bluuebunny/crossref_metadata_2025 huggingface dataset:
A pictorial case history of lateral rock creep in an open cut into the Niagara Escarpment rocks at Hamilton, Ontario
Authors: Quigley R. M. , Thompson C. D. , Fedorkiw J. P.
Published: July 2008

Excavation of an open trench to a total depth of 10–13 m including a 5.5 m penetration into the Eramosa Member of the Lockport dolomite formation resulted in an estimated 5–10 cm of lateral rock movement towards the excavation with slippage clearly defined at bedding planes and joints as illustrated in the accompanying photographs. The movements observed are the visual manifestation of release of high locked-in lateral stresses characteristic of rocks of the Niagara escarpment. If movement is not allowed, very high stresses are ultimately transferred to any rock encased structures.
A theoretical examination of the settlements induced by tunnelling: four case histories
Authors: Rowe R. K. , Kack G. J.
Published: July 2008

A theoretically based procedure for predicting and designing for settlement above tunnels constructed in soft ground is outlined. The application of this theoretical technique is discussed and its range of applicability is examined by consideration of four case histories that encompass a wide range of soil conditions and construction techniques. This technique is then used as the basis of a design approach that is described in the paper. It is suggested that this procedure will provide a convenient means of estimating settlement induced by tunnelling in many different soil deposits provided that reasonable construction procedures are adopted. Keywords: tunnels, tunnelling, soft ground, settlement, analysis, design, deformations.
Plastic deformation of an embankment on clay
Authors: Wu Tien H. , Hsu Jenq R. , Ali Elfatih M.
Published: July 2008

A simplified elastic, plastic, work-hardening stress–strain model was used to analyze the results of laboratory triaxial tests on kaolinite, grundite, and a lacustrine clay from Toledo. The necessary model parameters were determined from the test results.The stress–strain model was used to compute the displacements of an embankment on clay. A sensitivity analysis was performed to evaluate the influence of the various model parameters on the computer displacements. It was found that the preconsolidation pressure, which defined the yield point and the initial horizontal stress, had the largest influence. Most of the measured displacements fall within the range of values computed with the upper and lower limits of preconsolidation pressure. The effect of plane strain, variations in the elastic modulus, and compressibility are comparatively unimportant. Keywords: clay, elasticity, embankment, plasticity, settlement, stress–strain model, triaxial tests, yielding.
Acoustic characterization of fracture permeability at Chalk River, Ontario
Authors: Paillet Frederick L.
Published: July 2008

This study was undertaken to test recently formulated acoustic-analysis methods for fracture interpretation. The study area was selected because surface outcrops of igneous and metamorphic rocks have numerous, interconnected fractures and major lithology changes. In-situ acoustic-refraction data were obtained by digitally recording the entire pressure signal received by a conventional acoustic borehole logging system. The acoustic energy source had a centerband frequency of 34 kHz, and data were obtained at 60 and 90 cm source/receiver spacing. Borehole geometry produces waveforms with strong shear arrivals and high amplitudes associated with the fundamental guided fluid mode known as the tube wave. Waveforms refracted across fractures that are open on the borehole have shear mode excitation and tube-wave attenuation effects similar to previously described effects for isolated fractures in very uniform lithologies. Independent permeability data for the Chalk River boreholes are available in the form of effective-fracture apertures determined by straddle packer isolation and injection tests. The best correlation between the permeabilities measured by packer tests and acoustic data is obtained by integrating the difference between local tube-wave amplitude and an average amplitude from many adjacent stations. This synthetic amplitude-deficit log shows close correlation with zones of large measured permeabilities; however, there are some quantitative differences. These are attributed to: (1) differing radii of investigation, (2) effects of fracture interconnectivity, and (3) drilling damage in highly weathered and fractured zones. The tube-wave-amplitude method also does not seem applicable to depths less than about 50 m where the tube-wave mode is relatively unexcited. Keywords: fracture permeability, borehole acoustics, fracture hydrology.
Magat Dams: Design of internal filters and drains
Authors: Hillis Sydney F. , Truscott E. Glen
Published: July 2008

This paper describes the design and testing for the filter and drain zones for the Magat Dams. These four rockfill structures are located in the Philippines and range in height from 25 to 115 m. Construction was completed in late 1982. The project area is in a seismically active region and, as a result, the dam design had to be inherently conservative. This resulted in a highly zoned cross section and the provision of several wide filter and drain zones. The design of the filters and drains were checked by a series of large scale tests involving a 580 mm diam. permeameter and a large flume. Owing to the risk, however slight, of the dam cores being cracked during a major earthquake, the tests were carried out using both intact core material and core material into which a crack had been introduced. The results of the testing indicate that: (a) the filter gradations chosen are satisfactory, (b) it was prudent at Magat to introduce two filter zones between the dam core and the chimney drain, (c) conventional filter criteria are overly conservative when applied to the Magat core material, and (d) conventional criteria do not apply to the case of a cracked core. In this case the protective filter should contain a small amount of noncohesive fines. This is in accordance with developing practice. Keywords: filter design, testing, dam design, seismic effects, cracking.
Stress–strain–time behavior of deep sea clays
Authors: Silva A. J. , Moran K. , Akers S. A.
Published: July 2008

