emissions, mitigation against pile run and a potentially faster installation process, leading to a more cost-efficient project. Uncertainties arising from the scarcity of data on the lateral loading performance of vibro-installed monopiles hinder a more widespread use of the technique. This work presents the first evidence of laterally loaded model monopiles installed by vibro-driving in a geotechnical centrifuge, directly comparing the results with impact-hammered tests installed in the same soil sample. Model piles were installed in medium dense sand, under different drainage conditions and vibro-driving parameters. Results show that the vibro-installed piles had similar or stiffer lateral responses compared to impact-hammered piles, with this trend being maintained over the initial monotonic, cyclic and post-cyclic monotonic stages of the tests. A stiffer rotational response was observed for the vibro-driven piles in sand saturated with high-viscosity fluid, while the softest response occurred for impact-driven piles.
Knowledge gaps in gas transport through partially saturated granular bentonite (GB), characterised by an extended particle size distribution up to several millimetres, limit the long-term safety assessment of engineered barriers. Thus, gas transport in GB samples, starting from as-compacted states and including subsequent loading, progressive saturation and their combination, was investigated through variations in the effective gas permeability (Kg · eff). The microstructure of the samples was characterised using combined mercury intrusion porosimetry and X-ray micro-computed tomography, providing multi-scale insights into Kg · eff in relation to pore size distribution, effective connectivity, density heterogeneity and gas pathway development. A higher as-compacted degree of saturation, mechanical loading and progressive saturation each reduced Kg · eff by promoting the reduction, isolation and closure of inter-granular pores. Gas pressurisation also induced enlargement and reconnection of inter-granular pores in as-compacted states and, after progressive saturation, the formation of highly connected fissure-like features that enhanced gas flow, whereas prior loading constrained these responses. A gas permeability model incorporating granular-type microstructural evolution was developed to capture the main experimental trends. Overall, compared with powdered bentonite, the granular-type microstructure of GB facilitates controlled gas release, supporting its suitability for engineered barrier applications.
Water uptake through plant transpiration is a critical hydraulic boundary condition in modelling geostructures under climatic loading. Transpiration occurs in two regimes: energy-limited, controlled by atmospheric evaporative demand; and water-limited, governed by soil hydraulic conductivity around roots. While energy-limited (potential) transpiration is generally modelled using a physically based approach, the water-limited regime is usually modelled macroscopically by way of an empirical transpiration reduction function. This paper first presents an experimental investigation into the influence of soil hydraulic behaviour and potential transpiration rate on water-limited transpiration. Two soil textures were tested – silty sand and clayey-silty sand – planted with Medicago sativa. The use of high-capacity tensiometers enabled the investigation of an unprecedented suction range in clayey soils. Results show that the water-limited branch of the reduction function is non-linear, and its decay is strongly influenced by unsaturated hydraulic conductivity. Furthermore, the suction marking the transition from energy- to water-limited regimes varied with potential transpiration rate and soil hydraulic behaviour. A novel physically based, closed-form reduction function is then formulated to advance water uptake modelling in the water-limited regime. This function is shown to compactly capture the combined effects of soil hydraulic conductivity, root system architecture expressed through root length density and potential transpiration rate on transpiration in the water-limited regime, consistent with observations from both this experimental campaign and the literature data.
This paper presents a series of physical modelling tests designed to investigate the horizontal displacement, secant stiffness, hysteresis and natural frequency behaviour of a wind turbine with a monopile foundation in sand under cyclic lateral loads. The study addresses the knowledge gap in the long-term assessment of these parameters through centrifuge tests, modelling the complete mass distribution of an offshore wind turbine – including the tower and rotor–nacelle assembly – under macrogravity conditions to provide a realistic simulation of soil–structure interaction and prototype stress–strain fields. The results show a high rate of horizontal displacement increase during the first 1000 cycles, when most of the displacements occur, followed by a marked decrease. An equation is provided describing the increasing behaviour of the secant stiffness with cycles. Hysteresis analysis of horizontal displacement shows a sharp reduction in loop area during the early cycles, followed by stabilisation, indicating reduced damping and energy dissipation as the response becomes increasingly more elastic. For natural frequency variation, measurements show a final increase of approximately 3%, smaller than the values reported in conventional (1g) physical modelling tests. A series of N-increasing free-vibration tests was carried out to show how the system’s natural frequency rises with the soil’s effective stress around the pile. From these results, an equation is derived to estimate natural frequency directly from design parameters such as turbine mass, pile geometry and soil vertical stress.
