Settlement Stage Research Articles

Genetic affinities between the Yami tribe people of Orchid Island and the Philippine Islanders of the Batanes archipelago

BackgroundYami and Ivatan islanders are Austronesian speakers from Orchid Island and the Batanes archipelago that are located between Taiwan and the Philippines. The paternal genealogies of the Yami tribe from 1962 monograph of Wei and Liu were compared with our dataset of non-recombining Y (NRY) chromosomes from the corresponding families. Then mitochondrial DNA polymorphism was also analyzed to determine the matrilineal relationships between Yami, Ivatan, and other East Asian populations.ResultsThe family relationships inferred from the NRY Phylogeny suggested a low number of paternal founders and agreed with the genealogy of Wei and Liu (P < 0.01). Except for one Y short tandem repeat lineage (Y-STR), seen in two unrelated Yami families, no other Y-STR lineages were shared between villages, whereas mtDNA haplotypes were indiscriminately distributed throughout Orchid Island.The genetic affinity seen between Yami and Taiwanese aborigines or between Ivatan and the Philippine people was closer than that between Yami and Ivatan, suggesting that the Orchid islanders were colonized separately by their nearest neighbors and bred in isolation. However a northward gene flow to Orchid Island from the Philippines was suspected as Yami and Ivatan peoples both speak Western Malayo-Polynesian languages which are not spoken in Taiwan. Actually, only very little gene flow was observed between Yami and Ivatan or between Yami and the Philippines as indicated by the sharing of mtDNA haplogroup B4a1a4 and one O1a1* Y-STR lineage.ConclusionsThe NRY and mtDNA genetic information among Yami tribe peoples fitted well the patrilocal society model proposed by Wei and Liu. In this proposal, there were likely few genetic exchanges among Yami and the Philippine people. Trading activities may have contributed to the diffusion of Malayo-Polynesian languages among them.Finally, artifacts dating 4,000 YBP, found on Orchid Island and indicating association with the Out of Taiwan hypothesis might be related to a pioneering stage of settlement, as most dating estimates inferred from DNA variation in our data set ranged between 100-3,000 YBP.

Developmental shifts in functional morphology of the retina in Atlantic tarpon,Megalops atlanticus(Elopomorpha: Teleostei) between four ecologically distinct life-history stages

The Atlantic tarpon, Megalops atlanticus, is a large piscivorous fish that supports economically important recreational fisheries in the Gulf of Mexico, Caribbean, and Florida Atlantic coast. Megalops atlanticus undergoes ontogenetic shifts in morphology, hatching in the open ocean as larvae (less than 1 cm in length), moving into hypoxic turbid mangrove marshes as juveniles (around 10 cm in length), and then moving into coastal oceanic waters as adults (over 100 cm in length). In this study, photoreceptor distributions, opsin distributions, and photoreceptor absorbance characteristics were studied with light microscopy, transmission electron microscopy, antiopsin immunofluorescence, and microspectrophotometry, respectively, at four ecologically distinct life-history stages--premetamorphic larva, settlement stage, juvenile, and adult. The purposes of this study were 1) to determine the extent to which the retina of M. atlanticus changes over the course of development and 2) to relate these retinal changes with ecological shifts between developmental stages. The new data presented here indicate that the M. atlanticus retina changes substantially in rod and cone distributions and absorbance characteristics over the course of development and that these changes correlate closely with those in habitat and behavior. We show that M. atlanticus has a rod-dominated retina at the larval stage (which is unusual for teleost larvae) and that the scotopic visual system becomes far better developed with maturity, adding a substantial tapetum and high densities of small, bundled, and stacked rod cells. We also show that there are shifts in cone and rod spectral sensitivities and an increase in the diversity of spectrally distinct cone classes, including the addition of ultraviolet cones as fish mature into adults.

