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Muskeg soils are considered problematic. They are distinguished by their high initial void ratio and water content. Therefore, they exhibit high compressibility and low shear strength when they are subjected to external loads. Microbially induced calcite precipitation (MICP) is a promising soil stabilization technique because it is considered environmentally friendly. In this study, the MICP technique using the urease active bioslurry approach was coupled with sand collected from a local source to stabilize muskeg soils. The effect of changing the sand percentage on the compressibility properties of muskeg soil was studied. The results showed that the addition of 10% sand and injection of two-pore volumes of cementation solutions significantly improved the compressibility properties such that the initial void ratio decreased by 70%. Key words: muskeg soil, microbially induced calcite precipitation (MICP), urease active bioslurry, soil stabilization. Les sols de muskeg sont consideres comme problematiques. Ils se distinguent par leur taux de vide initial et leur teneur en eau eleves. Par consequent, ils presentent une grande compressibilite et une faible resistance au cisaillement lorsqu'ils sont soumis a des charges externes. La precipitation de calcite induite par voie microbienne (MICP) est une technique de stabilisation des sols prometteuse car elle est consideree comme respectueuse de l'environnement. Dans cette etude, la technique MICP utilisant le bioslurry actif a l'urease a ete couplee avec du sable collecte a partir d'une source locale pour stabiliser les sols de muskeg. L'effet de la modification du pourcentage de sable sur les proprietes de compressibilite du sol muskeg a ete etudie. Les resultats ont montre que l'ajout de 10 % de sable et l'injection de volumes de deux pores de solutions de cimentation ont considerablement ameliore les proprietes de compressibilite, de sorte que le taux de vide initial a diminue de 70 %. [Traduit par la Redaction] Mots-cles : sol de muskeg, precipitation de calcite induite par voie microbienne (MICP), bioslurry actif en urease, stabilisation du sol., Introduction Muskeg is the landform that represents the soil of high organic content. If the organic content is more than 75%, the soil is referred to as peaty soils (ASTM [...]

Significant regions of Canada are seismically active, and areas underlain by loose, saturated sediments in these regions are expected to experience liquefaction-induced lateral spread permanent ground displacements (PGDs) under earthquake shaking. The empirical predictive equations are commonly used for estimating the PGDs especially when detailed numerical analyses are not undertaken. The key input parameters for these equations comprise earthquake magnitude (M) and source distance (R), along with geotechnical and topographic parameters; however, there is ambiguity over choosing appropriate site-specific values of M and R. The current study predicts PGD probabilistic hazard curves that are applicable for locations in southwestern and southeastern regions of Canada using a probabilistic seismic hazard assessment (PSHA) framework. This was achieved by embedding two relevant empirical models for predicting lateral spread PGDs (replacing the ground motion prediction equations) within the 2015 National Building Code of Canada framework that is currently available in OpenQuake platform. Moreover, deaggregation analyses have been performed to understand the M and R contributions from different seismic sources on the predicted site-specific hazard. The developed PGD curves can be readily adopted for estimating site-specific lateral spread PGD demand as input to performance-based design of structures in seismically active areas of Canada. Key words: liquefaction-induced lateral spread permanent ground displacements, probabilistic seismic hazard assessment (PSHA), empirical model, National Building Code of Canada (NBCC) 2015, OpenQuake, site-specific, hazard curves. De nombreuses regions du Canada sont actives sur le plan sismique, et les zones reposant sur des sediments laches et satures dans ces regions sont susceptibles de subir des deplacements permanents du sol (DPS) induits par la liquefaction lors de secousses sismiques. Les equations predictives empiriques sont couramment utilisees pour estimer les DPI, en particulier lorsque des analyses numeriques detaillees ne sont pas entreprises. Les principaux parametres d'entree de ces equations sont la magnitude du seisme (M) et la distance de la source (R), ainsi que les parametres geotechniques et topographiques; cependant, il existe une ambiguite quant au choix des valeurs appropriees de M et R pour chaque site. L'etude actuelle predit des courbes d'aleas probabilistes PGD qui sont applicables a des emplacements dans les regions du sud- ouest et du sud-est du Canada en utilisant un cadre d'evaluation probabiliste des risques sismiques (PSHA). Pour ce faire, nous avons integre deux modeles empiriques pertinents pour la prediction des DPI de propagation laterale (en remplacement des equations de prediction des mouvements du sol) dans le cadre du Code national du batiment du Canada 2015 qui est actuellement disponible dans la plateforme OpenQuake. En outre, des analyses de desagregation ont ete effectuees pour comprendre les contributions M et R des differentes sources sismiques sur les risques specifiques au site predits. Les courbes PGD developpees peuvent etre facilement adoptees pour l'estimation de la demande PGD de propagation laterale specifique au site comme donnee d'entree pour la conception basee sur la performance des structures dans les zones sismiques actives du Canada. [Traduit par la Redaction] Mots-cles : deplacements lateraux permanents du sol induit par la liquefaction, cadre d'evaluation probabiliste des risques sismiques (PSHA), modele empirique, Code national du bratiment du Canada (NBCC) 2015, OpenQuake, courbes de risque, specifiques au site., Introduction During past earthquakes, liquefaction-induced lateral spread displacements have resulted in failure of many buildings, bridges, transportation infrastructure, and pipelines. Extensive research has been conducted on the subject of estimating [...]

