bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiple supernumerary chromosomes in the pseudogamous parthenogenetic flatwormPolycelis nigra: lineage markers or remnants of genetic leakage?
Authors: Sharbel Timothy F. , Beukeboom Leo W. , Pijnacker Laas P.
Published: May 2008

Polycelis nigra is a free-living simultaneous hermaphroditic flatworm that has amphimictic and pseudogamous parthenogenetic biotypes. Sexual individuals are always diploid (2n = 16) and pseudogamous parthenogens are polyploid (usually triploid). Two types of supernumerary chromosomes are found in parthenogens, those resembling autosomes ("A-like") and typical B chromosomes, both of which reach frequencies in populations of close to 100%. Experiments measuring the transmission rates of the B chromosomes indicated that they are potentially inherited via the male line, escaping expulsion by pseudogamous parthenogenesis. This study used the C-banding technique to demonstrate (i) that there is a single morphologically distinct B chromosome (B1) and (ii) that there are two "A-like" chromosomes that can be considered B chromosomes (B2 and B3) and which are not simple polysomics of one of the eight autosomes. As there is no genetic exchange between pseudogamous parthenogenetic lineages, two different individuals carrying a similar B morph must either have received it through common ancestry (a lineage marker) or have acquired it horizontally from another parthenogenetic lineage (leakage). C-banding further revealed intra-individual heteromorphy for band regions on chromosomes 5 and 8. This supports the karyotypic observation that oogenesis is preceded by premeiotic chromosome doubling followed by pairing of replicate homologues.Key words: B chromosome, C-banding, heterochromatin, heteromorphy, pseudogamous parthenogenesis.
Microisolation of the chicken Z chromosome and construction off microclone libraries
Authors: Zimmer Régis , Haberfeld Alon , Gibbins Ann M. Verrinder
Published: May 2008

A simple method was used to adapt a standard light microscope for the collection of chicken Z chromosomes from mitotic-metaphase spreads. The DNA of the collected chromosomes was enzymatically amplified using a partially degenerate primer. The resulting sequences, within a size range of 200–800 bp, were cloned to produce a Z chromosome DNA library, using blunt-end ligation into a SmaI-digested pUC18 plasmid (the SureClone system; Pharmacia, U.S.A.). The microcloning experiments produced 1250 clones; the size range of the cloned inserts was 250–800 bp, with an average of 480 bp (176 clones examined). Using male chicken genomic DNA as a probe, 10 out of 17 randomly selected clones showed strong positive signals on Southern blots, confirming the origin of the inserts as chicken DNA. In addition, the Z-chromosome origin of a selected microclone was verified in a semiquantitative Southern blot hybridization that showed positive signals with intensities that were approximately twice as strong for male (ZZ) as for female (ZW) chicken genomic DNA when the clone was used as a probe. The value of these libraries in further analysis of the chicken Z chromosome is discussed.Key words: microdissection, microcloning, chicken Z chromosome.
Comparative analysis of female and male meiosis in three meiotic mutants of tomato
Authors: Havekes Francis W. J. , Jong J. Hans de , Heyting Christa
Published: May 2008

Female meiosis was analysed in squash preparations of ovules from three meiotic mutants and wild-type plants of tomato. In the completely asynaptic mutant as6, chromosome pairing and chiasma formation were virtually absent in both sexes. In the partially asynaptic mutant asb, with intermediate levels of chromosome pairing at pachytene, there were a higher number of chiasmate chromosome arms in female meiosis than in male meiosis, whereas in the desynaptic mutant as5 there were normal levels of chromosome pairing at pachytene and a similar reduction in chiasma frequency in the two sexes. In wild-type tomato, we found slightly higher numbers of chiasmate chromosome arms in female meiosis than in male meiosis. We propose that the higher female chiasma frequencies in mutant asb and wild-type tomato result from a longer duration of female meiotic prophase. This would allow chromosomes more time to pair and recombine. It is possible that a longer duration of prophase I does not affect mutants as5 and as6, either because the meiotic defect acts before the pairing process begins (in as6) or because it acts at a later stage and involves chiasma maintenance (in as5).Key words: female meiosis, tomato, chiasma, mutant.
Seismic response of sands in centrifuge tests
Authors: Rayhani Mohammad H.T. , El Naggar M. Hesham
Published: May 2008

Seismic site response of sandy soils and seismic soil–structure interaction are investigated using an electrohydraulic earthquake simulator mounted on a centrifuge container at an 80g field. The results of testing uniform and layered loose to medium-dense sand models subjected to 13 simulated earthquakes on the centrifuge are presented. The variation of shear modulus and damping ratio with shear strain amplitude and confining pressure was evaluated and their effects on site response were assessed. The evaluated shear modulus and damping ratio agreed reasonably with laboratory tests and empirical relationships. Site response analysis using the measured shear wave velocity and estimated modulus reduction and damping ratio as input parameters produced good agreement with the measured site response. The effect of soil–structure interaction for structures situated on dry sand is also investigated. These tests have revealed many important insights with regard to the characteristics of seismic site response and seismic soil–structure behaviour. The tests showed that the seismic response of soil deposits, input motions, and overall behaviour of the structure are affected by soil stratification. The results showed that the seismic kinematic soil–structure interaction is not very significant for structures situated on loose sand.
A new modelling approach for unsaturated soils using independent stress variables
Authors: Sheng Daichao , Fredlund Delwyn G. , Gens Antonio
Published: May 2008