Indirect effects of an ectoparasite reduce successful establishment of a damselfish at settlement

1. The sublethal impact of parasites on host behaviour and the mechanism linking them to population level effects remain largely unquantified. On the Great Barrier Reef, juvenile gnathiid isopods (mobile ectoparasites) are one of the most common ectoparasites of fishes. Previous laboratory studies on damselfishes suggest that a single gnathiid can kill settlement-stage larvae and very young juveniles, while repeated attacks affect the growth of a juvenile damselfish. Nothing, however, is known of how gnathiids affect the performance, and the survival of settlement stage fishes in the wild. 2. We sampled juveniles of the damselfish Pomacentrus amboinensis for gnathiids and tested the effect of a single gnathiid (Gnathia auresmaculosa) on juvenile survival in the laboratory. We also tested the effect of this gnathiid on the swimming performance, oxygen consumption, and successful establishment in the wild of settlement-stage larvae. 3. Of the juvenile fish sampled at dawn, 3·5% had a gnathiid attached; at other times of the day, fish had no gnathiids. In the laboratory, most gnathiids (79%) remained attached to juvenile fish for up to 6 h and all fish survived exposure to one gnathiid. 4. When tested in pairs in a double-lane swim chamber, fish that had previously been fed on by one gnathiid ceased swimming first in 77% of the trials and had a lower critical swimming speed compared to fish not exposed to a gnathiid. Previously parasitized fish had a 35% higher oxygen consumption rate than did unexposed fish. When tagged fish were placed in pairs on dead coral patches in the wild and monitored, the previously parasitized fish disappeared from the reef first in 67% of the trials. 5. Our analysis indicates that a single ectoparasitic gnathiid isopod significantly decreases the performance of young P. amboinensis and their persistence on the reef. Gnathiids, by affecting fish performance, may therefore indirectly affect the successful establishment of fishes on the reef at settlement, a critical transitional stage for most coral reef fishes. Unsuccessful establishment on the reef most likely increases the interactions of settling fish with predators and thus gnathiids may contribute to the high mortality observed at this time.

Immigrants in Cultural Conflicts: Immigrant Issues at the Stage of Settlement in Contemporary France Ethnicity, Politics, and International Relations

Immigrants in Cultural Conflicts: Immigrant Issues at the Stage of Settlement in Contemporary France Ethnicity, Politics, and International Relations

China’s Path to the Center Stage of WTO Dispute Settlement: Challenges and Responses

In 2009, China stood at the center stage of the World Trade Organization (WTO) dispute settlement, accounting alone for half of new disputes. From three perspectives, this article examines China’s endeavors since WTO accession to respond challenges and support its meaningful participation in WTO dispute settlement. On ideological level, the prevailing attitude toward WTO dispute settlement in China remains legalistic and positive, but this article observes that pragmatism is rising and may lead to inconsistencies of China’s behavior in the future. Concerning institution and capacity building, China is currently equipped with initially fledging internal mechanisms, growing in-house legal capacities and expanding societal supports, and has swelling potentials to compete with its fellow WTO members. However, outside legal expertise is still needed. On the issue of government and industry interaction, China has established a formal mechanism, but its utility has not yet been proven, with only one unsatisfactory instance suggesting reform is needed, not just more time. This article argues that China will likely continue to be a leading actor in WTO dispute settlement and suggests that developing country members might benefit from a consideration of China’s experience.

Migration and Power Politics: The Settlement of Georgian Immigrants in Turkey (1878–1908)

