bluuebunny/crossref_metadata_2025 huggingface dataset:
Lineage and pluripotentiality of epithelial precursor cells in developing chicken skin
Authors: Chuong Cheng-Ming , Jung Han-Sung , Noden Drew , Widelitz Randall B
Published: April 2011

How do epithelial cells in developing skin accommodate the constantly growing embryo? Where do cells in skin appendages come from? Are they derivatives of a single appendage stem cell, or are they polyclonal? Here we analyze these issues in developing chicken skin using a replication-defective virus carrying beta-galactosidase and DiI microinjections. The results demonstrate that in early skin, epithelial cells labelled near the spine show a parallel linear stripe distribution pattern that is perpendicular to the midline of the trunk. This is similar to the human lines of Blaschko, a linear pattern on the skin, which many skin nevoid or acquired disorders follow. In later skin, feather buds form and contain a mixture of labeled and unlabeled cells, attesting to their polyclonal origin. When cells are traced for shorter time intervals, the labeled progeny appear to follow certain rules. The degree of cell dispersion and mixing increases with a longer incubation period between the time of labeling and detection. The spatial maturation sequence of skin appendages is not regulated by the order in which epithelial cells are generated. Epithelial cells at this developmental stage are pluripotent and competent to respond to new signals to assume appropriate fates according to their micro-environment. The results suggest that local interactions act upon the originally linearly deposited pluripotential epithelial cells to form skin appendages.Key words: cell lineage, organogenesis, stem cell, skin appendages, feather, hair.
Role of the membrane anchoring and cytoplasmic domains in intracellular transport and localization of viral glycoproteins
Authors: Ghosh Kakoli , Ghosh Hara P
Published: April 2011

Nuclear factor-κB (NF-κB) binds to nucleotide sequences between -80 and -70 bp upstream of the transcriptional start site in the interleukin-8 (IL-8) promoter and is crucial for transcription of the IL-8 gene. We showed that exogenous nitric oxide in the form of a nitric oxide donor significantly reduced IL-8 mRNA in cytokine-activated ECV304. Similarly, nitric oxide significantly reduced migration of polymorphonuclear neutrophils through cytokine-activated ECV304 monolayers, an IL-8-dependent process. Using a luciferase reporter construct containing the NF-κB site of the IL-8 gene, we showed that exposing cytokine-activated ECV304 to exogenous nitric oxide resulted in significant reduction of NF-κB binding. Follow-up studies using a luciferase reporter construct possessing a mutated NF-κB site confirmed that the luciferase activity observed in the NF-κB reporter resulted from NF-κB binding. These studies demonstrate that nitric oxide, supplied exogenously into reactions containing activated endothelium, down-regulates pro-inflammatory activity, such as the secretion of chemokines, and functional activity, such as transendothelial migration of neutrophils. Key words: interleukin-8, nuclear factor κ B, transendothelial migration, nitric oxide.
SUMO/sentrin: protein modifiers regulating important cellular functions
Authors: Kretz-Remy Carole , Tanguay Robert M
Published: April 2011

Regulation of protein functions can be achieved by posttranslational protein modifications. One of the most studied modifications has been conjugation to ubiquitin, which mainly targets substrate proteins for degradation by the 26 S proteasome. Recently, SUMO/sentrin, a ubiquitin-like protein has been characterized. This evolutionary conserved protein is conjugated to specific proteins in a way similar, but not identical, to ubiquitin and seems also to be involved in the regulation of protein localization or function. An increasing number of SUMO/sentrin substrates are currently described. We focus here on three major substrates of modification by SUMO: RanGAP1, PML, and I(kappa)B(alpha) proteins. These different examples illustrate how SUMO conjugation may be involved in the control of the level of critical proteins within the cell or in the modulation of subcellular localization and nucleocytoplasmic trafficking.Key words: protein modification, NF-(kappa)B, I(kappa)B, protein transport, nucleus, RanGAP1, PML.
Reconstitution of the glycosylphosphatidylinositol-anchored protein Thy-1: interaction with membrane phospholipids and galactosylceramide
Authors: Reid-Taylor Kara L , Chu Joseph WK , Sharom Frances J
Published: April 2011

