bluuebunny/crossref_metadata_2025 huggingface dataset:
Lateral displacements in clay foundations under embankments
Authors: Tavenas F. , Mieussens C. , Bourges F.
Published: April 2011

The lateral displacements developing in clay foundations under 21 different embankments during construction and consolidation have been analyzed. The development of a significant consolidation at the beginning of any embankment construction has been confirmed. As a result, lateral deformations initially develop in conformity to the theory of elasticity for a drained condition. Undrained shear distortions develop near the end of construction when the clay foundation has become partly or entirely normally consolidated. This sequence of drained and undrained response of the foundation governs both the magnitude and distribution with depth of the lateral displacements and is the main reason why previous displacement predictions based on undrained analysis have been unsuccessful. Delayed lateral deformations can be significant and develop linearly with the consolidation settlement, at least in the first years after the end of construction. The distribution of lateral deformations with depth is not modified during consolidation so that long-term predictions of deformations as well as of the behaviour of adjacent structures appear possible.
Field measurements in two tunnels in Edmonton, Alberta
Authors: Thomson S. , El-Nahhas F.
Published: April 2011

Observations of the deformation of the temporary lining of two tunnels are presented. The Whitemud Creek tunnel was 6.05 m in diameter and was bored through Upper Cretaceous clay shale. The 170 Street tunnel was bored through till and had a diameter of 2.56 m.In the Whitemud Creek tunnel, the vertical diameter decreased by 10–15 mm and the horizontal diameter decreased by 6 mm. Movement was essentially complete in about 3 months. There was a rigid body movement upward of the lining system probably due to unloading of the soil in the invert area. Deformation moduli indicate a softening of the soil around the tunnel, which is consistent with the deformation observations. A finite-element analysis suggests that this softened zone is as important with regard to lining deformation as increasing K0 from 0.67 to 1.0In the 170 Street tunnel, the ground surface showed significant movement despite the small diameter and considerable overburden thickness. The vertical and horizontal diameter decreases were about one half of those of the Whitemud Creek tunnel and were essentially complete in 4–5 weeks. Soil pressures calculated from the observations showed a wide variation. Values derived from lagging deflection yielded a maximum of 63% of overburden pressure whereas pressure cell readings were 3.3% of overburden.It appears that the space between the lagging and the moled surface of the soil is an important factor affecting the magnitude of stresses in the temporary lining. Diameter changes are considered to be the easiest and most reliable observation of tunnel linings. The deflection of the lagging is also simple to observe but may not satisfy simple beam theory. Pressure cell results were disappointing and their use is debatable.
A documentation of soil failure during the British Columbia earthquake of 23 June, 1946
Authors: Rogers Garry C.
Published: April 2011

All examples of soil failure, other than landslides, that could be identified as occurring during the magnitude 7.2 Vancouver Island earthquake of 23 June, 1946 have been documented. Slumping and liquefaction were common and caused a significant proportion of the earthquake related damage. Liquefaction occurred up to a distance of 100 km from the epicenter, a distance that agrees well with a previously established empirical relationship.
The energetics of an ablating headscarp in permafrost
Authors: Pufahl D. E. , Morgenstern N. R.
Published: April 2011

In arctic regions mass movements in thawing permafrost are common. Although different types of landslides have been identified, one type referred to as a "bimodal flow" has caused a significant amount of interest on account of the unusually high rate of mass wasting associated with this type of flow slide. The flow is characterized by a steep headscarp and a low angle mud flow or tongue at the base of the slide.Although more than one activity contributes to the retreat of the headscarp, the most important process is that of ablation. An obvious anomaly exists between the amount of heat required to sustain the high rates of observed ablation and the amount of heat available from net radiation.The components of the energy balance were identified and a field study was undertaken to quantify these terms. Instrumentation included radiometers, wet and dry thermocouples, anemometers, and a lysimeter to measure the latent heat of condensation of evaporation.The results of this study indicate that all the major terms in the energy balance equation combined to form the source of heat responsible for the high rates of observed ablation. Moreover, they provide a rational basis for controlling bimodal flow slides using different insulation materials.
A first approximation of the volume of ground ice, Richards Island, Pleistocene Mackenzie delta, Northwest Territories, Canada
Authors: Pollard W. H. , French H. M.
Published: April 2011

Using data contained in the Mackenzie Valley Geotechnical Data Bank together with data derived from morphometric analyses of topographic maps and air photographs, the volume of ground ice present in the upper 10 m of Richards Island is calculated to be 10.27 km3. Pore and segregated ice constitute over 80% of the total ice volume. Wedge ice constitutes between 12 and 16% of total ice volume in the upper 4.5 m, and approximately 36% of all excess ice. In the upper 1–2 m, wedge ice may exceed 50% of earth materials. Pingo ice is insignificant in terms of its contribution to total ice volumes. Excess ice constitutes 14% of the upper 10 m of permafrost; it follows that thawing of this layer of permafrost may lead to an average subsidence of 1.4 m.The results of this study are probably typical of other areas of the Pleistocene Mackenzie delta. There is also general agreement with data obtained from arctic Alaska.
Geotechnical applications of electrical borehole logging in southern Saskatchewan
Authors: Sauer E. Karl
Published: April 2011

