Settlement Response Research Articles

Insights from the numerical analysis of axially loaded piles in liquefiable soils

Axially loaded piles in liquefiable soils can undergo severe settlement due to an earthquake event. During shaking, the settlement is caused by the decreased shaft and tip capacity from excess pore pressures (ue) generated around the pile. Post shaking, soil settlement from the reconsolidation of liquefied soil surrounding the pile results in the development of additional load (known as drag load), causing downdrag settlement of the pile. Estimating the axial load distribution and pile settlement is essential for designing and evaluating the performance of axially loaded piles in liquefiable soils. In practice, a simplified neutral plane solution method is used, where the liquefied soils are modeled as a consolidating layer without considering the effect of ue generation/dissipation. A TzQzLiq analysis models the load and settlement response of axially loaded piles in liquefiable soils by accounting for the effect of excess pore pressure (ue) generation/dissipation on the shaft and tip capacity. This paper presents the deficiencies of the simplified neutral plane method in predicting the drag load as well as the downdrag settlement by comparing it with the TzQzLiq analysis validated with hypergravity model tests. The results show that the drag load and the downdrag settlement predicted by the neutral plane method might be over- or under-estimated depending on the pile load, the rate of ue dissipation, and the soil settlement. For the cases studied, it was found that most of the pile settlement occurs during shaking due to the decrease in the pile's tip resistance from the development of ue in the soil surrounding it. While large drag loads develop during reconsolidation, the resulting downdrag settlement is small. While the neutral plane method generally predicted a downdrag settlement comparable to that of the TzQzLiq analysis, it overpredicted drag load and could not predict co-seismic settlement. Finally, the study advocates for the development and use of a displacement-based procedure (accounting for all the mechanisms occurring during and after an earthquake event) such as based on TzQzLiq analysis in accurately evaluating the performance of the pile (i.e., the pile settlement and the maximum load), thus providing an overall safe, efficient, and optimized design.

Effects of changing adjacent building conditions on ground settlement profiles around deep excavation construction

ABSTRACT This study investigates the impact of deep excavation on ground settlement under various adjacent building conditions using the finite element method. It simulates diaphragm wall earth retention systems with plate elements and uses H-beam assemblies with preloaded anchors to represent temporary earth retention and ensure safety measures. Adjacent structures are also modeled with plate elements. Unlike traditional methods that often overestimate settlement by simulating only ground loads, this research includes the effects of neighboring basements and validates the model using field data. The study employs the HSS model, which provides a more accurate representation of soil deformation compared to the Mohr-Coulomb model. Findings indicate that ground settlement significantly increases when the adjacent building’s basement depth is about half the excavation depth, stabilizing as it approaches 1.6 times the excavation depth. Settlement is more pronounced for buildings closer to the diaphragm wall and decreases with distance. The relationships are described by normalized curves, and y = 1.9x−0.4 and 2.5/√x, representing the behavior of ground settlement in response to varying building conditions.

Microalgal biofilm induces larval settlement in the model marine worm Platynereis dumerilii.

A free-swimming larval stage features in many marine invertebrate life cycles. To transition to a seafloor-dwelling juvenile stage, larvae need to settle out of the plankton, guided by specific environmental cues that lead them to an ideal habitat for their future life on the seafloor. Although the marine annelid Platynereis dumerilii has been cultured in research laboratories since the 1950s and has a free-swimming larval stage, specific environmental cues that induce settlement in this nereid worm are yet to be identified. Here, we demonstrate that microalgal biofilm is a key settlement cue for P. dumerilii larvae, inducing earlier onset of settlement and enhancing subsequent juvenile growth as a primary food source. We tested the settlement response of P. dumerilii to 40 different strains of microalgae, predominantly diatom species, finding that P. dumerilii have species-specific preferences in their choice of settlement substrate. The most effective diatom species for inducing P. dumerilii larval settlement were benthic pennate species including Grammatophora marina, Achnanthes brevipes and Nitzschia ovalis. The identification of specific environmental cues for P. dumerilii settlement enables a link between its ecology and the sensory and nervous system signalling that regulates larval behaviour and development. Incorporation of diatoms into P. dumerilii culture practices will improve the husbandry of this marine invertebrate model.

