bluuebunny/crossref_metadata_2025 huggingface dataset:
Anion exchangers in the red cell and beyond
Authors: Casey Joseph R , Reithmeier Reinhart AF
Published: April 2011

The anion exchanger genes (AE1-3) encode a family of transport proteins responsible for the electroneutral exchange of bicarbonate and chloride across membranes. These transporters are important in processes such as pH regulation and bicarbonate metabolism. This article reviews recent progress in this field based on presentations made at a satellite workshop on anion exchangers held in conjunction with the 8th Fisher Winternational Symposium on Cellular and Molecular Biology entitled "Membrane proteins in health and disease." The transmembrane topology of AE1 has been refined using various combinations of protein chemistry and site-directed mutagenesis. The use of specific inhibitors and novel expression systems continues to reveal fundamental features of the anion exchanger mechanism and its regulation. The importance of anion exchangers in blood and kidney diseases is underscored by the identification and characterization of a plethora of novel mutations in the AE1 gene. Investigations of anion exchanger structure and function have moved beyond studies of the red cell protein into the larger arenas of cellular and molecular biology.Key words: anion exchanger, band 3, erythrocyte, membrane protein, pH regulation.
A new concept in polytopic membrane proteins following from the study of band 3 protein
Authors: Hamasaki Naotaka , Kuma Hiroyuki , Ota Kazuhisa , Sakaguchi Masao , Mihara Katsuyoshi
Published: April 2011

In the present communication, we introduce a novel concept in multispanning polytopic membrane proteins revealed by the study of the band 3 protein. The transmembrane domain of such proteins can be divided into three categories, that is, hydrophilic loops connecting transmembrane peptides (category 1), portions embedded by peptide-peptide interactions (category 2), and portions embedded by peptide-lipid interactions (category 3). Category 2 peptides of polytopic membrane proteins were found to stably reside in the lipid bilayer without peptide-lipid interactions that had been thought to be essential for transmembrane segments. Category 3 peptides are equivalent to single-spanning segments of bitopic membrane proteins. Three different experiments, namely proteolytic digestion, chemical modification of the band 3 protein, and cell free transcription and translation, were used to categorize the transmembrane peptides.Key words: band 3 protein, transmembrane (TM) peptide, classification of TM, category 2-TM, polytopic membrane protein.
A highly selective, high-affinity transporter for uracil in Trypanosoma brucei brucei: evidence for proton-dependent transport
Authors: de Koning Harry P , Jarvis Simon M
Published: April 2011

The presence of an uptake mechanism for uracil in procyclic forms of the protozoan parasite Trypanosoma brucei brucei was investigated. Uptake of [3H]uracil at 22°C was rapid and saturable and appeared to be mediated by a single high-affinity transporter, designated U1, with an apparent Km of 0.46 ± 0.09 µM and a Vmax of 0.65 ± 0.08 pmol·(107 cells)-1·s-1. [3H]Uracil uptake was not inhibited by a broad range of purine and pyrimidine nucleosides and nucleobases (concentrations up to 1 mM), with the exception of uridine, which acted as an apparent weak inhibitor (Ki value of 48 ± 15 µM). Similarly, most chemical analogues of uracil, such as 5-chlorouracil, 3-deazauracil, and 2-thiouracil, had little or no affinity for the U1 carrier. Only 5-fluorouracil was found to be a relatively potent inhibitor of uracil uptake (Ki = 3.2 ± 0.4 µM). Transport of uracil was independent of extracellular sodium and potassium gradients, as replacement of NaCl in the assay buffer by N-methyl-D-glucamine, KCl, LiCl, CsCl, or RbCl did not affect initial rates of transport. However, the proton ionophore carbonyl cyanide chlorophenylhydrazone inhibited up to 70% of [3H]uracil flux. These data show that uracil uptake in T. b. brucei procyclics is mediated by a single high-affinity transporter with high substrate selectivity and are consistent with a nucleobase-H+-symporter model for this carrier.Key words: uracil, trypanosome, proton-nucleobase cotransport, nucleobase transport.
A novel electron transfer mechanism suggested by crystallographic studies of mitochondrial cytochrome bc1 complex
Authors: Xia Di , Kim Hoeon , Yu Chang-An , Yu Linda , Kachurin Anatoly , Zhang Li , Deisenhofer Johann
Published: April 2011

