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Two water samples were collected in April from the “No. Similarities of 99% or greater of ballast water strain sequences to GenBank sequences led. ofballast) had activated allpumps atfull capacityandwas emptying the ballast tanks. it became evidentthat there was not onemalfunction but several. We pitch our tents on the railroad ballast and it rains. Accordingly we follow the bed of the torrent, which is not much better, but, at least. HET TORENTJE AMELIO ESTEVEZ We highly encourage To allow connections not be configuring any image or. the remote can be used part of it information about jobs. Provide a consolidated users and small list files after digital identities fo.
This observation corresponds to Figure 5 and demonstrates the feasibility of F ag max in analyzing the geogrid reinforcement effect of a ballast. As a result of the double geogrid layers, the reinforcement rate significantly increased. Thus, double or multiple geogrid layers are more efficient for the reinforcement of a ballast if cost is not considered.
The calculation results of the monotonic loading revealed no distinct enhancements of the reinforcement effects over rocky and good subgrades and the possibility of collapsing failure for the poor subgrade under long-term repeated loads due to the relatively weak strength. Therefore, the track model over the fair subgrade was adopted in the cyclic loading to investigate the reinforcement effect of the geogrid under repeated train loads.
The sinusoidal cyclic load as shown in Figure 9 was applied. The minimum value of cyclic load was set to zero because the overburden pressure caused by the rail-sleeper assembly was already considered in the gravity generation by PLAXIS. The peak value of the cyclic load was set to kN, which was equivalent to P s , as the impact caused by the different train travel speeds was already considered in the simulation by the loading frequency. The maximum loading number of cyclic load was , as the ballast usually enters the stable zone and the settlement of the ballast insignificantly changed after , cycles Shin et al.
The calculation results of S tu , S tr and R during the , load cycles are plotted in Figure 10 including the result of load cycle of 1, 10, , 1,, 10,, 50,, and , The settlement on the top of the ballast layer kept increasing during loading. The stable zone of the unreinforced track model cannot be observed within the , load cycles.
Conversely, the settlement on the top of the ballast layer of the track model, which was reinforced by the single geogrid layer, attained a constant value after 10, load cycles. Better reinforcement performance is observed under the conditions of the track model that was reinforced by double geogrid layers, and a very slight settlement difference occurred during loading.
Figure Results of cyclic loading: A settlement of ballast layer over fair subgrade; B reinforcement rate of single and double layers of geogrids. The logarithmic trend lines for the two series of reinforcement rates are shown in Figure 10B , and the regression equations are displayed in Figure 10B. Indraratna et al. The simulation results in this study indicate that the reinforcement rate of the geogrid can be described by the similar equation.
The simulation results of the cyclic loading is compared with the measured data from a field trial at a site near Bulli in New South Wales, Australia Indraratna et al. The settlements under the rail at the section of the fresh ballast with and without geocomposite reinforcement during the first , load cycles are plotted in Figure 11A.
The reinforcement rate of the geocomposite, its logarithmic trend line and the regression equation are displayed in Figure 11B. Measured settlement data of the fresh ballast sections at the site near Bulli, NSW, Australia modified after Indraratna et al. The comparison of Figure 10 with Figure 11 indicates that the simulation results for the ballast settlement of the unreinforced track over the fair subgrade was relatively larger than the field measurement data.
The reinforcement rates for the geogrid layers, which were obtained by the cyclic loading simulations, were more pronounced than the field measurement data. Thus, additional studies are needed to improve the understanding of the complex relationship between the behavior of a ballast and these factors. However, similar trends of the reinforcement rates for the geosynthetics are shown in Figures 10 , 11 , i.
The parameters a and b in Equation 4 should be varied in every case due to the variation in the mechanical properties of the ballast, the subgrade strength, the geogrid stiffness and the number of geogrid layers. The results indicate the successful application of PLAXIS for simulating and predicting the behaviors of reinforced railway tracks under cyclic loads.
The double geogrid layers were more effective than the single geogrid layer and were beneficial for the load bearing capacity of the ballast and geogrids. The simulation results of the monotonic loading indicate that double or multiple geogrid layers are more efficient for the reinforcement of a ballast if cost is not considered.
The variations of the parameters of subgrade strength were considered in the simulations, which revealed the important role of subgrade in the reinforcement of geogrids. However, the effect of the strength parameters and the constitutive models of ballast and sub-ballast warrant evaluation. The reduction in the degradation of the ballast aggregates caused by the confinement of the geogrids has not been considered.
The strength reduction factor R inter is influenced by the complex relationship between the aperture size of geogrids, the mean particle size of a ballast, the physical properties of geogrids and the mechanical behaviors of a ballast.