Summary results are presented of a comprehensive experimental study to investigate the strength, stress–strain properties, and creep behavior of fine-grained deep sea sediments. Isotropically (CIU) and anisotropically (CAU) consolidated undrained triaxial tests and drained triaxial creep tests were performed on undisturbed and reconstituted–reconsolidated (remolded) samples of smectite-rich and illite-rich deep sea clays from the North Central Pacific.The CIU Mohr–Coulomb parameters for remolded smectite [Formula: see text] were nearly identical to the undisturbed material [Formula: see text]. The parameters for remolded illite [Formula: see text] were also not significantly different than for the undisturbed material [Formula: see text].The undrained shear strength versus water content relationship (qf vs. wf) for remolded smectite is much lower than for the undisturbed material, whereas for illite the remolded strength is only slightly lower. Therefore it appears that smectite is much more sensitive than illite to the type of remolding used in these studies.The CAU tests showed that K0 agrees well with the Jaky equation, [Formula: see text]. The Mohr–Coulomb parameters were somewhat lower than the corresponding CIU results.Undisturbed and remolded samples were tested at stress levels of 10, 25, 40, and 65% of the Mohr–Coulomb strength for the determination of triaxial drained creep properties. Different relationships between stress level, strain, and time were determined for the two materials. A secondary state of creep, defined as a period of constant strain rate, was not consistently observed. Comparisons with terrestrial clays and near shore material display similar strengths of the deep sea sediments and greater deformation potential during long-term loading. Keywords: stress–strain behavior, creep, deep sea sediments, stress–strain–time behavior, triaxial compression tests.
Finite-element analysis of softening effects in fissured, overconsolidated clays and mudstones
Authors: Yoshida N. , Morgenstern N. R. , Chan D. H.
Published: July 2008

The softening process as observed in fissured, overconsolidated clays and mudstones is discussed in detail. Softening is classified into internal and external processes. The effect of softening is to decrease the shear strength of a material and its dilatant characteristics. This shear strength reduction is represented as a lowering of the failure envelope and a reduction in the degree of nonlinearity at low stress levels. There are some restrictions related to stress paths that affect the initiation of softening. The softening process may be formulated in terms of a time-dependent yield surface, and the finite-element method can be extended to analyze softening effects. A cut slope is analyzed as an example. The development with time of deformations is traced up to the collapse of the slope. This example contains the essentials to portray the role of the mechanism of softening. A distinction can be made between time-dependent deformation due to softening and those associated with conventional creep mechanisms. Key words: softening, time-dependent strength reduction, finite-element analysis.
Field test of electroosmotic strengthening of soft sensitive clay
Authors: Lo K. Y. , Ho K. S. , Inculet I. I.
Published: July 2008

A field test was undertaken to assess the effectiveness of electroosmosis in strengthening the soft sensitive (Leda) clay at the Gloucester test fill site. Specially designed copper electrodes were installed to prevent gas accumulation around the electrode and to allow pore water in the soil to flow out from the cathode without pumping. The variation of settlement, shear strength, and voltage distribution during treatment was measured, and tube samples were recovered before and after treatment for laboratory tests. The results of field vane tests at different locations within the treated area and at different times indicate that the undrained shear strength increased uniformly by approximately 50% for a period of 32 days throughout the depth of the electrodes. Concurrently, an average surface settlement of 50 mm was achieved. The total power consumption was less than 1% of the total project cost, indicating that the design of the treatment system was efficient. It is evident, therefore, that substantial increase in strength as well as general improvement in soil properties may be achieved by this improved version of electroosmosis. The elimination of pumping improved the economy of the process considerably. It is hoped that the process may receive wider application as a result of these improvements. Key words: electroosmosis, electrode, polarity reversal, Gloucester test fill, soft sensitive clay, uniformity of treatment, power consumption.
Geotechnical appraisal of the foundation rock mass behaviour of Narmada Sagar Dam project, central India: a case study
Authors: Choubey Vishnu D. , Chaudhari Shailendra
Published: July 2008

The Narmada Sagar Dam, a concrete gravity structure under construction across the Narmada River in central India, will have a crest length of 653 m and a maximum height of 92 m. The present paper discusses the results of geotechnical investigations undertaken for evaluating the rock mass strength parameters, applying the modern concepts of rock mechanics, especially the rock mass rating, modulus of deformation, shear parameters, and strength and permeability of the dam foundation rocks. The joint systems observed are used to interpret and explain the occasional zones of poor core recovery and to explain the location and orientation of the drilling programme. It is suggested that the estimate of spacing and opening of water-conducting joints may lead to useful estimates of the groutable volume of voids in the rock mass, and inclined drill holes are preferable for optimum grouting. The values of different parameters have been obtained and correlated. The studies have led to the conclusion that the foundation rocks of Narmada Sagar Dam are competent and suitable for designing the proposed concrete gravity dam. Key words: dam, strength, elastic modulus, deformability, rock discontinuity, rock quality designation, rock mass classification.
Selection of operative centrifuge radius to minimize stress error in calculations
Authors: Cooke Brian
Published: July 2008