The crystal structure of bovine mitochondrial cytochrome bc1 complex, an integral membrane protein complex of 11 different subunits with a total molecular mass of 242 kDa, demonstrated a tightly associated dimer consisting of three major regions: a matrix region primarily made of subunits core1, core2, 6, and 9; a transmembrane-helix region of 26 helices in the dimer contributed by cytochrome b, cytochrome c1, the Rieske iron-sulfur protein (ISP), subunits 7, 10, and 11; and an intermembrane-space region composed of extramembrane domains of ISP, cytochrome c1, and subunit 8. The structure also revealed the positions of and distances between irons of prosthetic groups, and two symmetry related cavities in the transmembrane-helix region upon dimerization of the bc1 complex. Extensive crystallographic studies on crystals of bc1 complexed with inhibitors of electron transfer identified binding pockets for both Qo and Qi site inhibitors. Discrete binding sites for subtypes of Qo site inhibitors have been mapped onto the Qo binding pocket, and bindings of different subtypes of Qo site inhibitors are capable of inducing dramatic conformational changes in the extramembrane domain of ISP. A novel electron transfer mechanism for the bc1 complex consistent with crystallographic observations is discussed.Key words: bc1 complex, electron transfer, structure, conformational change, inhibitor.
Recent advances in the molecular biology of nucleoside transporters of mammalian cells
Authors: Cass Carol E , Young James D , Baldwin Stephen A
Published: April 2011

Nucleosides are hydrophilic molecules and require specialized transport proteins for permeation of cell membranes. There are two types of nucleoside transport processes: equilibrative bidirectional processes driven by chemical gradients and inwardly directed concentrative processes driven by the sodium electrochemical gradient. The equilibrative nucleoside transport processes (es, ei) are found in most mammalian cell types, whereas the concentrative nucleoside transport processes (cit, cif, cib, csg, cs) are present primarily in specialized epithelia. Using a variety of cloning strategies and functional expression in oocytes of Xenopus laevis, we have isolated and characterized cDNAs encoding the rat and human nucleoside transporter proteins of the four major nucleoside transport processes of mammalian cells (es, ei, cit, cif). From the sequence relationships of these proteins with each other and with sequences in the public data bases, we have concluded that the equilibrative and concentrative nucleoside transport processes are mediated by members of two previously unrecognized groups of integral membrane proteins, which we have designated the equilibrative nucleoside transporter (ENT) and the concentrative nucleoside transporter (CNT) protein families. This review summarizes the current state of knowledge in the molecular biology of the ENT and CNT protein families, focusing on the characteristics of the four human (h) and rat (r) nucleoside transport proteins (r/hENT1, r/hENT2, r/hCNT1, r/hCNT2).Key words: nucleoside transporter, equilibrative, concentrative, ENT, CNT.
Nucleoside transporters and liver cell growth
Authors: Pastor-Anglada Marçal , Felipe Antonio , Casado F Javier , Del Santo Belén , Mata João F , Valdés Raquel
Published: April 2011

Liver parenchymal cells show a wide variety of plasma membrane transporters that are tightly regulated by endocrine and nutritional factors. This review summarizes work performed in our laboratory on these transport systems, particularly nucleoside transporters, which are up-regulated in physiological situations associated with liver cell growth. Rat hepatocytes show a Na+-dependent nucleoside transport activity that is stimulated by pancreatic hormones. Indeed, this biological activity appears to be the result of the co-expression of at least two isoforms of nucleoside carriers, CNT1 and CNT2 (also called SPNT). These two transporters are up-regulated during the early phase of liver growth after partial hepatectomy, although to different extents, suggesting differential regulation of the two isoforms. The recent generation of isoform-specific antibodies allowed us to demonstrate that carrier expression may also have complex post-transcriptional regulation on the basis of the lack of correspondence between mRNA and protein levels. The analysis of nucleoside transport systems in hepatoma cells and the comparison with those in hepatocytes has also provided evidence that the differentiation status of liver parenchymal cells may determine the pattern of nucleoside transporters expressed.Key words: liver, hepatocyte, regeneration, cell cycle, nucleoside, plasma membrane, transport systems.
An equation to represent grain-size distribution
Authors: Fredlund Murray D , Fredlund D G , Wilson G Ward
Published: April 2011

The grain-size distribution is commonly used for soil classification; however, there is also potential to use the grain-size distribution as a basis for estimating soil behaviour. For example, much emphasis has recently been placed on the estimation of the soil-water characteristic curve. Many methods proposed in the literature use the grain-size distribution as a starting point to estimate the soil-water characteristic curve. Two mathematical forms are presented to represent grain-size distribution curves, namely, a unimodal form and a bimodal form. The proposed equations provide methods for accurately representing uniform, well-graded soils, and gap-graded soils. The five-parameter unimodal equation provides a closer fit than previous two-parameter, log-normal equations used to fit uniform and well-graded soils. The unimodal equation also improves representation of the silt- and clay-sized portions of the grain-size distribution curve.Key words: grain-size distribution, sieve analysis, hydrometer analysis, soil classification, probability density function.
Fuzzy-based approach for determination of characteristic values of measured geotechnical parameters
Authors: Nawari N O , Liang R
Published: April 2011