Glycosylphosphatidylinositol (GPI)-anchored membrane proteins are proposed to interact preferentially with glycosphingolipids and cholesterol to form microdomains, which may play an important role in apical targeting and signal transduction. The objective of the present study was to investigate the interaction of the GPI-anchored protein Thy-1 with phospholipids and a glycosphingolipid. Purified Thy-1 was reconstituted into lipid bilayer vesicles of dimyristoyl-phosphatidylcholine (DMPC) alone or in combination with galactosylceramide (GC). The ability of Thy-1 to perturb the gel to a liquid-crystalline phase transition of DMPC was examined by differential scanning calorimetry. As the mole fraction of Thy-1 increased, the phase transition enthalpy, deltaH, declined. Analysis indicated that each molecule of Thy-1 perturbed over 50 phospholipids, suggesting that, in addition to the anchor insertion into the bilayer, the protein itself may interact with the membrane surface. Inclusion of 5% w/w GC in the bilayer resulted in a striking change in the interaction of Thy-1 with phospholipids. At low Thy-1 content, there was a reduction in the phase transition temperature and an increase in phospholipid cooperativity, suggesting the formation of Thy-1/GC-enriched domains. deltaH initially decreased with increasing Thy-1 content of the bilayer; however, at higher Thy-1 mole ratios, deltaH rose again. These results are interpreted in terms of a model whereby, at low protein:lipid mole ratios, Thy-1 preferentially sequesters GC to form enriched microdomains. At high protein:lipid mole ratios, Thy-1 may alter its conformation in response to steric crowding within these domains such that its interaction with the bilayer surface is reduced.Key words: glycosylphosphatidylinositol anchor, Thy-1 antigen, reconstitution, lipid bilayer, glycosphingolipid, differential scanning calorimetry, dynamic light scattering.
Organization of chromatin in cancer cells: role of signalling pathways
Authors: Davie J R , Samuel S K , Spencer V A , Holth L T , Chadee D N , Peltier C P , Sun J -M , Chen H Y , Wright J A
Published: April 2011

The role of mechanical and chemical signalling pathways in the organization and function of chromatin is the subject of this review. The mechanical signalling pathway consists of the tissue matrix system that links together the three-dimensional skeletal networks, the extracellular matrix, cytoskeleton, and nuclear matrix. Intermediate filament proteins are associated with nuclear DNA, suggesting that intermediate filaments may have a role in the organization of chromatin. In human hormone-dependent breast cancer cells, the interaction between cytokeratins and chromatin is regulated by estrogens. Transcription factors, histone acetyltransferases, and histone deacetylases, which are associated with the nuclear matrix, are components of the mechanical signalling pathway. Recently, we reported that nuclear matrix-bound human and chicken histone deacetylase 1 is associated with nuclear DNA in situ, suggesting that histone deacetylase has a role in the organization of nuclear DNA. Chemical signalling pathways such as the Ras/mitogen-activated protein kinase (Ras/MAPK) pathway stimulate the activity of kinases that modify transcription factors, nonhistone chromosomal proteins, and histones. The levels of phosphorylated histones are increased in mouse fibroblasts transformed with oncogenes, the products of which stimulate the Ras/MAPK pathway. Histone phosphorylation may lead to decondensation of chromatin, resulting in aberrant gene expression.Key words: histone acetylation, histone phosphorylation, nuclear matrix, cytoskeleton, histone deacetylase, cancer.
SR-related proteins and the processing of messenger RNA precursors
Authors: Blencowe Benjamin J , Bowman John AL , McCracken Susan , Rosonina Emanuel
Published: April 2011

The processing of messenger RNA precursors (pre-mRNA) to mRNA in metazoans requires a large number of proteins that contain domains rich in alternating arginine and serine residues (RS domains). These include members of the SR family of splicing factors and proteins that are structurally and functionally distinct from the SR family, collectively referred to below as SR-related proteins. Both groups of RS domain proteins function in constitutive and regulated pre-mRNA splicing. Recently, several SR-related proteins have been identified that are associated with the transcriptional machinery. Other SR-related proteins are associated with mRNA 3prime end formation and have been implicated in export. We review these findings and evidence that proteins containing RS domains may play a fundamental role in coordinating different steps in the synthesis and processing of pre-mRNA.Key words: SR protein, RNA polymerase, spliceosome, polyadenylation, nuclear matrix.
Cell adhesion and the actin cytoskeleton of the enveloping layer in the zebrafish embryo during epiboly
Authors: Zalik Sara E , Lewandowski Ewa , Kam Zvi , Geiger Benjamin
Published: April 2011