Although a number of constitutive models for unsaturated soils exist in the literature, some fundamental questions have not been fully answered. There are questions related to (i) the change of the yield stress with soil suction, (ii) modelling slurry soils, and (iii) the smooth transition between saturated and unsaturated soil states. This paper addresses these questions by proposing an alternative modelling approach. The paper first presents a volumetric model for unsaturated soils. This volumetric model is then used to derive the yield surface in the suction – mean stress space. Hysteresis associated with soil-water characteristic curves is then formulated in the same framework of elastoplasticity. It is shown that volume collapse during wetting and plastic shrinkage during initial drying are both direct results of a suction-dependent hardening law. The proposed model seems to be more flexible in modelling different types of unsaturated soils than most models in the literature. The model can be applied to soils that are dried or loaded from initially slurry conditions, for soils that have low to high air-entry values, and for compacted soils as well.
Target reliability based design optimization of anchored cantilever sheet pile walls
Authors: Basha B. Munwar , Babu G. L. Sivakumar
Published: May 2008

In this study, the stability of anchored cantilever sheet pile wall in sandy soils is investigated using reliability analysis. Targeted stability is formulated as an optimization problem in the framework of an inverse first order reliability method. A sensitivity analysis is conducted to investigate the effect of parameters influencing the stability of sheet pile wall. Backfill soil properties, soil – steel pile interface friction angle, depth of the water table from the top of the sheet pile wall, total depth of embedment below the dredge line, yield strength of steel, section modulus of steel sheet pile, and anchor pull are all treated as random variables. The sheet pile wall system is modeled as a series of failure mode combination. Penetration depth, anchor pull, and section modulus are calculated for various target component and system reliability indices based on three limit states. These are: rotational failure about the position of the anchor rod, expressed in terms of moment ratio; sliding failure mode, expressed in terms of force ratio; and flexural failure of the steel sheet pile wall, expressed in terms of the section modulus ratio. An attempt is made to propose reliability based design charts considering the failure criteria as well as the variability in the parameters. The results of the study are compared with studies in the literature.
Triaxial and Plane Strain Creep Rupture of an Undisturbed Clay
Authors: Campanella R. G. , Vaid Y. P.
Published: May 2008

A comparative study of the undrained creep rupture characteristics of a saturated, normally consolidated, undisturbed marine clay has been carried out under triaxial and plane strain conditions. Creep rupture tests were performed on samples which were consolidated both isotropically and under K0 conditions to the same vertical effective stress. It is shown that for a given minimum creep rate or creep stress, large differences in rupture life are observed between conventional isotropically consolidated triaxial samples and K0 consolidated triaxial or plane strain samples. Similar discrepancies are introduced when conventional triaxial results are used to estimate remaining rupture life during tertiary creep stage when the real situation corresponds to either K0 consolidation or plane strain. Effective stress failure in creep rupture for a given type of test is governed by the same linear failure envelope which is obtained during constant rate of shear testing.
Behavior of a Cemented Plastic Clay as an Embankment Foundation
Authors: Lefebvre Guy , Lefebvre Liguori M. , Rosenberg Peter
Published: May 2008

A 32 ft (10 m) high embankment has been built at Matagami, Quebec, on a varved clay deposit of the glacial lake Barlow–Ojibway. This paper reports on some aspects considered in the design, mainly the cementation and the high plasticity of the clay. The variation of settlements and pore pressure is presented and indicates that, 8 months after construction, the pore pressure dissipation is very small while the measured settlements reach 18 in. (45 cm).Triaxial tests, with various consolidation times, were carried out on specimens cut from undisturbed block samples obtained in the same area, in order to study the effect of consolidation on the shear strength of these cemented clays. Results indicate that the undrained shear strength decreases during consolidation until the degree of consolidation reaches 50%. This phenomenon together with the non-dissipation of pore pressure in the field is attributed to the collapse of the cemented structure when the applied pressure exceeds Pc.Similar behavior reported for two other cases of embankments built on deposits of the same origin, leads to the conclusion that the stage construction method is not suitable for embankment on cemented clays, at least those from the glacial lake Barlow–Ojibway, because no gain in shear strength is recorded over a normal consolidation period.
Slope Stability Analysis in Anisotropic Winnipeg Clays
Authors: Freeman W. S. , Sutherland Hugh B.
Published: May 2008