Single point resistance and spontaneous potential geophysical borehole logging is shown to be a valuable supplement to conventional coring methods in geotechnical site exploration. A continuous graphical record of the sediments is obtained without gaps caused by sample recovery problems. The log provides an effective capability for stratigraphic correlation. The technique is also shown to be of value as a format for a borehole data base and for use in instrumentation design such as piezometers and observation wells. The technique has limitations such as drift and maintenance difficulties but these can be overcome by adequate field supervision. Over 7000 testholes have been logged successfully and are in data storage in Saskatchewan.
Undrained shear strength in stability calculation of embankments and foundations on soft clays
Authors: Larsson Rolf
Published: April 2011

Undrained shear strength of soft clays is usually measured by field vane tests or laboratory tests. The relevance of the test results in stability calculations of embankments and foundations is discussed. Empirical relations for undrained shear strengths obtained from Scandinavian clays are compared with reported failures.
A new approach to the stability analysis of thawing slopes
Authors: Vallejo Luis E.
Published: April 2011

A new approach to the stability analysis of thawing slopes at shallow depths, taking into consideration their structure (this being a mixture of hard crumbs of soil and a fluid matrix), is presented. The new approach explains shallow mass movements such as skin flows and tongues of bimodal flows, which usually take place on very low slope inclinations independently of excess pore water pressures or increased water content in the active layer, which are necessary conditions in the methods available to date to explain these movements.
Development of pore pressures in quasi-static penetration tests in sensitive clay
Authors: Roy Marius , Tremblay Michel , Tavenas François , Rochelle Pierre La
Published: April 2011

The static cone penetration test is a valuable tool for the investigation of soil deposits but its potential may be further improved in the future if the pore pressures generated around the cone tip during the penetration are measured.A new sounding instrument called a piezocone was built at Université Laval to investigate the magnitude, effects of rates of penetration, and rate of dissipation of the excess pore pressures according to the location of the porous stone on the apparatus.The magnitude of the pore pressures induced during driving is a maximum at the cone tip and then decreases along the shaft as measured by porous stones located behind the cone tip. Induced pore pressures at the tip are independent of the rate of penetration, but a very small rate effect may influence the pore pressures measured behind the cone tip. The results show that the use of the ratio u/qc for soil characterisation may be considered only after adoption of standards regarding the location of the sensing element and the rate of penetration.The new sounding tool models the penetration of a single pile relatively well and its use is suggested for the study of pore pressures during the penetration of piles and their dissipation with time.
Effects of applied pressure on freezing soils
Authors: Konrad J.-M. , Morgenstern N. R.
Published: April 2011

Background studies illustrating the effect of externally applied pressure on frost heave are reviewed together with some of the thermodynamic aspects of pressure effects. New experimental data are presented to show how the segregation potential varies with applied pressure. This variation is explained in terms of the influence of applied pressure on the segregation-freezing temperature and the average permeability of the frozen fringe. An explanation is given of the change in mode from expulsion to attraction of water to the freezing front in a loaded soil and it is shown that segregation can be eliminated by externally applied loads. However, these loads are generally too high to be of engineering interest. While it has been concluded that, under laboratory freezing conditions, the segregation potential is dependent upon applied pressure, suction at the frost front, and rate of cooling of the frozen fringe, field conditions are often simpler. A simplified method of predicting frost heave under field conditions is developed that should lead to conservative results.
Clay–coal charge transfer and beneficiation by dry mineral removal
Authors: Quigley Robert M. , Inculet Ion I. , Beisser Ernest M. J.
Published: April 2011

Most coal requires upgrading (beneficiation) prior to burning to reduce the amount of ash left after combustion. Normal washing techniques may produce large amounts of clayey sludge requiring expensive storage behind dykes and dams.Dry coal powder, pulverized to 150 μm for burning, is suitable for dry beneficiation using electrostatic techniques. Such a process would eliminate clay sludge. Agitation of the powdered coal and its mineral wastes results in a charge transfer on contact, the coal becoming positive and the mineral matter negative. Separation in an electrostatic tower produces high quality coal and dry clay mineral waste.Clay minerals form the main component of the ash in most Canadian coals; kaolinite in eastern coals and montmorillonite in western coals. The cumulative amount of charge transfer controls the efficiency of separation. The test results show that the cumulative amount of charge transfer increases with increasing number of contacts, montmorillonite generating four times more charge than kaolinite at a given dry density. Typical values of cumulative charge after 100 contacts on montmorillonite and kaolinite pellets of 1.9 g/cm3 dry density are 0.3 × 10−10 and 0.07 × 10−10 C, respectively.
Saline leachate migration through clay: a comparative laboratory and field investigation
Authors: Crooks Valerie E. , Quigley Robert M.
Published: April 2011

