bluuebunny/crossref_metadata_2025 huggingface dataset:
Long-term behaviour of reconsolidated clay around a driven pile
Authors: Roy Marius , Lemieux Michel
Published: April 2011

Extensive in situ testing and undisturbed sampling were carried out near two steel piles to determine the long-term state of a clay in which these piles had been driven 7 years before. Results show that this material exhibits a rigidity that varies with the distance from the pile. The average rigidity in the zone of study is representative of a slightly destructured clay. The shear strength of this clay is, in most cases, equal to the shear strength of the intact material except in the zone located at depth greater than 3.5 m and within 30 cm of the pile wall, where lower shear strength values were consistently monitored. It is believed that reconsolidation after driving took place in this last case under relatively low stresses. Key words: piles, clays, ageing, destruction, reconsolidation, shear strength, rigidity, limit state.
Regina Beach — a town on a landslide
Authors: Clifton A. Wayne , Yoshida Richard T. , Chursinoff Roy W.
Published: April 2011

The town of Regina Beach is constructed on landslides along the Last Mountain Lake valley, a glacial meltwater channel in south-central Saskatchewan, Canada. The landslides are retrogressive in nature and are seated in bentonitic clay shale of the Bearpaw Formation. A study was conducted at Regina Beach to determine the sensitivity of the slopes to changes in slope geometry as a result of regrading, or groundwater changes. Back-calculated shear strength was compared with values from the laboratory and from other landslides in Cretaceous bedrock shales. Modest changes in grading of the toe areas would result in significant reductions in the local stability and future movements of upslope portions of the landslide. Development should minimize the amount of grading. Increased slope movement due to breaks in watermains was observed and measured. This correlated well with analysis. Development in landslide areas must assume that differential vertical and horizontal movements will occur. Proper site reconnaissance should identify optimum locations for buildings and services such that the risk of rupture or damage is minimized. Key words: landslide, retrogressive, back analysis, residual shear strength, Bearpaw Formation, inclinometer, slope movement.
An improved rotating cylinder technique for quantitative measurements of the scour resistance of clays
Authors: Chapuis Robert P. , Gatien Tony
Published: April 2011

The methods developed to predict the action of eroding fluid on cohesive soils lead to contradictory predictions. Most of them are questionable since they ignore the physicochemical parameters that seem to control the erosion process. In order to study the scour resistance of intact or remolded cohesive soils, a rotating cylinder technique allowing for the control of essential parameters was recently improved by the authors. Intact or remolded samples can be used. The water quality is controlled in order to respect the in situ physicochemical conditions. The shear stress transmitted by water to the clay surface is directly and accurately derived. The dry weight of eroded material per unit time and unit area, for given conditions, is also directly and adequately measured. The influence of water quality, or of any treatment of the clay, may be quantitatively analyzed. Key words: erosion, scour, clay, rotating cylinder, viscometry, physical chemistry, river channels.
Testing of model footings on reclaimed land, Wabamun, Alberta
Authors: Thomson S. , Scott J. D. , Sego D. C. , Schulz T. M.
Published: April 2011

The level to gently undulating ground on backfilled mined-out areas is referred to as reclaimed mine spoil. This paper deals with model footings for light structures placed on such soil. For the case considered, the spoil is dominated by a disaggregated clay shale. Settlement of the spoil arises from self-weight, an increase in overburden, and saturation. This last source takes place as the water table rises or when surface infiltration occurs. This latter cause is the source of potentially damaging settlement and is the focus of the research work. Four footings, each 1 × 1 m, were placed on a 1 m thick mat composed of either preloaded, compacted soil, compacted soil/flyash mixture, or compacted flyash. Each footing was loaded to 61 kPa. The settlement was small under this load but every footing settled intolerably when the soil below the footing was saturated. However, the results have merit. Further design consideration needs to be devoted to obviating the ingress of surface water. Key words: settlement, spoil, reclaimed land, model footings, slaking.
Le seuil 9 sur la rivière Opinaca
Authors: Dussault R. , Claisse M.
Published: April 2011

Geomembranes and geotextiles have been used efficiently and economically with steel mesh gabions in the construction of overflow weir No. 9 on the Opinaca River at James Bay. This overflow weir, built to restore the water level over a stretch of river of some 10 km, was built during the winter 1984. The use of geomembranes on the upstream top portion of the weir has been very efficient. Geotextiles were used as a transition between the compacted moraine and the bottom portion of the gabions and the concrete elements housing the three control gates. Geotextiles were also used in the slope protection systems at both ends of the weir. Key words: weir, overflow weir, geotextiles, geomembranes, environment, gabions.
A numerical method for modelling large displacements of jointed rocks. II. Modelling of rock bolts and groundwater and applications
Authors: Garga Vinod K. , Wang Baolin
Published: April 2011