In a centrifuge model, the vertical stress distribution is nonlinear because of the variation of the model's "gravity" field with the centrifuge radius from the top to the bottom of the model. Thus in calculating the centrifugal acceleration, and hence the scale of the model, care must be taken to use the definition of centrifuge radius that minimizes the stress error in the model profile. This paper demonstrates that this optimum radius is measured from the centre of rotation to a point 0.59 times the model height from the bottom of the model. Key words: centrifuge, stress, error.
Centrifuge modelling as a consulting tool
Authors: Mitchell R. J.
Published: July 2008

Modelling is a primary tool for understanding complex engineering problems. In geotechnical engineering, physical and numerical modelling should be considered as complementary tools, both able to contribute substantially to the development of knowledge but one usually emerging as being the most effective or efficient for obtaining solutions for a certain class of problems. By considering past practice, recent progress, and amenability to modelling, the suitability of centrifuge modelling as a practical tool for solving various classes of geotechnical problems is discussed. Those problems for which the author considers centrifuge modelling to be a state-of-the-art consulting tool are delineated. Scale effects, boundary effects, and the concept of modelling of models are examined. Some known limitations in the physical modelling of natural phenomenon are noted. Centrifuge size, type, and complexity are discussed with reference to some of the more complex geotechnical problems, and some suggestions regarding methodologies for prototype evaluations are advanced. Key words: centrifuge modelling, consulting, physical modelling, centrifuge size, centrifuge use.
Stress–strain behaviour of sands in triaxial and direct simple shear tests
Authors: Rossato Gianni , Simonini Paolo
Published: July 2008

The behaviour of a natural sand in triaxial compression and direct simple shear tests was compared by means of dimensionless analysis of parameters controlling the evolution of stresses and strains. The secant triaxial compression and direct simple shear moduli were interpreted in a dimensionless form. A criterion based on the equivalence between major principal strain in the two tests was considered to compare the results. Key words: sand, stress–strain behaviour, triaxial test, direct simple shear test, shear modulus, triaxial compression modulus.
Instrumentation and geotechnical monitoring techniques used in the Sydney Coalfield, Nova Scotia
Authors: Gallant W. D. , Aston T. R. C.
Published: July 2008

Since 1982, the Rock Mechanics Group of the Energy, Mines and Resources CANMET–CRL Cape Breton Coal Research Laboratory has been closely involved in assessing the behaviour of mine openings in the underground workings of the Sydney Coalfield, Nova Scotia. This paper examines a variety of geotechnical instrumentation and monitoring techniques used to assess strata behaviour during the different phases of longwall mining operations: gateroad deformation, floor heave, intersections, gateside pack behaviour, and subsidence monitoring. Key words: instrumentation, coal mining, longwall mining, geotechnical monitoring, subsidence, tunnels, Sydney Coalfield.
Evaluating Ko in Champlain clays with hydraulic fracture tests
Authors: Lefebvre G. , Bozozuk M. , Philibert A. , Hornych P.
Published: July 2008

Hydraulic fracture tests using piezometer tips 10–500 mm long were performed in Champlain clays at five different sites with overconsolidation ratios (OCR) varying from 1.6 to 4.8. Before the test, the piezometer fluid was replaced by a methylene blue solution (10 g/L) to dye the fissures resulting from the test. After the hydraulic fracture, the soil around the piezometer tips was recovered by means of a large-diameter sampler. For 300 and 500 mm long piezometers, the fissure pattern was radial and vertical, even in deposits with an OCR above unity, confirming that hydraulic fracturing is related to the total stress acting on the cavity walls. The results for the five sites define for the Champlain clay deposits a Ko–OCR relationship that gives higher Ko values than generally proposed in the literature. Key words: hydraulic fracture, piezometer tip, sensitive clay, fissure, stress ratio Ko, overconsolidation.
Effect of chloride ions on adsorption of cadmium from a landfill leachate
Authors: Yong Raymond N. , Sheremata Tamara W.
Published: July 2008