This study is an examination of the relationship between migration and politics, focusing on the case of Georgian immigrants settled in the central Black Sea districts of Ottoman Turkey during the last quarter of the nineteenth century. Based on the extensive use of Ottoman and British archival material as well as interviews conducted in the region, the study reveals insights into the intriguing power politics behind migration in the Ottoman Empire. Scrutinizing certain characteristics of the settlement process, it also demonstrates the complex imperial network of power that linked the most distant border districts of the Batum-Çürüksu (modern Kobuleti) region of Ottoman Caucasus directly to Istanbul via the Black Sea region of Ordu. The central argument of the study is that the leader of the immigrant group, namely Çürüksulu Ali Pasha, not only successfully managed the settlement process of his fellow Georgians but also masterfully manipulated all the stages of migration and settlement, making use of the conditions in his fierce power struggle against the appointed Ottoman governors as well as the native Muslim nobility of the region. The study thus shows how the personal agenda and the central position of a local Pasha in such a struggle for domination can dangerously destabilize life in an Ottoman province and sow the seeds of animosity between the immigrant community and the natives that eventually accelerated into warfare in the 1890s, creating a serious ‘Immigrant Problem’, the legacy of which lasted up to the early Republican period.

Presentación: En torno a los actores sociales

We wanted to dedicate this issue to some social actors who were the protagonists of two decisive moments in Peruvian history: the culminating expansive period of the Inca Empire and the stage of exploration, demarcation and territorial settlement of the conquering expeditions. Recent historiography has been largely enriched by research on various agents involved in both deeply connected historical processes. The purpose of this issue of Allpanchis is to broaden the discussion around the protagonists of Andean history, whose trajectories can and should be studied in detail from various perspectives.

Brokers and the control of postcontractual opportunism in the Nigerian insurance market

PurposeThe purpose of this paper is to examine how insurance brokers control opportunism at the postcontractual stage of insurance contract in the Nigerian insurance market. Such opportunism, widely reported of insurance commercial customers, threatens the survival of the entire insurance institution while brokers' role is grossly ignored.Design/methodology/approachThe paper involved the use of semi‐structured interviews of insurance broking executives and documentary analyses of how insurance brokers gather and pass on information between clients and insurers to control opportunism in the insurance market.FindingsFindings suggest that the involvement of the insurance brokers from the claim notification stage, claim auditing to actual settlement and dispute mediation are instances of control over customers' opportunistic tendencies. Also, it is found that fear of reputation damage and brokers' professional way of handling clients' over‐exaggeration and suspicious claiming might considerably control insurance opportunism.Practical implicationsInvolving insurance brokers in the claim settlement stage is capable of reducing insurers' claim auditing costs while guaranteeing hassle‐free claiming experience for customers and boosting the image of the insurance industry. Hence, findings are relevant for insurance companies and regulators desirous of controlling opportunism in the insurance market.Originality/valueThe paper extends the marketing role of brokers to the claim settlement stage by highlighting their potentials to control clients' opportunistic behaviours which threaten the insurance market.

The analysis of consolidation in organic soils

The analysis of consolidation in organic soils. This paper is devoted to the specifi c diffi culties connected to construction on problematic soils. Different type of structures like: road embankments, fl ood control levees, dykes and dams are often located in soft subsoil areas, which consists mainly of peat, calcareous soil with a very high content of calcium carbonate and other high plasticity organic and no organic soils. These soils can be characterized as highly deformable with low initial shear strength and an insuffi cient bearing capacity. Soft soils show a large deformation, both vertically and horizontally, under load. The settlements often appear very quickly and can also continue for a long time. The consolidation process consists here of two main stages: primary settlement and secondary (and tertiary) settlement (creep). It is essential to have a good quality description of physical and mechanical properties of soil before the calculation and construction stage. For calculations of each stage of settlement the different physical and mechanical parameters of problematic soil are applied. In this paper the analysis of organic soils deformation process is presented. The deformation characteristics were defi ned on the basis of laboratory tests results. Soil investigations were performed on peat samples taken from test site located in Olsztyn region. Laboratory test of physical properties and consolidation tests in oedometer were carried out. Based on laboratory test results the empirical relationships between stress and deformation as well as stress and time were elaborated in order to describe the primary consolidation in organic soils.