Determination of the nominal (characteristic) values of geotechnical properties plays a crucial role within the limits states design (LSD or LRFD) concepts. The interrelationship between the process of the selection of the nominal value and the safety level is not clearly addressed in most of the new limits states design codes of practice for geotechnical engineering. Estimation of the characteristic values (p% fractile or the mean value) using the stochastic models is often linked up with some assumptions regarding the probability distribution functions. Probability theory has been perceived as a unique methodology to handle uncertainty in these geotechnical parameters despite the fact that some of the uncertainties associated with these geotechnical properties may be nonstochastic in nature. In this paper, the uncertainty connected with measured geotechnical properties is modeled using the fuzzy-reliability techniques. The measured parameters are rendered into fuzzy variables and the nominal values are characterized by fuzziness. The procedure presented is proposed as an alternative or complementary method to the estimate of the nominal values of geomaterials. The approach is illustrated with computational algorithms and a numerical example.Key words: characteristic value, nominal value, fuzzy model, fuzzy variable, resistance factor, probability.
Undrained and drained (?) stress-strain response
Authors: Vaid Y P , Eliadorani A
Published: April 2011

The deformation response of saturated soils to a total stress increment at the ambient void ratio and effective stress state is shown to be dependent on the direction of the effective strain increment. It is argued that in a given field problem, most soil elements neither deform fully drained nor undrained, but do so partially drained. The degree of partial drainage controls the direction of the effective stress increment and hence the deformation response. Experimental data are presented which demonstrate how shear stiffness changes with the direction of effective stress increment as a function of the ambient effective stress state.Key words: stress-strain, undrained, drained, partially drained, stress path, stiffness.
The Canadian Liquefaction Experiment: an overview
Authors: Robertson P K , (Fear) Wride C E , List B R , Atukorala U , Biggar K W , Byrne P M , Campanella R G , Cathro D C , Chan D H , Czajewski K , Finn WDL , Gu W H , Hammamji Y , Hofmann B A , Howie J A , Hughes J , Imrie A S , Konrad J -M , Küpper A , Law T , Lord E RF , Monahan P A , Morgenstern N R , Phillips R , Piché R , Plewes H D , Scott D , Sego D C , Sobkowicz J , Stewart R A , Watts B D , Woeller D J , Youd T L , Zavodni Z
Published: April 2011

The Canadian geotechnical engineering community has completed a major collaborative 5 year research project entitled the Canadian Liquefaction Experiment (CANLEX). The main objective of the project was to study the phenomenon of soil liquefaction, which can occur in saturated sandy soils and is characterized by a large loss of strength or stiffness resulting in substantial deformations. In many areas of Canada, large structures are constructed on or comprise sandy soils, e.g., some major hydroelectricity earth dams and many tailings impoundments in the mining industry. The behaviour of loose sandy soils can be difficult to predict, but can have a significant financial impact on these types of engineering structures. Consequently, the intent of the CANLEX project was to improve the overall understanding of soil liquefaction. This paper provides an overview of the CANLEX project, outlining the project objectives, major achievements, and conclusions. Four companion papers describe different aspects of the project; thus, together, the five papers provide a summary of the CANLEX project.Key words: geotechnical, liquefaction, CANLEX, collaborative project.
Strength behaviour of lime-treated soils in the presence of sulphate
Authors: Sivapullaiah P V , Sridharan A , Ramesh H N
Published: April 2011

Lime has been used extensively to improve the shear strength of fine-grained soils. It has been recently reported that the presence of sulphate causes abnormal volume changes in lime-stabilized soil. The paper presents the strength behaviour of lime-treated montmorillonitic natural black cotton soil in the presence of varying sulphate contents after curing for periods of up to 365 days. Alteration of soillime reactions in the presence of sulphate affects the strength development by cementation. Consequently, the stressstrain behaviour effective stress paths of soil cured with sulphate are similar to those of normally consolidated soil rather than cemented soils. The reduction in shear strength due to a reduction in effective cohesion intercept occurs for lime-treated soil cured with sulphate for long periods.Key words: clays, cohesion, fabric, friction, shear strength.
Laboratory properties of mine tailings
Authors: Qiu Yunxin (Jason) , Sego D C
Published: April 2011

A vast amount and variety of mine tailings are produced around the world each day. These mining wastes must be properly managed. To evaluate mine tailings disposal technology, the appropriate engineering properties of the tailings must be ascertained. The results of a laboratory investigation on the engineering properties of four different tailings are presented. First, some of the basic properties of the tailings are described. Large-strain consolidation tests and hydraulic conductivity tests are then described. The techniques for saturating and placing the tailings sample prior to carrying out the consolidation tests are given. Column drying and shrinkage tests for investigating the desiccation behavior of mine tailings are outlined. Furthermore, water retention characteristic tests using both the pressure-plate extractor and the saturated salt solution desiccator are outlined. Finally, shear strength parameter tests are described. The engineering properties derived from these tests are then presented and compared with the published results on similar types of tailings.Key words: mine tailings, engineering properties, consolidation, hydraulic conductivity, water retention curve, evaporation rate.
Geocomposite capillary barriers to reduce frost heave in soils
Authors: Henry Karen S , Holtz Robert D
Published: April 2011