In addition to the well-understood effects of void ratio and effective confining stress on the mechanical behavior of finegrained soils, past experimental research at the University of British Columbia (UBC), Vancouver, Canada, has revealed a considerable effect of particle fabric on the monotonic and cyclic shear behavior of silts. With this background, an experimental research program was undertaken to further investigate the particulate nature and arrangement of silts. The fabric of soils has been traditionally associated with the matrix void ratio, but can be directly associated with fabric parameters like the coordination number. Furthermore, grain morphology has a significant impact on these characteristics. Advancements in acquiring digital images and associated processing have made it possible to obtain individual soil particle parameters such as length, width, breath, thickness, volume, etc., along with information on spatial location and orientation of a given particle - thus providing the data needed to determine contact fabric and morphology of a soil matrix. In order to calculate these parameters and look for any potential correlations, commercially available, precalibrated, standard-size silica having particles within the size range from 40 μm to 60 μm, were imaged and analyzed. This study establishes an approach for extracting void and morphological information from tomographic images using image analysis techniques and algorithms developed in-house. Initial observations related to particle morphology and preliminary fabric scalar parameters are discussed. This work contributes to the accounting for fabric in understanding the macroscopic shear behavior of silts from the Fraser River Delta, British Columbia, Canada.

In current geotechnical seismic design practice, the empirical correlation between equivalent number of uniform cycles ([N.sub.eq]) of shaking and earthquake magnitude ([M.sub.w]) forms an integral part of liquefaction potential evaluation. This relationship, in turn, is used to derive the magnitude scaling factors that are commonly used in field-based liquefaction evaluation procedures. The [N.sub.eq] versus [M.sub.w] relationship for liquefaction assessment was examined for fine-grained soils using time-histories in the range 5 < [M.sub.w] [less than or equal to] 9, especially including strong ground motion time-histories from the latest subduction zone earthquakes with [M.sub.w] > 8.0. The experimental database available from cyclic direct simple shear tests conducted on natural fine-grained soils retrieved from undisturbed soil sampling was used to obtain the cyclic shear resistance weighting curves for the study. The work presented herein has contributed to further improving the current models used to represent magnitude scaling factor (MSF) values for large earthquake magnitudes and the functional dependency of this parameter on soil type. The MSF-[M.sub.w] curve derived for low-plastic Fraser River Delta silt lies in-between the MSF curves derived for clean sand and clay, resonating with the inferences that have been made that the silt behavior can neither be considered sand-like nor clay-like. Key words: equivalent number of uniform cycles, low-plastic silts, liquefaction, fine-grained soils, magnitude scaling factor. Dans la pratique actuelle de conception geotechnique sismique, la correlation empirique entre un nombre equivalent de cycles uniformes ([N.sub.eq]) d'agitation et la magnitude du seisme ([M.sub.w]) fait partie integrante de l'evaluation du potentiel de liquefaction. Cette relation, a son tour, est utilisee pour deriver les facteurs d'echelle de magnitude couramment utilises dans les procedures d'evaluation de la liquefaction sur le terrain. Le [N.sub.eq] en fonction de [M.sub.w] pour l'evaluation de la liquefaction a ete examine pour les sols a grain fin en utilisant des historiques allant de 5 < [M.sub.w] < 9, en particulier les historiques de temps de mouvement du sol forts de la derniere zone de subduction tremblements de terre avec [M.sub.w] > 8.0. La base de donnees experimentale disponible a partir des tests de cisaillement simple direct cyclique conduits sur des sols naturels a grains fins extraits d'un echantillonnage de sol non perturbe a ete utilisee pour obtenir les courbes de ponderation de la resistance au cisaillement cyclique de l'etude. Les travaux presentes dans le present document ont contribue a ameliorer encore les modeles actuels utilises pour representer les valeurs du facteur d'echelle de magnitude (MSF) pour les grandes magnitudes de seismes et la dependance fonctionnelle de ce parametre par rapport au type de sol. La courbe MSF-[M.sub.w] calculee pour le limon a faible plasticite du delta du fleuve Fraser se situe entre les courbes MSF calculees pour le sable et l'argile propres, ce qui resonne avec les deductions qui ont ete faites que le comportement du limon ne puisse etre considere comme du sable ou de l'argile comme. [Traduit par la Redaction] Mots-cles : nombre equivalent de cycles uniformes, silts de faible plasticite, liquefaction, sols a graines fins, facteur d'echelle de magnitude., Introduction In the seismic liquefaction assessment of soils, the irregular cyclic loading history from a real-life earthquake is converted to the occurrence of some equivalent number of constant-amplitude sinusoidal uniform [...]