The migration of salt solutions (NaCl) through remoulded, compacted clay in a laboratory physical model is compared with field migration through a similar but undisturbed clay located below a domestic waste landfill. In both the laboratory and field systems, the salt profiles indicated that migration was dominated by diffusion.After 12 years of leachate exposure at the landfill site, both Na+ and Cl− had migrated about 1.5 m from the soil/refuse interface compared to an estimated advance of the seepage front of only 3–4 cm. The pore water Na+ and Cl− values versus depth exhibited considerable scatter, requiring data from three boreholes to delineate the concentration boundaries of the vertical migration.Diffusion coefficients, D, were obtained using an analytical solution to the one-dimensional dispersion–convection equation. Laboratory values of D, corrected to the estimated field temperature, were similar to field values. The D values of 3 to 6 × 10−6 cm2/s for Cl− and 2.5 × 10−6 cm2/s for Na+ appear suitable for preliminary design in nonfractured clays. Key words: salt migration, diffusion, domestic landfill, pollution.
Internal stresses in frozen ground
Authors: Williams P. J. , Wood J. A.
Published: April 2011

Small transducers that were inserted 1.2 cm apart in a frozen soil subjected to a temperature gradient have shown differences in pressure of more than 0.1 MPa. The pressures are generated by growth of ice lenses taking place against the resistance of the surrounding frozen soil.The observations, which are compatible with reports by others from various field studies, illustrate the importance of both the thermodynamic and mechanical constraints on the process of frost heave and the development of frost heave pressures. Key words: frozen ground, frost heave, frost heave pressures, phase relations, internal stresses.
A yield equation for rock
Authors: Michelis Paul , Brown E. T.
Published: April 2011

A yield equation for isotropic, homogeneous, geotechnical materials has been developed and applied to the work-softening and work-hardening behaviour of granular rocks. The development of this yield equation was based on a comparison of the work done and the energy dissipated within a sample undergoing yield in triaxial compression. The formulation takes into account friction and dilatancy and also an experimental observation leading to the derivation of a nonassociated flow rule. The analysis of extensive experimental data indicates that the flow rule is consistent for work-softening and -hardening behaviour, and validates the application of the incremental theory of plasticity to the irrecoverable strain behaviour of rocks in which the predominant mode of deformation is cataclastic. The yield equation, which is expressed in terms of readily indentifiable material parameters, predicts yield strength or strength at a given value of plastic strain invariant, and relates stress and strain increments at yield. Key words: rocks, yield, plastic strain, work softening, work hardening, energy, dilatancy, nonassociated flow.
Flexibility coefficients and interaction factors for pile group analysis
Authors: Sharnouby Bahaa El , Novak Milos
Published: April 2011

Flexibility coefficients of single piles and interaction factors established for groups of two piles are presented to facilitate analysis of arbitrary pile groups exposed to static horizontal loads. Such an analysis may yield pile group flexibility, stiffness, deflection, and distribution of loads on individual piles. The data given are complete in that they include horizontal translation, rotation in the vertical plane, and cross effects between the two, making it possible to establish complete stiffness and flexibility matrices of pile groups provided with either rigid caps or arbitrarily flexible caps. Homogeneous, parabolic, and linear (Gibson's) soil profiles are considered and the piles may have a free length sticking above the ground surface. The methods of group evaluation based on superposition of interaction factors are reviewed and compared and numerical examples are given. Key words: piles, pile groups, lateral loads, flexibility, stiffness, load distribution.
Behaviour of rigid piles in layered soils under eccentric and inclined loads
Authors: Sastry V. V. R. N. , Meyerhof G. G. , Koumoto T.
Published: April 2011

The lateral soil pressures, ultimate bearing capacity, and displacements of instrumented vertical single rigid model piles in a layered system consisting of soft clay overlying loose sand and subjected to vertical eccentric and central inclined loads have been investigated. The variation of lateral soil pressures and the tip resistance of the pile are analysed with respect to the total load or moment on the pile. Theoretical estimates of pile capacity in homogeneous soils under pure moment and under horizontal load have been extended to piles in a layered system. For intermediate eccentricities and inclinations of the load, the pile capacity can be estimated from simple interaction relations or semiempirical eccentricity and inclination factors. The pile displacements are analysed in the light of linear elastic theory and nondimensional p − y curves. Reasonable agreement has been found between the measured and predicted values. Key words: bearing capacity, clay, displacements, eccentric load, horizontal load, lateral pressure, layered system, model test, pile, sand.
Comportement de pieux d'essais instrumentés sous charge horizontale
Authors: Frank R. , Zervogiannis H. , Christoulas S. , Papadopoulos V. , Kalteziotis N.
Published: April 2011