The present paper is an extension of the companion paper in which the formulation of a new numerical model called the block-spring model for jointed rock mass was presented. The work reported herein presents further investigations of the model which include the simulation of rock bolts for ground support and groundwater pressure. The rock bolts are modelled by a series of one-dimensional elements interacting with the rock blocks through nodal points. The model can be used to analyze both the end-anchored and the fully grouted rock bolts, either pretensioned or untensioned. The model also evaluates the water pressures imposed on the surfaces of the rock blocks which are then introduced into the equilibrium equations of the blocks. Several applications of the proposed model are presented including detailed analyses of two case histories. The numerical results have been compared with the field instrumentation data. Good agreement has been observed between the results of the proposed model and the field measurements in both cases. It is demonstrated that the proposed model can be used for the analysis of excavations in jointed rocks in practice. Key words : jointed rocks, stress, deformation, analysis, numerical model, excavation, anchors, groundwater.
Hydraulic conductivity and diffusion monitoring of the Keele Valley Landfill liner, Maple, Ontario
Authors: King K. S. , Quigley R. M. , Fernandez F. , Reades D. W. , Bacopoulos A.
Published: April 2011

The 99-ha Keele Valley Landfill is located in a former sand and gravel pit at Maple, Ontario. The base and sides of the pit are lined with a minimum of 1.2 m of excavated clayey silt till recompacted to achieve a design hydraulic conductivity of 1 × 10−8 cm/s or less. Extensive construction controls and monitoring programs have been implemented to determine the hydraulic conductivity and advective performance of the liner. A total of 267 postcompaction laboratory hydraulic conductivity (k) tests indicated that the first two stages of the liner had a geometric mean k of 7.7 × 10−9 cm/s. Calculations of in situ hydraulic conductivity based on lysimeter effluent collection rates show decreases in k to field values close to the laboratory values. In situ electrical conductivity sensors and lysimeter effluent chemistry measurements have monitored the advance of leachate-derived chemicals into the liner. Concurrent field verification by liner exhumation and chemical analysis has confirmed the importance of diffusion as the dominant migration mechanism through this low-k liner. Similar concentration trends for major ions have been observed in the field lysimeter effluents, effluents from laboratory liner–leachate compatibility tests, and pore water extracted from core samples of sections of exhumed liner exposed to leachate. The multicomponent field and laboratory testing and monitoring programs have shown good cross-agreement, and the actual performance of the liner has been close to preconstruction predictions. Key words : landfill, clayey liner, field hydraulic conductivity, field diffusion, municipal solid waste leachate, field lysimeter test, laboratory hydraulic conductivity, liner–leachate compatibility.
Probabilistic stability analysis of excavations in jointed rock
Authors: Leung C.F. , Quek S.T.
Published: April 2011

Excavations in jointed rock may liberate rock blocks that may fall by gravity or slide along the discontinuity. The orientation of discontinuities is one of the major input parameters in the conventional deterministic stability analysis of rock blocks. As the mean orientation of a discontinuity is often derived from a large number of joint-set data obtained from site investigation, Fisher's constant is commonly employed to represent the degree of dispersion of individual discontinuity orientation. However, such dispersion factors are rarely used in the conventional analysis. A probabilistic-based approach is proposed in this paper to incorporate Fisher's constant in the stability analysis of rock blocks. To account for the uncertainty reflected by the sample dispersion, data are generated systematically around each mean discontinuity normal, based on its Fisher's constant. The probability of rock block failure at a certain location and the largest possible block volume are determined in a logical manner. A microcomputer program has been developed to automate the analysis, and illustrative examples are shown to demonstrate the importance of incorporating the Fisher's constant of individual discontinuity in the stability analysis. In addition, risk mapping plots are presented to enable visual selection of an optimal route for excavation from one location to another. Key words : discontinuity, factor of safety, probability of failure, rock block, rock excavation, stability analysis.
Field quality control of an earth dam: random versus purposive sampling
Authors: Kotzias P C , Stamatopoulos A C
Published: April 2011

There are two sampling operations for field quality control of an earth dam: the random and the purposive. Both have been well established by their long use in engineering projects, but are fundamentally different in their basic assumptions, approach, and interpretation of results. They are analyzed herein and their basic similarities and differences are compared. The intent is to provide the proper perspective for an objective selection and subsequent implementation of one or the other operation. It is concluded that both operations can be implemented, singly or jointly, on a project, provided that inherent potentialities and limitations are clearly recognized and evaluated throughout design and construction.