Two major aspects of an investigation dealing with the stability of natural and cut slopes in the Winnipeg area are described. The first concerns an experimental investigation of the anisotropic shear strength characteristics of the layered Lake Agassiz clays and the second is a study of the mechanism of failure for slopes in these layered clays.Four main types of clay were investigated and it was found that the effective shear strength parameters were greater for failure across the layers than for failure along the layers. Residual shear strength parameters were also determined.Stability analyses were carried out for representative slope cross sections using circular and noncircular failure surfaces, taking into account the anisotropic shear strength effects measured in the laboratory tests.Factors of safety were found for the conventional method of analysis assuming circular arc failure surfaces and isotropic shear strength properties. These factors of safety were found to be up to 0.5 greater than those obtained from noncircular failure surfaces which partially passed along the layers and so mobilized the lower shear strength properties of these layers.
Immediate Settlements of Three Test Embankments on Champlain Clay
Authors: Tavenas F. A. , Chapeau C. , Rochelle P. La , Roy M.
Published: May 2008

As part of an extensive field testing program, three full scale test fills were built on a soft Champlain clay deposit in Saint-Alban, Quebec.The fills were built to the same height of 11 ft (3.3 m) but with different slopes of 1.5/1, 2.5/1, and 4/1, and with resulting factors of safety of 1.24, 1.32, and 1.52. The foundations were heavily instrumented.From the observed construction behavior it was shown that the foundations behave elastically up to a critical height equal to 6, 8, and 9 ft (1.8, 2.4, and 2.7 m), respectively, or to about 50% of the failure height of each fill. Beyond this limit, local yielding of the clay occurred.The behavior in the elastic phase could be predicted adequately on the basis of CIU tests, provided Poisson's ratio be assigned a value of 0.3 instead of the usual 0.5. To obtain an adequate settlement prediction over the full range of heights, the finite element method could be used but a modified clay model should be developed which includes a yield criterion in addition to the classical failure criterion and which allow for a certain compressibility of the clay at yielding.
An Evaluation of the Stability of Natural Slopes in Plastic Champlain Clays
Authors: Lo K. Y. , Lee C. F.
Published: May 2008

A method of stability analysis was developed to accommodate the distinctly nonlinear nature of the strength envelopes for Champlain Sea clays in the low stress range appropriate to stability problems. Using this method an evaluation of natural slope failures in Champlain Sea clays was carried out based on strength characteristics determined with block samples from the sites of recent slides in Quebec. In view of some similarities in geotechnical properties and shear behavior, the strength characteristics so determined were also used to examine some of the recent slides in the Ottawa area. The results of stability analysis for eleven slides indicate that the field strength generally approaches the post-peak condition.To verify this condition, the state of stress of two slopes before sliding was determined by a finite element method accounting for work-softening behavior. The results of analysis show that the post-peak factor is very close to unity in the Quebec sites. The same observation may be applied to the slides in the Ottawa areas, provided that the post-peak strengths of the clays in these areas are verified.
Contrôle de la stabilité des remblais par la mesure des déplacements horizontaux
Authors: Marche René , Chapuis Robert
Published: May 2008

The horizontal displacements measured at the toe of eight embankments are analyzed as a function of the factor of safety. The embankments are built on layers of soft clay. Only the undrained stage is studied.When the factor of safety of the embankments is higher than about 1.4, the horizontal displacements on the ground surface, at the toe of the embankment seem to follow an elastic law which is highly dependent on the ratio of the thickness of the soft layer to the width of the embankment. When the factor of safety is lower than about 1.4, the horizontal displacements do not follow an elastic law, they increase considerably. Consequently, it is suggested that the horizontal displacements be precisely measured at the toe of embankments during construction. These measurements are simple and sensitive to the approach of failure, they can be efficiently used to control the stability of embankments. This study also gives some information concerning the variation of horizontal displacements versus depth.
Thaw–Consolidation Tests on Undisturbed Fine-grained Permafrost
Authors: Nixon J. F. , Morgenstern N. R.
Published: May 2008

A series of thaw–consolidation tests on undisturbed frozen samples of Arctic soils is described. The tests were carried out in a special oedometer, and thawing was induced by the application of a sudden constant increase in surface temperature. Settlements, pore water pressures, and rates of thaw are measured, and interpreted in the light of current theories of heat transfer and thaw–consolidation. Excellent agreement is obtained between predicted and observed thaw rates, using published thermal properties. The observed pore pressures and settlements also are consistent with predicted behavior.These test results on a variety of undisturbed permafrost samples increase the level of confidence when applying the theory of consolidation for thawing soils to natural permafrost deposits.
An efficient three-dimensional soil–structure interaction model for analysis of earth retaining structures
Authors: Vaziri H. H. , Troughton V. M.
Published: May 2008