The reliability of fibre optic strain monitoring depends on an efficient strain transfer from soil to sensor. Previous studies on this soil-sensor strains transfer have relied on shear lag theory implicitly assuming homogeneous soils, while strain transfer effects in heterogeneous soils have not yet been studied. In this paper, the implications of spatial variability in deep mixed columns on strain measurement reliability are investigated. Governing strain transfer equations are analysed by global variance-based sensitivity analysis and synthetic random fields, and it is found that interface stiffness and interface strength are the most important soil-sensor interface parameters. A novel, near-element-scale interface testing procedure is developed to accurately determine these parameters. The findings suggest that boundary effects are negligible for field conditions, but that the heterogeneity in the deep mixed soil results in a requirement for accurate determination of the interface stiffness. Furthermore, it is shown that pre-peak interface behaviour is likely to be achieved by proper sensor selection. A generic framework to analyse vertical strain monitoring data is introduced and exemplified with field monitoring data. While the paper focuses on ground improvement, the framework is generally applicable to other spatially variable soil conditions.
Debris flows, consisting of mixtures of poorly sorted soil, rock and water, surge downstream along channelised paths, causing significant casualties and infrastructure damage. Mitigation typically involves installing barriers along potential flow paths to arrest the material. Laboratory flume experiments are established methods for investigating the physical mechanisms of debris flow mobility and flow-barrier interactions, although they often fail to capture the scale-dependent nature of debris flows reliably. To address this limitation, a new 190 m long, 6 m wide flume facility, the largest of its kind, has been constructed in Kunming, China. In this study, a test was conducted using a total volume of 180 m & sup3; of debris material to explore debris flow interactions with multiple flexible barriers, monitored by various sensors and instruments installed in the flume and the barriers. Results highlight the effectiveness of multiple flexible barriers in mitigating debris flows, showing progressive reduction of impact forces, landing distance and retention volume while moving downstream. Existing design criteria for estimating impact forces and barrier spacing in a multiple barrier system are validated. This research underscores the flume's capability to provide valuable, reproducible data, offering new insights into flow-barrier interactions, calibrating numerical models and contributing to the development of rational design guidelines.
Mass flow models are widely used for hazard assessment and risk mitigation, yet their predictive reliability is constrained by uncertainties in key input parameters. This study examines how incorporating failure characteristics influences runout predictions by coupling limit-equilibrium-derived source geometries with depth-averaged, two-phase D-Claw simulations. Thirty candidate source geometries were selected based on observations from the 2012 Te Maari debris avalanche (New Zealand). The coupled approach demonstrated a good ability to back-calculate complex, channelised mass flows, with the best-performing simulations achieving a critical success index (CSI) greater than 0·6, comparable to values reported in other studies. However, the ensemble of scenarios revealed substantial variability in runout extent and model performance, largely driven by differences in source geometry, volume and alignment. The potential of the method for predicting inundation extent in small-volume scenarios was evaluated using an exceedance probability map of flow depth. An unweighted version was compared with a factor of safety (FOS)-weighted version, in which the FOS served as a proxy for relative failure probability. The FOS-weighted map provided a closer match to the observed debris avalanche extent and demonstrated the potential of this approach to incorporate epistemic uncertainty, offering a more robust framework for probabilistic hazard assessment of future debris flows.
Antiskarn refers to skarn-like assemblages formed by reactions between carbonatite melts and silicate wall rocks and provides critical insights into carbonatite petrogenesis and related mineralization. Here we report calc-silicate assemblages associated with Triassic (229-206 Ma) carbonatite dikes at Huayangchuan, Qinling orogen, central China. Two texturally distinct andradite-rich garnets are distinguished. Fine-grained euhedral garnets yield a U-Pb age (213 +/- 5 Ma) coeval with carbonatite emplacement and represent syn-magmatic "antiskarn" reactions between carbonatite melt and silicate wall rocks. Euhedral garnets intergrown with sulfides yield a U-Pb age of 130.0 +/- 5.2 Ma, identical to nearby granite (132 +/- 1 Ma), and possibly represent a later skarn reaction between granite-derived fluids with solidified carbonatite rocks. Mineral paragenesis in the Triassic assemblages defines three successive stages, reflecting the melt and fluid evolution during carbonatite solidification. These results demonstrate that direct geochronology is essential for distinguishing syn-magmatic antiskarnisation from later hydrothermal modification in carbonatite-related systems.