Key words: earth dam, rockfill, sampling, statistical analysis, quality control, quality assurance.
Modelling impacts due to multiple landfill cells and clogging of leachate collection systems
Authors: Rowe R Kerry , Booker John R
Published: April 2011

A semianalytic (finite layer) technique that will readily allow modelling of the interaction between different landfill cells is presented. The cells may be either adjacent or separated and may have different dimensions (length, thickness) and different source leachate characteristics. The technique also allows modelling of the finite service life of engineered components of the barrier system such as the service life of the primary leachate collection system and, if present, geomembrane liner. The application of the technique is illustrated by first considering the longitudinal expansion along the alignment of leachate migration of a landfill and examining the interaction between the original and subsequent landfill in terms of impact on the underlying aquifer. Consideration is then given to the vertical expansion of existing landfills and finally to the modelling of the finite service life of a primary leachate collection system and geomembrane liner. It is demonstrated that a vertical expansion has considerable potential for increasing long-term impact and that the impact is also controlled by the service life of the engineered system.Key words: landfill, expansion, analysis, service life.
Numerical analysis of a multipropped excavation in stiff clay
Authors: Ng Charles WW , Simpson B , Lings M L , Nash DFT
Published: April 2011

This paper presents the procedures and the results of numerical analyses of a multipropped deep excavation at Lion Yard, Cambridge, using the nonlinear Brick model. The computed results are compared with the comprehensive case record. The observed small deflections and bending moments of the wall, low prop forces, and relatively small ground movements during the main excavation have been taken into account. Shear strains which developed around the site during the main excavation were generally less than 0.3%. Significant reduction of lateral stress in the ground during wall installation and the highly nonlinear stress-strain characteristics of the Gault Clay are the chief reasons for the observed unusual behaviour. The Gault Clay exhibits first yield at a threshold shear strain of about 0.001%, beyond which the stiffness deteriorates significantly from an initial very high value. This high stiffness at very small strains may be due to cementation bonding between soil particles, as a result of the presence of calcium carbonate. Simple drainage assumptions for the stiff fissured clay on both sides of the diaphragm wall appear to be inadequate for design analyses.Key words: numerical analysis, multipropped excavation, Gault Clay, nonlinear brick model, small strain stiffness.
Design and performance of deep well dewatering: a case study
Authors: Sargent D W , Beckie R D , Smith G
Published: April 2011

This paper reviews the process used to design the construction dewatering system at the Influent Pumping Station at Annacis Island Wastewater Treatment Plant. The design process followed the "observational method," as applied to soil mechanics by K. Terzaghi and set out by R.B. Peck in the Ninth Rankine Lecture. The design was based on a working hypothesis of behaviour anticipated under the most probable conditions identified in the data gathering and assessment program. The sensitivity of the design was evaluated by considering potentially unfavourable conditions evident in the available data. The design development included a review of monitoring feedback obtained during the pumping-well installation, a pumping test, and the dewatering system start-up. The monitoring program and review process are presented.Key words: dewatering, observational method, case study, pumping test.
Behavior of a fine-grained soil during the Loma Prieta earthquake
Authors: Boulanger Ross W , Meyers Mark W , Mejia Lelio H , Idriss Izzat M
Published: April 2011

Results of an investigation into the behavior of a fine-grained clayey soil at Moss Landing during the 1989 Loma Prieta earthquake are presented. A deposit of this soil underlies portions of the Moss Landing Marine Laboratory that experienced up to 1.3 m of lateral spreading deformations during this magnitude 7 earthquake. Silty clay from the deposit erupted to the surface in a "soil boil" characteristic of liquefaction, during and immediately after the earthquake. A sample from the silty clay boil had a liquid limit of 38, a plasticity index of 17, and a <5 µm fraction of 24%, and thus would be considered nonliquefiable according to commonly used criteria. Analysis of cyclic triaxial test data suggests that portions of the silty clay deposit likely developed high residual excess pore pressures (ru,r approx 80-90%) and significant shear strains during the earthquake and thus likely contributed to the observed lateral deformations. The field and laboratory data show that commonly used criteria for identifying "liquefiable" clayey soils should be applied with caution and should not be indiscriminately viewed as a substitute for detailed laboratory and in situ testing of low plasticity fine-grained soils.Key words: liquefaction, cyclic loading, silt, clay, earthquake, case history.
Modelling the responses of Athabasca oil sand in triaxial compression tests at low pressure
Authors: Samieh Ahmed M , Wong Ron CK
Published: April 2011

Experimental data from drained triaxial compression tests on Athabasca oil sand at low confining pressures ranging from 50 to 750 kPa are presented. The tested specimens exhibited severe strain-softening with significant dilation but did not approach the critical state entirely by the end of the tests due to the formation of localized shear zones. A homogeneous deformational response in which the entire specimen would reach to the critical state was derived from the experimental response and the critical state parameters. A constitutive model is established to simulate both the experimental and homogeneous deformational responses of Athabasca oil sand. The model is based on describing the evolution of internal microstructural changes with shear loading through a scalar disturbance function. The deformational response of the material is expressed in terms of the responses of its reference states, namely the virgin and fully disturbed states, through the scalar disturbance function. The virgin state of the material is modelled by a generalized single surface plasticity model, whereas the fully disturbed state is assumed to be the critical state. The parameters required to define the model were identified and evaluated. Comparisons between the predicted results and experimental data were made for model performance evaluation.Key words: oil sand, disturbance, plasticity, critical state, shear band.
A comparison between observed and calculated large settlements of raft foundations
Authors: Milovic Sasha D
Published: April 2011