Using the integrated form of Mindlin's equations that relate the stress and displacement field anywhere within a three-dimensional space in an isotropic and elastic soil medium, a boundary-element-based numerical model is presented for analyzing soil–structure interaction problems involving excavations around embedded structures. The solution procedure involves combining the stiffness matrix of the wall and soil system and computing the displacements from a knowledge of the stress changes due to excavation. An interative approach is adopted to apply the correcting forces at locations that reach active or passive states, thus resulting in correct displacements for plastic conditions that cannot be accounted for by the Mindlin's elastic solutions. The model is shown to provide matching results against a finite-element model under plane-strain conditions. Application of the proposed model within the context of a practical project has demonstrated its role both as a predictive tool and as a theoretical model for performing sensitivity analysis and establishing practical guidelines to control magnitude and mode of wall deflections, which are important design considerations in excavations close to movement-sensitive structures. Key words : numerical modelling, elasticity, three-dimensional effects, soil–structure interaction, retaining wall, excavation.
Standard penetration test energy measurements using a system based on the personal computer
Authors: Robertson Peter K. , Woeller David J. , Addo Kofi O.
Published: May 2008

According to the International Reference Test procedure for the standard penetration test (SPT), in situations where comparisons of SPT results are important, calibrations should be made to evaluate the efficiency of the equipment in terms of energy transfer. However, equipment to measure the energy transfer of the hammer anvil system is not commonly available. Ten years ago a system was developed and made commercially available. However, this system is no longer available. An SPT energy calibration system is described that has been developed based on a microcomputer. The load cell to measure the compressive stress wave beneath the SPT anvil consists of a 0.5-m length of strain-gauged AW rod. Specialized software has been developed to record the force–time record for each hammer blow on a portable microcomputer. Examples of energy measurements are presented and discussed. Key words : standard penetration test, in situ, microcomputer, energy.
Shear-wave velocity measurement of soils using Rayleigh waves
Authors: Addo K. O. , Robertson P. K.
Published: May 2008

A modified version of the spectral analysis of surface waves (SASW) equipment and analysis procedure has been developed to determine in situ shear-wave velocity variation with depth from the ground surface. A microcomputer has been programmed to acquire waveform data and perform the relevant spectral analyses that were previously done by signal analyzers. Experimental dispersion for Rayleigh waves is now obtainable at a site and inverted with a fast algorithm for dispersion computation. Matching experimental and theoretical dispersion curves has been automated in an optimization routine that does not require intermittent operator intervention or experience in dispersion computation. Shear-wave velocity profiles measured by this procedure are compared with results from independent seismic cone penetration tests for selected sites in western Canada. Key words : surface wave, dispersion, inversion, optimization, shear-wave velocity.
Analytical model for an innovative pile test
Authors: Naggar M. H. El , Novak M.
Published: May 2008

In recent years a new type of pile test employing a short-duration load was developed that became known as pile statnamic test. The paper describes a method of dynamic analysis specifically formulated for this test. The aim of the analysis is twofold: to calculate the pile load displacements in such a way that a satisfactory match with the data measured during the test is obtained; and using the model parameters established from this comparison to predict the bearing capacity of the pile. The mathematical model is one-dimensional and accounts for slip as well as energy dissipation in the far field. Unlike the empirical parameters of the Smith model for pile driving analysis, the parameters of the proposed model are, for the most part, directly related to standard geotechnical parameters. The case studies conducted thus far and described in the paper indicate that the proposed mathematical model works very well and that the statnamic test may become a useful tool for pile capacity prediction. Key words : piles, pile driving, dynamic response, dynamic tests, bearing capacity.
Probabilistic bearing capacity analysis of jack-up structures
Authors: Nadim Farrokh , Lacasse Suzanne
Published: May 2008

A probabilistic approach to the analysis of the bearing capacity of jack-up spud can foundations is described. The procedure includes three steps: (i) a priori deterministic and probabilistic calculation of bearing capacity interaction diagram for the soil foundation under each leg of the jack up, (ii) updating of the interaction diagram from the measured vertical preloading values, and (iii) one-leg component and multileg system reliability analyses of the structure under environmental loads. The probabilistic formulation is based on the first- and second-order reliability approximations. An example calculation of a jack-up spud can structure on a layered clay profile is made to illustrate the procedure. Key words : jack up, bearing capacity, probabilistic analysis, system reliability.
Stability of unsupported tunnels in clay
Authors: Eisenstein Z. , Samarasekera L.
Published: May 2008