New Design Criteria for Long, Large-Diameter Bored Piles in Near-Shore Interbedded Geomaterials: Insights from Static and Dynamic Test Analysis

This paper presents an analysis of long, large-diameter bored piles’ behavior under static and dynamic load tests for a megaproject located in El Alamein, on the northern shoreline of Egypt. Site investigations depict an abundance of limestone fragments and weak argillaceous limestone interlaid with gravelly, silty sands and silty, gravelly clay layers. These layers are classified as intermediate geomaterials, IGMs, and soil layers. The project consists of high-rise buildings founded on long bored piles of 1200 mm and 800 mm in diameter. Forty-four (44) static and dynamic compression load tests were performed in this study. During the pile testing, it was recognized that the pile load–settlement behavior is very conservative. Settlement did not exceed 1.6% of the pile diameter at twice the design load. This indicates that the available design manual does not provide reasonable parameters for IGM layers. The study was performed to investigate the efficiency of different approaches for determining the design load of bored piles in IGMs. These approaches are statistical, predictions from static pile load tests, numerical, and dynamic wave analysis via a case pile wave analysis program, CAPWAP, a method that calculates friction stresses along the pile shaft. The predicted ultimate capacities range from 5.5 to 10.0 times the pile design capacity. Settlement analysis indicates that the large-diameter pile behaves as a friction pile. The dynamic pile load test results were calibrated relative to the static pile load test. The dynamic load test could be used to validate the pile capacity. Settlement from the dynamic load test has been shown to be about 25% higher than that from the static load test. This can be attributed to the possible development of high pore water pressure in cohesive IGMs. The case study analysis and the parametric study indicate that AASHTO LRFD is conservative in estimating skin friction, tip, and load test resistance factors in IGMs. A new load–settlement response equation for 600 mm to 2000 mm diameter piles and new recommendations for resistance factors φqp, φqs, and φload were proposed to be 0.65, 0.70, and 0.80, respectively.

Vertical bearing capacity of spun precast concrete pile in liquefiable soil: a case study

Spun precast prestressed concrete (SPC) pile has been used in many parts of the world as a viable foundation alternative. This study assesses the load-carrying capacity of SPC piles passing through a deep soft subsoil layer and resting on a dense sand layer. The vertical bearing capacity of the SPC pile has been estimated using various analytical methods and static pile load tests for the Jolshiri area of Dhaka. The liquefaction potential of the site has been assessed using local seismic site conditions, field and laboratory test data. The liquefaction analysis suggests that the topsoil layer is liquefiable to a depth of 4.5 m. The capacity obtained from the load test is compared with those obtained from the different methods, ultimate push-in load, and local design guidelines. Finite Element Analysis (FEA) was performed considering the hardening soil (HS) model using PLAXIS 3D to simulate field conditions. The load settlement response obtained from FEA shows a good agreement with the test results. The capacity examinations primarily suggest that the SPC pile can be a viable foundation solution for the subsoil conditions of Jolshiri Abasion area of Dhaka.

Effects of including fully wraparound geogrid layers on the load-bearing capacity and settlement of a strip footing resting on sandy soil

In this study, a series of small-scale physical model tests were conducted to investigate the effects of fully wrapped geogrid sheets on the load‒settlement response of medium-dense sandy soil beneath a single-strip foundation. Recent research has provided evidence of how different parameters affect the behavior of dense sandy soil when reinforced with fully wraparound geogrid sheets. Additionally, a parametric analysis was conducted to investigate the influence of various factors on the system. These factors include the presence of a folded geogrid sheet, the depth and length of an embedded wraparound geogrid sheet, the thickness of the fully wrapped geogrid layer, the impact of tensile strains along the geogrid sheet, and the effect of additional confinement pressure. The inclusion of a single sheet of full wraparound geogrid sheets has been found to significantly affect the pressure-bearing capacity of medium-dense sandy soil and settlement beneath the strip footing. The carrying capacity increases by 280%, and the settlement ratios decrease by 50% when using one layer of full wraparound geogrid. Moreover, when using one fully folded geogrid sheet, the strain induced beneath the center of the footing decreases significantly by approximately 45.5% and the applied pressure by approximately 15.5% in comparison with two inclusions of planar geogrid layers. In addition, the stress distributions are spread over a larger region within the soil mass. One significant finding is that the presence of two overlapping parts prevents the rupture of the geogrid sheet, as opposed to the planar geogrid sheet.