As the zebrafish embryo undergoes gastrulation and epiboly, the cells of the enveloping layer (EVL) expand, covering the entire yolk cell. During the epiboly process, the EVL cells move as a coherent layer, remaining tightly attached to each other and to the underlying yolk syncytial layer (YSL). In view of the central role of the actin cytoskeleton, in both cell motility and cell cell adhesion, we have labeled these cells in situ with fluorescent phalloidin and anti-actin antibodies. We show that, throughout their migration, the EVL cells retain a conspicuous cortical actin cytoskeletal belt coinciding with cell surface cadherins. At the margins approaching the YSL, the EVL cells extend, from their apicolateral domains, actin-rich filopodial protrusions devoid of detectable cadherin. We have studied the role of the actin cytoskeleton in the maintenance of EVL cohesion during epiboly. Cytochalasin treatment of embryos induces EVL dissociation accompanied by general detachment of the rest of the embryonic cells. In the dissociating EVL cells, the cortical actin belt undergoes fragmentation with the formation of actin aggregates; cadherins, on the other hand, remain evenly distributed at the junctional cell surface. Removal of Ca2+by ethyleneglycolbis (amino-ethyl-ether)-tetraacetic acid (EGTA) treatment also induces cell dissociation without visible disruption of the cortical actin belt. The protein kinase inhibitor (1-isoquinolinylsulfonyl)-2-methyl-piperazine dihydrochloride (H-7), which blocks acto-myosin contractility and disrupts actin cables in cultured cells, also potentiates cytochalasin-induced dissociation and promotes the projection of numerous actin-rich lamellipodial extensions. The fact that EVL cells produce microspike-like structures towards the YSL and are capable of lamellipodial activity lend further support to the suggestion (R.W. Keller and J.P. Trinkaus. 1987. Dev. Biol. 120: 12-24) that the EVL cells are not passively mobilized on the expanding YSL but actively participate in epiboly.Key words: actin, adhesion, cadherin, cytochalasin, embryo, zebrafish.
1999 Roche Diagnostics Prize for Biomolecular and Cellular Research / Prix Roche Diagnostics 1999 pour la recherche en biologie moléculaire et cellulaireStudies on a "jumping gene machine": Higher-order nucleoprotein complexes in Mu DNA transposition
Authors: Chaconas George
Published: April 2011

Studies in my lab have focused on DNA transposition in the bacterial virus, Mu. In vitro studies have shown that Mu DNA transposition is a three-step process involving DNA breakage, strand transfer and DNA replication. In the first step, a nick is introduced at each end of the transposon. The liberated 3'-OH groups subsequently attack a target DNA molecule resulting in strand transfer. The transposon DNA, now covalently linked to the target, is finally replicated to generate the transposition end-product, referred to as a cointegrate. The DNA cleavage and strand transfer reactions are mediated by a "jumping gene machine" or transpososomes, which we discovered in 1987. They are assembled by bringing together three different DNA regions via a process involving multiple protein-DNA and protein-protein interactions. The action of four different proteins is required in addition to protein-induced DNA bending or wrapping to overcome the intrinsic stiffness of DNA, which would ordinarily prohibit the assembly of such a structure. Transpososome assembly is a gradual process involving multiple steps with an inherent flexibility whereby alternate pathways can be used in the assembly process, biasing the reaction towards completion under different conditions.Key words: DNA transposition, transposons, higher-order nucleoprotein complexes, DNA breakage and reunion, site-specific recombination.
Camel (camelus dromedarius) milk PP3: evidence for an insertion in the amino-terminal sequence of the camel milk whey protein
Authors: Girardet Jean-Michel , Saulnier Franck , Gaillard Jean-Luc , Ramet Jean-Paul , Humbert Gérard
Published: April 2011

The camel (camelus dromedarius) milk proteose peptone 3 (PP3) was purified successively by size exclusion fast protein liquid chromatography and reversed phase high performance liquid chromatography and then characterized by amino acid residue composition determination and chemical microsequencing after CNBr or trypsin cleavages. In comparison with the previously reported structure of camel milk whey protein, the camel PP3 contains an insertion in the N-terminal region which has approximately 24 residues, whereas the remaining C-terminal regions of these two homologous proteins are essentially identical. The camel PP3 seems to contain a potential O-glycosylation site localized in this insertion and 2 or 3 phosphorylated serine residues. PP3 belongs to the glycosylation-dependent cell adhesion molecule 1 (GlyCAM-1) family and could therefore play an immunological role in the camel or its suckling young.
Model tests on single piles in soft clay
Authors: Pan J L , Goh A TC , Wong K S , Teh C I
Published: April 2011

Laboratory model tests in soft clay were conducted to investigate the behaviour of single piles subjected to lateral soil movements ('passive' pile), and to determine the ultimate soil pressure acting along the pile shaft. A specially designed apparatus for the tests was manufactured and calibrated. Reasonably consistent soil samples were prepared for the tests by a consolidometer. The limiting soil pressures acting along the model pile shaft were measured by pressure transducers. The ultimate soil pressure was then determined based on the maximum value of the limiting soil pressures acting along the pile shaft. The ultimate soil pressure obtained from the single passive pile tests was 10.6su(where suis the undrained shear strength of the clay) and agreed well with those from the literature.Key words: pile, foundation, lateral soil movement, clay, model test.
Shakedown analysis of anisotropic asphalt concrete pavements with clay subgrade
Authors: Boulbibane M , Collins I F , Weichert D , Raad L
Published: April 2011