The interaction between a buried pipeline and surrounding soil during large ground displacements is typically simulated using numerical nonlinear soil-restraint springs aligned with the longitudinal axis of the pipeline and in the two directions orthogonal to it. There are only very limited experimental data available to characterize the soil springs for simulating pipelines crossing reverse faults where large oblique soil displacements relative to the pipe could occur. Full-scale model testing was undertaken to evaluate this complex soil-pipe interaction problem. The tests simulated the performance of ~400 mm diameter (nominal pipe size, NPS 16) pipe specimens buried in moist sand and crushed limestone trench backfill. The peak normalized oblique soil restraint ([N.sub.[theta]]) values for oblique pipe movement angles (0), when [theta] = 0[degrees] (horizontal movement) and [theta] = 90[degrees] (vertical movement), estimated based on state-of-practice approaches, were in agreement with those from full-scale testing. The value of [N.sub.[theta]] was found to depend significantly on the peak friction angle of soil ([[phi]'.sub.p]) when [theta] was closer to 0[degrees], whereas [N.sub.[theta]] was less sensitive to [[phi]'.sub.p] when [theta] was beyond about 35[degrees]. The theoretical values of [N.sub.[theta]] based on limit-equilibrium approaches compared well with the experimental findings. Key words: soil-pipe interaction, reverse-thrust fault crossings, earthquake-induced ground movements, buried steel pipelines, soil restraints on pipes. L'interaction entre une canalisation souterraine et le sol environnant lors de grands deplacements au sol est generalement simulee a l'aide de ressorts de restreints d'un sol non lineaire numerique simule et aligne avec l'axe longitudinal de la canalisation et dans les deux directions orthogonales a celle-ci. Il n'y a que tres peu de donnees experimentales pour caracteriser le ressort de sol pour la simulation de pipelines traversant les failles inverses ou de grands deplacements de sol oblique par rapport a la canalisation qui peut se produire. L'essai de modeles a grande echelle a ete entrepris pour evaluer ce complexe probleme d'interaction sol-conduite. Les essais ont simule le comportement de specimens de tuyaux d'environ 400 mm de diametre (dimension nominale du tuyau, NPS 16) enfouis dans de remblai de tranchee de sable humide et de calcaire concasse. Les valeurs de restreints de sol oblique normalise pic ([N.sub.[theta]]) pour des angles de deplacement de tuyau obliques ([theta]), lorsque [theta] = 0[degrees] (deplacement horizontal) et [theta] = 90[degrees] (mouvement vertical) estimes a partir d'approches de meilleures pratiques en accord avec ceux de l'essai a grande echelle. La valeur de N0 est averee significativement en fonction de l'angle de frottement pic de sol ([[phi]'.sub.p]) lorsque 0 etait plus proche a 0[degrees], alors que [N.sub.[theta]] etait moins sensible a [[phi]'.sub.p] lorsque [theta] a ete au-dela de 35[degrees]. Les valeurs theoriques de [N.sub.[theta]] basee sur des approches a la limite equilibre compare avec les resultats experimentaux. [Traduit par la Redaction] Mots-cles : interaction de tuyau au sol, passages de failles de poussee inverse, mouvements de terrain induits par le seisme, canalisations en acier enterrees, restrictions du sol sur les tuyaux., Introduction Buried pipeline systems, including oil and gas pipelines, form an important part of lifeline infrastructure, and major disruption to the performance of these systems can result in undesirable impacts [...]

The cyclic shear response of soils is commonly examined using undrained (or constant-volume) laboratory element tests conducted using triaxial and direct simple shear (DSS) devices. The cyclic resistance ratio (CRR) from these tests is expressed in terms of the number of cycles of loading to reach unacceptable performance that is defined in terms of the attainment of a certain excess pore-water pressure and (or) strain level. While strain accumulation is generally commensurate with excess pore-water pressure, the definition of unacceptable performance in laboratory tests based purely on cyclic strain criteria is not robust. The shear stiffness is a more fundamental parameter in describing engineering performance than the excess pore-water pressure alone or shear strain alone; so far, no criterion has considered shear stiffness to determine CRR. Data from cyclic DSS tests indicate consistent differences inherent in the patterns between the stress-strain loops at initial and later stages of cyclic loading; instead of relatively 'smooth' stress-strain loops in the initial parts of loading, nonsmooth changes in incremental stiffness showing 'kinks' are notable in the stress-strain loops at large strains. The point of pattern change in a stress-strain loop provides a meaningful basis to determine the CRR (based on unacceptable performance) in cyclic shear tests. Key words: liquefaction, cyclic failure, strain criteria, shear stiffness, cyclic shear strength, sands, silts, mine tailings. La reponse de cisaillement cyclique des sols est generalement examinee a l'aide d'essais d'elements non draines (ou a volume constant) de laboratoire effectues en utilisant des appareils de cisaillement simples triaxiaux et directs (DSS --<< direct simple shear >>). Le rapport de resistance cyclique (CRR - << cyclic resistance ratio >>) de ces essais est exprime en termes de nombre de cycles de charge pour atteindre un rendement inacceptable qui est defini en fonction de la realisation d'une certaine pression d'eau interstitielle en exces et/ou un niveau de deformation. Alors que l'accumulation de deformation est generalement proportionnelle a la pression d'eau interstitielle en exces; la definition de la performance inacceptable dans les essais de laboratoire basee uniquement sur des criteres de deformation cyclique n'est pas robuste. La rigidite de cisaillement est un parametre plus fondamental dans la description de la performance technologique de l'exces de pression d'eau interstitielle seul ou la deformation de cisaillement seule; jusqu';! present, aucun critere n'a examine la rigidite de cisaillement pour determiner le CRR. Les donnees provenant des essais DSS cycliques indiquent des differences constantes inherentes aux modeles entre les boucles de contrainte-deformation a des etapes initiales et ulterieures de chargement cyclique; au lieu d'obtenir des boucles relativement << lisses >> de contrainte-deformation dans les parties initiales de chargement; les modifications non lisses de la rigidite par incrementation montrent des << plis >> remarquables dans les boucles de contrainte-deformation a de grandes deformations. Le point de changement de modele dans la boucle de contrainte-deformation fournit une base significative pour determiner le CRR (base sur le rendement inacceptable) dans des essais de cisaillement cycliques. [Traduit par la Redaction] Mots-cles: liquefaction, echec cyclique, criteres de deformation, rigidite en cisaillement, resistance au cisaillement cyclique, sables, limons, residus miniers., Introduction The response of soils under cyclic shear loading is a subject that has received wide attention particularly due to the well-observed occurrence of liquefaction and associated geotechnical hazards in [...]