This paper shows the results of large settlements observed over several years in Belgrade for a hotel founded on four rectangular rafts with expansion joints of 1 m width, and for a silo group built on the right bank of the Danube River. The capacity of the silo group is 400 MN. The settlement calculation for these structures was made using deformation parameters deduced from cone penetration test results. The theoretical solution for stresses and displacements was obtained by the finite difference method. Observed and calculated settlements show satisfactory agreement.Key words: settlement, raft foundation, finite difference, cone penetration tests.
High-frequency complex permittivity of shales (0.02-1.30 GHz)
Authors: Fam M A , Dusseault M B
Published: April 2011

This study describes a new approach to analyze complex permittivity data of shales and to extract fundamental properties relevant to engineering applications. The complex permittivity at high frequencies was measured for three different shales: Queenston, Mancos, and Pierre shales. Plane surfaces parallel and perpendicular to the bedding plane were cut from well-preserved cores. Permittivity data were acquired using a coaxial termination probe and a network analyzer (0.02-1.30 GHz). It is shown that Pierre shale displays high complex permittivity values relative to Queenston and Mancos shales. A simple approach is adopted to extract the volumetric free-water content of shales based on permittivity data at high frequencies. Shales with high specific surface (e.g., Pierre shale) show the lowest free-water content among tested cores. The slope of the relationship between real permittivity and frequency in a semi-log plot is suggested to relate permittivity data to the specific surface. The anisotropy in complex permittivity is a potential parameter in shale characterization. The permittivity anisotropy depends on the reactivity and the clay content of the shale, as well as on the inherent fabric anisotropy.Keywords: permittivity, clay content, specific surface, free-water content, anisotropy
Modelling of deep seated hill slope creep in permafrost
Authors: Foriero A , Ladanyi B , Dallimore S R , Egginton P A , Nixon F M
Published: April 2011

Attempts have been made to simulate hillslope creep observations at a site near the village of Tuktoyaktuk, Northwest Territories. Unlike other creep studies in permafrost, this site was unique in that the deformations occurred within a massive ice body, forming the core of a 30 m high concentric hill approximately 1200 m long and 700 m wide. The described simulation model of slope creep is based on both an extension of a closed-form solution originally proposed for two- and three-dimensional ice caps and a finite element creep analysis. The solution covers cyclic temperature fluctuations and incorporates spatial variations of the temperature-dependent creep parameters. Results of simulations are compared with in situ measurements of creep displacements in the hill.Key words: permafrost, slope, creep, in situ measurements, numerical simulation.
Physical, chemical, and mineralogical properties of Mexico City sediments: a geotechnical perspective
Authors: Díaz-Rodríguez JA , Cruz R Lozano-Santa , Dávila-Alcocer VM , Vallejo E , Girón P
Published: April 2011

Geotechnical, physical, chemical, and mineralogical properties of the sediments of Ramón López Velarde Park were examined. The site is located in the ancient lacustrine zone of Mexico City. In situ tests included a resistivity survey, soundings with an electric cone, and cross-hole seismic tests. In addition, a continuous core was obtained for the upper 40 m. This core was extensively studied in the laboratory to determine the variation of mineralogy, pH, organic matter, cation exchange capacity (CEC), and structural features with depth. The information is unique with respect to previous studies which focused on specimens at a single depth. Results facilitate the interpretation of the deposit evolution, leading to the current properties of this unique lacustrine sequence.Key words: Mexico City, geotechnical properties, lacustrine sediments, physical properties, mineralogy, chemical properties.
Experimental study of axial behaviour of tapered piles
Authors: Wei Jinqi , El Naggar M Hesham
Published: April 2011

Tapered piles, which have greater top cross sections than bottom ones, have the potential for substantial cost advantages for static loading conditions. However, tapered piles have not often been considered a design option because of the lack of design tools and knowledge about the behaviour of these piles. The objectives of this study are to explore and better understand the operating characteristics of the axial response of tapered piles. A large laboratory facility for testing model piles was developed. In this facility, the soil was contained in a steel soil chamber and pressurized using an air bladder to model the confining pressure. Three instrumented steel piles with different degrees of taper were used in this study. As expected, it was found that as the taper angle increased, the shaft resistance increased. It was found that the shaft resistance of the tapered pile was up to 40% larger than that of the cylindrical pile. The difference in the shaft resistance of the two types decreased for higher values of confining pressure. It was also found that the load distribution along the pile shaft for both pile types had the same pattern. However, this pattern varied as the confining pressure increased. Furthermore, the unit load transfer was significantly affected by the initial sand density for both pile types at low confining pressure, but as the confining pressure increased, this effect diminished. It is concluded that the tapered piles offer a larger resistance than the cylindrical piles. However, for longer piles, it is suggested that the taper be limited to the top length corresponding to 20 diameters.Key words: tapered piles, shaft friction, axial response, load transfer, model testing.
Nineteenth Canadian Geotechnical Colloquium: The soil-water characteristic curve: a historical perspective
Authors: Barbour S Lee
Published: April 2011