This study examines possible formation of neutral and negative complex ions between trace quantities of cadmium (Cd) and chloride ions (Cl−). Experiments were first performed for the adsorption of Cd, from 2 to 10 mg/L, onto kaolinite in a soil suspension from a landfill leachate. A companion set of experiments was performed involving Cd, also from 2 to 10 mg/L, onto kaolinite in a soil suspension from a pure solution. By comparing the results from these two sets of experiments, it was apparent that there were constituents in the leachate which interfered with the adsorption of cadmium onto kaolinite. With the use of thermodynamic equilibrium calculations, it is seen that the chloride ions could account for some of the interference. Further experiments involving adsorption of Cd, from 5 to 80 μg/L, in the presence of Cl−, at 1000 mg/L, indicate that there is less adsorption of Cd than in an experiment involving [Formula: see text] at pH values from 4 to 5. This result is in agreement with the thermodynamic equilibrium calculations. Additional experimental results of adsorption of Cd at 80 μg/L for pH values of from 2 to 9 indicate that the apparent Cd – Cl complex formation interferes with the precipitation of Cd as Cd(OH)2 and is in agreement with those obtained from predicted thermodynamic equilibrium. The study demonstrates that if accurate and precise predictions of Cd transport are required, detailed aqueous hydrogeochemistry studies may be important and necessary. Key words: adsorption, cadmium, leachate, speciation, cadmium–chloride complexes, thermodynamic equilibrium.
Creep behavior of fine-grained frozen soils
Authors: Wijeweera H. , Joshi R. C.
Published: July 2008

Uniaxial compressive creep tests were conducted on saturated samples of six fine-grained frozen soils. The creep behavior of the soils with respect to variation in the creep stress, temperature, and total water content is examined. The test results indicate existence of a unique relationship between the secondary creep rate, [Formula: see text], and the time to the onset of the secondary creep stage, ts, which is dependent only on the soil type. The values [Formula: see text], ts, and the initial strain rate are found to be directly related to the relative creep load (creep stress to peak strength ratio) acting on the soil. Results indicate these relationships to be independent of temperature. A method of analysis is presented whereby the creep behavior of a fine-grained frozen soil at various stresses, temperatures, and total water contents can be predicted, using data from a few creep tests conducted at only one reference temperature and total water content. A secondary creep model is introduced that predicts the creep behavior reasonably well in fine-grained frozen soils. The results obtained from this study are of importance to practicing engineers. Key words: fine grained, frozen soils, creep, load, temperature, water content, compressive strength, creep model.
Yielding and damage of intact rock
Authors: Ofoegbu G. I. , Curran J. H.
Published: July 2008

This paper presents a description of the elastic deformability and strength of intact rock. Structural defects such as microcracks cause the load-bearing capacity and elastic stiffness of rock to decrease, because the imposed load is supported by a diminished fraction of the solid volume. This is accounted for using a continuum damage variable, which describes the effect of cracks on the capacity of rock to support distortional loading. Values of the variable are computed using an incremental evolution law, which describes the effects of confinement and distortional load intensity on cracking. Elastic deformability is described in terms of the damage variable (function of stress and deformation) and the constant elastic stiffness of uncracked rock. It is argued that inelastic deformation is caused by tensile and shear stresses induced at the tips and surfaces of microcracks, which can be related to the ratio of the distortional to the hydrostatic intensities of the stress tensor (transformed to account for damage). Rock strength is described in terms of the permissible values of this ratio, which are shown to vary with the accumulated inelastic deformation. Laboratory data from 45 triaxial tests on host-rock specimens from an Ontario deep mine are presented to illustrate the measurement of damage and shear resistance. Key words: damage, yielding, shear resistance, tensile strength, elastic stiffness, uncracked rock.
The Hepburn landslide: an interactive slope-stability and seepage analysis
Authors: Misfeldt G. A. , Sauer E. Karl , Christiansen E. A.
Published: July 2008

Mechanisms of active landslides are continuous processes involving the dynamics of slope failure interacting with the groundwater regime. This process is simulated in phases by combining stability calculations interactively with a seepage analysis to determine the factor of safety for a dormant landslide near Hepburn, Saskatchewan. The landslide is a multiple retrogressive failure with two parallel slip surfaces at different elevations. The slip surfaces are in originally overconsolidated Cretaceous and Tertiary clays softened by shear from glaciation. An artesian aquifer is present at the base of the slip surface, causing saline springs at the base of the valley slope. A residual effective friction angle of 6.7° with zero cohesion was found to best characterize the shear strength of the clays in the failure zone. Potential nets and head profiles from the seepage analysis illustrate the strong influence of changing topography on the groundwater flow system. The present-day factor of safety for the dormant landslide was estimated to be 1.10. Key words: multiple retrogressive landslides, dormant landslide, seepage modelling, residual strength, artesian conditions, glacial drift, Cretaceous clays.
Nouveau coulis à base de ciment pour le scellement d'ancrages dans le roc gelé du Grand Nord
Authors: Benmokrane Brahim , Ballivy Gérard , Hernandez Pedro , Aitcin Pierre-Claude
Published: July 2008