Therefore, additional experimental research is needed to correctly define the behaviors of the interfaces in the simulations. A complex relationship exists between the ballast behavior and cyclic loads. The degradation and breakage of a ballast were not considered in the simulation.
Therefore, additional studies are needed to investigate the ballast behaviors and the reinforcement effect of geogrids under cyclic loads of varied amplitude and varied frequency. Three-dimensional simulations and Discrete Element Method DEM may provide a better understanding of the long-term geogrid reinforcement effects of railway ballast under cyclic train loads. The FE simulations that were conducted in this study investigated the geogrid reinforcement effect on a railway ballast that was subjected to monotonic loads.
The reinforcement mechanisms of a geogrid and the influences of different factors, including the subgrade strength, the stiffness, placement depth and effective width of a geogrid; the strength reduction factor of the interfaces between a geogrid and a ballast; and the combination of double geogrid layers, were discussed based on the numerical simulation results. The following conclusions are obtained from this study:.
The interlock is the most important reinforcement mechanism of geogrids. The geogrid reinforcement reduces the lateral deformations of a ballast and provides a more uniform vertical stress distribution in the soil layers. Consequently, a more uniform load distribution and less vertical deformation in a ballast can be expected. This depth is practical for the application of a geogrid in a railway track and can provide protection for geogrids from damage due to track maintenance.
However, excessive width of the geogrid layer does not provide additional benefits. However, the effect of R inter is relatively insignificant compared with the results of the factor of subgrade strength. Thus, increasing the number of geogrid layers is an effective method for reinforcing a ballast over weak subgrades and increasing the geogrid stiffness. However, the parameters in this equation should be varied based on the conditions of each case under different cyclic loads.
SN elaborated the paper guidelines and corrected the paper. YJ prepared the paper draft. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The authors acknowledge their support.
Amsler, P. Bathurst, R. Geogrid reinforcement of ballasted track. Google Scholar. Brown, S. Identifying the key parameters that influence geogrid reinforcement of railway ballast. Chen, C. Discrete element modelling of cyclicloads of geogrid-reinforced ballast under confined and unconfined conditions. Coleman, D. Doyle, N. Esveld, C. Modern Railway Track. Zaltbommel: MRT-Productions. Fernandes, G.
Performance of geosynthetics reinforced alternative sub-ballast material in a railway track. Gao, G. Effect of particle shape on the response of geogrid-reinforced systems: insights from 3D discrete element analysis. Ghosh, C. Reinforced granular fill-soil system: confinement effect. Gobel, C. Effectiveness of a reinforcing geogrid in a railway subbase under dynamic loads.
Goodhue, M. Interaction of foundry sands with geosynthetics. J Geotech. Geoenvironmental Eng. Guido, V. Haeri, S. Effect of geotextile reinforcement on the mechanical behavior of sand. Han, J. DEM analysis of stresses and deformations of geogrid-reinforced embankments over piles.
Indraratna, B. Behaviour of geocell reinforced subballast subjected to cyclic loading in plane strain condition. The lateral displacement response of geogrid-reinforced ballast under cyclic loading. Effect of confining pressure on the degradation of ballast under cyclic loading. Behavior of geogrid-reinforced ballast under various levels of fouling. Stress-strain degradation response of railway ballast stabilized with geosynthetics. Field assessment of the performance of a ballasted rail track with and without geosynthetics.
Performance assessment of reinforced ballasted rail track. Ground Improv. Track stabilisation with geosynthetics and geodrains, and performance verification through field monitoring and numerical modelling. Railway Technol. From theory to practice in track geomechanics-Australian perspective for synthetic inclusions. Deformation and degradation mechanics of recycled ballast stabilised with geosynthetics.
Soils Found. Advanced Rail Geotechnology-Ballasted Track. Stabilisation of granular media and formation soil using geosynthetics with special reference to railway engineering. Jeffs, T. Jirousek, O. Numerical modelling of the reinforcing effect of geosynthetic material used in ballasted railway tracks.
F , — Khordehbinan, M. Sensitive analysis of granular layers of rail support system in the ballasted railway tracks of Iran Master Thesis. University of Tehran, Iran. Kwon, J. Lackenby, J. Li, L. Finite element model of ballasted railway with infinite boundaries considering effects of moving train loads and Rayleigh waves. Soil Dyn. Lieberenz, K. Geosynthetics in dynamically stressed earth structures of railway lines. Rail Int.
Moghaddas-Nejad, F. Effect of geogrid reinforcement in model track tests on pavements. Ngo, N. A study of the geogrid-subballast interface via experimental evaluation and discrete element modelling. Granular Matter 19, 51— Nimbalkar, S. Improved performance of ballasted rail track using geosynthetics and rubber shockmat. Improved performance of railway ballast under impact loads using shock mats. Palmeira, E. Soil-geosynthetic interaction: modelling and analysis.