An overall long-term stability of unsupported shallow tunnels in overconsolidated clays which is directly related to the stand-up time is investigated. A new approach that combines finite element methods and the limit equilibrium theory is used to overcome limitations of current design practice. A more realistic initial stress field, unloading due to excavation, and variation of strength and modulus with depth are used. The pore-pressure change is analysed using a finite element model that incorporates an uncoupled consolidation theory. These pore pressures along with the previously obtained stress field are utilized to predict the variation of stability with time for given soil parameters such as strength and coefficient of earth pressure at rest. The results obtained employing a simple mechanism are presented using non-dimensional quantities. These results relate time, stability of the tunnel, and soil strength. The analysis showed that, under certain circumstances, the initial undrained stability may be of no practical value and may only be used as a starting point for more practical long-term stability. This procedure explains the stand-up time phenomenon in tunnels and may also be used in design as a direct tool for its evaluation. Key words : overconsolidated clay, long-term stability, stand-up time, shallow tunnels, finite elements, limit equilibrium.
The rockslide and debris flow from Mount Cayley, B.C., in June 1984
Authors: Cruden D. M. , Lu Z. Y.
Published: May 2008

A major rockslide and debris flow occurred on Mount Cayley, British Columbia, in June 1984. Approximately 3.2 million cubic metres of volcanics travelled 2.0 km down Avalanche Creek at velocities up to 35 m/s to dam the confluence of Avalanche and Turbid creeks. The breaking of the landslide dam caused an extremely fast debris flow. The velocity of the debris flow and associated wind gusts, up to 34 m/s, caused superelevations, hurled rocks and wood through the air, uprooted trees, and spattered mud 16 m up trees. The debris flow removed the logging road bridge and road approaches at the mouth of Turbid Creek, blocked the Squamish River during surges, and introduced huge quantities of sediment to the Squamish River. The uniaxial compressive strength of wet tuff collected from the head scarp of the rock slide is 1.0–1.5 MPa, about two thirds of the strength of dry specimens, the friction angle on wet tuff bedding surfaces is 30°, and the slake durability index is 26%. Weak tuffs form the rupture surface of the 1984 rockslide on Mount Cayley, and their slaking contributed fines to the debris flow. The tuff, steep, narrow creeks intersecting at high angles, high precipitation, and snow and ice accumulation in creeks combine to make the western slopes of Mount Cayley extremely hazardous. Key words : rockslide, debris flow, volcano, landslide dam, Coast Mountains.
Interpretation of field vane strength of an anisotropic soil
Authors: Garga Vinod K. , Khan Mahbubul A.
Published: May 2008

Determination of the undrained shear strength (Su) of overconsolidated soils such as the weathered clay crust overlying Leda clay is important for the design of shallow foundations and embankments. In situ vane shear tests and isotropically consolidated undrained triaxial tests have been conventionally used for this purpose. Contrasting test results from these two methods, low Su obtained from triaxial tests and high Su obtained from in situ vane shear tests, motivated further research into this problem. Strength anisotropy, due to in situ anisotropic state of stress and orientation of soil fabric during deposition, is believed to be the reason for these contrasting results. Improved testing and interpretation techniques for this type of anisotropic soil have been proposed. Weathered crusts are generally heavily over-consolidated, with K0 values greater than unity. Undrained triaxial shear tests conducted to date by various researchers are either isotropically consolidated or are anisotropically consolidated assuming K0 smaller than unity. Neither of these two methods represents the in situ state of stress of a clay crust. Therefore, in this investigation, the undisturbed samples were reconsolidated anisotropically to the in situ state of stress (K0 > 1) before shearing undrained in the triaxial test. Direct shear tests on horizontal and vertical specimens consolidated to normal stresses equal to σvo′ and σho′, respectively, were also conducted to investigate the strength anisotropy. Field vane tests have been reinterpreted in terms of this strength anisotropy. The undrained shear strength on top and bottom horizontal planes (Suh) obtained from these field vane tests within the crust provided comparable results with those from laboratory triaxial and direct shear tests which were reconsolidated to in situ stresses. Key words : in situ vane test, undrained shear strength, strength anisotropy, rate effect, anisotropic in situ state, weathered clay crust, overconsolidation.
Rock mass characterization around Saskatchewan potash mine openings using geophysical techniques: a review
Authors: Gendzwill D. J. , Stead D.
Published: May 2008

Saskatchewan potash deposits are found in relatively uniform, flat-bedded strata with few irregularities. Potash mines are highly automated and efficient, taking advantage of the uniform strata. However, anomalous geological conditions can lead to severe problems, especially with water inflows. One mine has been lost to flooding, and other mines now have or previously had large inflows of water. Geophysical techniques, especially the method of vertical seismic reflection from the surface, are used to predict anomalous geological conditions. Seismic, electric, and other geophysical methods are also used underground, sometimes in boreholes, to detect conditions around the mine openings such as the thickness of the salt cover over the mine, fractures around the opening, shale beds, the presence of water, and other rock properties. The mines generate seismic activity ranging from magnitude 3.7 earthquakes to tiny micro-earthquakes, and various field monitoring and laboratory testing programs have analyzed these. To avoid hazards discovered by geophysical methods, mine managers have often changed their plan of operation or even deleted large ore reserves. Key words : geophysics, potash mining, seismic, earthquakes.
Seismic cone penetration test for evaluating liquefaction potential under cyclic loading
Authors: Robertson P. K. , Woeller D. J. , Finn W. D. L.
Published: May 2008