At present time, in frozen rock, the anchors are not grouted with conventional cement grouts as these are inefficient, or deteriorate with the formation of ice lenses during the freezing of the mixing water. The problem is avoided by boring deeper into the rock mass, until the unfrozen horizon is reached, if accessible, or by using thermal protection systems, which result in additional costs. Substantial economies may be obtained by grouting the anchor in the frozen rock, along a length necessary and sufficient to insure the stability of the structure, by using an antifreeze grout with a Portland cement base without resorting to thermal protection. In this context, the results of a study carried out in the Far North are presented, including pull-out tests of anchors grouted with a Portland cement base grout in a rock frozen at −12 °C. The resistance to frost of the cement grout has been achieved by using an antifreeze chemical admixture, the sodium nitrate (NaN02), which has allowed the setting of the anchors without heating the steel bars, the rock, or the grout. The results obtained show that the cement grout used may be considered as an efficient grouting product for the design of grouted anchors in the frozen rock or in the permafrost of the Canadian Far North. Key words: frozen rock mass, permafrost, grouted anchor, pull-out test, Portland cement grout, antifreeze chemical admixture, Canadian Far North, Arctic.
The Nerlerk berm case history: some considerations for the design of hydraulic sand fills
Authors: Konrad Jean-Marie
Published: July 2008

Back-analyses of recent large-scale slides during the hydraulic placement of an articial sand island at the Nerlerk site (Beaufort Sea) using different methods have resulted in contradictory conclusions with respect to the state of the fill. All the interpretation methods assume a unique relationship between steady-state strength and void ratio. This assumption is, however, not verified, since steady-state strength depends also on effective confining stress. This paper presents the results of a back-analysis at the Nerlerk site using a modified concept proposed by the author which isbased on nonunique values of steady-state strength for a given sand. It is established that the density conditions at Nerlerk, on average at a relative density of about 40%, and the initial stress conditions are conducive to strain softening, with a steady-state strength corresponding to the minimum strength defined by the LF line. For Nerlerk sand,the minimum undrained strength is about 18% of the steady-state strength determined with conventional methods using high confining stresses. The Nerlerk berm failures were thus "liquefaction" slides induced most likely by progressive straining. Key words: sand, undrained, strength, steady state, hydraulic fill.
Laboratory evaluation of K0 for overconsolidated clays
Authors: Garga Vinod K. , Khan Mahbubul A.
Published: July 2008

Most of the laboratory testing methods available for the evaluation of in situ horizontal stresses are applicable to normally consolidated or lightly overconsolidated clays. This paper describes a new laboratory method for the determination of in situ horizontal stresses of heavily overconsolidated clays using a stress-path triaxial apparatus. The proposed method is based on the concept that if the radial stress exceeds the in situ horizontal stress, while maintaining the axial stress constant and equal to the in situ vertical effective stress, only then will the sample experience significant axial strain. The results obtained for undisturbed samples of an overconsolidated clay crust are found to be in agreement with some available methods. For verification of the applicability of the proposed method, K0 was determined for artificially prepared samples that had been subjected to known stress paths simulating field stress history. Key words: K0, overconsolidation, in situ stress, in situ test, clay crust, laboratory test.
Tassement et consolidation au dégel d'un silt argileux à Kangiqsualujjuaq
Authors: Leroueil Serge , Dionne Guy , Allard Michel
Published: July 2008

The physical characteristics, the compressibility, and the consolidation of a permafrost clayey silt of Kangiqsualujjuaq, Quebec, have been studied, in the laboratory and in the field, by melting the permafrost in the foundation of an excavation. It appears that the values of the thawing settlement parameter (A0) obtained in the laboratory and in the field coincide perfectly with one another, and with those found in the literature for the same type of soil. It has also been observed, on that site, that the thawing of the permafrost, even though ice-rich, does not generate excess pore pressures. Key words: permafrost, compressibility, consolidation, laboratory, in situ. [Journal translation]
Determination of the Oldman River Dam foundation shear strength
Authors: Davachi M. M. , Sinclair B. J. , Hartmaier H. H. , Baggott B. L. , Peters J. E.
Published: July 2008

The paper describes the results of site investigation and laboratory testing and the analysis performed for the determination of foundation shear strength at the Oldman River Dam site in southwestern Alberta, Canada. Horizontally bedded claystones, siltstones, and sandstones at the site contain relatively weak bedding-plane shears that adversely affect foundation stability. Data on the bedding-plane shear characteristics were collected by mapping, borehole coring, shaft exploration, and large-diameter sampling. Shear planes of structure-wide continuity were identified. Numerous laboratory direct shear tests were done to measure in situ and residual shear strengths. The design angle of shearing resistance of selected continuous bedding-plane shears was evaluated by summing the representative residual angle of shearing resistance and components of the angle of shearing resistance due to in situ state, roughness, and thickness of the bedding-plane shears. Relatively flat dam slopes were found to be required for stability. The methods used at the Oldman River Dam should be applicable at other sites located in flat-lying mudrock sequences. Key words: Oldman River Dam, foundation shear strength, sedimentary rocks, bedding-plane shear, residual angle of shearing resistance, in situ state, roughness, thickness.
Stress-induced response from both natural and construction-related processes in the deepening of the Peace River valley, B.C.
Authors: Imrie A. S.
Published: July 2008