Effects of stocking density, algal density, and temperature on growth and survival of larvae of the basket cockle, Clinocardium nuttallii

This study determined optimal rearing conditions – stocking density, algal density, and temperature – for hatchery production of the basket cockle, Clinocardium nuttallii, from newly-hatched D-larvae to pediveligers using static rearing systems and discontinuous feeding. The combined effect of initial stocking density (2, 4, and 8 larvae ml − 1 ) and algal density (10, 25, and 50 × 10 3 cells ml − 1 ) on larval growth and survival was examined using a bi-algal diet of Chaetoceros muelleri (CM) and Isochrysis sp. (Tahitian strain, TISO). The effect of algal density (0, 2.5, 5, 10, 20, 40, 60, and 80 × 10 3 cells ml − 1 ) as a single factor was assessed using a single-algal diet of TISO and a fixed stocking density (2 larvae ml − 1 ) held constant throughout the experiment. The effect of temperature (5.9, 10.2, 14.2, 18.2, 21.9, and 26.3 °C) on larval growth and survival was also evaluated. The results showed that, when feeding the bi-algal diet of CM and TISO, an initial stocking density of 2 larvae ml − 1 combined with an algal density of 25 or 50 × 10 3 cells ml − 1 or an initial stocking density of 4 larvae ml − 1 combined with an algal density of 50 × 10 3 cells ml − 1 were optimal conditions for larval growth, and survival rate was significantly better in the treatment with 4 larvae ml − 1 . When feeding the single-algal diet of TISO, optimal larval growth was observed at algal densities of ≥ 40 × 10 3 cells ml − 1 . These optimal rearing conditions translated into minimum food rations of 18.4 and 20 × 10 3 algal cells larva − 1 day − 1 using the bi-algal and single-algal diets, respectively, to support maximum larval growth from newly-hatched D-larvae to pediveligers. Within the tested temperature range of 5.9 to 21.9 °C, larval growth was greater with increasing temperature but survival to settlement stage was not affected by temperature. The larvae failed to survive at the highest tested temperature of 26.3 °C.

Housing Experiences of Turkish (Im)migrants in Berlin and Istanbul: Internal Differentiation and Segregation

This paper presents the findings of a comparative qualitative study of Turks who migrated to Istanbul from elsewhere in the country, and Turks who immigrated to Berlin. The main objective of the study is to describe and explain the segregation process affecting Turks in both cities. As the paper focuses on the process of segregation, the article follows the three basic stages along which the history of Turkish (im)migration to Germany and Istanbul has proceeded: the labour migrant stage, the family reunification stage and the settlement stage. Voices of (im)migrants are presented throughout the paper by reflecting their perceptions, values, experiences and dilemmas. The paper argues that internal differences within immigrant groups deserve more attention in order to better understand why some of them, despite being able to afford it, do not move out of concentration areas for better housing opportunities. In this context, the paper focuses on the internal cultural differentiation of Turkish migrants in Istanbul and Turkish immigrants in Berlin, with particular reference to their highly divergent religious understandings. We argue that conservatism—especially when it takes its roots from Islamism—has played an important role in shaping the residential preferences and choices of individuals.

Assessment of Egg and Larval Quality during Hatchery Production of the Temperate Sea Cucumber, Australostichopus mollis (Levin)

Abstract A greater understanding of the causes of variation in egg and larval quality during larval rearing of sea cucumbers will assist in the development of methods to further improve production in hatcheries. For Australostichopus mollis the techniques and methods used in other hatcheries during fertilization resulted in polyspermy occurring in 10–60% of spawned eggs. Despite this, hatch rates were usually greater than 90%. By Day 18 when fed the diatom Chaetoceros muelleri at 2000 cells/mL/day, survival in cultures varied between 35 ± 26% and 57 ± 25%. Of remaining larvae, 10–12% remained in the water column for long periods and did not complete metamorphosis. Furthermore, observation of development in relation to growth and feeding rather than gut content was a better indicator of larval competence. Larvae that were between 700 and 1000 ± 50 μm in length had between four and eight hyaline spheres in the folds of the ciliated band and were in various stages of metamorphosis and settlement. Assessment and comparison of current and previous methods enabled a greater understanding of sources of variation in egg and larval quality, impacts on the production cycle, and suggested improvements.