A laboratory research program was undertaken to study the large-strain shear strength characteristics of fine-grained soils under low effective normal stresses (~3-7 kPa). Soils that cover a wide range of plasticity and composition were utilized in the program. The interface shear strength of these soils against a number of solid surfaces having different roughness was also investigated at similar low effective normal stress levels. The findings contribute to advancing the knowledge of the parameters needed for the design of pipelines placed on sea beds and the stability analysis of shallow soil slopes. A Bromhead-type torsional ring-shear apparatus was modified to suit measuring soil-soil and soil-solid interface residual shear strengths at the low effective normal stresses. In consideration of increasing the accuracy of assessment and depicting the full-scale field behavior, the interface residual shear strengths were also measured using a macroscale interface direct shear device with a plan interface shear area of ~3.0 [m.sup.2]. Correlations are developed to estimate the soil-soil and soil-solid interface residual shear strengths at low effective normal stresses. The correlations are compared with soil-soil and soil-solid interface drained residual shear strengths and correlations presented in the literature. Key words: pipelines, offshore engineering, residual strength, large-strain shear strength, interface strength, shear strength, roughness, coating, slope stability, normal stress, soils. Un programme de recherche en laboratoire a ete monte pour etudier les caracteristiques de resistance au cisaillement a grand deplacement de sols fins soumis a des contraintes normales effectives faibles (~3 a 7 kPa). Pour ce programme, des sols couvrant une grande variete de plasticite et de composition ont ete utilises. La resistance au cisaillement a l'interface entre ces sols et plusieurs surfaces solides ayant differentes rugosites a ete investiguee pour des niveaux de contrainte normale effective faibles et similaires. Les resultats contribuent a ameliorer les connaissances sur les parametres necessaries pour la conception de pipelines places sur les fonds marins, et sur les analyses de stabilite de pentes de sol peu profond. Un appareil de cisaillement en anneau de torsion de type Bromhead a ete modifie pour permettre les mesures des resistances au cisaillement residuelles aux interfaces sol-sol et sol-solide pour des contraintes normales effectives faibles. Afin d'augmenter la precision de revaluation et pour representer le comportement a l'echelle du terrain, les resistances au cisaillement residuelles a l'interface ont aussi ete mesurees a l'aide d'un appareil a l'echelle macro de cisaillement direct a l'interface, avec une surface plane de cisaillement a l'interface d'environ 3,0 [m.sup.2]. Des correlations sont developpees pour estimer les resistances au cisaillement residuelles a l'interface sol-sol et sol-solide pour des contraintes normales effectives faibles. Ces correlations sont comparees aux resistances au cisaillement residuelles (trainees a l'interface sol-sol et sol-solide de meme qu'aux correlations presentees dans la litterature. [Traduit par la Redaction] Mots-cles : pipelines, ingenierie en mer, resistance residuelle, resistance au cisaillement a grande deformation, resistance a l'interface, resistance au cisaillement, rugosite, revetement, stabilite de pente, contrainte normale, sols., Introduction It has been recognized that the drained residual shear strength envelope of fine-grained soils is nonlinear. This stress dependency is more pronounced for plastic soils especially at low effective [...]

A series of full-scale experiments was conducted to estimate lateral soil constraints on pipes buried in dense sandy slopes at different burial depths. The experimental data indicated that the soil force on the pipe increases with increase in the slope grade and burial depth ratio. The lateral soil force against relative pipe displacement response observed from the experiments is presented and compared to those arising from level ground conditions. The study was extended to larger burial depth ratios by simulating pipes under sloping ground conditions using a numerical (finite-element) model that was initially calibrated using the results from physical modelling. The findings from the study in terms of the variation of peak lateral soil restraint as a function of the slope grade and burial depth ratio are presented for consideration in pipeline design. [ABSTRACT FROM AUTHOR]

Muskeg soil is widespread in Canada. It covers around 15% of the Canadian landscape. Its problematic nature is attributed to its high compressibility and low shear strength when subjected to loads because of its high initial void ratio and water content. Therefore, in this study, microbially induced calcite precipitation (MICP), an emerging and potentially environmentally friendly technique for soil stabilization, is used for enhancing the compressibility and shear strength properties of muskeg soil. The urease active bioslurry approach is adopted in this study, which comprises the mechanical mixing of bioslurry with soil and the injection of cementation solutions in subsequent phases. Muskeg soil was collected from Bolivar Park, Surrey, British Columbia, Canada. Different bioslurry concentrations were tested for the compressibility properties to determine the optimum concentration. Afterward, the optimum concentration was used to check the effect of the bioslurry percentage by weight and the number of cementation solutions injected on the soil stiffness and strength. Microstructure analysis by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were conducted for untreated and treated samples to check the change in the soil microstructure due to stabilization. The results showed that the 0.4 mol/L bioslurry concentration demonstrated the best compressibility properties. [ABSTRACT FROM AUTHOR]