This paper describes the behaviour of two test piles (one bored and postgrouted and one simply bored, both 31.7 m long and 0.75 m in diameter) subjected to horizontal loads. These full-scale pile tests were carried out for the actual design of the pile foundation of a pier of the Evripos cable-stayed bridge. This bridge will link the Euboea Island to mainland Greece. The two piles have already been subjected to bearing capacity tests under axial loadings. The inclinometer measurements, taken during the present tests, yielded, in particular, the deformed shape of the piles as well as the bending moments. Conclusions could be drawn for the final design of the pile foundation with respect to horizontal loadings. Furthermore, various calculation methods using p–y reaction curves for cohesionless soils have been checked: the Ménard pressuremeter method, the method of the American Petroleum Institute recommendations, and the Standard penetration test method of Christoulas. These pile tests show that simple measurements, taken on construction sites, can yield interesting results on the actual behaviour of horizontally loaded piles. Key words : pile, horizontal loading, full-scale test, horizontal loads, bending moment, subgrade reaction modulus, p–y curve, cohesionless soil, Standard penetration test, pressuremeter test.
Dissolution and oxidation of mudstone under stress
Authors: Chigira Masahiro
Published: April 2011

Weathering of soft mudstone in nature, characterized by the presence of an oxidized zone and an underlying dissolved zone, was simulated in the laboratory in 15 °C water with a pH of 3–7 and dissolved oxygen contents of 4–16 mg/L under stresses up to 0.49 MPa for as long as 70 days. When the water is acid, hydrogen ions diffuse from the rock–water interface through the rock and attack acid-labile calcite in mudstone preferentially and easily at a well-defined dissolution front, leaving a dissolved zone behind the front. Density decreases, porosity increases, ultrasonic P-wave velocity decreases, and shear strength decreases in the dissolved zone. The dissolution front migrates toward unreacted rock, and the migration rate is controlled by the diffusion of hydrogen ions in the reacted dissolved zone, so the rate is influenced by the stress exerted on the rocks; the effective diffusivity becomes smaller when the rock is stressed. Oxygen also diffuses through the rock to a well-defined oxidation front and changes the rock color from greenish grey to pale brown by oxidation. Slight deterioration occurs with the color change and change in density, P-wave velocity, and porosity. Depletion of pyrite by oxidation and the complete color change take a long time in comparison with the slight color change. Chlorite seems to transform into smectite in acid and highly oxidizing conditions. Key words : mudstone, dissolution, oxidation, weathering.
A numerical method for modelling large displacements of jointed rocks. I. Fundamentals
Authors: Wang Baolin , Garga Vinod K.
Published: April 2011

A numerical method called the block-spring model for analyzing heavily jointed rocks is presented in this paper. This model permits the assessment of stability of both underground and surface excavation in jointed rock mass and is capable of simulating large displacements. The model simulates the jointed rock mass by an assemblage of rigid blocks interacting through contacts. By relating the contact forces to the relative displacements between the blocks and directly applying the equilibrium equations, the displacements of the blocks and subsequently the contact forces can be determined. An iteration procedure is applied to describe the progressive failure along the joints. The proposed model can identify unstable blocks by considering the rearrangement of the blocks. A computer program has been written in FORTRAN based on the procedures of the proposed model. Some simple examples are presented in the present paper to demonstrate the capability of the proposed model. Advanced features of the model including simulation of rock bolts and groundwater are presented in a companion paper, in which two case histories have been analyzed in detail with the proposed model. Key words : jointed rocks, stress, deformation, analysis, numerical model, excavation, anchors, groundwater.
A shear-dependent fracture-zone transmissivity model
Authors: Tannant D. D. , Kaiser P. K.
Published: April 2011

Shear displacements caused by excavation through a fracture zone can decrease the overall fracture-zone transmissivity. The complex arrangement of flow channels found in fracture zones creates a situation where imposed shear displacements will reduce the aperture of critically oriented fractures. This paper presents a simple flow model based on the en echelon structure found in many fracture zones from which a phenomenological relationship between shear displacement and transmissivity change is established. This model is then used to demonstrate the effect of shear displacement around a circular opening. The effects of shear-induced decreases in transmissivity are most dramatic when a continuous low-transmissivity zone is created around the opening. In this case, the steady-state heads can be relatively high and the resulting hydraulic gradient into the excavation can be extremely large. If the low-transmissivity zone around the opening is discontinuous because, for example, the shear displacements are nonaxisymmetric, then the inflow becomes channelled and the steady-state heads and hydraulic gradients near the excavation substantially decrease. The concept of shear-induced transmissivity reduction in fracture zones provides an alternative mechanism to shear-induced dilation and normal stress induced fracture closure for interpreting and explaining the observed hydraulic response in fracture zones. Key words : transmissivity, shear displacement, fluid flow, en echelon fractures, fracture zone, excavation.
Limit equilibrium computation of dynamic passive earth pressure
Authors: Morrison Jr. Ernest E. , Ebeling Robert M.
Published: April 2011