Gene expression analyses of essential catch factors in the smooth and striated adductor muscles of larval, juvenile and adult great scallop (Pecten maximus)

The scallop adductor muscle consists of striated fibres responsible for the fast closure of the shells, and smooth fibres able to maintain tension in a prolonged state of contraction called catch. Formation of the force-bearing catch linkages has been demonstrated to be initiated by dephosphorylation of the key catch-regulating factor twitchin by a calcineurin-like phosphatase, while the involvement of other thick filament proteins is uncertain. Here we report on the development of catchability of the adductor smooth muscle in the great scallop (Pecten maximus) by analysing the spatio-temporal gene expression patterns of the myosin regulatory light chain (MLCr), twitchin, myorod and calcineurin using whole mount in situ hybridization and real-time quantitative PCR. The MLCr signal was identified in the retractor and adductor muscles of the pediveliger larvae, and the juvenile and adult scallop displayed abundant mRNA levels of MLCr in the smooth and striated adductor muscles. Twitchin was mainly expressed in the smooth adductor muscle during metamorphosis, whereas the adult striated adductor muscle contained seven-folds higher twitchin mRNA levels compared to the smooth portion. Calcineurin expression predominated in the gonads and in the smooth adductor, and five-folds higher mRNA levels were measured in the smooth than in the striated fibres at the adult stage. In contrast to the other genes examined, the expression of myorod was confined to the smooth adductor muscle suggesting that myorod plays a permissive role in the molluscan catch muscles, which are first required at the vulnerable settlement stage as a component of the predator defence system.

Response and condition of larvae of the scallops Nodipecten subnodosus and Argopecten ventricosus reared at the hatchery with different seawater sources

Larvae of the scallops Nodipecten subnodosus and Argopecten ventricosus were reared at a hatchery under five seawater sources: (1) filtered seawater, as the control group; (2) pasteurized seawater; (3) seawater taken from a well; (4) synthetic seawater, and (5) seawater containing a commercial probiotic (Epicin). The quality of each seawater source was measured in terms of counts of Vibrio pathogenic bacteria, levels of nitrites, nitrates, and ammonium, and content of suspended and organic matter. Overall response of larvae under each treatment was measured in terms of growth, survival, biochemical composition, and recruitment rate of spat. Differences in all these parameters, as a function of the seawater source, were analyzed with one-way ANOVA. Larvae survived more, grew faster and larger, had higher protein levels, and recruited more in filtered seawater (in N. subnodosus) and pasteurized seawater (in A. ventricosus), but significant differences between treatments were slight. In A. ventricosus cultures, filtered seawater favored significantly higher Vibrio counts than pasteurized seawater, but this result did not affect the response and condition of larvae. The well seawater treatment ranked third in terms of low bacterial counts, high nitrate levels, larvae showing relatively high survival and growth rates, and spat reaching the settlement stage (only in A. ventricosus ). The synthetic seawater and Epicin treatments did not yield satisfactory results for any of the indicators measured. In fact, in the Epicin treatment, larvae survived only the first days of hatchery cultivation and settlement occurred only in A. ventricosus. The results from these first set of trials are useful for planning additional experiments aimed to improve the protocol of seawater use at our research hatchery.