The constitutive relationship between water content or degree of saturation and suction is called the soil-water characteristic curve. The soil-water characteristic curve provides a conceptual framework in which the behavior of unsaturated soils can be understood. A historical review illustrates how the work of early researchers in soil science and geotechnical engineering laid the foundation for our current understanding of this relationship. Key elements of these early studies were a conceptual understanding of the soil-water characteristic curve as a relationship between the mass or volume of water stored within the soil and the energy in the water phase. It was on the basis of this conceptual model that current methods of measuring the soil-water characteristic curve were developed. Interpretative models for the distribution and geometry of the water phase in an unsaturated soil based on the capillary model have provided a useful conceptual model for understanding the effects of soil texture, gradation, void ratio, and compaction on the soil-water characteristic curve. The capillary model has also provided the foundation for recently developed techniques to predict the functional relationship between degree of saturation and shear strength, coefficient of permeability, coefficient of diffusion, and adsorption for unsaturated soils.Key words: unsaturated soils, soil-water characteristic curve, suction, shear strength, permeability, contaminant transport.
Soil clogging during surfactant-enhanced flushing of naphthalene-contaminated sand-kaolinite
Authors: Gabr M A , Chen J , Thomas R
Published: April 2011

The removal of naphthalene from soils using a surfactant-enhanced flushing process was studied. Column tests were conducted on sand-kaolinite specimens (0, 5, and 20% kaolinite content) with water and sodium dodecylsulfate (SDS) surfactant used as permeants. Upon the introduction of surfactant, the hydraulic conductivity (k) of the various test specimens containing kaolinite decreased by up to two orders of magnitude but then recovered gradually to its initial value upon further flushing. Although more than 90% of the naphthalene contaminant was removed from the test soils, excessively long periods of flushing were needed due to the clogging phenomenon. Upon varying the concentration of the liquid constituents (SDS, naphthalene, and NaCl), the micellar solutions were observed to convert into phases including liquid crystals and gel. The viscosity of these phases was measured to range from 10 to 1000 cP. Several hydraulic conductivity tests conducted with SDS amended with NaCl indicated the alleviation of the reduction in k when sufficient NaCl concentration was used.Key words: surfactant, hydraulic conductivity, kaolinite, sand, naphthalene, SDS, contaminant, remediation, viscosity.
A study on the subsoil of the Tower of Pisa based on results from standard and high-quality samples
Authors: Rampello Sebastiano , Callisto Luigi
Published: April 2011

In this paper, an updated geotechnical characterization of the soils underlying the leaning Tower of Pisa is presented, based on results from a recent experimental investigation as well as on results from previous investigations. Careful analysis of the cone penetration tests carried out in the past have permitted a detailed distinction between the cohesive and the cohesionless portions of the upper deposits. The mechanical behaviour of the soils has been investigated through a large number of laboratory tests performed on samples retrieved with standard tube samplers and with a large diameter thin-walled sampler. The mechanical behaviour of the soft upper clayey deposit is shown to be rather sensitive to sampling disturbance; the large diameter sampler allowed for the observation of a high compressibility that had not been evidenced in the previous investigations. A comprehensive set of soil parameters is derived for the clay strata. Normalized triaxial stress paths describe a state boundary surface similar to that predicted by the simple Modified Cam Clay model fitted on the experimental data. Also, the undrained shear strength predicted by the model is shown to be in good agreement with the experimental results obtained from standard unconsolidated undrained triaxial compression tests. Values of the small-strain shear modulus determined experimentally compare satisfactorily with those given by an empirical relationship. A profile for the small-strain shear modulus is proposed accordingly.Key words: case history, clays, compressibility, in situ testing, laboratory testing, sampling.
Shape of ground surface settlement profiles caused by excavation
Authors: Hsieh Pio-Go , Ou Chang-Yu
Published: April 2011

There are two general types of settlement profiles induced by excavation, the spandrel type and the concave type. Based on a regression analysis of the field observations of settlement curves with predominantly cohesive subsurface conditions, an empirical method for predicting the spandrel and concave settlement profiles is proposed. The proposed method is verified through several case histories. For comparison, the results obtained from other empirical methods are also presented. The proposed method provides a fairly good prediction of ground surface settlement and yields better prediction of angular distortion than other empirical methods for the concave- and spandrel-type settlement profiles. Furthermore, the relationship of cantilever area and deep inward area of wall deflection is established which can be used as the first approximation to predict the type of settlement profile.Key words: prediction, excavation, settlement profile, spandrel, concave.
Measurement of low-strain material damping and wave velocity with bender elements in the frequency domain
Authors: Brocanelli Diego , Rinaldi Victor
Published: April 2011