Delft: A. Balkema Publishers. Raymond, G. Railway rehabilitation geotextiles. Reinforced ballast behaviour subjected to repeated load. The effect of geogrid reinforcement on unbound aggregates. Sadeghi, J. Improvement of railway ballast maintenance approach, incorporating ballast geometry and fouling conditions.
Development of railway ballast geometry index using automated measurement system. Measurement , — Selig, E. Track Geotechnology and Substructure Management. London: Thomas Telford. Shin, E. Geogrid-reinforced railroad bed settlement due to cyclic load. Sun, Q. Deformation and degradation mechanisms of railway ballast under high frequency cyclic loading. Sun, Y. Loss of genetic diversity can far below traditional microscopical analysis. Here, we be fatal for introduced populations if they are unable to use NGS to assess community changes in zooplankton respond to selective pressures in the new region e.
Impov- Canada to Brazil. We assess temporal changes in zoo- erished genetic diversity also may result from postestab- plankton community and determine the severity of lishment processes, notably genetic drift and selection in population attenuation and whether genetic bottlenecks the new environment e. Few studies have focused on dynamics that occur while nonindigenous species NIS are carried by the invasion Materials and Methods pathway Olenin et al.
Two ballast carry dozens or more species at once Sylvester et al. Wonham et al. In total, 19 ballast et al. The endpoint a total sample volume of L, following which it was for ballast populations that have suffered severe demo- processed through a lm plankton net. Filtered sam- graphic decline could be local extirpation. Figure 1. Voyage routes and the sampling locations at the initial int , middle mid , and final fin point of the experiment. Two replicates of extraction.
This was carried out to evaluate the results 1. As not all taxa were present in all eppendorf tubes. Tubes were centrifuged at Total genomic DNA was extracted from Copepoda. All copepods including nauplii were counted. A 25 lL PCR cocktail contained ence existed given our small sample size. Two PCR replicates were prepared for each sample.
Samples were prepared for A total of 3,, sequences were obtained from 19 sam- amplicon sequencing on an Ion Torrent Personal Gen- ples taken from ballast tanks during the three voyages. OTUs varied between 12 and 64 among samples Table 1. The tanks Fig. Conversely, the mean number of sequences line Seed v. These results indicate that differences in OTU increase the chance of error when comparing genetic depletion rate over time were not due to the number of diversity of different samples Lee ; Brown et al.
Hence, we defined taxa at the family level to avoid Voyage one exhibited the highest loss of OTUs from uncertainty in defining intraspecific genetic diversity initial to final samples, declining by In voyage two, mented in SPSS v. There were the blocking factor. Phylogenetic relationships of OTUs slightly more OTUs in final samples than those collected were reconstructed using neighbor-joining NJ analysis at the midpoint of the trip Table 1.
In voyage three, in MEGA v. Table 1. Operational taxonomic units OTUs and number of cope- pods recovered from three ballast tanks A, B, and C during three Atlantic voyages of a vessel. Each tank was sampled at the beginning, middle, and near the end of the voyage. Days refer to the time since start of the voyage when sampling was conducted. Number of OTUs total counts recovered from initial, middle, and final samples. Three different ballast tanks were sampled: A black line , B gray line , and C dashed line.
Voyage 3 was sampled only at beginning and end. The initial sample collected from tank 3A contained the final 4 than initial samples 3 Fig. In total, 38 highest number of OTUs 64 and recovered taxa 34 taxa were obtained from initial samples of voyage three, taxa Fig. The num- exhibited the lowest number of OTUs 12 and recovered ber of OTUs declined over time in all groups, with proto- only seven taxa Fig.
Some major groups zoa and copepods containing the highest number of such as copepods, molluscs, and protozoans appeared in OTUs in final samples relative to other groups Fig. However, bryozoans, cnidarians, Similar to the number of OTUs, the abundance of gastrotriches, nematodes, platyhelminthes, poriferans, and copepods declined from the start to the end of each voy- rotifers were present in only some samples Table 2.
The highest and lowest number of copepod age, representing six taxa Fig. The mean zoa in final samples. The overall number of OTUs declined or communities in ballast water during the course of three remained the same in all major groups in this voyage, Atlantic voyages. We also demonstrate that genetic dominant among groups whose genetic diversity did not diversity is lost prior to an introduction event, although decline during voyages.
Consistent age, and initial samples contained taxa that were not with Wonham et al. The loss of diversity is generally perceived Copepods, mollusks veliger larvae , and protozoans were as a significant barrier to successful establishment that must be overcome at the initial stage of an invasion Blackburn et al.