We investigated the potential for geosynthetic capillary barriers to reduce frost heave in soils by freezing upright, cylindrical soil specimens with horizontal disks of geosynthetics placed in them. During freezing, water was freely available at 25 mm above the base of 150 mm high specimens. The geosynthetics were located 5 mm above the water supply. We measured frost heave and final water content profiles of specimens containing geosynthetic capillary barriers and control specimens. The thermal conditions of the tests were typical of pavements in cold regions. Geotextiles prepared to simulate field conditions (i.e., moistened and containing soil fines) failed to significantly reduce frost heave. However, geocomposites comprising needle-punched polypropylene geotextiles sandwiching a drainage net, prepared in the same way as the moistened geotextiles containing soil fines, reduced frost heave when the soil water suction head in the overlying soil was 1800 mm or more. The geocomposites did not significantly reduce heave when the soil water suction head in the overlying soil was 800 mm or less. This is probably due to water migration between the two layers of soil, through the geotextiles and along the net of the geocomposite.Key words: capillary barrier, frost heave, geosynthetic, geotextile, geocomposite, soil freezing.
Influence of placement method on the cone penetration resistance of hydraulically placed sand fills
Authors: Lee K M
Published: April 2011

The reclamation for the new airport at Chek Lap Kok in Hong Kong included the placement of a substantial volume of sand fill by various hydraulic placement techniques, which resulted in a wide range of as-placed densities of the sand fill. This paper described the use of cone penetration tests (CPT) on the evaluation of the possible ranges of density achievable by various hydraulic placement methods adopted in the construction of the new airport. The results of the CPT indicated that the placement technique is one of the most important factors in controlling the as-placed density of hydraulically placed sand fill. There is a marked contrast in cone tip resistance (and the associated relative density) profiles for the sand fills formed by subaerial and subaqueous placement methods, in which the cone tip resistance of the sand fill formed by subaerial placement is substantially higher than that of the sand fill formed by subaequeous placement. The results confirm that dense sand fill cannot be formed by subaqueous placement methods. The weakest zone is generally located just beneath the water level where fill is placed by subaqueous discharge.Key words: sand, hydraulic fill, cone penetration test, calibration chamber test, in situ density.
Determination of diffusion and adsorption coefficients for volatile organics in an organophilic clay - sand - bentonite liner
Authors: Headley John V , Boldt-Leppin Brigitte EJ , Haug Moir D , Peng Jimin
Published: April 2011

In the design of barriers for containment of petroleum products it is essential to know the conditions for contaminant transport. In this work, a batch test method was used to determine the adsorption coefficients (Kd) of benzene, toluene, and 2-fluorotoluene (a tracer for toluene) on three soils. For Ottawa sand using soil to water ratios of 0.100.30 g/mL, Kd values were 2.51.2 mL/g (benzene), 11.33.6 mL/g (toluene), and 10.93.7 mL/g (2-fluorotoluene), respectively. Using organophilic clay at similar soil to water ratios, the Kd values were 40.950.0 mL/g (benzene), 154129 mL/g (toluene), and 157114 mL/g (2-fluorotoluene), respectively. Kd values for bentonite were 37.60.14 mL/g (benzene), 60.316.5 mL/g (toluene), and 51.233.6 mL/g (2-fluorotoluene) using soil to water ratios in the range 0.010.05. In general, for a given mixture, toluene was two to five times more adsorptive than benzene, indicating that hydrophobicity was an important factor in their adsorption. The diffusion coefficients in material comprised of 3% organophilic clay, 12% bentonite, and 85% Ottawa sand ranged from 0.48 × 106 to 2.5 × 106 cm2/s at 20°C. These values are lower than those measured for natural clay with low organic carbon content.Key words: diffusion, adsorption, volatile organics, organophilic clay, liner materials.
Terrain-based mapping of landslide susceptibility using a geographical information system: a case study
Authors: Dai F C , Lee C F
Published: April 2011

This paper deals with the development of a technique for mapping landslide susceptibility using a geographical information system (GIS), with particular reference to landslides on natural terrain. The method has been applied to Lantau Island, the largest outlying island within the territory of Hong Kong. Landslide susceptibility in the study area is related to a number of terrain variables, viz., lithology, slope gradient, slope aspect, elevation, land cover, and distance to drainage line. Multiple correspondence analysis (MCA) was carried out to generate the principal axes that are linear combinations of these terrain variables using occurrence data of landslides and terrain variables. A GIS is used to project the values of the principal axes, and subsequently to relate these principal axes to landslide susceptibility by logistic regression modeling. The spatial landslide susceptibility response in the study area can then be obtained by applying this logistic regression model to the study area. The results from this study indicate that such a GIS-based model is useful and suitable for the scale adopted in this study.Key words: landslides, geographical information systems, multiple correspondence analysis, logistic regression, terrain analysis.
Failure in MohrCoulomb soil cavities
Authors: Gesualdo A , Minutolo V , Nunziante L
Published: April 2011