The essence of a shakedown analysis is to determine the critical shakedown load for a given pavement. Pavements operating above this load are predicted to exhibit increased accumulation of plastic strains under long-term repeated loading conditions that eventually lead to incremental collapse (e.g., deep ruts). Those pavements operating at loads below this critical level may exhibit some initial distress, but will eventually settle down to a steady state in which no further mechanical deterioration occurs. Conventional pavement design procedures assume that the pavement deteriorates indefinitely. However, there is now ample field evidence that this is not always true and that steady-state conditions are frequently achieved. The materials in the various layers of the pavement are modeled as elastic-plastic Mohr-Coulomb materials. Anisotropic strength effects are studied as well as the influences of variable temperature, stiffness, strength, and thickness of the asphalt concrete layer. A lower bound approach is used to provide safe estimates of the critical shakedown load.Key words: shakedown theory, multilayered pavements, anisotropy.
A revision of Blight's model of field vane testing
Authors: Morris Peter Henri , Williams David John
Published: April 2011

Vane shear test data obtained by a number of researchers show that the excess pore pressures generated within the soil surrounding the vane by vane insertion and rotation and their effects on the measured vane shear strength have been misinterpreted for many years. The accepted model developed by Blight of field vane testing and the accepted criteria for determining undrained and fully drained vane shear strengths are based on this misinterpretation. Consequently, estimates that are based on this model of the degree of drainage that has been attained at the time the vane shear strength is measured may be significantly in error, and the measured undrained shear strengths may be unconservative. A revision of Blight's approximate theory of field vane testing is presented which is consistent with the available experimental data. Revised practical criteria for determining the undrained and fully drained shear strengths are also presented, and a simple revision of current standard vane shear test methods is proposed which would eliminate, for all but those soils with very high coefficients of consolidation, the possibility that estimates of the undrained vane shear strength may be unconservative.Key words: vane shear, undrained strength, drained strength, excess pore pressure.
Fundamental factors affecting liquefaction susceptibility of sands
Authors: Vaid Y P , Sivathayalan S
Published: April 2011

Liquefaction phenomena in saturated sands are examined. Fundamental factors that influence liquefaction susceptibility are considered from the background of comprehensive experimental evidence from test results on reconstituted specimens. These include those related to the loading system characteristics which do not enable measurements of the true post-peak behaviour. In particular, several issues related to the influence of initial state variables, on which there appears to be a lack of consensus in the literature, are dealt with. It is shown that at identical initial void ratio - effective stress state, undrained (constant volume) behaviour is profoundly affected by the fabric that ensues upon sample reconstitution. Very loose moist-tamped states are unlikely to be accessible to in situ sands. The susceptibility to liquefaction, both static and cyclic, is not only dependent on the initial state variables, but is also strongly affected by the effective stress path during undrained shear. Comparative tests on undisturbed samples retrieved by in situ ground freezing and their reconstituted counterparts show that water-pluviated specimens closely mimic the behaviour of in situ sands. Very small expansive volumetric strains due to pore-pressure gradients during short-duration loading, or after its cessation, could transform a sand into a strain-softening type, which otherwise would be dilative if completely undrained.Key words: anisotropy, laboratory tests, liquefaction, sampling, sands, shear strength.
Experimental validation of a finite strain theory for gassy mud
Authors: Wichman BG HM , Sills G C , Gonzalez R
Published: April 2011

In the Netherlands large quantities of polluted mud must be stored in large-scale disposal sites. The storage capacity of these sites and the outflow of contaminated pore water can be predicted by means of one-dimensional finite strain theory. By making various theoretical assumptions, a self-weight consolidation computer program for gassy sludge has been developed. These assumptions are verified by simulating a small-scale column test with biogenic gas production. Good agreement was obtained between the measured and simulated density profiles, excess pore pressures, and settlements. This paper also deals with the validation of simulations with this computer program by means of field measurements from the Slufter disposal site, which is used to store polluted mud from Rotterdam harbour. The field measurements consist of mud level measurements and profiles of water content, gas content, bulk density, and pore-water pressure for two locations in the disposal site. The computer simulations are in reasonable agreement with the field data. The method described here can be used to predict the future disposal capacity on the basis of estimates of the supply of mud and the production of gas.Key words: consolidation, unsaturated, disposal, experimental, validation, soft soil.
Lateral earth pressure at rest and compressibility of municipal solid waste
Authors: Landva A O , Valsangkar A J , Pelkey S G
Published: April 2011

The paper presents the results of laboratory testing of municipal solid waste samples subjected to one-dimensional compression with measurement of lateral stresses. The details of a large-size split-ring apparatus specially developed for this research are presented along with the data on earth pressure at rest and compressibility characteristics. The results show the influence of fibre content on the coefficient of earth pressure at rest in waste materials. The "delayed compression" behaviour observed in the laboratory is shown to be similar to the concepts developed by Bjerrum for normally consolidated sensitive marine clays. Issues such as validity of laboratory testing and sample-size effects are also discussed.Key words: earth pressure at rest, municipal solid waste, compressibility.
The effect of anisotropic elasticity on the yielding characteristics of overconsolidated natural clay
Authors: Sivakumar Vinayagamoorthy , Doran Isaac Gregg , Graham Jim , Johnson Arvee
Published: April 2011