This paper discusses the application of piezoceramic bender elements for measurement of damping ratio in the frequency domain in a triaxial cell under isotropic confinement. The emitter was excited with a constant voltage and varied frequency sine signal while the phase difference and amplitude in the receiver were measured. The resonant frequency and dynamic characteristics of cell components were analyzed to study the influence of possible additional modes when the modal analysis of a soil sample is performed. Damping ratio and shear wave velocity were determined in a sample of dry silica sand at different confinements from the first resonant mode of the sample. A relationship was found between measured travel time and resonant frequency that satisfies the solution for the general wave equation. The measured damping ratio compares very well with approximated empirical models. It is concluded that the methodology assumed in this work performs satisfactory when the dynamic response of the cell components is properly identified.Key words: wave velocity, shear modulus, material damping, bender elements, frequency analysis, silica sand.
Instability and liquefaction of granular soils under undrained and partially drained states
Authors: Vaid Y P , Eliadorani A
Published: April 2011

An experimental investigation of the initiation of instability (liquefaction) in saturated sand under partially drained conditions is presented. The domain of stress space in which this instability develops is identified under various degrees of drainage, and its relationship to the zone of instability observed under undrained shear is explored. It is shown that partially drained conditions may render sand unstable that would otherwise be stable in a completely undrained state. Extremely small void ratio increases that cannot be regarded as physical loosening of sand, if sand is partially drained, contribute to instability. Implications of the findings are discussed in practical problems of liquefaction.Key words: sand, liquefaction, undrained, partially drained, instability, triaxial test.
Numerical analysis of the breakwater construction of Sergipe Harbour, Brazil
Authors: Brugger Paulo José , Soares de Almeida Márcio de Souza , Sandroni Sandro Salvador , Lacerda Willy Alvarenga
Published: April 2011

The numerical simulation of the breakwater construction at Sergipe Harbour, Brazil, is described and the results compared with instrumentation data. The numerical simulation was carried out in plane-strain conditions using the modified Cam-Clay model and the Biot consolidation theory. Field observations and the numerical simulation show that the horizontal displacements under the breakwater toe increase with time. This happens during the loading and consolidation stages. It is argued that the process does not necessarily derive only from undrained creep, since the model used does not simulate this phenomenon. The shear strains, measured by an inclinometer, increase more rapidly near the free-draining surfaces, in a process similar to the dissipation of excess pore pressure.Key words: clay, embankment, numerical analysis, shear strain, consolidation.
A numerical study of coupled consolidation in unsaturated soils
Authors: Wong Tai T , Fredlund Delwyn G , Krahn John
Published: April 2011

This paper first describes the numerical implementation of the coupled formulation for the theory of consolidation of unsaturated soils. The developed computer code is verified using the Mandel-Cryer problem and then is applied to the solution of coupled multidimensional consolidation problems. Using a parametric study, it is demonstrated that, in unsaturated soils, the Mandel-Cryer effect is suppressed and the consolidation process in unsaturated soils is affected significantly by the shape of the soil-water characteristic curve. Finally, the developed model is used to analyze the consolidation of an unsaturated-saturated soil column. Analysis results indicate that the classical "undrained" pore-water pressure response to an externally applied load only occurs in the saturated zone while the pore-water pressure response is subdued in the unsaturated zone. This paper also shows a method of deriving one of the two additional material parameters required for the analysis of unsaturated soils from laboratory test results.Key words: coupled consolidation, unsaturated soils, Mandel-Cryer effect, soil-water characteristic curve.
Reliability of self-boring pressuremeter in sand
Authors: Roy Debasis , Hughes JMO , (Dick) Campanella Richard G
Published: April 2011

The cone penetration test (CPT) is viewed by a majority in the geotechnical engineering profession as a preferred in situ testing tool, while the self-boring pressuremeter test (SBPMT) is sometimes viewed to be of questionable reliability. A comparative statistical study of SBPMT data and CPT cone tip resistance is undertaken in this research to examine whether the test data do actually support the perceived notion. Data from seven sand and silt sites in western Canada and one location in the United States have been examined. The sensitivity of the SBPMT to the variability in the state of packing is quantified and compared with the corresponding values for the cone tip resistance. The results indicate that the sensitivity of cone tip resistance and the SBPMT data to the variability in the in situ state of packing is comparable. Comparison of estimates of procedural uncertainties in the SBPMT and the CPT also leads to a similar conclusion. These observations do not support the notion of a general lack of reliability of the self-boring pressuremeter at sand-silt sites.Key words: reliability, sand, self-boring pressuremeter, piezocone, inherent variability, procedural uncertainty.
Response of tapered piles subjected to lateral loading
Authors: El Naggar M Hesham , Wei Jin Qi
Published: April 2011