However, our results suggest that the same barrier may also occur within species. This high loss of OTUs relative to other voyages may be due to enhanced fluctuations in temperature and salinity during the sampling period Table S1. Temperature decreased by 5. During the same voyage, mean salinity increased in middle samples 3. Such fluctuations in environmental characteristics could trigger physiological shock in some taxa with adverse effects on genetic diversity in zooplank- ton e.
In contrast, voyage two exhibited the lowest loss in OTU number, ranging from 8. Environmental temperature increased by This voyage was the longest trip 12 and number of sequences B obtained from all initial black bar , middle 14 days before taking final sample for tanks 3A and 3B, gray bar , and final white bar samples. Groups that are significantly respectively , which lasted for 7 days before final sam- different are not joined by the same line above the bars.
Temperature of ballast Table 2. Numbers indicate results for 18S marker obtained from Ion Torrent Personal Genomic Machine at the initial int , middle mid , and final fin day of the voyage. Refer Table 1 for number of days between initial, middle, and final samples. NGS data are used for polymorphism studies Bragg et al. Even though the UPARSE method might not represent the exact number of OTUs present in each sample, it appears to be among the most reliable methods currently available for such analyses Edgar ; Flynn et al.
Results from BLAST may not be fully accurate in part due to a lack of online sequence references for particular taxonomic groups Briski et al. Moreover, studies have shown that some groups of zooplankton—such as copepods and rotifers—form species complexes that are poorly defined taxonomically e.
We acknowledge that the number of sequences might not directly correspond to the number of propagules in ballast water Weber and Pawlowski ; Flynn et al. Figure 4. Groups that are significantly different are not joined by the same line above the bars. Therefore, our results are based upon genetic composition of the zooplankton community in the water decreased by 5. Based on the above, environ- abundance of species. However, results from the abundance mental factors in ballast tanks during each voyage appear of copepods were in agreement with the genetic composi- to influence the rate at which OTUs were lost or, more tion of zooplankton found in our ballast tanks.
The appearance of some taxa or an In conclusion, this study highlights the possible cre- increase in their OTU number in final samples could be ation of population bottlenecks prior to introduction of the result of random sampling errors Olenin et al.
It appears that the voyage, perhaps from hatching of dormant stages population loss caused the attenuation of OTUs in final Briski et al. Therefore, our findings highlight that events that The total number of copepods decreased along all voy- occur prior to introduction may influence genetic diver- ages. In voyage one, more than could affect subsequent establishment success. However, voy- age two exhibited the lowest loss in number of copepods. A conceptual model developed by Briski et al.
Qureshi S. Indels introduced by inaccurate flow gram from the Chinese Academy of Sciences to AZ, calls appear at a rate of 1. However, much improve- ment is required to increase the efficiency of these meth- Conflict of Interest ods. Effects of such errors are more pronounced when None declared. Grigorovich, and H. Data Accessibility Propagule pressure: a null model for biological invasions.
Invasions — OTUs and their matching accession numbers for each Dlugosch, K. Founding events in sample: Dryad doi: References Dlugosch, K. Anderson, J. Braasch, F. Cang, and Barrett, S. Foundations of invasion genetics: the H. The devil is in the details: genetic Baker and Stebbins legacy. Bacher, J. Carlton, V. Duncan, et al. A proposed unified framework Edgar, R.
Trends Ecol. Methods — Blackburn, T. Lockwood, and P. The Facon, B. Genton, J. Shykoff, P. Jarne, A. Estoup, et al. A general eco-evolutionary framework for — Bragg, L. Stone, M. Butler, P. Hugenholtz, and Flynn, J. Brown, F. Chain, H. MacIsaac, and G. Shining a light on dark sequencing: M. PLoS identification of species in complex environmental samples: Comput.
Bailey, M. Cristescu, and H. Walters, F. Fernandes, and E. Lakes from biological invasions by invertebrate eggs in Hoffman. Ghabooli, S. Bailey, and H. Assessing invasion risk across taxa and habitats: life stage as a Divers. Gomez, A. Serra, G. Carvalho, and D. Briski, E. Bailey, O. Casas-Monroy, et al. Taxon- Speciation in ancient cryptic species complexes: evidence and vector-specific variation in species richness and from the molecular phylogeny of Brachionus plicatilis abundance during the transport stage of biological Rotifera.
Evolution — Gotelli, N. EcoSim: null Briski, E. Chan, H. MacIsaac, and S. Version 7. Acquired A conceptual model of community dynamics during the Intelligence Inc. Gray, D. Diapausing Briski, E. Are zooplankton eggs remain viable despite exposure to open- genetic databases populated enough to detect non-indigenous ocean ballast water exchange: evidence from in situ exposure species?
Invasions — submitted. Brown, E. Chain, T. Crease, H. MacIsaac, and Hajibabaei, M. Shokralla, X. Zhou, G.
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