The Peace River rises in the Rocky Mountain Trench and flows easterly through the Rocky Mountains before flowing onto the Plains in northeastern British Columbia near the Alberta border. Stress measurements conducted at two of three damsites near the boundary of the Foothills and the Plains reveal high remnant lateral stresses and a K0 of about 2. In proceeding 90 km downriver from the W.A.C. Bennett Dam, past the Peace Canyon Dam to the proposed site C dam near Fort St. John, the stratigraphic section changes from competent, massive sandstones of Lower Cretaceous age to soft, weak shales at the top of the Lower Cretaceous section. Valley downcutting by the Peace River through these highly stressed rocks has led to valley rebound features that have both similarities and differences where observed at each of the three damsites. Differences in rock strength at each site contribute to the variations in features noted. These valley rebound features include vertical relief joints, horizontal bedding plane joints, upward arching of the riverbed, and shear zones that both parallel and cross the bedding. The challenge for the geotechnical engineer is first to find these features and account for them in the design, as they tend to govern the foundation and slope strength even though they may only be a few millimetres in thickness. A second challenge is to appreciate that the remnant stresses that led to the formation of the features are still present and these may cause further response when excavation proceeds at a site. A geologic model for the Peace Valley is used to explain the natural and construction response to deepening of the river valley. Key words: stress measurements, damsite, remnant lateral stress, valley rebound, Lower Cretaceous shale and sandstone, relief joints, bedding plane joints, arching, shear zones, foundation design.
Behaviour of cemented sandfills under repeated loadings
Authors: Nnadi G. N. , Mitchell R. J.
Published: July 2008

Two series of tests were conducted to study the behaviour of cemented tailings backfills materials under repeated loading conditions. Drained triaxial and drained plane strain boundary conditions were used in this experimental work. Two distinct patterns of behaviour were found to exist, and these were separated by a critical stress level close to the static strength of the cemented materials. These materials can sustain instantaneous repeated loading deviatoric stresses of 1.2 times the static strength for up to a dozen stress applications but generally reach a failure state with multiple applications of repeated loads in excess of 0.9 times the static failure loads. The behaviour of the cemented backfill was found to progressively become more plastic with increased number of stress applications. The resilient modulus was found to initially decrease before increasing with increased number of stress applications. Key words: repeated loadings, cemented backfills, resilient modulus.
Pore-water pressures in soft to firm clay during driving of piles into underlying dense sand
Authors: Eigenbrod K D , Issigonis T
Published: July 2008

During driving of steel piles through soft, sensitive clay into very dense sand and gravel, pore-water pressure responses were monitored. As a result of the large length of the piles and also because of the high sensitivity of the soft clays, the piles were driven in two stages. During the initial stage of driving in the soft clay, only very small pore-water pressure increases were recorded together with very low pile driving resistances; however, during the second stage of driving, high pore-water pressure increases were observed in the clay as soon as the piles penetrated into the underlying very dense sand and gravel. It was concluded that the clay deposit was loaded from below, as the piles were driven into very dense sand. The total stress changes and the resulting pore-water pressure changes in the clay were analyzed, assuming that the pile driving load was equivalent to a flexible load acting on the surface of an elastic half-space, which represents the soft clay deposit. This interpretation of the pore-water pressure increases is important for the assessment of the bearing capacity of engineering structures affected by piles driven through soft soils into very dense deposits. The potential for high pore-water pressure increases in the clay during undrained loading as well as for volume increases in the dense sand due to pile driving can be predicted from piezocone test data.

Key words: pile driving, pore-water pressure, piezocone testing, soft sensitive clays, dense sand deposits.
Numerical study of parameters influencing the response of flexible retaining walls
Authors: Vaziri Hans H
Published: July 2008

A practical numerical model is described for analysis of flexible retaining walls. In terms of capabilities, the model fits between traditional limit equilibrium methods and full finite element approaches; it overcomes many of the limitations associated with the former but is not equipped with the versatility offered by the latter. Using an approach similar to that adopted in boundary-element based models, the wall stiffness is represented by a series of elastic beam elements whose stiffness is combined with that of the prestressed struts and the soil to form, the overall stiffness matrix. The stiffness matrix of the soil is obtained by inversion of flexibility matrices generated by interpolation and sealing of flexibility matrices calculated for a simplified soil model using finite element methods. The soil behaves linearly elastically, as long as the pressures correspond to stress levels lying between the limits. Where the lateral displacement of the wall corresponds to a pressure outside of these allowable limits, correction forces are added until the resulting pressures are within the active or passive pressures. Arching is permitted by considering the forces acting on the wall compared with the forces consistent with possible failure surfaces within the soil. Other features that can be accomodated by the model include struts, variations in water table, and the effects of surcharges. The proposed model has been shown to capture the displacement, anchor loads, and lateral stresses for several field problems. Based on these studies and other field applications of the model a number of points have been observed that are of practical interest; these points are separately listed.