Few solution techniques exist for the determination of pseudostatic dynamic passive earth pressures for cohesionless soils. The widely accepted Mononobe–Okabe equation can result in the computing of unconservative values if the wall interface friction angle is greater than half the soil internal friction angle. As an alternate solution, equilibrium equations were formulated assuming a log spiral failure surface, and a research computer program was written to calculate the dynamic passive earth pressure coefficient. The primary purpose of this paper is to present a comparison of results obtained using the Mononobe–Okabe equation with those obtained using the log spiral formulation. Key words : pseudostatic, dynamic, passive earth pressure.
The static equilibrium of drag anchors in sand
Authors: Neubecker S R , Randolph M F
Published: April 2011

This paper examines the static equilibrium of drag anchors during embedment in sand. A limit equilibrium method is developed to allow the anchor holding capacity to be predicted given a specific anchor geometry and position relative to the free surface of the sand. The method is based on the earlier approach of Le Lievre and Tabatabaee, but is extended to include a three-dimensional soil wedge, which is consistent with experimental observation. The solution procedure is also extended to be more applicable for anchors at a preultimate stage by incorporating a force behind the anchor fluke. To calibrate the method, a series of centrifuge model anchor tests has been performed in silica and calcareous sands. The static capacity of the anchor during embedment is compared with the static limit equilibrium solution and good agreement is demonstrated.

Key words: drag anchor, statics, sand, limit equilibrium, ultimate holding capacity.
Mechanical and hydraulic behaviour of a soft inorganic clay treated with lime
Authors: Locat Jacques , Trembaly Hélène , Leroueil Serge
Published: April 2011

A comprehensive series of laboratory tests was conducted on an inorganic clayey sediment in order to predict the mechanical behaviour of dredged sediments used in reclamation projects. The soil used was a Louiseville clay, which was mixed with various quantities of lime (010%) and had a varied water content (122650%). Tests were carried out with special large cells and standard oedometers to look at both the compressibility and the hydraulic conductivity. Once pozzolanic reactions are begun, for a given curing time, a linear relationship between preconsolidation pressure and lime concentration is observed. Compressibility results indicate that it is possible to define a separate compression curve for each lime concentration and curing time. Adding lime will influence the hydraulic conductivity both by flocculation and by the formation of secondary minerals. If only flocculation occurs, an increase in hydraulic conductivity follows. If enough lime is added, the resulting secondary minerals will create major changes in the micropore network and this will decrease the hydraulic conductivity by up to one order of magnitude. The development of a secondary micropore network along with the cementation of large flocs induce significant increases in both the liquid and plastic limits. This results in a significant increase in the water sorption potential and higher Atterberg limits.

Key words: dredged sediments, compressibility, hydraulic conductivity, lime, stabilization, microstructure.
Application of the Cα/Cc concept to secondary compression of sabkha soils
Authors: Al-Shamrani Mosleh A
Published: April 2011

Sabkha soils are coastal and inland saline deposits of arid climates consisting mainly of loosely cemented sandy silt to silty clay particles. Invariably the soils contain an appreciable amount of organic material and are characterized as being highly compressible. Despite increased interest in various aspects of sabkha soil behavior, little is yet known about the nature and magnitude of secondary compression of these distinct sediments. In this paper, the secondary compression behavior of a typical sabkha formation from the southwestern coast of Saudi Arabia was investigated. Series of conventional and long-term, one-dimensional consolidation tests were conducted on natural and preloaded undisturbed samples taken from the compressible sabkha layer. The results of the laboratory investigation, substantiated by existing field data, indicated that a significant portion of sabkha settlements takes place as a secondary compression. The coefficient of secondary compression, Cα, was found to be constant, and the ratio of Cα to the compression index, Cc, is within the range reported in the published literature for various geotechnical materials. The applicability of the Cα /Cc concept to sabkha soils was further ascertained by comparing the secondary settlements estimated based on this concept with those measured directly in the field under an instrumented test embankment. Reasonable agreement was found between predictions and field observations.Key words: sabkhas, consolidation, coefficient of secondary compression, preloading, test embankment.
The settlement and bearing capacity of very large foundations on strong soils: 1996 R.M. Hardy keynote address
Authors: Clark Jack I
Published: April 2011