Quantitative application of elastoplastic theory to the yielding behaviour of natural soils has always been uncertain. Part of the reason is that the theory was developed for reconstituted materials with isotropic structure, in contrast to natural soils that are usually anisotropic. The approach considered in this study assumes that pre-yielding behaviour is governed by the theory of linear anisotropic elasticity and that yield loci in the mean effective stress ( p')  deviator stress (q) plane are aligned approximately along the coefficient of earth pressure (K0) line. The assumption of a rotated yield locus associated with anisotropic elastic behaviour within the state boundary surface indicates that the elastic wall within the state boundary surface is inclined. The form of the state boundary surface has been determined mathematically in terms of anisotropic elastic and Cam-Clay soil parameters. Stress path tests were conducted on samples of Belfast Upper Boulder Clay removed from a depth of 28 m below ground surface. Good agreement was found between predicted and measured yield loci. The study also examined the influence of subsequent isotropic compression on the yielding characteristics of the natural clay. The indications are that the anisotropy developed during deposition disappears when the sample is loaded to a stress level at least twice the stress generated during the original deposition process. The methods developed in the paper have also been applied to test results reported previously on Winnipeg clay, and good agreement was obtained.Key words: sampling, anisotropy, elasticity, suction, stiffness, yielding.
Compressibility and hydraulic conductivity of a chemically treated expansive clay
Authors: Nalbantoglu Zalihe , Tuncer Erdil Riza
Published: April 2011

The paper presents a series of laboratory tests and evaluates the effect of lime and fly ash on the compressibility and hydraulic characteristics of an expansive soil in Cyprus. The tests were performed at different percentages of lime (07%) and fly ash (15 and 25%) by dry weight of soil, and additional tests were also performed on soils treated with 15% fly ash plus 3% lime. Previously published research reveals that few data are available concerning the compressibility and hydraulic conductivity of lime-treated soils. The results of this study indicate an increase in the vertical effective yield stress (apparent preconsolidation pressure) and a decrease in the compressibility characteristics of the treated soils. Moreover, unlike some of the findings in the literature, higher hydraulic conductivity values were obtained with time. This finding has been substantiated by the reduced cation exchange capacity (CEC) values, which indicate that the pozzolanic reaction causes the soils to become more granular in nature, resulting in higher hydraulic conductivity.Key words: cementation, compressibility, fly ash, hydraulic conductivity, lime.
Effect of cementation on the small-strain parameters of sands
Authors: Fernandez A L , Santamarina J C
Published: April 2011

Natural cementation affects the properties of soils, the interpretation of in situ and laboratory test results, and the selection of criteria for geotechnical design. In this paper, published experimental studies are reviewed, a microscale analysis is presented of the effect of cementation on small-strain stiffness for distinct stress-cementation histories, and the effect of cementation on small-strain velocity and damping is experimentally studied. Observations include the prevailing effects of cementation over effective stress, the coexistence of frictional and viscous losses, and the effects of decementation when the medium is unloaded from the level of confinement prevailing during cementation.Key words: wave velocity, seismic response, stiffness, damping, sampling effects, loading history.
Thermal performance of trench backfills used for frost protection of water service lines
Authors: Zhao Jack Q , Rajani Balvant B , Daigle Lyne
Published: April 2011

This paper describes the thermal performance of different configurations of trenches using various trench geometries and backfill and insulation materials. A limited number of laboratory tests were conducted to confirm the thermal properties of the backfills reported in the literature. The frost protection of water service is measured in terms of the number of days it takes for the frost front to reach the depth of water service lines under sustained subzero surface temperatures. The study specifically included typical granular materials used within the City of Ottawa (formerly the Region of Ottawa-Carleton), but the findings can be equally applied to other urban areas in Canada where the surficial terrain is rocky. The thermal analyses of the trenches were conducted using the finite element method that appropriately represents phase changes when the temperature falls below the freezing point of water. The analyses indicate that the use of sandwich insulation is ineffective, and that latent heat of backfill and native soils has a great impact on the frost protection of water service lines. A list of possible trench depths with different backfills and their thermal performance is provided.Key words: backfill, thermal performance, frost penetration, water service, finite element analysis.
Effect of microstructure on undrained behaviour of sands
Authors: Wan R G , Guo P J
Published: April 2011

This paper presents a mathematical modelling of the effects of initial fabric on the mechanical behaviour of sand. A stress-dilatancy model that incorporates microstructural aspects of sand is hereby obtained while writing energy conservation for an ensemble of particles over a representative elementary volume at micro- and macro-scales. The resulting stress-dilatancy model, when used within an elastoplastic framework, successfully reproduces certain aspects of sand behaviour that are reflective of its microstructure under both drained and undrained conditions. The role of microstructure in relation to the characterization of steady, quasi-steady, and phase-transformation states is discussed within the framework of the model. Numerical simulations obtained from the proposed model are generally very consistent with experimental observations and provide insightful information.Key words: sand, liquefaction, fabric, dilatancy, constitutive laws, granular materials, plasticity.
Electrokinetic strengthening of a marine sediment using intermittent current
Authors: Micic S , Shang J Q , Lo K Y , Lee Y N , Lee S W
Published: April 2011