Impressive progress has been made in the last 25 years in recognizing liquefaction hazards, understanding liquefaction phenomena, and analyzing and evaluating the potential for liquefaction at a site. Recent findings related to the application of the seismic cone penetration test (SCPT) for the evaluation of liquefaction potential under cyclic loading are presented and discussed. The SCPT provides independent measurements of penetration resistance, pore pressures, and shear-wave velocity in a fast, continuous, and economic manner. The current methods available for evaluating liquefaction using penetration resistance are presented and discussed. Recent developments in the application of shear-wave velocity to evaluate liquefaction potential are discussed, and a new method based on normalized shear-wave velocity is proposed. Limited case-history data are used to evaluate and support the proposed correlation. A worked example is presented to illustrate the potential usefulness of the SCPT for evaluating liquefaction potential at a site. Key words : liquefaction, in situ tests, seismic.
Nonlinear vibration of pile groups under lateral loading
Authors: Vaziri Hans H. , Han Yingcai
Published: May 2008

Dynamic response of a pile group, comprising six full-size cast-in-place reinforced concrete piles, is investigated under varying levels of lateral harmonic excitation in two directions: along a plane composed of three piles (X-direction) and along a plane normal to it composed of two piles (Y-direction). The measured response is compared with the theoretical predictions using the dynamic interaction factors approach. To account for the nonlinear response of the pile group using the theoretical model, provisions are made for yielding of soil around the piles by introducing the boundary-zone concept. It is shown that the proposed theory adequately captures the measured response of the pile group under both linear (weak excitation) and nonlinear (strong excitation) conditions. The study performed indicates that although the rocking stiffness of the pile group is strongly influenced by the number of piles along the direction of excitation, the horizontal stiffness remains virtually unaffected. The results obtained show that the stiffness and damping ratio of the pile group reduce as the excitation intensity increases. It is also found that the pile–soil–pile interaction plays a major role in the overall dynamic response of the pile group; this effect is manifested by a reduction in the stiffness and an increase in the damping of the pile group. Key words : dynamics, vibration, piles, pile group, nonlinear vibration, full-scale tests, modelling, resonance, soil separation, soil yielding.
A numerical and experimental study of the artificial freezing of sand
Authors: Gioda Giancarlo , Locatelli Livio , Gallavresi Francesco
Published: May 2008

A study is presented of the transfer of heat within a saturated sand with reference to the analysis of artificial freezing of the ground. First, the main characteristics of the adopted finite element approach and of the technique that introduces the latent-heat effects during the water–ice phase transition are illustrated. Subsequently, the results of some laboratory freezing tests are presented on the basis of which the computer program and the procedure for working out the thermal constants of the soil were calibrated. Finally, a parametric study is discussed that concerns the effects of pipe diameter, distance between pipes, and coolant temperature on the progress of the 0 °C isotherm. Key words : artificial freezing, finite elements, heat transfer, laboratory test, Stefan problem.
Risk-reduction factor for bearing capacity of shallow foundations
Authors: Basma Adnan A.
Published: May 2008

In this paper an ultimate bearing capacity risk-reduction factor is proposed to account for the variation and randomness in soil properties. Through a first-order Taylor series expansion, the mean and variance of the ultimate bearing capacity were assessed. Consequently, the variation of the ultimate bearing capacity is expressed as a function of the variation in cohesion and internal friction angle. To develop a risk-reduction factor, several probability density functions were utilized. The asymptotic type II extreme-value distribution for maxima was found best suited to represent the ultimate bearing capacity. The results indicate that the risk-reduction factor FR decreases with an increase in the coefficient of variation of ultimate bearing capacity and a decrease in the selected probability of failure pf. For pf = 0.0001, however, FR was found to range between 0.20 and 1.0. A numerical example is presented to illustrate the use of the proposed reduction factor. Key words : bearing capacity, coefficient of variation, probability distribution, probability of failure, risk factor, shallow foundations.
Stress-level effects in model tests on piles
Authors: Craig William H. , Sabagh Suhail K.
Published: May 2008

Results are presented from several series of centrifuge model tests of piles installed in beds of uniform dry sand. Using identical model geometries, but varying acceleration factors, the tests demonstrate quite clearly the nature and extent of stress-level variations on the performance of piles. The results are interpreted initially in terms of bearing capacity coefficients Nt and lateral earth pressure coefficients Ks, and subsequently in terms of angle of friction [Formula: see text], determined using available relationships. Controlled laboratory experiments with varying levels of overburden pressure around the piles indicated consistent reductions in Nt, and to a lesser extent in Ks. Quantitative interpretations in terms of angle of friction variations depend on selection from a range of empirical correlations available and have been made for two of those commonly used. Comparison of shaft loads in compression and extension confirms the widespread belief that there is a difference, which is found to vary quantitatively depending on the relative density. Key words : model tests, piles, sand, centrifuge, stress level.
Equivalent times and one-dimensional elastic viscoplastic modelling of time-dependent stress–strain behaviour of clays
Authors: Yin Jian-Hua , Graham James
Published: May 2008