Eighteen lateral loading tests were conducted on large-scale steel piles to establish the lateral behaviour of tapered piles in cohesionless soil. Three piles 1.52 m in length with different taper angles but the same average embedded diameter of 168 mm were installed in sand enclosed in a steel chamber 1.5 m in diameter and 1.445 m in depth. The soil chamber was lined with an air bladder so that sand inside the chamber could be pressurized to vary the confining pressure. The piles were instrumented with electrical resistance strain gauges and the horizontal pile movements at grade and the loading point were measured with displacement transducers. The bending-moment functions along the pile were calculated from the strain measurements by curve fitting the measured strain data. The soil resistance (p) and pile displacement (y) relationships were developed in the form of p-y curves by differentiating and integrating these bending-moment functions. It was found that tapered piles carried up to 77% more lateral loads than straight-sided-wall piles with the same average diameter. The maximum bending moment occurred in all piles at almost the same depth of one third of the embedded length of the pile. Hence, the cross section of tapered piles at the location of maximum bending moment was larger than that of straight-sided-wall piles, resulting in lower stresses in the pile. It was concluded that the tapered piles represent a more efficient distribution of the pile material and display better performance under lateral loading conditions.Key words: tapered piles, lateral response, p-y curves, modulus of subgrade reaction.
Rapid method of consolidation testing
Authors: Sridharan A , Nagaraj H B , Srinivas N
Published: April 2011

The determination of consolidation characteristics forms an important aspect in the design of foundations and other earth-retaining structures. The conventional consolidation test as originally proposed by Terzaghi takes considerable time (more than 15 days in highly compressible soils with low coefficient of consolidation) and effort. Any effort to reduce the duration of testing will be desirable from several considerations. In this paper, an attempt has been made to propose a rapid method of consolidation testing. In the proposed method, the next load increment is applied as soon as the necessary time required to identify the percent consolidation is reached and to evaluate the coefficient of consolidation by one of the popular curve-fitting procedures. The rectangular hyperbola method has been used to identify the percent consolidation reached after any load increment, and to determine the coefficient of consolidation, before making the next load increment. The time required to complete the test using the rapid consolidation method could be as low as 4-5 h compared with 1 or 2 weeks in the case of the conventional consolidation test.Key words: clays, compressibility, consolidation, settlements, soil tests.
A microstructural investigation of Osaka Bay clay: the impact of microfossils on its mechanical behaviour
Authors: Tanaka Hiroyuki , Locat Jacques
Published: April 2011

A recent microstructural investigation of Osaka Bay clay sediments has revealed the presence of abundant microfossils, particularly in the marine layers, which appear to influence directly the microstructural framework of the sediments and eventually its geotechnical behaviour. The microfossils act as a structural component which provides a high compressibility when most of the interaggregate pore space is closed. In addition, they can introduce some bias on the measurements of physicochemical properties.Key words: microstructure, porosimetry, Atterberg's limits, compressibility, mineralogy, microfossils.
Seismic lateral pressures for design of rigid walls
Authors: Wu Guoxi , Finn WD Liam
Published: April 2011

Design charts for seismic pressures against rigid walls subjected to horizontal earthquake shaking are presented for both uniform and nonuniform backfills. Solutions are based on a simplified model of soil response which gives results that agree almost exactly with rigorous solutions. Peak seismic thrusts are presented for three different soil profiles. For each profile, 250 combinations of ground accelerations and distributions of soil shear moduli with depth are analysed to provide data points of peak seismic thrust ratios for the construction of design envelopes. The seismic thrust ratios for design are presented as a function of the ratio of the predominant frequency of the earthquake motion and the fundamental frequency of the wall-soil system. An approximate method is given for evaluating the latter frequency without a full analysis.Key words: rigid walls, seismic lateral pressures, design lateral pressures.
Oxidation of flooded mine tailings due to resuspension
Authors: Yanful Ernest K , Verma Ajay
Published: April 2011

Laboratory experiments were performed to assess the contribution of resuspension to the oxidation of pyrrhotite mine tailings flooded with a shallow water cover (up to 80 cm). Resuspension was produced by a paddle rotated at prescribed speeds in the water cover. The quality of the water cover was monitored over a 126 day period and the results were compared to the case where the tailings were kept still (no resuspension). The results showed that resuspended tailings oxidized considerably more than tailings at rest. The pH and dissolved oxygen concentration of the stirred water covers were 2.6 and 14 times lower, respectively, than those of the static water covers where there was no resuspension. Sulphate production increased by about 26-64 times, while the release of metals such as zinc, copper, and nickel was 1020, 318, and 138 times greater, respectively. The suspended tailings were finer and had lower pyrrhotite content at the end of the experiments than the tailings at rest and the original tailings. Tailings oxidation and metal release increased with increasing stirrer speed and decreasing depth of water cover. These findings pertain to laboratory conditions and the water-quality data cannot necessarily be extrapolated to the field, except in a general sense. Key words: acid generation, oxygen flux, mass transfer, precipitation, ripples, hydraulic sorting.
Parametric study of resilient response of tracks with a sub-ballast layer
Authors: Shahu J T , Kameswara Rao NSV , Yudhbir
Published: April 2011