An experimental program on electrokinetic strengthening of a marine sediment using intermittent current was conducted on a high-salinity marine clay recovered from a land reclamation site on the Korean coast. The study focused on the use of electrokinetics to enhance the effect of surcharge preloading consolidation to improve mechanical and physical properties of soil. This paper presents the design, execution, and results of the electrokinetic tests performed in a custom-designed electrokinetic cell. The test results demonstrate that electrokinetic treatment combined with preloading consolidation is an effective method of increasing the shear strength and decreasing the water content of the marine sediment beyond that achievable by preloading consolidation alone. For the same consolidation pressure over the identical time period, the increase in the average undrained shear strength of the marine sediment after electrokinetic treatment combined with preloading consolidation was up to 145% greater than that achieved by the preloading consolidation alone. A corresponding decrease in the soil water content of approximately 125% was measured. The power consumption and electrode corrosion are reduced by using intermittent current. The process developed in this research has potential applications in strengthening soft clayey soils at and around foundations of new onshore and offshore structures embedded in marine sediments and for rehabilitation of existing offshore platforms.Key words: marine sediment, electrokinetics, preloading consolidation, soil improvement, soil shear strength, land reclamation.
An analysis of long-term pile load tests in permafrost from the Short Range Radar site foundations
Authors: Biggar Kevin W , Kong Vivien
Published: April 2011

During the installation of the Short Range Radar (SRR) facilities at 35 sites across the Canadian Arctic, in excess of 7 000 piles were installed for the SRR foundations. A total of 137 pile load tests were performed during the SRR construction. Only a small number of these were installed external to the foundations and were loaded well in excess of design loads to attempt to determine their ultimate load carrying capacity. Only eight of these piles were loaded for extended durations (>12 h). This paper presents the results of these long-term load tests and compares the results with design guidelines based on allowable pile deformations and creep in ice-rich, saline permafrost. In nonsaline permafrost, at high normalized displacement rates (>30 year1) the stresses on the piles at failure were less than those predicted by design guidelines for piles in ice-rich soil. At lower normalized displacement rates (<15 year1) the failure stresses on the piles were reasonably well predicted by the design guidelines. Significant reductions in pile capacity were observed in ice-rich, saline permafrost. Without detailed knowledge of the unfrozen water content in the soil, however, prediction of the behaviour of the piles could only be bounded by current design guidelines.Key Words: permafrost, field pile testing, cold-temperature grout, long-term creep.
Failure and reconstruction of a gantry crane ballasted track
Authors: Raymond Gerald P
Published: April 2011

The paper deals with the reconstructions that were undertaken to correct multiple ballasted track foundation failures for a heavy gantry crane initially constructed in 1985. A satisfactory design was obtained in 1988 that incorporated geosynthetics.Key words: gantry crane, ballasted track, failure, reconstruction, geosynthetics, soil mechanics, foundation.
Canadian Geotechnical Research Site No. 1 at Gloucester
Authors: McRostie G C , Crawford C B
Published: April 2011

A parcel of land just south of Ottawa at Gloucester has been the site of an unusual amount of geotechnical research over the past 45 years. The parcel was recently to have been placed on the open real estate market but has been saved for scientific purposes and is now designated as "Canadian Geotechnical Research Site No. 1 at Gloucester". This paper presents an outline of the research that has been conducted at the site, in four general divisions, namely compressibility, strength, deformation, and soil property improvement. It is hoped that the site will stimulate the development and evaluation of new tools and techniques, foster scientific cooperation and information exchange, and allow the results of research involving the site to improve the state of practice, education, and research.Key words: sensitive clay, compressibility research, strength research, deformation research, soil improvement research.
Osmotic flow through a Cretaceous clay in southern Saskatchewan, Canada
Authors: Cey Bradley D , Barbour S L , Hendry M Jim
Published: April 2011

Clays and shales can act as semipermeable membranes, causing osmotic flow and (or) osmotically induced fluid pressures. Despite laboratory proof of the osmotic behaviour of clay-rich geologic material, the influence of this osmotic behaviour on in situ groundwater flow and solute transport is inconclusive. This is due in part to the lack of laboratory experimental work involving undisturbed core samples, and to the lack of field-scale research. The ability of undisturbed clay samples to conduct flow hydraulically and osmotically was investigated using dilute salt solutions. Undisturbed Cretaceous clay samples from southern Saskatchewan were used in a laboratory experimental program. The experiments included constant-head hydraulic conductivity (Kh) tests and osmotic flow tests conducted over a range of pore-fluid concentrations of 0.0541.12 equiv./L. The clay samples exhibited semipermeable membrane behaviour by conducting flow osmotically. The hydraulic conductivity of the clay increased by a factor of two as the pore-fluid concentration increased from 0.070 to 0.56 equiv./L. Osmotic efficiencies ranged from 0.0028 to 0.42 for concentrations from 0.84 to 0.096 equiv./L. Both the osmotic compressibility and osmotic efficiency decreased with increasing pore-fluid concentration. The behaviour of the clay was consistent with diffuse double-layer theory.Key words: osmotic flow, Cretaceous clay, salt, hydraulic conductivity.
A simplified nonlinear approach for pile group settlement analysis in multilayered soils
Authors: Lee K M , Xiao Z R
Published: April 2011