Dakota skipper distribution model for North Dakota, South Dakota, and Minnesota aids conservation planning under changing climate scenarios

Species distribution models are useful conservation planning tools for at-risk species, especially if they are linked to planning efforts, conservation delivery, and a changing environment. The Dakota skipper (Hesperia dacotae) is an endemic butterfly of mixed and tallgrass prairie of the northern Great Plains that is listed as federally threatened in the United States and Canada. We modeled broad-scale habitat suitability for the Dakota skipper by relating occurrence observations collected via non-probabilistic population surveys and a stratified sample of pseudo-absences to environmental predictors using a machine learning approach (i.e. Random Forest classification model). Predictors were summarized at two local scales and one landscape scale to reflect a potential spatial hierarchy of settlement responses. We used recursive feature elimination to select the top 25 covariates from a suite of predictor variables related to climate, topography, vegetation cover, biomass, surface reflectance, disturbance history, and soil characteristics. The top model included six bioclimatic, one soil, and 18 local- and landscape-scale vegetation variables and indicated an association with undisturbed grasslands with higher perennial grass and forb cover and biomass. The model performed well, with kappa and AUC estimates of 0.92 and 0.99, respectively, for 20% of data withheld for validation. To understand how climate change might affect Dakota skipper distribution, we applied the model using future 30-year bioclimatic predictions. Predicted suitable habitat declined and the climate envelope associated with Dakota skipper occurrence shifted north into Canada. While it is unknown to what degree the bioclimatic relationships in the model are biologically meaningful or are simply correlative with our non-probabilistic sample of occurrences, our results present an urgency to improve data collection for Dakota skipper populations and better understand climatic relationships, as climate change could have profound effects on populations and conservation planning. Regardless of climate or model uncertainty, our results demonstrate the importance of maintaining sufficient quantities and quality of grass on the landscape to support populations of Dakota skipper.

Larval precompetency and settlement behaviour in 25 Indo-Pacific coral species

Knowledge of coral larval precompetency periods and maximum competency windows is fundamental to understanding coral population dynamics, informing biogeography and connectivity patterns, and predicting reef recovery following disturbances. Yet for many species, estimates of these early-life history metrics are scarce and vary widely. Furthermore, settlement cues for many taxa are not known despite consequences to habitat selection. Here we performed a comprehensive experimental time-series investigation of larval settlement behaviour, for 25 Indo-Pacific broadcast-spawning species. To investigate the duration of precompetency, improve predictions of the competency windows, and compare settlement responses within and amongst species, we completed replicated and repeated 24-hour assays that exposed larvae to five common settlement cues. Our study revealed that larval competency in some broadcast-spawning species begins as early as two days post fertilization, but that the precompetency period varies within and between species from about two to six days, with consequences for local retention and population connectivity. We also found that larvae of some species are competent to settle beyond 70 days old and display complex temporal settlement behaviour, challenging the assumption that competency gradually wanes over time and adding to the evidence that larval longevity can support genetic connectivity and long-distance dispersal. Using these data, we grouped coral taxa by short, mid and long precompetency periods, and identified their preferred settlement cues. Taken together, these results inform our understanding of larval dynamics across a broad range of coral species and can be applied to investigations of population dynamics, connectivity, and reef recovery.

Comparative Investigation of Axial Bearing Performance and Mechanism of Continuous Flight Auger Pile in Weathered Granitic Soils

Axial bearing performance and mechanism of continuous flight auger (CFA) pile in weathered granitic soils, i.e., a widespread special soil in South China, were investigated by field test in this study. Load–settlement responses of four CFA piles were examined, and evolutions of shaft/base resistances were captured by ultra-weak fiber Bragg gratings (UWFBG) with a reflectivity ≤−40 dB. Performances of CFA piles were compared with those of a slurry displacement (SD) pile at the same site, thirteen pretensioned spun high-strength concrete (PHC) piles in the literature and empirical data in design code. Test results show that the ultimate bearing capacity of the CFA pile is highest among different pile types, and typically is twice that of the SD pile. Again, CFA pile produces the highest shaft resistances at 140 kPa and 153 kPa in two weathered granitic soils, while the base resistance of 3080 kPa is between those of the SD pile and the PHC pile. By field excavation, the superior mechanism of the CFA pile is suggested to avoid the formation of in-between bentonite layers and prevent preferential baseflow along fissures, both of which can weaken the soil–pile interface. Overall, this study provides fundamental data through UWFBG and explanations based on field observations which underpin the need for developing a design code specified for CFA piles in South China.