In many cavities, resulting from both natural excavation and anthropic action, the phenomenon of the collapse of blocks from the cavity roof presents a serious safety hazard. In a previous publication the authors proposed a method to calculate the shape and dimensions of the collapsing block by means of the upper bound theorem of the plasticity theory. The soft rock material was modelled by means of the MohrCoulomb yield criterion, and the associated flow rule was considered for strain plastic velocity. The linear yield criterion was suitably regularized by means of a circle in the tensile zone. The boundary of the collapsing block is described by a paraboloid surface. An optimization procedure formulated in standard KuhnTucker form and an analytical solution were obtained. The above-mentioned algorithm has been successfully applied to common soils of southern Italy. To validate the theoretical formulation, several numerical tests are performed. These tests show an optimal agreement with the closed-form solution. Therefore the proposed modelling may be used as an efficient guideline for the cavity-strengthening design.Key words: roof stability, regularized MohrCoulomb material, limit analysis, failure mechanics.
Impact of density on the hydraulics of peat filters
Authors: Kennedy Paula L , Van Geel Paul J
Published: April 2011

Peat filters have been used to treat septic tank effluents from domestic and commercial sources, landfill leachate, and acid mine drainage. A better understanding of the hydraulics and impact of the organic loading on these types of systems will enhance the application of peat filter systems. This paper presents the results of a field study to evaluate the hydraulics of a peat filter used to treat the septic tank effluent from a public school west of Ottawa, Ontario, Canada. The filter was instrumented with tensiometers and transducers to monitor the pore-water pressures in response to a pulse of septic tank effluent. Samples of peat were collected to determine the dry density profile with depth. The soil moisture retention curve, effective porosity, and hydraulic conductivity as a function of dry density were determined in laboratory experiments. A one-dimensional unsaturated flow model was used to predict the pressure response due to a pulse. Two model scenarios were evaluated to demonstrate the impact of density variations on model simulations. Model simulations that accounted for dry density variations with depth measured in the field more accurately simulated the pressure responses measured in the field.Key words: unsaturated flow, peat, filters, septic, modelling, density.
Coulomb wedge analysis of cuts in steep slopes
Authors: Wesley Laurence D
Published: April 2011

Coulomb's trial wedge method for estimating the active force on retaining walls is applied to situations where there are steep slopes at limiting equilibrium behind the walls. The analysis is applied initially to slopes of dry cohesionless material; in this case the slope angle is equal to the friction angle of the material. The analysis produces two interesting, and perhaps surprising, results. The first is that the critical wedge angle equals the slope angle, and the critical wedge becomes a "slab" extending an unlimited distance up the slope above the wall. The second is that as the inclination of the slope and friction angle (which are equal) increase the active force on the wall decreases. The method is then applied to more general slopes involving cohesion, friction, and seepage. Back-analysis is first used to obtain combinations of cohesion and friction corresponding to limiting equilibrium; these are then used in the wedge analysis. The results obtained are similar to those for the dry cohesionless slope. The method provides a means of estimating required retaining forces for cuts made in steep slopes of residual soil or partly weathered rock where estimation of strength parameters is often very difficult.Key words: slopes, steep, back-analysis, Coulomb, wedge, analysis.
Three-dimensional numerical investigations of groundwater responses in an unsaturated slope subjected to various rainfall patterns
Authors: Ng C WW , Wang B , Tung Y K
Published: April 2011

Three-dimensional (3D) numerical analyses were conducted to investigate groundwater responses in an initially unsaturated cut slope at Lai Ping Road in Hong Kong subjected to rainfalls with various patterns, durations, and return periods. Initial and boundary conditions were established from field monitoring data. The computed results show that rainfall pattern has a significant influence on pore-water pressures in soil layers near the ground surface but its influence gradually diminishes with depth. Rainfall with an advanced storm pattern of 24 h duration was found to be the most critical because it results in the highest pore-water pressure in the slope. At a given depth, the influence of rainfall pattern on pore-water pressures depends on the initial groundwater conditions: the higher the initial water table, the smaller the influence of rainfall pattern on pore-water pressures. Under a given rainfall duration, the rise of pore-water pressure at the study site is significant only when the return period increases from 10 years to 100 years, but not from 100 years to 1000 years. Short-duration, intense rainfall causes larger variations in pore-water pressure at shallow depths, whereas long-duration rainfall has a greater influence on groundwater in deep soils because of the generally greater amount of rainfall. For prolonged rainfalls, the difference in pore-water pressure distribution resulting from different rainfall patterns is less significant than that from short-duration, intense rainfalls.Key words: Lai Ping Road, rainfall patterns, pore-water pressure distributions, suction, unsaturated slope.
The effect of air flow on the shear strength of soil in compressed-air tunneling
Authors: Javadi A A , Snee C PM
Published: April 2011