The effect of initial particle fabric on the one-dimensional compression response of Fraser River sand was investigated. One-dimensional compression with lateral stress measurement was carried out on reconstituted Fraser River sand specimens using an instrumented oedometer. Laboratory specimens were reconstituted by air pluviation, tamping, and vibration and were prepared with an initial relative density ranging from medium loose to very dense. For Fraser River sand in one- dimensional compression, air-pluviated specimens yielded the highest values for the coefficient of lateral earth pressure at rest ([K.sub.o]), tamped specimens produced the lowest [K.sub.o] values, and vibrated specimens produced intermediate [K.sub.o] values. The results from the present study demonstrate that specimens resulting from different laboratory reconstitution methods (i.e., different initial particle fabrics) exhibit different one-dimensional compression responses and produce different [K.sub.o] values. A 'fabric factor' was introduced to account for the effect of the initial particle fabric on the measured coefficient of lateral earth pressure at rest. Using the fabric factor, the constant volume friction angle, and the specimen relative density, a new empirical equation defining the coefficient of lateral earth pressure at rest during normally consolidated loading is proposed. Key words: sand, one-dimensional compression, particle fabric, coefficient of lateral earth pressure at rest. L'effet de la structure initiale des particules de sable de la riviere Fraser sur leur comportement en compression unidimensionnelle a ete etudie. Des mesures de compression unidimensionnelle avec contraintes laterales ont ete realisees avec un odometre instrumente sur des echantillons reconstitues de sable de la riviere Fraser. Les echantillons de laboratoire ont ete reconstitues par pluviation a l'air, par pilonnage et par vibration, et ont ete prepares avec une densite relative initiale variant de moyennement lache a tres dense. Pour les echantillons de sable de la riviere Fraser en compression unidimensionnelle, les echantillons prepares par pluviation a l'air ont donne les valeurs les plus elevees du coefficient de pression laterale des terres au repos ([K.sub.o]), les echantillons pilonnes ont produit les valeurs de [K.sub.o] les plus faibles, et les echantillons vibres ont genere des valeurs de [K.sub.o] intermediaires. Les resultats de cette etude demontrent que les echantillons produits par differentes methodes de reconstitution de laboratoire (c'est-a-dire differentes structures initiales des particules) presentent des comportements en compression unidimensionnelle differents, et produisent des valeurs de [K.sub.o] differentes. Un facteur de ≪ structure des particules ≫ a ete introduit pour tenir compte de l'effet de la structure initiale des particules sur le coefficient de pression laterale des terres au repos mesure. A partir du facteur de structure des particules, de l'angle de friction a volume constant et de la densite relative de l'echantillon, une nouvelle equation empirique qui defini le coefficient de pression laterale des terres au repos durant le chargement normalement consolide est proposee. [Traduit par la Redaction] Mots-cles: sable, compression unidimensionnelle, structure des particules, coefficient de pression laterale des terres au repos., Introduction The coefficient of lateral earth pressure at rest, [K.sub.o], is used to define the stress state in soil where no lateral deformation occurs. [K.sub.o] is expressed as the ratio [...]

The dynamic response of tailings from a gold mine located in western Quebec was evaluated using cyclic laboratory testing. These tailings are classified as non-plastic silt and sand. Specimens of the tailings were prepared as slurries, consolidated to vertical effective stresses of 100--400 kPa, and subjected to cyclic direct simple shear testing with cyclic stress ratio, CSR, values between 0.075 and 0.15. The shear modulus reduction of the tailings under cyclic loading was found to be fairly similar to that described for clean sands in the literature. The cyclic resistance ratio, CRR (which reflects the liquefaction resistance), of the samples was not significantly affected by the effective consolidation stress (in the range considered here). Analysis of test results with the simplified method of liquefaction evaluation indicates that this method may be applicable to these tailings. However, other factors, such as the possible effects of layering and ageing of the tailings in situ, should also be considered in such an assessment. Key words: tailings, dynamic behaviour, liquefaction, shear modulus, cyclic direct simple shear test. Le comportement dynamique des residus miniers d'une mine d'or de l'ouest du Quebec a ete evalue a l'aide d'essais cycliques de laboratoire. Ces residus sont de la classe des silts et sables non plastiques. Les specimens ont ete prepares a partir d' une boue, consolides sous une contrainte verticale effective de 100 a 400 kPa, puis soumis a des essais cycliques en cisaillement simple sous un rapport de contrainte cyclique (CSR) entre 0,075 et 0,15. La baisse du module de cisaillement des residus sous chargement cyclique est semblable a celle rapportee dans la litterature pour des sables. Le rapport de la resistance cyclique (CRR), qui reflete la resistance a la liquefaction des echantillons n'a pas ete affectes de facon notable par la contrainte de consolidation (pour la plage consideree ici). L'analyse des resultats avec la methode simplifiee d'evaluation de la liquefaction semble indiquer que cette methode serait applicable a ces residus miniers. Toutefois, d'autres facteurs, comme la stratification des materiaux in situ et leur vieillissement, devraient etre pris en compte lors de telles analyses. Mots-cles : residus miniers, comportement dynamique, liquefaction, module de rigidite, essai cyclique en cisaillement simple. [Traduit par la Redaction], Introduction Tailings are one of the primary waste products of mining operations. They are made of fine-grained particles of the parent rock from which the ore is extracted by crushing, [...]

The postcyclic reconsolidation response of low-plastic Fraser River silt was examined using laboratory direct simple shear testing. Specimens of undisturbed and reconstituted natural low-plastic Fraser River silt and reconstituted quartz powder, initially subjected to constant-volume cyclic loading under different cyclic stress ratios (CSRs) and then reconsolidated to their initial effective stresses ([[sigma]'.sub.vo]), were specifically investigated. The volumetric strains during postcyclic reconsolidation ([[epsilon].sub.v.ps]) were noted to generally increase with the maximum cyclic excess pore-water pressure ([DELTA][u.sub.max]) and maximum cyclic shear strain experienced by the specimens during cyclic loading. The values of [[epsilon].sub.v-ps] and maximum cyclic excess pore-water pressure ratio ([r.sub.u-max]) were observed to form a coherent relationship regardless of overconsolidation effects, particle fabric, and initial (precyclic) void ratio of the soil. The specimens with high [r.sub.u-max] suffered significantly higher postcyclic reconsolidation strains; [[epsilon].sub.v-ps] ranging between 1.5 and 5% were noted when [r.sub.u-max] > 0.8. The observed [[epsilon].sub.v-ps] versus [r.sub.u-max] relationship, when used in combination with the observed dependence of cyclic excess pore-water pressure on CSR and number of load cycles, seems to provide a reasonable approach to estimate postcyclic reconsolidation strains of low-plastic silt. DOI: 10.1061/(ASCE)GT.1943-5606.0000349 CE Database subject headings: Shear tests; Soil liquefaction; Earthquakes; Silts; Cyclic loads; Soil consolidation; Pore water; Water pressure; Canada. Author keywords: Direct simple shear testing; Liquefaction; Earthquake response of silts; Cyclic loading; Postcyclic reconsolidation strains.