Strong soils are not typically problem soils, and hence their behaviour has not been extensively studied. Strong soils are best defined on the basis of their geologic history, but for this paper they can be roughly defined as cohesive soils with an N value of about 15 or over and cohesionless soils with N values over 30. Settlement of tall buildings on strong soils has always been of interest. The means of estimating settlement of the large foundations or pile foundations associated with these structures varies but is generally understood to be predominantly elastic. Although predictions of settlement based on laboratory tests or in situ tests may vary as much as an order of magnitude, there now exists a reasonable data base which suggests that large buildings will settle similar amounts regardless of the size or bearing pressure of the foundations or, for that matter, the type of foundations. No data base exists for quantifying the maximum bearing pressure that will be tolerated by large foundations without failure. The angle of internal friction is known to be critical and to decrease with increasing pressure. It is difficult to measure the undisturbed strength of strong soils, since undisturbed samples are very difficult to secure. Centrifuge model tests of large foundations of different shapes confirm that the bearing capacity factor N gamma decreases with increased size of footing, but the decrease of N gamma may not be accounted for entirely by the friction angle change with pressure. Selection of a friction angle to determine the peak capacity of very large foundations must be done very carefully and with a great deal of judgement, since it cannot be accurately measured.Key words: settlement, bearing capacity, foundation behaviour.
Surface settlement during shield tunnelling at CH218 in Taipei
Authors: Ou Chang-Yu , Hwang Richard N , Lai Wei-Jung
Published: April 2011

This paper presents the surface settlement performance induced by the foamed type of earth pressure balance shield in contract CH218 of the Hsintien Line of the Taipei Rapid Transit System. The surface settlement characteristics caused by the single tunnel and by twin tunnels with reference to two sections spaced at 87 m are studied. Field observations indicate that the surface settlement trough due to the single tunnel can be represented by the normal distribution. The distance of the inflection point to the tunnel center and maximum surface settlement value are consistent with those found in the literature. The characteristics of the surface settlement trough are related to the type of the soil, particularly where the crown of the tunnel is located in a layered soil deposit. The ground surface settlement induced by twin tunnels was found to be larger than estimated using the principle of superposition.Key words: shield tunnelling, surface settlement, field observation.
Comparison of limits states design methods for bearing capacity of shallow foundations
Authors: Baikie L D
Published: April 2011

A comparison is made between several limit states design methods for the bearing capacity of shallow foundations. It is found that the main reason for the difference between the methods is the variation in the load factors.Key words: limit states design, shallow foundations, sand, clay.
Load-strain-displacement response of geosynthetics in monotonic and cyclic pullout
Authors: Raju D M , Fannin R J
Published: April 2011

Mobilization of the pullout resistance of geosynthetics in monotonic and cyclic modes is described from both displacement- and load-controlled tests performed at normal stresses in the range 4-17 kPa. The tests were performed on three geogrids and two geomembranes embedded nearly 1.0 m in a uniformly graded sand. Results for load-controlled tests at a constant rate of 0.25 kN/(m ·min-1), followed by several series of load cycles of increasing amplitude, are compared with displacement-controlled tests at a constant rate of 0.5 mm/min. In general the geogrids behave as an equivalent textured sheet. Pullout behaviour, and especially the incremental displacement mobilized at cyclic loads close to the maximum resistance, is found to vary with type of geogrid. In only one case was cyclic pullout resistance of a grid found to exceed the monotonic resistance. A comparison of the cyclic and monotonic response yields a constant ratio of pullout resistance at large displacement, but one which is not unique to a particular specimen. Cyclic strains of decreasing amplitude are mobilized along a test specimen, with most of the necessary relative displacement occurring close to the loaded end and the embedded end showing little response.Key words: pullout testing, monotonic, cyclic, dynamic, geosynthetics, reinforced walls.
Void ratio redistribution in undrained triaxial extension tests on Ottawa sand
Authors: Ayoubian A , Robertson P K
Published: April 2011

Water-pluviated samples of Ottawa sand were tested in monotonic, undrained triaxial extension tests. The specimens exhibited similar "limited strain softening" behavior, and they all experienced phase transformation from contraction to dilation at small axial strains. The tests were stopped at different stages and the samples were frozen to obtain void ratio distribution along the length of the specimens. It was shown that void ratio redistribution can start at very low axial strains in an undrained triaxial extension test. Before phase transformation, void ratio redistribution was very small, but after phase transformation void ratio redistribution started rapidly and continued until the end of the tests at ultimate state. The location of the ultimate state line in a void ratio - mean normal effective stress plot was shown to be affected by localized failure at large strains in undrained triaxial extension tests. The actual ultimate state line with respect to void ratios and effective stresses within the failure zone in the samples can be located above the average ultimate state line obtained from average measurements of void ratios and effective stresses of the entire specimens.Key words: liquefaction, testing, void ratio.
Measurement of the coefficient of permeability for a deformable unsaturated soil using a triaxial permeameter
Authors: Huang Shangyan , Fredlund D G , Barbour S L
Published: April 2011

The development of a specially designed triaxial permeameter for the measurement of the coefficient of permeability of deformable unsaturated soils is presented in this paper. The triaxial permeameter makes it possible to directly measure the coefficient of permeability at various combinations of net normal stresses and matric suction values. The volume change of the soil specimen during the permeability measurement can also be monitored. The performance of the permeameter is demonstrated for a group of tests conducted on slurried specimens of a silty sand.Key words: unsaturated soil, coefficient of permeability, triaxial permeameter, volume change.
Laterally loaded piles in sand: slope effect on P-Y reaction curves
Authors: Mezazigh S , Levacher D
Published: April 2011