This paper presents a method for studying the variation in shear strength of soil due to the air flow in compressed-air tunneling. The method is based on application of the shear strength theories of unsaturated soils in conjunction with a finite element model, developed by the authors, for analyzing the flow of the air through soils. The formulation of the problem, the numerical model, the design and modification of the triaxial cell and the laboratory testing program, and the results are presented and studied with particular reference to compressed-air tunneling. The results are presented and interpreted using the concepts and theory of shear strength for unsaturated soils. The results of the tests indicate the way in which the air pressure increases the stability of the ground, besides being an internal support, prior to the installation of the temporary or permanent lining. From the results of the tests, a three-dimensional failure envelope was plotted that can be used to predict the change in shear strength of the soil due to a change in the air pressure, in compressed-air tunneling. This information can be used to assess the risk of tunnel collapse and blow out. It also improves the current understanding of the interaction between the compressed-air tunneling method and the ground.Key words: compressed-air tunneling, air flow, unsaturated soils, shear strength.
Describing the geometrical packing of gravelly cobble deposits using pair-correlation functions
Authors: Yang Zon-Yee , Lo Shin-Chen
Published: April 2011

There is a close correlation between the mechanical behavior of gravelly cobbles and their geometrical fabric. In geotechnical engineering, the particle-size distribution curve is used to describe the particle gradation. However, a group of particles with the same particle-size distribution can result in several packing arrangements due to the different sedimentation processes. The particle-size distribution curve does not distinguish this characteristic. This study attempts to employ the pair-correlation function of point field theory for describing the geometric packing of gravelly cobble deposits. In the point field, a single gravel- or cobble-sized particle is represented by a point of its geometric center. The pair-correlation function can statistically illustrate the characteristics of a geometrical point pattern and is helpful in interpreting the neighborhood relationship between particles, such as the frequency of interpoint distances and the dominant particle sizes in a point process. Some examples based on ideal particle shapes and arrangements are analyzed to illustrate the interpretations from the pair-correlation functions. The characteristics of pair-correlation functions of field examples are also explained. It is shown that the pair-correlation function can provide another approach to understanding the geometrical packing characteristics of a gravelly cobble formation.Key words: gravelly cobble deposit, geometrical packing, interpoint distance, particle-size distribution, pair-correlation function, point field theory.
A simplified method to estimate saturated and unsaturated seepage through dikes under steady-state conditions
Authors: Chapuis Robert P , Aubertin Michel
Published: April 2011

The seepage rate through homogeneous or zoned dikes includes saturated and unsaturated flow. The latter is often neglected but should be considered to obtain the positions of the water table and the seepage face that may develop either on the downstream slope of a homogeneous dike or within the filter layer behind the core of a zoned dike. Different dikes with heights of 5, 10, 20, and 50 m have been analyzed numerically with a two-dimensional finite element code. The cases investigated include the most frequent types of small dikes designed to retain municipal or industrial wastewater. Solutions are proposed to solve numerically two difficulties related to the representation of saturated and unsaturated physical flow conditions. One difficulty is treating a downstream seepage face. The other is treating the passage of water from the core into a draining layer. The paper presents simple expressions to predict the total (saturated and unsaturated) seepage flow rate through a dike and discusses precautions to be taken.Key words: dams, dikes, seepage, saturated soil, unsaturated soil, numerical modeling.
Performance Measurements on Two New Anchored Bulkheads
Authors: Matich M J , Henderson R P , Oates D B
Published: April 2011

This paper describes the results of the instrumentation of two new anchored bulkheads. The purpose of the instrumentation was to obtain a complete stress history of the steel sheet piling and tie-rods, particularly to examine the deflections and bending stresses induced in the piling by driving.Included in this paper are the deflected shapes and stresses in the bulkheads during different loading cycles together with the tie-rod stress measurements. Information on the soil conditions at the two sites and the details of construction are also given.An attempt has been made to compare the results of the field observations with conventional design approaches. The bending moments and tie-rod stresses have been calculated using the methods of fixed earth support and moment reduction. It is not possible, on the basis of such limited information, to draw conclusions on the methods presently used in the design of bulkheads. The main purpose of this paper is to add to the limited field evidence pertaining to the performance of steel sheet pile bulkheads.
Triaxial Compression of a Cohesive Soil with Effective Octahedral Normal Stress Control
Authors: Kondner R L , Horner J M
Published: April 2011

The influence of the first invariant of the effective stress tensor upon the deviatoric response of a cohesive soil is investigated. Triaxial compression tests with effective octahedral normal stress control show the deviatoric stress-strain response to be definitely affected by the value of the effective octahedral stress, [Formula: see text]. The values of [Formula: see text] range from 7.5 psi to 30.0 psi. For a constant value of strain, the deviatoric stress increases with an increase in [Formula: see text]. The ultimate shear strength can be approximated as a linear function of [Formula: see text]. Hyperbolic representation of the stress-strain response provides a convenient method for obtaining a measure of the ultimate shear strength using the response of stress states other than failure. The deviatoric stress-strain response as a function of the effective octahedral stress, [Formula: see text], can be expressed in the normalized form[Formula: see text]where ε is the strain, [Formula: see text] is a measure of the shear strength expressed in terms of [Formula: see text] , and A as well as B are numerical coefficients.
The Influence of Depth of Frost Penetration on the Frost Susceptibility of Soils
Authors: Osler J C
Published: April 2011