Otolith development and daily increment formation in laboratory-reared larval and juvenile black-spot tuskfish Choerodon schoenleinii

Microstructures of lapilli were examined for reared larvae and juveniles of black-spot tuskfish Choerodon schoenleinii. Lapilli of larvae at 1 day after hatching have one diffuse and obscure ring with an otolith radius of 4.3 ± 0.50 μm (mean ± SD, N = 8). The slope and intercept of the regression between the number of days after hatching and increment counts did not differ significantly from one and zero, respectively, indicating that lapillus increments were formed on a daily basis after hatching. There was an ontogenetic shift in the relative values of somatic and otolith growth, which corresponded to the transition from pelagic larvae to settlement stage. Simultaneously, the daily increment width reached the maximum value. These findings suggest that age at maximum value of increment width can be used as an indicator of the planktonic larval duration while settlement mark is not found. Since ontogenetic shift in the relationship between otolith radius and body size was observed, back-calculation of somatic growth in black-spot tuskfish using the otolith radius during the early life stages should be analyzed with caution, and the method requires further validation.

Treatment of an Iron-rich ARD Using Waste Carbonate Rock: Bench-Scale Reactor Test Results

The treatment of acid rock drainage (ARD) places extraordinary financial burdens on governments and companies worldwide, and an improved efficiency in treatment by as little as 1% can save many millions of dollars in rehabilitation. We investigated a system for treating Fe-rich ARD using a three-stage reactor design. In the first reaction cell, Fe-rich ARD was partially neutralised using rapid periodic carbonate resuspension with a rotating axial mixer. This was followed by an air-sparged oxidation chamber and then a second reaction cell, with more carbonate periodically resuspended until a pH of 6.3 was reached, which was followed by a settlement chamber. This reactor design has a high capacity for neutralisation, with an efficiency of ≈70% of acidity neutralised by the acid neutralising capacity (g of CaCO3 equivalent) added to the reactor. Axial mixers were tested because of their low-energy requirements and their high reliability. The intermediate chamber effectively removes Fe by oxidising Fe(II) to Fe(III). Given the amount of acidity neutralised, the sludge volume produced was low compared to other technologies, providing further potential savings in sludge handling. Waste carbonate rock proved to be an effective neutralising agent, even though it was about 60% dolomite and 40% magnesite, with minor calcite, and despite the fact that magnesite has substantially slower dissolution kinetics compared to the more dominant dolomite. The mixed waste carbonates were capable of raising the pH sufficiently to reduce the heavy metal loadings in Fe-rich ARD by more than two orders of magnitude. The final settlement stage of the process was shown to be essential for metal precipitation, for the carry-over of fine carbonates, and CO2 loss. This was associated with a rise in pH, from 6.3 to 7.5. In addition, residual slow-reacting magnesite from the mixed carbonate remains in the sludge from the first reactor and provides acid buffering capacity within the sludge, which is commonly lacking in the ARD neutralisation sludge of other systems.

Feeding on intertidal microbial mats by postlarval tiger shrimp, Penaeus semisulcatus De Haan

A series of experiments investigated the potential role of microbial mats in nutrition of the early settlement stages of Penaeus semisulcatus. From 3 days post-metamorphosis, the microbial mat supported high growth and survival rates in postlarvae, equivalent to that supported by a control diet of Artemia nauplii and mussel. Examination of gut contents indicated that benthic postlarvae feed indiscriminately on the microbial mat. However, when postlarvae were fed separated size-fractions of the microbial mat, only the fraction containing a high concentration of infauna (mainly nematodes) was able to support the same growth as intact microbial mat. This appears to be due to the low nitrogen content (0.4–0.9 mmol g−1) of the various size-fractions, compared to that of infauna (4.0 mmol g−1). The stable isotope composition of the dietary size-fractions and postlarval shrimp tissue supports the hypothesis that the shrimp assimilated C and N primarily from the associated infauna. This may be due to selective feeding that is not apparent from stomach contents, due to rapid digestion of fauna soft tissues, or to differential assimilation of infaunal prey relative to other microbial mat components. The results demonstrate that microbial mats may support survival and growth in early-stage penaeid shrimp postlarvae on intertidal mud flats.