An extensive program of centrifuge tests was undertaken to study the effect of slopes on P-Y curves in dry sand. The paper concerns the method developed in a previous series of centrifuge tests to experimentally determine P-Y curves. Bending-moment curves are fitted by local quintic spline functions through a crossed validation method and then differentiated twice. These experimental P-Y curves are validated by back analysis. The program of tests on piles near slopes is given. It includes studies of the effect of distance to the slope, slope angle, and soil properties. Sample preparation method, model piles, and the lateral-loading device are described. Deflection versus load curves, bending-moment curves, and derived P-Y curves for piles close to slopes are compared to horizontal-ground response. The coefficients that can apply to the P-Y reaction curves of the reference piles (a single pile in horizontal ground) are proposed for use in practice.Key words: pile, slope effets, models, centrifuge, bending moment, P-Y reaction curves.
Modeling of soil behavior with a recurrent neural network
Authors: Zhu Jian-Hua , Zaman Musharraf M , Anderson Scott A
Published: April 2011

A recurrent neural network (RNN) model is developed for simulating and predicting shear behavior of both a fine-grained residual soil and a dune sand. The RNN model with one hidden layer of 20 nodes appears very effective in modeling complex soil behavior, due to its feedback connections from a hidden layer to an input layer. A dynamic gradient descent learning algorithm is used to train the network. By training part of the experimental data, which include strain-controlled undrained tests and stress-controlled drained tests performed on a residual Hawaiian volcanic soil, the network is able to capture significant variability of shear behavior existing in the residual soil. The unusual characteristics that the denser soil samples dilate under a higher stress level and the looser soil samples contract under a lower stress level are well represented by the RNN model. The RNN model also shows encouraging results in simulation and prediction of behavior of a dune sand which experienced loading-unloading-reloading conditions. Excellent agreements between the measured data and the modeling results are observed in both stress-strain behavior and volumetric-change characteristics. As compared with a traditional model, the RNN model shows more effectiveness and less effort.Key words: neural network, modeling, soil behavior, shear tests, simulation, prediction.
Simulating transient infiltration in unsaturated soils
Authors: McDougall J R , Pyrah I C
Published: April 2011

Transient responses to various infiltration events have been examined using an unsaturated flow model. Numerical simulations reveal a range of infiltration patterns which can be related to the ratio of infiltration rate to unsaturated hydraulic conductivity. A high value of this ratio reflects a prevailing hydraulic conductivity which cannot readily redistribute the newly infiltrated moisture. Moisture accumulates in the near-surface region before advancing down through the soil as a distinct wetting front. In contrast, low values of the ratio of rainfall to unsaturated hydraulic conductivity show minimal moisture accumulation, as the relatively small volumes of infiltrating moisture are readily redistributed through the soil profile.Key words: numerical modelling, infiltration, unsaturated soil, soil suction, groundwater.
Borehole variable-head permeability tests in compacted clay liners and covers
Authors: Chapuis Robert P
Published: April 2011

The performance of clayey liners and covers is assessed by several methods including borehole variable-head permeability (k) tests. Different interpretations of the end-of-casing and Lefranc tests are discussed. In Quebec, most tests have been interpreted using the velocity-graph method. Its equations are presented and differences are illustrated by examples. Numerical simulations confirm the validity of the velocity-graph method. It eliminates a frequent error in the k value resulting from a poor evaluation of the piezometric level for the test. Using an incorrect interpretation method may yield a k value up to 50 times lower than the actual value. Smearing the clayey surface in the injection zone may be a source of uncertainty in the k value. A numerical analysis shows that a 1 or 2 cm smeared zone may change the test k value by over one order of magnitude. It is also shown that it is illusory to try to extract the anisotropy in hydraulic conductivity of the compacted clay.Key words: clay liners, clay covers, permeability, in situ test, interpretation.
The hydraulic and mechanical response of an oil sand fracture under a varying confining pressure
Authors: Walters D A , Wong R CK
Published: April 2011

An experimental study was conducted to investigate the effect of the variable-aperture system of an oil sand fracture on its hydraulic and mechanical response to an increasing confining pressure. The oil sand fracture was induced in core samples along the axis of the sample using the Brazilian tensile test. A computer-assisted tomography (CT) scanning analysis was performed to determine the initial fracture geometry and monitor the closure process. The fracture was shown to be a variable-aperture system, with surface roughness and tortuosity playing an increasing role as the fracture closed under pressure. Flow tests revealed a nonlinear behaviour, deviating from the cubic law, and indicated the roughness effects of a natural oil sand fracture are significant. The mechanical response was similar to that of the hydraulic behaviour, indicating the strong relationship between the two. The nature of the uncemented oil sand was shown to strongly affect the strength of the fracture contacts and, therefore, the general closure process.Key words: oil sand, fracture roughness, fracture aperture, computer-assisted tomograhy, hydraulic conductivity.
Analytical solution for monovalent-divalent ion exchange transport in groundwater
Authors: Jin Yee-Chung , Ye Songlin
Published: April 2011