This paper describes the recent concept of equivalent time and how it can be used in a revised version of an earlier elastic viscoplastic model for one-dimensional straining of clays. It clarifies how parameters in the model can be determined using data from single-stage or multistage creep tests. The model can describe one-dimensional stress or strain responses under general conditions that include multistage loading with creep straining, continuous loading, and unloading or reloading. It also describes modelling for constant rate of straining tests, constant rate of stressing tests, and relaxation tests. Preconsolidation pressures are shown to depend on unloading–reloading, aging, and other loading processes. Key words : clay, compression, creep, equivalent time, elastic viscoplastic, preconsolidation pressure.
Laboratory and field determinations of small-strain shear modulus for a structured Champlain clay
Authors: Lefebvre Guy , Leboeuf Denis , Rahhal Muhsin E. , Lacroix Alain , Warde Joseph , Stokoe II Kenneth H.
Published: May 2008

Values of small-strain shear modulus Gmax, for a Champlain Sea clay deposit were obtained both under an embankment built 18 years ago, and outside of the area influenced by this embankment. The small-strain shear moduli Gmax were measured in the laboratory by using resonant column tests and in the field by spectral analysis of surface waves. In addition to verifying the two methods, comparison of the in situ and laboratory values allowed evaluation of the influence of the sampling and the need to correct the laboratory values to account for the age of the deposit. The test program also made it possible to verify the influence of the deposit's consolidation and the existing models predicting small-strain shear moduli in clay deposits. Key words : shear modulus, shear-wave velocity, resonant column, in situ test, surface waves, soft clay.
Large-strain undrained pressuremeter interpretation based on loading and unloading data
Authors: Ferreira R.S. , Robertson P.K.
Published: May 2008

Traditionally pressuremeter tests results are interpreted using only the loading pressure–expansion data. An interpretation method has been developed that makes use of both the loading and unloading portions of a pressuremeter test and incorporates nonlinear, undrained soil behaviour. This method has been modified to handle large trains. The proposed interpretation accepts that some level of soil disturbance exists during the early stages of a pressuremeter test, and hence more emphasis is placed on the unloading portion of the test. A methodology is described to allow this interpretation procedure to be applied to self-bored, prebored, and full-displacement undrained pressuremeter tests. The proposed method is evaluated using self-boring and full-displacement pressuremeter test results from various published field projects. The interpretation is accomplished using commercially available microcomputer software that can perform the curve-matching process for both loading and unloading portions of the test. Key words : pressuremeter, loading data, unloading data.
An analytical study of cone penetration tests in granular material
Authors: Huang An-Bin , Ma Max Y.
Published: May 2008

A numerical technique that couples the distinct-element and boundary-element methods was developed to simulate a granular soil deposit as a two-dimensional, circular disk assembly. A series of simulated penetration tests of a 60° apex angle cone was performed in normally consolidated and overconsolidated disk assemblies. The simulations allowed the cone penetration mechanisms to be evaluated from microscopic as well as the conventional, continuum mechanics points of view. Results show that the soil loading history can affect the characteristics of the soil failure mechanism and dilatancy. Lateral stress measurement behind the cone base is not sensitive to soil loading history. Finer particles appear to experience higher contact stresses and hence are more likely to be crushed by the cone penetration. Key words : cone penetration, sand, shear strength, loading history, distinct-element method.
The effect of a nonlinear Mohr–Coulomb criterion on borehole stresses and damage-zone estimate
Authors: Wang Yarlong
Published: May 2008

To investigate the possible error introduced by the assumption of a linear Mohr–Coulomb criterion on the stress distribution near a circular opening, a numerical approach is used to calculate both the damage-zone radius and the stresses near a circular opening. A general solution procedure for the stress calculation under a uniform far-field loading is presented and a closed-form solution for the near-opening stresses is given for a cohesionless medium. Based on the numerical results calculated, it is concluded that the linear assumption is acceptable for a strong rock with an unconfined compressive strength that is of similar magnitude to the far-field stress. However, the tangential stress calculated with this linear assumption may be overestimated, but the damage zone may be underestimated in weaker rock or soil such as an oil sand formation. Key words : Mohr–Coulomb criterion, circular opening, nonlinearity, oil sands, Gauss–Legendre method.
Sample disturbance from shear wave velocity measurements
Authors: Sasitharan S. , Robertson P.K. , Sego D.C.
Published: May 2008