Mixing of waste rock and tailings as a homogeneous mixture (referred to as 'paste rock') has been suggested as a favourable approach to overcome deficiencies associated with traditional methods of mine waste disposal. In consideration of the current limited understanding of the fundamental mechanical response of paste rock, a laboratory research program was undertaken to investigate the monotonic and cyclic shear response of paste rock. This paper presents the findings from undrained cyclic triaxial shear testing conducted on saturated paste rock specimens reconstituted such that the tailings would 'just fill' the void spaces between the coarse particles of the skeleton. During undrained cyclic loading, paste rock typically exhibited a cumulative decrease in effective stress along with a progressive degradation of shear stiffness. The material generally displayed a higher tendency for strain development under cyclic loading when compared with rock-only and tailings-only specimens subjected to similar consolidation and cyclic loading conditions. However, no strain-softening or loss of shear strength was observed, suggesting that the material is unlikely to experience flow failure under undrained cyclic loading. The cyclic shear resistance was relatively insensitive to the initial effective confining pressure ([σ'.sub.3c]) for the tested stress levels of [σ'.sub.3c] < 400 kPa. Key words: liquefaction, mine tailings, mine waste rock, cyclic shear response, triaxial testing, cyclic mobility. Le melange des roches steriles et des rejets de concentrateur sous forme de pate homogene (appeleepate residus-sterile ou PRS) a recemment ete suggere comme approche de gestion des residus miniers qui permet de contourner certains problemes associes aux approches traditionnelles. Puisque les connaissances sont limiteees dans le domaine du comportement meecanique fondamental de la PRS, une etude en laboratoire a ete initiee dans le but d'eevaluer le comportement en cisaillement monotonique et cyclique de la PRS. Cet article presente les resultats obtenus lors des essais triaxiaux en cisaillement cyclique non drainees effectuees sur des echantillons de PRS satureis reconstituees de telle facon a ce que les rejets remplissent tout juste les vides entre les particules de roches steriles. Pendant le chargement cyclique non draine,la PRS presente typiquement une diminution cumulative de la contrainte effective ainsi qu'une degradation progressive de la rigidite en cisaillement. Le materiau demontre geneiralement une plus grande tendance au developpement de deformations en conditions de chargement cyclique, comparativement aux echantillons de sterile seul et de residu seul soumis aux memes conditions de consolidation et de chargement cyclique. Cependant, aucun relachement des deformations ou perte de resistance au cisaillement n'a ete observe, ce qui suggere que le materiau n'est pas susceptible de subir une rupture en ecoulement lors de chargement cyclique. La resistance au cisaillement cyclique etait relativement insensible a la pression initiale de confinement ([σ'.sub.3c]) pour les contraintes testees de [σ'.sub.3c] < 400 kPa. Mots-cles: liquefaction, residus miniers, roches steriles, comportement en cisaillement cyclique, essai triaxial, mobilite cyclique. [Traduit par la Redaction], Introduction Mine waste commonly consists of two main waste types: relatively fine-grained tailings and coarse-grained blasted-crushed rock. While fine-grained tailings are typically discharged in slurry form to a tailings impoundment, [...]

The idea of mixing mine tailings and waste rock to form 'paste rock' prior to disposal is now receiving significant attention from the point of view of sustainable mine waste management practices. This approach has been viewed as a favourable alternative to traditional methods of mine waste disposal because paste rock has the potential to overcome deficiencies (e.g., acid rock drainage and liquefaction-induced failures) associated with traditional methods. To advance the current limited knowledge, a laboratory research program was undertaken to study the mechanical response of paste rock. Testing was undertaken on paste rock specimens prepared so that the tailings would 'just fill' the void spaces within the waste rock particle skeleton. The findings suggest that the material is unlikely to experience flow deformation under monotonic shear loading conditions, at least up to the tested initial effective confining stress conditions of 400 kPa. The monotonic shear response of paste rock was found to be similar to that of rock-only material; this finding is in agreement with previous observations from one-dimensional consolidation testing where it had been shown that the rock particle skeleton would carry almost 90% of the externally applied stress on a given paste rock mass. Key words: mine tailings, mine waste rock, triaxial testing, monotonic shear loading. Le concept de << pate residus-steriles >> (PRS), c'est-a-dire le melange de rejets de concentrateur et de roches steriles avant leur deposition, recjoit maintenant beaucoup d'attention d'un point de vue de gestion durable des residus miniers. Cette approche est consideree comme une alternative favorable aux methodes traditionnelles de gestion des residus miniers puisque la pate residus-steriles peut potentiellement pallier a certaines preoccupations (ex. drainage minier acide et ruptures induites par liquefaction) associees aux methodes traditionnelles. Afin d'ameeliorer les connaissances actuelles, un programme de recherche en laboratoire a ete elabore pour etudier le comportement meecanique de la PRS. Les essais ont ete effectuees sur des echantillons de PRS prepares de facon ace que les rejets remplissent << tout juste >> les vides entre les particules des roches steeriles. Les resultats suggerent que le mateeriau a de faibles chances de subir des deformations sous des conditions de chargement en cisaillement monotonique, du moins jusqu'aux conditions testees de contraintes effectives de confinement initiales de 400 kPa. Le comportement en cisaillement monotonique de la PRS est similaire a celui de la roche sterile seule. Ce resultat concorde avec des observations precedentes obtenues lors d'essais en consolidation unidimensionnelle avec lesquels il avait ete; deemontre que le squelette des particules rocheuses pouvait supporter pres de 90% des contraintes externes appliqueees sur une masse de PRS. Mots-cles: rejets de concentrateur, roches steriles, essais triaxiaux, chargement en cisaillement monotonique. [Traduit par la Redaction], Introduction The disposal of mine waste mainly involves management of the following two main waste types: relatively fine-grained tailings and coarse-grained waste rock. Fine-grained tailings are typically discharged in slurry [...]