Research on heaving pressures associated with the formation of ice lenses in soils indicates that the magnitude of the heaving pressure in silt soils is governed by the geometry of the ice-water interface. This geometry involves a double curvature of the ice front, into the voids and around the adjacent particles, and thus depends on both particle and pore size distribution. A theory for predicting frost heaving pressures, which takes into account the geometry of the ice-water interface, is described and it predicts greater heaving pressures for decreasing particle and pore sizes. Supporting experimental results are given.The formation of ice lenses in a freezing soil can be arrested if the frost heaving pressure is counteracted by an equal or greater external pressure, such as overburden pressure. From the theory, the frost heaving pressure for a given particle and pore size distribution can be obtained. If this pressure is equal to the pressure of the frozen overburden, a state of equilibrium will exist and ice lenses will not form. Thus, a critical particle and pore size for a given depth of frost penetration can be predicted for which a soil will be non-frost-susceptible.
SOME OBSERVATIONS ON THE UNDRAINED SHEARING STRENGTH USED TO ANALYZE A FAILURE
Authors: Lory F. A. De , Salvas R. J.
Published: April 2011

The undrained shearing strength of the foundation soil at the site of a failure of a low embankment was investigated by several methods. It was found that both field vane and laboratory compression tests tended to underestimate the strength required for stability. Further consideration of the test specimens from sample tubes showed the undrained shearing strength varied considerably with the position of the sample in the tube. Specimens from tubes from another site yield the same type of results. The two silty clay soils involved were studied in more detail using CIU and CAU triaxial tests and comparing cu/p′ ratios. It was found that in general they yielded the values usually obtained for lacustrine clays.
SELECTION AND PERFORMANCE OF ANCHORS FOR GUYED TRANSMISSION TOWERS
Authors: Robinson K. E. , Taylor H.
Published: April 2011

This paper presents information on the selection and performance of anchors for guyed EHV transmission towers. The information used was obtained during the design and construction of two transmission lines each over 540 miles (>869 km) long in British Columbia.Five anchors have been designed and tested: (1) buried plate with compacted backfill; (2) buried steel mat or grillage with loose backfill; (3) cast-in-place concrete with loose backfill; (4) power installed helical; and (5) grouted rod anchors.The highly variable soil and access conditions along the line necessitated an anchor that could economically be installed in nearly all soil types and by ordinary construction equipment that could easily move between tower sites in rugged terrain.The simply installed, conservatively designed, cast-in-place concrete anchor was found to satisfy these requirements at reasonable cost. Power-installed helical anchors and grouted rod anchors may provide an economical anchor in more uniform soil conditions and where easier access conditions exist. However, these anchors require more detailed soil exploration and contract inspection than the cast-in-place concrete anchors.
A SIDE-WALL SAMPLER: RESEARCH NOTE
Authors: Morrison B.
Published: April 2011

A side-wall sampler which is capable of taking samples from the walls of test-holes to a depth of 1000 ft or more is described. Samples have been extracted from till, clay, silt, and fine- to coarse-grained sands in drift and non-indurated bedrock from more than 1000 test-holes in southern Saskatchewan. Side-hole sampling is faster and cheaper than conventional sampling methods and is ideally suited for geological investigations. Mineralogical, paleontological, and radio-carbon analyses have been determined on side-hole cores.
Microstructural changes in soft quick clay at failure
Authors: Pusch Roland
Published: April 2011

A series of unconfined compression tests has been made on a marine, quick clay and small specimens were extracted for microstructural investigation. The natural microstructural pattern was characterized by a network of small aggregates connected by links of particles. The links broke down successively at increasing shear deformation and formed domain-like groups of particles. In the macroscopic shear zone the shear forces tended to orient and deform the aggregates.The aggregates behaved as rigid bodies to a certain stress level during the shear process. The concept of residual strength may correspond to the state where the majority of the links have been broken while the aggregates are still intact.
Gravitational stress field around a tunnel in soft ground
Authors: Hoyaux B. , Ladanyi B.
Published: April 2011

The finite element method has been used for determining the stress distribution and the displacements due to gravity around an unlined tunnel driven through a semi-infinite medium, characterized by three idealized material behaviors reflecting approximately a short term behavior of natural undisturbed insensitive and sensitive clays. The knowledge of stress and displacement fields around an unlined tunnel can be used for evaluating the need for supports according to the acceptability of expected deformations.
On the yielding and mechanical strength of Leda clays
Authors: Mitchell R. J.
Published: April 2011

The pronounced yielding observed in laboratory tests on Leda clay has been associated with the destruction of cementation bonds in the clay. Triaxial test data presented in this paper show that a yield curve can be established for a Leda clay. The form of the yield curve deviates from that expected for an isotropic material and the pre-yield strains are shown to be different for vertically and horizontally orientated specimens.The shear strength of the clay is dependent on the mean normal stress at failure. A portion of the failure envelope is different for specimens orientated in different directions and this 'strength anisotropy' is associated with anisotropic yielding.
Downdrag Measurements on a 160-Ft Floating Pipe Test Pile in Marine Clay
Authors: Bozozuk M.
Published: April 2011