Realistic numerical representation of soil behaviour requires both constitutive models that are theoretically sound and a good understanding of the associated parameters for the soil to be modelled. This paper explores the multivariate probability distributions of critical state model parameters of a decomposed granite soil type in Hong Kong, including the correlations among these parameters and the engineering implications of such material variability. The parameters were determined through calibrating the NorSand model against a database of stress path measurements from 97 multi-staged consolidated–undrained triaxial tests of specimens retrieved from a region in Hong Kong. Based on the test data, the vine copula method is utilised to unveil the non-linear dependence structure of various constitutive model parameters. Apart from the probability distributions of model parameters, the approach also reveals the model bias associated with the NorSand model in representing the behaviour of decomposed granite soils, as an indicator of its accuracy based on this large dataset. The value of probabilistic parameter characterisation is demonstrated through settlement analyses of a hypothetical case of a shallow footing founded on this soil type, whereby the probability of failure can be rationally determined with consideration of material variability in dilatancy features and hence the stress–strain response.
High-resolution seafloor data from the Gulf of Corinth, Greece, reveal new insights into rift-margin submarine fans deposited at the base of fault scarps. The steep (13 degrees) Sythas canyon cuts into the submarine Lykoporia fault and is carpeted by low-relief, elongate rhomboidal bed forms. Across the fault, the canyon passes abruptly into the 6-km-radius Sythas submarine fan. The proximal fan (similar to 3 degrees gradient) contains multiple discontinuous channels, erosional cyclic steps, and scour fields. Channels shallow and broaden onto the medial fan (similar to 1 degrees gradient), which is characterized by trains of depositional cyclic steps that pass into low-relief lobes on the distal fan (similar to 0.18 degrees gradient). These morphological relationships compare to the submarine slopes of fan deltas and submarine fans in fjords but contrast markedly with established channel-levee distributary models of submarine fans. Sediment gravity flows were likely stratified, with a thin, concentrated, coarse-grained, and supercritical basal layer. Smooth interchannel areas suggest the basal layer (<5 m thick) was contained within erosional relief, before dissipating rapidly within similar to 3 km of the canyon mouth, with flows transformed into dilute, subcritical turbidity currents on the distal fan. This is the first time a continuum of proximal to distal bed forms has been documented on an active base-of-fault-scarp submarine fan and linked to sediment-gravity-flow structure and transitions from supercritical through transcritical to subcritical conditions.
Recent experimental work has demonstrated that tourmaline (tur) can serve as a relatively high-temperature (400-600 degrees C) 40Ar/39Ar geochronometer. Incremental heating of tur from two mineralized localities in the Yukon (Canada), the Casino Cu-Au-Mo porphyry (74.8 +/- 0.74 Ma) and Seagull Batholith (96.9 +/- 0.14 Ma), yield 40Ar/39Ar plateau ages that overlap with zircon U-Pb ages from the host plutons, indicating rapid development of hydro-thermal mineralization following regional magmatism. However, differences in K contents between Casino and Seagull tur and differing crystallization textures between successful (age plateaus) and unsuccessful (discordant) heating experiments illustrate that crystallochemical features (e.g., partial replacement) exert a strong control on geochronology. A petrochronologic approach integrating tur texture, chemistry, and 40Ar/39Ar ages can contribute insights into the formation conditions of tur-bearing mineralized systems.
The history of deep-water circulation between the Norwegian-Greenland Sea (NGS) and the North Atlantic Ocean is poorly constrained for the Paleocene to early Eocene-a period characterized by prolonged rifting and subsequent seafloor spreading. We integrate seismic stratigraphy and biostratigraphy from the NGS to demonstrate several phases of bottom-current erosion and deposition, indicating deepwater circulation before and during breakup. A confined contourite depositional system developed in the central NGS during the late Paleocene. This phase was followed by an-2 m.y. period of reduced circulation in the earliest Eocene, when a volcanic landmass restricted the marine connections to the North Atlantic. Renewed bottom-current activity in the earliest Eocene led to widespread contourite deposition along an-350 km stretch of the western NGS. This circulation system consisted of a southward-flowing western branch and a northward-flowing eastern branch, resembling Neogene to modern circulation patterns. Our results indicate that bottom-current activity predates previous records of contourite drift deposits in the NGS, and that the timing and distribution of contourite deposition were strongly controlled by the evolving basin configuration. We link early Eocene deepwater circulation to the formation of new seaways during breakup and seafloor spreading, rather than bathymetric changes of distant ocean gateways. These results have important implications for basin segmentation during the rift-to-drift transition and for reconstructing early deepwater exchange between the NGS and the North Atlantic.