Otolith barium profiles verify the timing of settlement in a coral reef fish

Otolith microstructure has been shown to record valuable information about fishes including age, growth, and the timing of life history transitions, while microchemical analysis can reveal information about environmental history, dispersal, and migration. For the bluehead wrasse Thalassoma bifasciatum, a common coral reef fish on an oceanic island, we examined whether otolith chemistry could be used to identify the timing of settlement from the pelagic larval phase to the reefbased juvenile phase. This species has a distinct settlement mark visible in its otolith microstructure. Using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), we found that Ba:Ca ratios increased abruptly at the time of settlement. On average, Ba:Ca ratios were 6.5× greater in the juvenile than the larval phase. Other elements (Mg, Mn, and Sr) also displayed ontogenetic changes in concentration; however, those changes were not associated with the settlement mark. We demonstrate the potential utility of otolith chemistry as a method to identify the timing of settlement (and thereby the larval duration) in other marine fishes with similar early life histories, whose otoliths may not produce distinct settlement checks or those whose settlement stage larvae may not be captured by other means.

Role of post-settlement mortality in the establishment of Acropora reef slope zonation in Ishigaki Island, Japan

The relative contributions of larval recruitment and post-settlement mortality to the establishment of the zonation of Acropora communities, a dominant group in reef corals, remain unknown. Our field research revealed that the relative abundances of juveniles between two morphological categories of acroporid corals were different on shallow and deep slopes: tabular species dominated in shallow waters (1.5-2.5m), whereas arborescent species dominated in deep waters (5.5-11m). These abundances were consistent with the distributional patterns of the adults, suggesting that the zonation structure is formed during the initial life stages of settlement and early post-settlement periods. To determine to what extent Acropora zonation is determined by depth-related differences in initial mortality among species, a transplant experiment using artificially settled corals (10 days after settlement) of four dominant species (the shallow-dominants Acropora digitifera and A. selago and the deep-dominants A. muricata and A. tenuis) was performed at four depths (1.5, 2.5, 5.5, and 11m). Survivorship of all four species was lower at 5.5m than the other depths and that the survival rate of A. muricata was much higher than that of other species at all depths. However, there was no species-specific survival related to adaptation to a particular habitat (i.e., depth), implying that Acropora spats do not possess species-specific tolerance for the environmental stresses of their own particular habitat, at least during the first 6 months after settlement. Post-settlement survival rate during this period is therefore not a major factor in forming the vertical zonation pattern of these Acropora species in subtropical reefs around Japan.

Centrifuge modeling of geotextile-reinforced slopes subjected to differential settlements

Today, geosynthetic-reinforced soil structures are widely used to support bridge abutments and approach roads in place of traditional pile supports and techniques. In such situations, foundation conditions have been shown to adversely affect the stability and deformation behaviour of overlying geosynthetic-reinforced slopes and walls. This paper addresses the response of geotextile-reinforced slopes subjected to differential settlements in a geotechnical centrifuge. Centrifuge model tests were carried out on model geotextile-reinforced sand slopes with two different types of reinforcement. A wrap-around technique was used to represent a flexible facing. In order to initiate failure in the reinforcement layers, the ratio of length of reinforcement to height of the slope was maintained as 0.85. One of the objectives of this paper is to present about a special device developed for inducing differential settlements during centrifuge test at 40 g for a reinforced soil structure. A digital image analysis technique was employed to arrive at displacement vectors of markers glued to the reinforcement layers. The displacements were used to compute and analyze the strain distribution along the reinforcement layers during different settlement stages. Results of the centrifuge test indicate that even after inducing a differential settlement equivalent to 1.0 m in prototype dimensions, the geotextile-reinforced soil structure with a flexible facing was not found to experience a collapse failure. Analysis of geotextile strain results shows that the location of the maximum peak reinforcement strain occurs along the bottom-most reinforcement layer at the onset of differential settlements, at the point directly below the crest of the slope.