Key words: numerical analysis, retaining wall, anchor, arching, soilstructure interaction, deflection.
A metamodel for federation architectures
Authors: Topçu Okan , Adak Mehmet , Oǧuztüzün Halit
Published: July 2008

This article proposes a metamodel for describing the architecture of a High Level Architecture (HLA) compliant federation. A salient feature of the Federation Architecture Metamodel (FAMM) is the behavioral description of federates based on live sequence charts. FAMM formalizes the standard HLA Object Model and Federate Interface Specification. FAMM supports processing through automated tools, and in particular through code generation. It is formulated in metaGME, the metamodel for the Generic Modeling Environment.
Modeling, scheduling, and simulation of switched processing systems
Authors: Hung Ying-Chao , Michailidis George
Published: July 2008

Switched Processing Systems (SPS) serve as canonical models in a wide area of applications such as high performance computing, wireless networking, call centers, and flexible manufacturing. In this article, we model the SPS by considering both slotted and continuous time and analyze it under fairly mild stochastic assumptions. Two classes of scheduling policies are introduced and shown to maximize the throughput and maintain strong stability of the system. In addition, their performance with respect to the average job sojourn time is examined by simulating small SPS subject to different types of input traffic. By utilizing the simulation result of the proposed policies, a hybrid control policy is constructed to reduce the average job sojourn time when the system has unknown and changing input loads.
Tree model guided candidate generation for mining frequent subtrees from XML documents
Authors: Tan Henry , Hadzic Fedja , Dillon Tharam S. , Chang Elizabeth , Feng Ling
Published: July 2008

Due to the inherent flexibilities in both structure and semantics, XML association rules mining faces few challenges, such as: a more complicated hierarchical data structure and ordered data context. Mining frequent patterns from XML documents can be recast as mining frequent tree structures from a database of XML documents. In this study, we model a database of XML documents as a database of rooted labeled ordered subtrees. In particular, we are mainly concerned with mining frequent induced and embedded ordered subtrees. Our main contributions are as follows. We describe our unique
embedding list
representation of the tree structure, which enables efficient implementation of our
Tree Model Guided
(
TMG
) candidate generation.
TMG
is an optimal, nonredundant enumeration strategy that enumerates all the valid candidates that conform to the structural aspects of the data. We show through a mathematical model and experiments that
TMG
has better complexity compared to the commonly used join approach. In this article, we propose two algorithms, MB3-Miner and iMB3-Miner. MB3-Miner mines embedded subtrees. iMB3-Miner mines induced and/or embedded subtrees by using the
maximum level of embedding constraint
. Our experiments with both synthetic and real datasets against two well-known algorithms for mining induced and embedded subtrees, demonstrate the effectiveness and the efficiency of the proposed techniques.
OpenAD/F
Authors: Utke Jean , Naumann Uwe , Fagan Mike , Tallent Nathan , Strout Michelle , Heimbach Patrick , Hill Chris , Wunsch Carl
Published: July 2008

The Open/ADF tool allows the evaluation of derivatives of functions defined by a Fortran program. The derivative evaluation is performed by a Fortran code resulting from the analysis and transformation of the original program that defines the function of interest. Open/ADF has been designed with a particular emphasis on modularity, flexibility, and the use of open source components. While the code transformation follows the basic principles of automatic differentiation, the tool implements new algorithmic approaches at various levels, for example, for basic block preaccumulation and call graph reversal. Unlike most other automatic differentiation tools, Open/ADF uses components provided by the Open/AD framework, which supports a comparatively easy extension of the code transformations in a language-independent fashion. It uses code analysis results implemented in the OpenAnalysis component. The interface to the language-independent transformation engine is an XML-based format, specified through an XML schema. The implemented transformation algorithms allow efficient derivative computations using locally optimized cross-country sequences of vertex, edge, and face elimination steps. Specifically, for the generation of adjoint codes, Open/ADF supports various code reversal schemes with hierarchical checkpointing at the subroutine level. As an example from geophysical fluid dynamics, a nonlinear time-dependent scalable, yet simple, barotropic ocean model is considered. OpenAD/F's reverse mode is applied to compute sensitivities of some of the model's transport properties with respect to gridded fields such as bottom topography as independent (control) variables.
Efficient Contouring on Unstructured Meshes for Partial Differential Equations
Authors: Goldani-Moghaddam Hassan , Enright Wayne H.
Published: July 2008

We introduce three fast contouring algorithms for visualizing the solution of partial differential equations based on the PCI (pure cubic interpolant). The PCI is a particular piecewise bicubic polynomial interpolant defined over an unstructured mesh. Unlike standard contouring approaches, our contouring algorithms do not need a fine-structured approximation and work efficiently with the original scattered data. The basic idea is to first identify the intersection points between contour curves and the sides of each triangle and then draw smooth contour curves connecting these points. We compare these contouring algorithms with the built-in Matlab
contour
procedure and other contouring algorithms. We demonstrate that our algorithms are both more accurate and faster than the others.
Algorithm 876
Authors: Atkinson Kendall E. , Shampine Lawrence F.
Published: July 2008