Large negative skin friction loads were observed on a 160 ft (49 m) steel pipe test pile floating in marine clay. The test pile was driven, open-ended, on the centerline of a 30 ft (9 m) high granular approach fill on the Quebec Autoroute near Berthierville. Since the installation was made in 1966 the fill has settled 21 in. (53 cm), dragging the pile down with it. Negative skin friction acting along the upper surface of the pile was resisted by positive skin friction acting along the lower end as it penetrated the underlying clay. Under these conditions the pile compressed about [Formula: see text] (2 cm). Analysis of the axial strains indicated that a peak compressive load of 140 t developed at the inflection point between negative and positive skin friction 73 ft (22 m) below the top of the pile. Negative and positive skin friction acting on the upper surface of the pile exceeded the in situ shear strength and approached the drained strength of the soil where excess pore water pressures had dissipated. At the lower end where the positive excess pore pressures were high and relative movement between the pile and the soil was large, the positive skin friction approached the remoulded strength as measured with the field vane. Skin friction was increasing, however, as positive escess pore pressures dissipated.This paper shows that skin friction loads are related to the combination of (a) in situ horizontal effective stresses, (b) horizontal stresses due to embankment loads, and (c) horizontal stresses due to differential settlement of the fill.
Use of Radiographs in a Geological and Geotechnical Investigation of Varved Soil
Authors: Kenney T. Cameron , Chan H. T.
Published: April 2011

The paper presents a description of several uses of radiographs of soil samples that have been found valuable in a geological and geotechnical investigation of varved soil. The radiographs were taken while the soil was still in the sampling tubes, thus enabling examinations to be made of the samples before they were extruded.The uses to which the radiographs have been primarily made are to record in detail the soil stratigraphy, to make examinations of the soil structure and texture, and to help plan laboratory-test programs.Damage to 'undisturbed' samples, in the form of transverse cracks created during the sampling process, was detected by examination of the radiographs. Such features as these might not be detected in extruded samples because they are obscured by smeared soil on the surface of the sample and because cracks would tend to become closed during extrusion.A brief discussion is included of the requirements for making radiographs.
Functional Effects of Vegetation on the Radiant Energy Budget of Boreal Forest
Authors: Haag Richard W. , Bliss L. C.
Published: April 2011

In contrast to tundras, where the mass of vegetation is low and its effect on energy exchange relatively small, boreal forest vegetation exerts a more important buffering effect on energy flux to and from the ground surface. Air movement below the canopy is reduced, and a relatively high proportion of solar radiation is absorbed by the canopy directly, to be lost as sensible or latent heat. Removal of the buffer provided by stratified vegetation results in increased soil heat flux and ground temperatures, and increased depth of the active layer, which in areas of ice rich permafrost can lead to surface subsidence.
In situ stress measurements in some near-surface rock formations – Thorold, Ontario
Authors: Palmer J. H. L. , Lo K. Y.
Published: April 2011

Performance of some structures constructed in rocks in southern Ontario have shown severe distress. It has been hypothesized that the problem is due to the high horizontal stresses existing in the rock formations. As part of a comprehensive investigation into the stress relief and time-dependent behavior of the rocks in this area, in situ stress measurements were carried out at a location near the Thorold Tunnel to a depth of 81 ft (25 m). The technique and procedure used are described in detail. It was found that high horizontal stresses, varying from 1200 to 2100 psi (8300 to 14500 kPa) exist in each rock unit encountered. The direction of the major principal stress in the horizontal plane appears to be orientated at N 60° E.
Slab avalanche measurements
Authors: Perla R.
Published: April 2011

From a study of 205 slab avalanches it is concluded that failure initiates where the slope is 25° or steeper, that slab failure stress is in the range 102–104 N/m2, and that the slab failure plane is most commonly at a temperature of −5 °C or warmer.The in situ measurement of shear strength is still an unresolved problem. A statistical analysis of a shear-frame device shows that the device is sensitive to the rate of pull and to the frame area. The larger the frame area, the smaller the measured shear strength. Approximately 10 measurements are required to sample a mean shear strength of a slab failure plane to within 15% accuracy at 90% confidence.
One-dimensional consolidation theory: unsaturated soils
Authors: Fredlund Delwyn G. , Hasan Jamshed U.
Published: April 2011

A one-dimensional consolidation theory is presented for unsaturated soils. The assumptions made are in keeping with those used in the conventional theory of consolidation for saturated soils, with the additional assumption that the air phase is continuous. Two partial differential equations are derived to describe the transient processes taking place as a result of the application of a total load to an unsaturated soil.After a load has been applied to the soil, air and water flow simultaneously from the soil until equilibrium conditions are achieved. The simultaneous solution of the two partial differential equations gives the pore-air and pore-water pressures at any time and any depth throughout the soil. Two families of dimensionless curves are generated to show the pore-air and pore-water dissipation curves for various soil properties.For the case of an applied total load, two equations are also derived to predict the initial pore-air and pore-water pressure boundary conditions. An example problem demonstrates the nature of the results.