A simplified analytical method is presented for nonlinear analysis of the behaviour of pile groups under vertical loads. A hyperbolic approach is adopted to describe the nonlinear relationship between the shaft shear stresses and the relative shaft displacements along a confined disturbed soil zone around a pile-soil interface. Outside the disturbed zone, the soils are assumed to behave in a linearly elastic state. By adopting the elastic closed-form analytical solution to approximate the displacement fields around a single vertically loaded pile, and the principle of superposition, a new transfer function is presented for analysis of the behaviour of pile groups in multilayered soils. Furthermore, with a simplified assumption of separating the shaft from the base interaction factors for individual piles in a pile group, a highly effective iterative procedure is developed to examine the nonlinear loaddisplacement behaviour of a pile group up to the failure state. Comparisons of the loadsettlement responses for a number of well-instrumented field pile group test results are given to demonstrate the effectiveness and accuracy of the proposed analytical method. The computed nonlinear responses of the pile group compare favourably with measured field test results under both rigid and flexible pile cap conditions.Key words: pile groups, interface, transfer function, settlement analysis, nonlinear behaviour.
Interpretation of pressuremeter tests in sand
Authors: Silvestri Vincenzo
Published: April 2011

This paper presents a method to obtain the constitutive relationships of sand from drained self-boring pressuremeter tests. Plane-strain conditions and Rowe's stressdilatancy theory are assumed to hold to determine stress and finite strain distributions and paths. The proposed method, which has been validated using both calibration chamber studies and field tests, appears to correctly render the response behaviour of relatively loose to dense sands.Key words: stressstrain relations, self-boring pressuremeter tests, sands, finite strains, stress distributions, paths.
Some aspects of the compressibility behaviour of a clayey sand
Authors: Martins Flavia Burmeister , Bressani Luiz Antônio , Coop Matthew Richard , Bica Adriano Virgilio Damiani
Published: April 2011

The intrinsic behaviour of a residual clayey sand derived from sandstone was investigated in one-dimensional compression. The data show some interesting differences when compared with other published data, in that no unique normal compression line can be identified. Although the compressibility on first loading is similar to that for many sandy materials at states on their normal compression lines, the locations of the compression curves were found to be a function of the initial voids ratio, and there was no convergence at higher stresses. Tests on a model clay-sand mixture indicated that this behaviour is common to gap-graded clayey sands.Key words: sands, compressibility, oedometer tests.
Determination of plane-strain shear strength of sand from the results of triaxial tests
Authors: Hanna Adel
Published: April 2011

Experimental investigation of the shear strength of dry sands was carried out using triaxial and plane-strain apparatus. The results were used to evaluate Rowe's stressdilatancy theory, the relationships between the shear strength components due to friction and interlocking, and the volume-change characteristics for cases of plane-strain and axisymmetric boundary conditions. Because of the complexity of the plane-strain testing apparatus in the normal soil mechanics laboratory and the difficulties involved in performing this type of shear test, it is becoming costly to obtain plane-strain test results for consulting purposes. Based on Rowe's stressdilatancy theory, the results of the present investigation, and the available test results in the literature, two simple methods are proposed to predict the angle of shearing resistance for plane-strain conditions from the results of the conventional triaxial compression tests.Key words: shear strength, plane-strain test, triaxial test, sand, experimental investigation, geotechnical engineering.
The Resistance of Soil Structure to Consolidation
Authors: Crawford C B
Published: April 2011

The rate at which soil specimens are compressed in the standard consolidation test is farther from reality than the rate of strain in any other test. For a short period after the application of a load increment the rate of compression may be several million times faster than that experienced in the field. This paper describes a series of tests carried out at constant rates of compression varying from 0.16 to 8 per cent per hour in which pore pressures were measured. The effective stress-compression curves are compared with an average curve obtained by incremental loading. Based on these results, it is concluded that the compressibility of this soil is dependent on the average rate of compression and that the soil structure has a substantial time-dependent resistance to compression. This time-dependent resistance may be expected to have a significant influence on computed permeability coefficients and field rates of consolidation.
Settlement of an Embankment on Leda Clay
Authors: Burn K N , Hamilton J J
Published: April 2011