We present here the algorithms and user interface of a
Matlab
program, Fie, that solves numerically Fredholm integral equations of the second kind on an interval [
a
,
b
] to a specified, modest accuracy. The kernel function
K
(
s
,
t
) is moderately smooth on [
a
,
b
] ×[
a
,
b
] except possibly across the diagonal
s
 = 
t
. If the interval is finite, provides for kernel functions that behave in a variety of ways across the diagonal, that is,
K
(
s
,
t
) may be smooth, have a discontinuity in a low-order derivative, have a logarithmic singularity, or have an algebraic singularity. Fie also solves a large class of integral equations with moderately smooth kernel function on [0, ∞ ).
Managing a man-rated software development program via risk mitigation
Authors: Varnell-Sarjeant Julia F.
Published: July 2008

This paper discusses a different approach to managing risk in a man-rated software system. This approach emphasizes identifying and targeting the right risks in order to apply effective mitigation activities. It addresses the risk of not understanding the customer wishes, of unreliable software product, and selection of inappropriate reuse. When the right risks are identified with sufficient granularity, resources can be focused on mitigating only those risks. Resources are not spent mitigating general risks or non-risks. The cost can be more correctly estimated and overruns controlled.
Surfing the net for software engineering notes
Authors: Doernhoefer Mark
Published: July 2008

This column usually focuses on web sites that explore various software engineering topics such as requirements engineering, development methodologies, test strategies, data and database engineering and so on. This month, however, I thought I'd talk about the people who have contributed to the state of the software engineering art by developing and refining the approaches and methodologies that we use every day. Sometimes we take the simple things for granted. For example, the notion of software modules seems second nature to most of us. That would not have been true had it not been for David Parnas. So for this month's column I thought I'd focus on web sites dedicated to the people and, by extension, their work.
Risks to the public
Authors: Neumann Peter G.
Published: July 2008

Edited by Peter G. Neumann (Risks Forum Moderator and Chairman of the ACM Committee on Computers and Public Policy), plus personal contributions by others, as indicated. Opinions expressed are individual rather than organizational, and all of the usual disclaimers apply. We address problems relating to software, hardware, people, and other circumstances relevant to computer systems. To economize on space, we include pointers to items in the online Risks Forum: (R i j) denotes RISKS vol i number j. Cited RISKS items generally identify contributors and sources, together with URLs. Official RISKS archives are available at www.risks.org (which redirects to Newcastle and gets you nice html formatting and a search engine courtesy of Lindsay Marshall; http://catless.ncl.ac.uk/Risks/i.j.html gets you (R i j)) and at ftp://www.sri.com/risks.
History of computers can raise student's interest
Authors: Chroust Gerhard
Published: July 2008

What was software development back in the 1960's and how did it evolve?
Intracranial and Abdominal Aortic Aneurysms: Similarities, Differences, and Need for a New Class of Computational Models
Authors: Humphrey J.D. , Taylor C.A.
Published: July 2008

Intracranial saccular and abdominal aortic aneurysms (ISAs and AAAs, respectively) result from different underlying disease processes and exhibit different rupture potentials, yet they share many histopathological and biomechanical characteristics. Moreover, as in other vascular diseases, hemodynamics and wall mechanics play important roles in the natural history and possible treatment of these two types of lesions. The goals of this review are twofold: first, to contrast the biology and mechanics of intracranial and abdominal aortic aneurysms to emphasize that separate advances in our understanding of each disease can aid in our understanding of the other disease, and second, to suggest that research on the biomechanics of aneurysms must embrace a new paradigm for analysis. That is, past biomechanical studies have provided tremendous insight but have progressed along separate lines, focusing on either the hemodynamics or the wall mechanics. We submit that there is a pressing need to couple in a new way the separate advances in vascular biology, medical imaging, and computational biofluid and biosolid mechanics to understand better the mechanobiology, pathophysiology, and treatment of these lesions, which continue to be responsible for significant morbidity and mortality. We refer to this needed new class of computational tools as fluid-solid-growth (FSG) models.
Molecular Engineering of Viral Gene Delivery Vehicles
Authors: Schaffer David V. , Koerber James T. , Lim Kwang-il
Published: July 2008

Viruses can be engineered to efficiently deliver exogenous genes, but their natural gene delivery properties often fail to meet human therapeutic needs. Therefore, engineering viral vectors with new properties, including enhanced targeting abilities and resistance to immune responses, is a growing area of research. This review discusses protein engineering approaches to generate viral vectors with novel gene delivery capabilities. Rational design of viral vectors has yielded successful advances in vitro, and to an extent in vivo. However, there is often insufficient knowledge of viral structure-function relationships to reengineer existing functions or create new capabilities, such as virus-cell interactions, whose molecular basis is distributed throughout the primary sequence of the viral proteins. Therefore, high-throughput library and directed evolution methods offer alternative approaches to engineer viral vectors with desired properties. Parallel and integrated efforts in rational and library-based design promise to aid the translation of engineered viral vectors toward the clinic.