Hydraulic conductivity and consolidation behaviour are examined for an alternative mine waste disposal technique. One type of waste rock, one type of tailings, and mixtures of the same waste rock and tailings were tested in benchscale and column studies. Specimens 150 mm in diameter were tested for hydraulic conductivity by falling-head method alternated with one-dimensional consolidation, specimens 300 mm in diameter were tested for one-dimensional consolidation response, and specimens 1 m in diameter were tested for self-weight consolidation behaviour in 6 m high columns. Deformation of mixtures under one-dimensional loading was similar to that of waste rock alone and much less than that of tailings alone. Hydraulic conductivity of mixtures was similar to that of tailings alone and independent of specimen diameter. Mixture behaviour was attributed to a homogeneous structure including waste rock in particle-to-particle contact and a continuous, saturated matrix of tailings. The results indicate that mixing waste rock and tailings can produce dense deposits with values of hydraulic conductivity that are orders of magnitude lower than those of waste rock alone, thereby limiting fluxes through the waste and the associated potential for acid rock drainage. Mixture deposits will also have less consolidation-related settlement than tailings, thus improving stability and aiding reclamation. Key words: co-disposal, hydraulic conductivity, consolidation, tailings, waste rock. La conductivite hydraulique et le comportement en consolidation sont examines dans le cadre d'une technique alternative de deposition des residus miniers. Des essais a petite echelle et en colonnes ont ete effectues sur un type de roches steriles, un type de rejets de concentrateur, ainsi qu'un melange de ces deux materiaux. La conductivite hydraulique a ete evaluees pour des echantillons d'un diametre de 150 mm a l'aide de la methode a charge variable en alternance avec de la consolidation unidimensionnelle. Des echantillons d'un diametre de 300 mm ont ete testes en consolidation unidimensionnelle. Le comportement en consolidation sous son propre poids d'echantillons de 1 m de diametre a ete evalue dans des colonnes de 6 m de haut. Les deformations des melanges rejets-steriles en consolidation unidimensionnelle etaient semblables a celles des steriles seuls, et beaucoup plus faibles que pour les rejets seuls. La conductivite hydraulique du melange etait semblable a celle des rejets seuls et etait independante du diametre de l'echantillon. Le comportement du melange est decrit comme une structure homogene qui comprend des roches steriles en contact entre elles ainsi qu'une matrice de rejets de concentrateur continue et saturee. Les resultats indiquent que le fait de melanger les roches steriles et les rejets de concentrateur peut produire des depots denses avec des valeurs de conductivite hydraulique de plusieurs ordres de grandeur sous les valeurs des steriles seuls, ce qui permet de limiter les flux a travers le depot et le potentiel de generation de drainage minier acide. Les depots mixtes presentent aussi moins de tassements relies a la consolidation que les rejets de concentrateur, ainsi la stabilite est amelioree et la restauration du site est plus facile. Mots-cles : co-deposition, conductivite hydraulique, consolidation, rejets de concentrateur, roches steriles. [Traduit par la Redaction], Introduction Hydraulic conductivity and consolidation response of mixtures of mine waste rock and tailings are investigated in laboratory and column studies. Mixing mine wastes is an alternative mine waste disposal [...]

The performance of buried steel pipelines subjected to relative soil movements in the axial direction was investigated using full-scale pullout testing in a soil chamber. Measured axial soil loads from pullout testing of pipes buried in loose dry sand were comparable to those predicted using guidelines commonly used in practice. The peak values of axial pullout resistance observed on pipes buried in dense dry sand were several-fold (in excess of 2 times) higher than the predictions from guidelines; the observed high axial pullout resistance is primarily due to a significant increase in normal soil stresses on the pipelines, resulting from constrained dilation of dense sand during interface shear deformations. This reasoning was confirmed by direct measurement of soil stresses on pipes during full-scale testing and numerical modeling. The research findings herein suggest that the use of the coefficient of lateral earth pressure at-rest (K0) to compute axial soil loads, employing equations recommended in common guidelines, should be undertaken with caution for pipes buried in soils that are likely to experience significant shear-induced dilation. Key words: buried pipelines, pipe--soil interaction, dilation, soil loading on pipes, interface friction. La performance de tuyaux en acier enfouis soumis a des mouvements axiaux de sol a ete investiguee a l'aide d'essais d'arrachement des tuyaux a l'echelle reelle dans une boite de sol. Les charges axiales de sol mesurees dans les essais a l'echelle reelle effectues sur des tuyaux enfouis dans un sable sec non compacte etaient comparables a celles predites en utilisant les directives usuelles. Dans le cas d'un sable dense, le pic de resistance axiale observe sur les tuyaux enfouis etait de plusieurs fois plus eleve (plus de deux fois) que les predictions provenant des directives. Ceci est principalement du a une augmentation significative des contraintes normales globales du sol sur les tuyaux en raison de la dilatation en milieu restreint du sable dense durant les deformations en cisaillement des interfaces. Cette explication a ete confirmee par des mesures directes des contraintes du sol sur les tuyaux durant les essais a l'echelle reelle, en plus d'etre supportee par des modelisations numeriques. L'utilisation du coefficient de pression laterale des terres au repos ([K.sub.0]) pour representer les contraintes du sol sur les tuyaux lors des essais d'arrachement, tel que recommande par les directives usuelles, devrait etre faite avec precautions dans le cas de tuyaux enfouis dans des sols qui peuvent se dilater lors du cisaillement des interfaces. Mots-cles: tuyaux enfouis, interaction tuyau--sol, dilatation, chargement du sol sur les tuyaux, friction a l'interface. [Traduit par la Redaction], Introduction Buried pipeline systems form a key part of global lifeline infrastructure and any significant disruption to the performance of these systems often translates into undesirable impacts on regional businesses, [...]