Induction of larval settlement in crown-of-thorns starfish is not mediated by conspecific cues

Population irruptions of crown-of-thorns starfish (COTS; Acanthaster spp.) remain a major cause of coral reef degradation throughout the Pacific and Indian Oceans and are inherently modulated by larval settlement and recruitment success. Gregarious larval settlement, as exhibited by many other ecologically important marine invertebrates, can catalyse population growth and replenishment. However, whether conspecific cues induce or influence the settlement of COTS larvae remains a critical information gap. This experimental study examined the induction of COTS settlement in response to a range of conspecific cues associated with early- and late-stage herbivorous juveniles, corallivorous juveniles and adults. Competent COTS larvae were generally not induced to settle by the presence of conspecifics or cues associated with conspecifics, while the settlement success of COTS in the presence of coralline algae was not inhibited or enhanced by adding conspecific conditioned seawater. Rather than being reinforced by gregarious settlement, the recruitment of COTS populations appears dependent on associative settlement cues (i.e., coralline algae and/or associated microbial communities) signalling suitable benthic habitat.

Response of true limpet Patella aspera (Patellogastropoda) pediveliger larvae to a range of settlement cues

Context Settlement and metamorphosis are key processes influencing the natural recruitment and aquaculture production of aquatic organisms. Recruitment requirements in limpets (Patellogastropoda) are mostly unknown, because of the lack of reliable settlement inducers. Aims This study tested the reliability of different cues as settlement inducers for competent larvae of the economically valuable Patella aspera. Methods Natural crustose coralline algae (CCA) and biofilms of the benthic diatom Navicula salinicola were tested as positive controls. The following four pharmacological agents were tested as chemical inducers in a wide range of concentrations: gamma-aminobutyric acid (GABA), acetylcholine (ACH), 3-isobutyl-1-methylxanthine (IBMX) and potassium chloride (KCl). Settlers were identified by the velum loss and teleoconch development. Key results CCA were strong settlement cues in all the assays. Contrary to previous hypotheses, GABA was a weak inducer with a peak effect at 10−5 M. Neither the diatom biofilms nor the other pharmacological agents (ACH, IBMX and KCl) promoted the settlement response. All pharmacological agents at high concentrations influenced larval behaviour. Conclusions CCA were reliable positive controls and settlement inducers for the production of post-larvae. With regard to pharmacological agents, P. aspera showed restrictive settlement requirements that should be considered for ecological and aquaculture studies in other limpet species. Implications This method allows the study of the settlement biology of limpets. It provides a positive control and integrates animal monitoring and comparative response to other cues.

Experimental and numerical evaluations of load settlement response of helical piles in soft clay

Use of helical piles has become increasingly popular since last few decades for numerous advantages and installation convenience. They may consist of isolated helical plate welded to a central shaft or continuous screw type piles. The load transfer mechanism of helical piles is complex compared to the conventional vertical driven piles. Although limited contributions are available on the performance of helical piles including theoretical and experimental studies, still there are major scopes for further research. The authors have conducted a series of laboratory experimentations on axial load-settlement characteristics of model helical piles made of high tension steel in soft clayey soil, followed by 3D finite element analysis using ABAQUS. The numerical results were found to be close to the experimental observations. Using the numerical model, extensive parametric studies were conducted. The load-settlement response was found to be mostly logarithmic. The pile capacity was found to be influenced significantly by the pitch and embedded pile length. The FEM analysis revealed maximum plastic strain and displacement to develop adjacent to the pile-tip and the interface, while negligible at the boundaries. The interface shear stress distributions are also studied. From the entire investigation, a set of important conclusions are drawn.