Formulation of a rational design methodology for laying or upgrading tracks for heavier and faster trains requires investigation of the effect of various track parameters on overall track responses. For this purpose, a three-dimensional linear elastic finite element model, 3D20N, is developed that uses 20-noded brick elements and 16-noded surface elements and models rails as one-dimensional beam elements. Modelling details related to rail elements enable this model to predict the track responses accurately. Assessment of predictive capabilities of the model has been carried out by detailed comparisons with other numerical models and measured field test results. A detailed parametric study of the track responses was carried out using this model for a typical track with a sub-ballast layer and by adopting a practical range of track variables. Subgrade modulus was found to be the most influential track parameter on the overall track responses. The next most important track parameters were depth of sub-ballast, rail moment of inertia, and tie spacing. Practical implications of predicted parametric trends are discussed.
Investigation of a landslide in Maskinongé, Québec
Authors: Demers Denis , Leroueil Serge , d'Astous Jacques
Published: April 2011

Several first-time landslides occurred in the Maskinongé area, Quebec, during the summer, which is rather unusual. They have been studied in detail, including a site investigation. The results show the following: (i) piezocone tests indicate that the clay mass close to the slopes of precarious stability is softened; (ii) the failure surface develops within the softened zone; and (iii) three of the four landslides occurred during the summer period when pore pressures are low, indicating that failure could be due to fatigue phenomena.
Mechanisms controlling the undrained shear strength behaviour of clays
Authors: Sridharan A , Prakash K
Published: April 2011

The undrained shear strength behaviour of kaolinitic soils is shown to be quite opposite to that observed for montmorillonitic soils under different physico-chemical environments. The mechanism controlling the undrained shear strength behaviour of soils is a function of clay mineralogy of the soils. The present investigation proposes two mechanisms to explain the contradictory behaviour of kaolinitic and montmorillonitic soils under undrained conditions. The undrained shear strength of kaolinitic soils is a result of the net attractive forces and the mode of particle arrangement as governed by the interparticle forces, whereas that of montmorillonitic soils can be attributed to the viscous shear resistance of the double-layer water. The validity of the proposed mechanisms is confirmed by the results of the present investigation and those in the literature.
Axial capacity of tapered piles established from model tests
Authors: El Naggar M Hesham , Wei Jin Qi
Published: April 2011

Tapered piles represent a more efficient distribution of pile material than uniform cross section piles in several respects. An extensive experimental research program was conducted to study the efficiency of tapered piles compared with piles of uniform cross section with the same material input. Three instrumented model steel piles with different degrees of taper were used in this program. The piles were tested in a large-scale laboratory setup under compressive and tensile loads. The pile head load and displacement and the strain along the piles were measured simultaneously. The objectives of the present paper were twofold: to examine the validity of the experimental results, and to use the unit load transfer curves established from the experimental results to predict the bearing capacity of prototype tapered piles. The shaft resistance for straight-sided wall piles established from the experimental results compared well with the theoretical predictions using the standard design procedure. The beneficial effect of pile taper was significant up to a depth of 20 pile diameters. The negative effect of the pile taper on the uplift capacity diminished quickly with depth and hence the performance of actual tapered piles (with greater length) would be comparable to that of straight-sided wall piles.
Diffusion of oxygen through a pulp and paper residue barrier
Authors: Cabral Alexandre , Racine Isabelle , Burnotte Fabien , Lefebvre Guy
Published: April 2011

Acid mine drainage can be curbed or reduced significantly by covering tailings sites with an oxygen barrier. In this study, the ability of pulp and paper residues, more specifically deinking residues, to function as such a barrier was investigated. Field data from two sites show that O2 diffusion through the barriers can be greatly reduced. To better understand how oxygen migrates through deinking residues and to develop prediction tools for future design with deinking residues, one-dimensional effective diffusion coefficients (De) were determined by fitting laboratory experimental curves (O2 concentration versus time data) to curves obtained from computer simulations. The results obtained confirmed the behaviour observed in soil covers: the effective diffusion coefficients are highly dependent on the degree of saturation (Sr) of the compacted material. The De values obtained in this study compare well with those published in the literature for several materials compacted at similar Sr. The De values varied from 8.3 × 10-9 m2/s (Sr approximately 91%) to 9.7 × 10-7 m2/s (Sr approximately 76%). The O2 consumption by biodegradation appears to be an important factor in the reduction of the O2 flux that can reach the bottom of the barrier.Key words: oxygen diffusion, pulp and paper residues, barrier, acid mine drainage.