Yellowstone's vigorous hydrothermal system has long been recognized, but it remains challenging to quantify its magmatic heat supply. Here, we use two controlled-source seismic reflection transects and 3-D passive-source tomography to guide a simple model of magmatic heat supply coupled to a thermodynamic model of hydrothermal reservoir convection. Key model properties are the surface area of the magmatic-hydrothermal interface, conductive-boundary-layer thickness, and the temperature difference between the top of the magma reservoir and the base of the hydrothermal system. Magmatic temperature is set to an estimated rhyolite solidus, and the base of the hydrothermal system is estimated near the critical point for water. Seismic reflections are consistent with a conductive boundary layer thickness of similar to 120 m or less, and a shear-velocity-tomography contour that encloses the reflections has an area of similar to 1190 km2 (40% of the 0.63 Ma caldera). The magmatic heat supply model predicts at least 7.5 GW, which is consistent with a prior geochemical estimate of 6.6 GW of output to surface water and similar to 12% convective heat loss. The new results support the feasibility of system-scale geothermal budget estimation for onshore magmatic and hydrothermal reservoirs.
Subduction transference occurs when an existing subduction zone is choked by the arrival of buoyant crust, and a new subduction zone is generated on the down-going plate to accommodate continuing convergence. Although subduction transference triggered by microcontinent collision was conceptually proposed as a viable tectonic mechanism across several Tethyan oceanic branches, evidence remains controversial, and geodynamic controls are unclear. Here, we report geological data from central Tibet documenting the Early Jurassic northward subduction initiation of the Bangong-Nujiang Ocean, followed by collision with a presently X70-km-wide microcontinent, ophiolite obduction, foreland-basin development, and initiation of a new north-dipping subduction zone to the south of the microcontinent in the late Middle to Late Jurassic. According to numerical geodynamic simulations, such a process can be triggered by an increase in buoyancy and/or lithospheric mantle strength of the collided microcontinent. Our study provides a geological example of subduction transference triggered by a narrow microcontinent collision, able to explain the progressive suturing of microcontinents in the Tethyan realm.
The development of a soil plug is significant during the installation of open-ended piles, particularly those with high aspect ratios. Predicting the soil plug length, plug stress and penetration resistance presents challenges in practical applications. This paper investigates the entire evolution of the soil plug and its effects on the plug resistance of jacked open-ended piles in clay both numerically and analytically. Numerical analyses are undertaken with a large-deformation finite-element method to reveal the mechanisms behind the soil plug evolution. The degree of soil plugging is quantified by a mechanism-based approach with force equilibrium and adjusted bearing capacity theory, through which the incremental filling ratio and penetration resistance against installation depth can be estimated. The effectiveness of this framework has been confirmed through comparisons with field testing and numerical simulation. The method is straightforward to implement in practical applications.
In the analysis of slope stability under slow drawdown conditions, it has been shown that there exists a critical pool level that results in the minimum factor of safety. This paper will use the random finite-element method () to conduct reliability analyses of slopes subjected to slow drawdown. It is shown that the critical pool level corresponding to the maximum probability of failure is affected by a non-dimensional stability number in relation to shear strengths, unit weight and slope height. For flatter slopes, the critical pool level is also affected by the depth ratio. At the critical pool level, more slope failures will be obtained by RFEM, due to the trade-off between the destabilising influence of internal pore pressures and the stabilising influence of exterior hydrostatic pressures.
Greenalite, a ferrous Fe-clay, has been increasingly regarded as the primary precipitate during hydrothermal vent fluid-seawater mixing in early anoxic oceans, leading to widespread deposition of Fe-and Si-rich sediments, namely, iron formations (IFs). However, due to elevated surface oxygen levels, both greenalite and IFs have not been documented in Phanerozoic oceans. Here, we report a rare Triassic sedimentary greenalite-dominated deposit analogous to IFs, the Huimin Fe deposit, SW China. This deposit is hosted in mafic volcanic rocks formed in a deep-water setting within a localized, redox-stratified basin with hydrothermal venting. The Fe ores are laminated, composed mainly of greenalite and siderite, stilpnomelane, and apatite, and locally dominated by hematite. Greenalite is the earliest-formed mineral and occurs as nanoparticles with features of primary sediments, indicative of a primary origin. Rare earth element analysis suggests that the greenalite was likely formed during vent fluid-seawater mixing and deposited at a vent-distal site. Diagenetic alteration of greenalite produced 13C-depleted siderite and stilpnomelane, whereas secondary oxidation formed hematite. Our study highlights that restricted, anoxic basins with hydrothermal vents held potential to form young greenalite IF analogues. Moreover, these findings reinforce the emerging view that greenalite is the primary mineral of IFs and provide new insights into its postdepositional fate, such as the origin of 13C-depleted siderite, thereby offering new constraints on the origin of IFs.