Effective techniques are currently available to obtain undisturbed samples of cohesive soils. However, little advance has been made in the procurement of undisturbed samples of cohesionless soils such as sands, silty sands, and clayey sands. In the area of earthquake design and liquefaction, researchers and practitioners are becoming increasingly aware of the importance of obtaining high-quality undisturbed samples of cohesionless soils. In situ ground-freezing techniques can be used to obtain undisturbed samples of cohesionless soils. However, there is still concern regarding the possibility of disturbance during the freezing and thawing of the samples. Shear wave velocity is a direct measurement of the stiffness of the soil skeleton at small strains (<10−4%). Hence, shear wave velocity can be a sensitive measurement to detect changes in void ratio and soil structure due to freezing and thawing. A laboratory study has been performed to evaluate the use of shear wave velocity measurements to detect sample disturbance due to freezing and thawing of cohesionless soils. Samples prepared with different amounts and type of fines were frozen using uniaxial freezing techniques and subsequently thawed. Shear wave velocity measurements were made before and after freezing and thawing of the reconstituted samples. The measured shear wave velocities were unchanged for samples that did not heave (undisturbed) during the freeze–thaw cycle. Samples that heaved (disturbed) showed an associated change in shear wave velocity. Hence, measurements of shear wave velocities in situ and in the laboratory have the potential to identify sample disturbance in granular soils. Key words : in situ, sampling, freezing, disturbance, shear wave velocity.
Acclimation to low temperature is associated with an increase in long-chain acyl-CoA synthetase in rainbow trout (Oncorhynchus mykiss) heart
Authors: Hicks Jason M. T. , Bailey John R. , Driedzic William R.
Published: May 2008

Rainbow trout (Oncorhynchus mykiss) were acclimated to 5 and 15 °C. Uptake of radiolabelled palmitate by isolated cardiomyocytes was linear for at least 65 min. Myocytes from fish acclimated to 5 °C and tested at 5 °C showed higher rates of uptake than those from fish acclimated to 15 °C and tested at 5 °C. There was no significant difference in fatty acid uptake between myocytes from fish acclimated to 5 and 15 °C and tested at their respective acclimation temperature. Acclimation temperature had no effect on levels of intracellular fatty acid binding protein or carnitine palmitoyltransferase. However, acclimation to low temperature resulted in a twofold enhancement in fatty acyl-CoA synthetase activity, which increased in a linear fashion over a 28-day period. An increase in fatty acyl-CoA synthetase, which occurs on the outer mitochondrial membrane and the endoplasmic reticulum, is possibly related to low temperature-induced changes in fatty acid oxidation and synthesis of complex lipids.
Availability and consumption of food by common eiders wintering in the Gulf of St. Lawrence: evidence of prey depletion
Authors: Gulllemette Magella , Himmelman John H. , Reed Austin
Published: May 2008

To quantify the influence of common eiders (Somateria mollissima) on their food supply in the Gulf of St. Lawrence, eastern Canada, we measured prey availability and patch utilization during two consecutive winters. In this region, eiders fed predominantly near submerged reefs where large populations of blue mussels (Mytilus edulis) and green sea urchins (Strongylocentrotus droebachienensis) were present. Density and biomass of mussels and urchins were estimated for two reefs at the beginning of the winter of 1985 – 1986 using SCUBA and quadrat sampling. Prey selection was assessed by comparing the size of prey from stomach contents of shot eiders with that of prey found in the habitat. Patch use was quantified from elevated blinds by regularly counting eiders from December to April. Mussels in the habitat were small (mean length 6.5 mm) and formed dense beds (mean density 25 398 individuals/m2), whereas urchins were large (mean diameter 35 mm) and occurred at lower densities (114 individuals/m2). However, the average biomass for these two prey species was similar, 2.8 and 3.1 kg wet mass/m2 for mussels and urchins, respectively. The mussels eaten by common eiders tended to be larger than the average size of those available. In contrast, urchins eaten were smaller than the average size present in the habitat. Depending on the reef, consumption of food by eiders ranged from 48 to 69% of the biomass for eiders feeding on mussels and from 3 to 6% of the biomass for urchins. We compared these estimates with those from similar studies and concluded that eiders substantially deplete mussel beds in winter, which in turn seems to affect their distribution.
Genotyping North American black flies by means of mitochondrial ribosomal RNA sequences
Authors: Tang Jianming , Pruess Kenneth , Unnasch Thomas R.
Published: May 2008

Subregions in the mitochondrial small (12S) and large (16S) subunits of rRNA genes were amplified by polymerase chain reaction (PCR) from 14 species of North American black flies and assayed using directed heteroduplex analysis (DHDA). All 14 species could be distinguished from one another on the basis of the diagnostic mobilities of their heteroduplex products in either 12S or 16S DHDAs, utilizing PCR products derived from Simulium bivittatum as probes. Only minimal intraspecific variations were noted for two sibling species of Simulium vittatum s.l. collected from 10 locations, while S. luggeri appeared to have multiple mitochondrial haplotypes. DHDA banding patterns based on mitochondrially encoded sequences are shown to be an informative and easily interpreted taxonomic character, which should prove useful for future studies of black fly taxonomy and ecology.