Before construction, standard consolidation tests indicated that the stresses imposed by a high embankment on a deep and relatively homogeneous deposit of Leda clay would exceed the preconsolidation stress and result in settlements of up to 18 in. Later, the results of more refined sampling and testing methods showed that the preconsolidation pressure had been underestimated by 1 ton/sq. ft. and that the imposed stresses would in fact fall within the recompression range. Time-settlement relationships, however, were not elastic; vertical strains continued to increase long after the embankment was completed. Field measurements of settlement are compared with values computed using compression moduli determined both from consolidation and compression tests in the laboratory.
Post-Peak Behaviour of Sensitive Clays in Undrained Shear
Authors: Ladanyi B , Morin J P , Pelchat C
Published: April 2011

The post-peak stress-strain behaviour in undrained shear of three different clays has been investigated by using an indirect method. This method, which is in principle similar to that used by Kallstenius (1963), consists in first compressing a clay specimen to a given post-peak strain between two parallel platens and subsequently determining its current remoulded strength by the laboratory vane method. By a repeated compression procedure, axial strains of up to 200 per cent have been attained. As the three clays tested differed widely in sensitivity, a comparison of their post-peak behaviour made clearly apparent the effect of structural breakdown on the reserve shear strength at large strains.
DYKES ON PERMAFROST, KELSEY GENERATING STATION, MANITOBA
Authors: Johnston G. H.
Published: April 2011

Performance studies of two major, but relatively small (2000-ft (~610m) long, maximum height 20 ft (6.1 m)), sand dykes constructed on perennially frozen ground were initiated in 1958 at the Kelsey Generating Station of Manitoba Hydro on the Nelson River. Permafrost occurred under these dykes in scattered islands or patches of variable thickness and size.Preliminary analyses, though only approximate, indicated that within a 50-year period significant thawing would occur beneath the dyke–water interface and that the permafrost under the reservoir would thaw completely. Ground settlements of as much as 6 ft (1.8 m) were to be expected as thawing took place. To check the estimated performance, field instrumentation was installed and an observational program begun in 1959.A distinct pattern of thawing and settlement each year has been observed. Major thawing and settlement occur during the summer months at rates that are greater than those experienced during the winter. The change in rate of thaw (and thus also the rate of settlement, which is partly a function of thawing) is directly connected with the change in water temperature or rate of heat flow into the ground.
The mechanics of landslides in Leda clay
Authors: Eden W. J. , Mitchell R. J.
Published: April 2011

An appraisal of the drained shear strength of Leda clay under low effective normal stresses has resulted in a new appreciation of its behavior in this stress range which can be applied to consideration of the stability of slopes. Closely spaced planes of weakness existing in the apparently intact clay give rise to dilatant behavior and predominantly frictional shearing resistance. This mode of failure is consistent with field observations that have been compiled from numerous landslides; three of these landslides are analyzed in this paper.
The Behavior of Piles Driven in Clay. II. Investigation of the Bearing Capacity Using Total and Effective Strength Parameters
Authors: Clark J. I. , Meyerhof G. G.
Published: April 2011

This paper outlines research of large model piles and some full scale piles driven into insensitive clay to study the phenomenon of load transfer and the effect of pile driving on the soil. It is divided into two parts. Part I dealt with the stress field set up by driving a large model pile into an instrumented clay bed and the stresses measured for some full scale timber piles. Part II presents an evaluation of the load carrying capacity of the model pile and compares the results with full scale load tests. Soil properties are evaluated in terms of effective stress for an estimate of the bearing capacity of the piles.The short term bearing capacity of the pile shaft and base can be estimated by conventional methods based on the undrained shearing strength of the clay at the time of driving. However, after several load cycles and for long term bearing capacity, closer estimates are obtained by use of the effective skin friction and shearing strength parameters from drained tests. Previous bearing capacity theory can be used for estimating the ultimate base capacity and an approximate theory is presented to estimate the average effective radial stress on the pile shaft in connection with the ultimate shaft capacities. This proposed approach is supported by observations in some clays of low sensitivity, but requires further research in other types of clays.
Finite Element Analysis of El Infiernillo Dam
Authors: Skermer N. A.
Published: April 2011

A simple trapezoidal element is presented for use in the analysis of thin core rockfill dams with nonlinear soil parameters. Handling of nonlinear soil parameters and allowance for the intermediate principal stress in plane strain problems are discussed. The analysis of El Infiernillo rockfill dam using trapezoids in the core and transitions, and variable Young's modulus and Poisson's ratio, reveals the transfer of stress that takes place around the core. Comparisons of strain observations at El Infiernillo Dam with results from the analysis are good, except in zones of compacted rockfill. It appears that the actual stiffness of compacted granular fills may be seriously underestimated, if soil parameters are based on data obtained from triaxial tests on normally consolidated samples. A fundamental understanding of soil deformation behavior would lead to an improvement in the finite element analysis of soil structure.