Deformation of adjacent buildings and ground settlement induced by shield construction of three-line small-spacing tunnels

Metro tunnels are often constructed between dense building foundations and underground pipelines, thus the spacing between adjacent tunnels is usually small. A decrease in the spacing can significantly increase the severity of tilting of adjacent piles or ground settlement on either side of the metro. In order to analyse the settlement response of the ground surface and adjacent buildings, as well as the movement of the building piles, field monitoring and numerical simulations were carried out for a section of three small-spacing tunnels. A three-stage analysis method was proposed for the calculation of the ground settlement curve induced by the excavation of the three-line tunnels. The results show that the construction of the three-line small-spacing tunnels caused significant tilting of neighboring piles. Furthermore, the excavation of a new tunnel near the completed tunnel extended the area of settlement, thus increasing the possibility of tunnel construction affecting the adjacent buildings and piles. The maximum axial stress increased as the excavation face approached the pile when the distance reached 4D (D is the diameter of the tunnel), then it stabilized when the excavation face passed a distance of 2.5D. As the excavation face approached the pile, the settlement of the pile top gradually increased and stabilized after passing a distance of 8D. The horizontal displacement of the pile bottom reached stability when the excavation face passed a distance of 2D.

Settlement of the Tropical Box Mussel, Septifer bilocularis: Effects of Site, Position, and Substratum

The box tropical mussel Septifer bilocularis lives attached to a hard substratum, forming a dense aggregation or patch. The aggregation occurs at the time of larvae settlement in response to different cues. Larvae may have a positive response whereas larvae may settle and attach to the substratum, while in a negative response, postpone settling occurs. Byssus threads are produced and attached to the substratum, and for some reason, they are affected by many variables. We studied whether the attachment was affected by sites, position in the patch, and substratum. Large and small patches of mussel beds were selected arbitrarily, each in 3 replicates. Substrata of palm, coconut, polypropylene fibres, and mussel shells with byssus threads, each in 4 replicates, were distributed randomly into a PVC plate with 16 holes. The PVC plates with experimental substrata were placed along the edge and in the middle of large and small patches. A three-factorial ANOVA was then performed on samples of sites, position in patches, and substratum as main effects. A significant effect of sites, position within patches, and substratum as well were found. A significantly high number of new settlers in small patches than in other positions within patches occurred. The larger number of new settlers was found on coconut, palm, and polypropylene fibres, while low numbers on the mussel shells with byssus threads were found. The new settlers of S. bilocularis (<1 mm) with transparent shells were observed attached to coconut, palm, and polypropylene fibres. In contrast, the new settlers ranged from >1 mm to 3 mm with dark green shells attached to mussel shells with byssus threads. This study suggests that early settlement occurs when mussels’ larvae first settle and attach to coconut, palm, and polypropylene fibres before reattaching to adult shells with byssus threads.

Multisensory integration by polymodal sensory neurons dictates larval settlement in a brainless cnidarian larva.

Multisensory integration (MSI) combines information from more than one sensory modality to elicit behaviours distinct from unisensory behaviours. MSI is best understood in animals with complex brains and specialized centres for parsing different modes of sensory information, but dispersive larvae of sessile marine invertebrates utilize multimodal environmental sensory stimuli to base irreversible settlement decisions on, and most lack complex brains. Here, we examined the sensory determinants of settlement in actinula larvae of the hydrozoan Ectopleura crocea (Cnidaria), which possess a diffuse nerve net. A factorial settlement study revealed that photo-, chemo- and mechanosensory cues each influenced the settlement response in a complex and hierarchical manner that was dependent on specific combinations of cues, an indication of MSI. Additionally, sensory gene expression over development peaked with developmental competence to settle, which in actinulae, requires cnidocyte discharge. Transcriptome analyses also highlighted several deep homological links between cnidarian and bilaterian mechano-, chemo-, and photosensory pathways. Fluorescent in situ hybridization studies of candidate transcripts suggested cellular partitioning of sensory function among the few cell types that comprise the actinula nervous system, where ubiquitous polymodal sensory neurons expressing putative chemo- and photosensitivity interface with mechanoreceptive cnidocytes. We propose a simple multisensory processing circuit, involving polymodal chemo/photosensory neurons and mechanoreceptive cnidocytes, that is sufficient to explain MSI in actinulae settlement. Our study demonstrates that MSI is not exclusive to complex brains, but likely predated and contextualized their evolution.