An approximate analytical solution is derived for solute transport with monovalent-divalent ion exchange in saturated, steady, groundwater flow. The analytical solution is obtained by simplifying the complicated heterovalent ion exchange. Using a coordinate system that moves at the average solute advection velocity, a solution is obtained by direct integration with given boundary and initial conditions. The results agree well with a numerical solution using the original isotherm. The analytical solution presented is similar to that of monovalent-monovalent exchange, which suggests that a simple ion exchange model may be assumed for approximation.
Contribution à l'analyse de la déformation et de la rupture des grands versants rocheux en terrain cristallophyllien
Authors: Vengeon Jean-Marc , Giraud André , Antoine Pierre , Rochet Louis
Published: April 2011

In mountainous regions, the study of the stability of rock slopes is of major importance for land management and safety of populations. The monitoring of several unstable alpine slopes has shown the existence of continuous movements with periods of acceleration, but the interpretation of these measurements is still difficult and makes any longer time prediction very uncertain. Three unstable slopes in the Alps, chosen in foliated metamorphic rocks are presented to illustrate the different deformation mechanisms that can be encountered. In particular, we present an analysis of the slope movement at Séchilienne, which is a case of gravity deformation associated with internal rupture of the rocks. The common characteristic of all of these mechanisms is the emergence of an important spatial complexity in the displacements and the stress distribution. This complexity, combined with local ruptures spread in time, allows one to account for the field observations and to integrate them in geomechanical models at the scale of the slope.
Extreme avalanche runout in space and time
Authors: McClung D M
Published: April 2011

The distribution of avalanche runout varies in space and time for individual avalanche paths and from mountain range to mountain range. In this paper, such variations are considered based on the assumption (supported by data worldwide) that the spatial distribution of extreme avalanche runout follows a Gumbel distribution and that the arrival rate of avalanches can be modelled as a Poisson process. The input required is a set of extreme avalanche runout distances for the mountain range and a knowledge of avalanche frequency at the beginning of the runout zone for the path in question. Such information allows theoretical estimation of the effective return period as a function of position, which is very important in zoning applications. In addition, general expressions are derived to relate Gumbel parameters for different mountain ranges to a frequency index to explore general frequency implications from one mountain range to another. The estimated Gumbel parameters imply consistent relationships for expected avalanche frequency and terrain from one mountain range to another.Key words: snow avalanches, runout distances, return period, frequency, terrain.
Stabilisation de la berge rive nord de l'aménagement hydroélectrique La Grande 1
Authors: Massiéra Michel , Tournier Jean-Pierre
Published: April 2011

The La Grande 1 (LG-1) hydroelectrical project, part of the La Grande Complex in Northern Quebec, required the construction of a 2444 m long dyke on the north bank of the river. The presence of sensitive marine clay, covered with deltaic sand and silt deposit, and river sand deposit, called for special design features such as downstream bank and upstream bank stabilization berms to avoid the occurrence of potentially disastrous retrogressive slides. This paper describes the geotechnical and hydrogeological conditions of the northern terrace and presents the different construction phases of the riverbank stabilization, with emphasis on the control of groundwater pressures in the lower aquifer by the use of relief wells.Key words: sensitive clay, river bank, dyke, rockfill, relief well, slope stability.
Flexible pavements in cold regions: a geotechnical perspective
Authors: Konrad Jean-Marie , Roy Marius
Published: April 2011

This paper summarizes recent research on the behaviour of flexible pavements in cold regions. One of the major objectives is to show that basic geotechnical engineering principles can be extremely useful for the analysis of pavement structures subjected to freezing and thawing. The frost susceptibility of subgrade soils should be analyzed for three distinct zones: (i) unsaturated zone, (ii) zone saturated by capillary action, and (iii) zone below the water table. Field observations on instrumented highway sections suggest the existence of a swelling mechanism during thaw in subgrade soils well below the maximum frost penetration. The magnitude of strength reduction associated with this swelling phenomenon depends on the frost susceptibility and the swelling index of the subgrade soil.Key words: frost susceptibility, subgrade, saturation, swelling, strength, field observations.
Layer Structured Sulfur/Expanded Graphite Composite as Cathode for Lithium Battery
Authors: Li Sheng , Xie Ming , Liu JingBing , Wang Hao , Yan Hui
Published: April 2011

We report that a sulfur/expanded graphite (EG) composite as cathode material for lithium-sulfur (Li-S) battery was synthesized by heating sublimed sulfur and EG in certain conditions. EG could be considered as micro containers and current collectors to provide sufficient electrons for the reaction between cathode materials and Li ions. Meanwhile, the rich volume of containers retains the S species at the cathode region. It suggests that the cycle ability and the utilization of S in the Li-S batteries have been improved.