Hierarchical settlement behaviours of coral larvae to common coralline algae

Natural regeneration of degraded reefs relies on the recruitment of larvae to restore populations. Intervention strategies are being developed to enhance this process through aquaculture production of coral larvae and their deployment as spat. Larval settlement relies on cues associated with crustose coralline algae (CCA) that are known to induce attachment and metamorphosis. To understand processes underpinning recruitment, we tested larval settlement responses of 15 coral species, to 15 species of CCA from the Great Barrier Reef (GBR). CCA in the family Lithophyllaceae were overall the best inducer across most coral species, with Titanoderma cf. tessellatum being the most effective species that induced at least 50% settlement in 14 of the coral species (mean 81%). Taxonomic level associations were found, with species of Porolithon inducing high settlement in the genus Acropora; while a previously understudied CCA, Sporolithon sp., was a strong inducer for the Lobophyllidae. Habitat-specific associations were detected, with CCA collected from similar light environment as the coral inducing higher levels of settlement. This study revealed the intimate relationships between coral larvae and CCA and provides optimal coral-algal species pairings that could be utilized to increase the success of larval settlement to generate healthy spat for reef restoration.

Redefining shelter: humanitarian sheltering.

Shelter is one of the most 'intractable problems' in humanitarian aid and yet there is little clarity on an overarching definition. Terminology for shelter and housing is often conflated, and the most prominent definition does not fully reflect recent progress in the Shelter and Settlements Sector. This paper explores the varying terminology utilised in definitions of shelter within humanitarian aid since 1990, reflecting on the concepts of 'shelter' and 'housing', alongside surrounding perceptions of 'house' versus 'home', and related measures of adequacy. The current, most prolific definition is also deconstructed, demonstrating ambiguity in some of terminology such as 'dignity' and 'privacy', and revealing that interpretation of this definition depends on the reader's knowledge. Lastly, a new definition of 'sheltering' is proposed, encompassing five key reflections: the concept of process over object; the inclusion of communities and individuals; the commonality of long-term sheltering; the wider effects of shelter; and the impacts on host communities and environment.

Settlement analysis of shallow strip footing under combined static and cyclic loadings

ABSTRACT Shallow foundations in the vicinity of industrial zones are often subjected to machine induced cyclic loads. One of the key problems associated with these kinds of foundation is the determination of amount of settlement under cyclic load. A close observation of the existing studies reveals lack of studies explaining the influence of depth of embedment and frequency of loading on the cyclic load induced settlement of the foundation. An attempt has been made to fill these voids in this study. In the present study, the soil structure interface is modeled using nonlinear elasto-plastic springs and settlement is observed by varying different parameters like the relative density of soil, embedment ratio, factor of safety, intensity and frequency of cyclic loading. It is found that the settlement becomes negligible after certain number of load cycles, i.e. the critical number of load cycles. An empirical expression is developed to estimate the non-dimensional settlement of the foundation using nonlinear regression. It is found that the static load on the foundation is the most important factor influencing the combined static and cyclic settlement response of the foundation. Also, the ultimate settlement is attained earlier for higher values of frequency of loading.

Comparative settlement response of soft clays reinforced with granular columns under widespread loads

This paper examines the consolidation and settlement behaviour of soft clay deposits treated with granular columns (single and in groups). Two Rowe cell loading chambers were used to conduct the investigations on samples of kaolin and a local Belfast natural estuarine alluvium called ‘sleech’. Tests were carried out on unreinforced samples and then reinforced samples with single and multiple column configurations. The test duration for each test was between 3 and 4 months, depending on the test material and the granular column configuration. The settlement reduction factors based on primary and secondary consolidation were examined. The study suggests that the effectiveness of granular columns at mitigating primary and/or secondary settlement is directly related to the loading intensity, the stress history and the creep characteristics of the subsoil. It was also found that the stress concentration ratio reduced with the stress level. Secondary consolidation also has some effects on the stress concentration ratio.

Investigation of the Load–Settlement Response of Piles in Sand Using an Interface Constitutive Model

Investigation of the Load–Settlement Response of Piles in Sand Using an Interface Constitutive Model