The performance of buried, medium-density polyethylene (MDPE) pipes subject to movements relative to the soil in the direction of the pipe axis is investigated by full-scale physical model testing conducted using a large soil box. A new closed-form solution was developed to account for the nonlinear material response of MDPE pipes under axial loading, and the analytical results are compared with the results obtained from the full-scale pipe pullout testing. The closed-form solution provides a rational framework to estimate the response of the pipe (i.e., level of strain, force) and the mobilized frictional length along the pipe for a known relative axial pipe movement. The approach, in turn, could be used to estimate the relative axial movements needed for pipe failure, which is an important considderation in the evaluation of field-performance of pipe systems located in areas of potential ground movement. The methodology is an important initial step towards the development of representative axial soil-springs representing complex pipe-soil interaction encountered in relatively extensible, buried polyethylene (PE) pipe systems subject to soil loading arising from ground movements. Key words: pipe-soil interaction, axial soil loading, full-scale modeling, polyethylene pipes, ground displacement. On etudie la performance de tuyaux de densite moyenne en polyethylene (MDPE) enfouis et soumis a des mouvements relatifs au sol dans la direction de l'axe du tuyau par un modele d'essai physique a pleine echelle realise dans une grosse boite de sol. Une nouvelle solution exacte a ete developpees pour tenir compte de la reaction non lineaire du materiau des pieux MDPE sous un chargement axial, et les resultats analytiques sont compares avec les resultats obtenus des essais d'arrachement des tuyaux a l'echelle naturelle. La solution exacte fournit un cadre de reference rationnel pour estimer la reaction du tuyau (c.-a-d. niveau de deformation, force) de meme que la longueur mobilisee en frottement le long du tuyau pour un mouvement axial relatif connu du tuyau. L'approche a son tour pourrait etre utilisee pour estimer les mouvements axiaux relatifs requis pour la rupture du tuyau, qui est une consideration importante dans l'evaluation de la performance en nature des systemes de tuyaux localises dans des regions de mouvements potentiels du terrain. La methodologie est une importante etape initiale vers le developpement de << solressorts >> axiaux representatifs representant une interaction complexe tuyau--sol rencontree dans des systemes de tuyaux PE enfouis, relativement extensibles, soumis a du chargement de sol resultant de mouvements de terrain. Mots-cles : interaction tuyau--sol, chargement axial de sol, modelisation a pleine echelle, tuyaux de polyethylene, depla-cement du terrain. [Traduit par la Redaction], Introduction Polyethylene (PE) pipes are becoming increasingly popular in natural gas distribution networks since their introduction in the late 1960s. In North America, 90% of the natural gas distribution systems [...]

Abstract: The drained response of loose sand (relative density of 30%) under simultaneous increase in principal stress ratio (R = [σ'.sub.1]/[σ'.sub.3]) and the inclination of major principal stress to the [...]

Abstract: The technique of mixing mine waste rock and tailings for disposal has the potential to avoid the problems of acid rock drainage and tailings liquefaction. This paper presents a [...]

The direct simple shear (DSS) device is one of the commonly used laboratory element testing tools to characterize the shear behaviour of soil. The interpretation of results from an element test requires understanding of the degree of stress and strain non-uniformities in a given test specimen. So far, studies on stress and strain non-uniformities in the DSS test have been conducted using direct boundary measurements of stresses in laboratory specimens supported by a continuum based analytical approach. Discrete element modelling now provides a means of modelling the soil behaviour in a realistic manner using a particulate approach. Accordingly, the performance of a DSS specimen was modelled using discrete element modelling with emphasis on assessing stress and strain non-uniformities in the specimen during shearing. The approach allowed for the numerical determination of stresses not only at the boundaries, but also within the DSS specimen. It was shown that mobilised stress ratio distribution throughout the shearing phase for the majority of specimen volume at locations near the central planes parallel and perpendicular to the direction of shearing is fairly uniform. Finally, it was noted that the potential for particle slippage at locations near the specimen centre can result in non-uniform shear strain distributions. [ABSTRACT FROM AUTHOR]

The performance evaluation of buried extensible plastic pipelines, such as polyethylene pipes in the gas distribution industry, in areas prone to ground movement is a key consideration for many utility owners. Considering the relatively smaller deformation stiffness and nonlinear stress-strain response of these pipes compared with those of steel pipes, a good understanding of the basic soil–pipe interaction mechanisms forms a critical part in these evaluations. The increase in soil normal stress on the pipe attributable to soil dilation and gradual degradation of interface friction with axial pipe displacement was investigated. An analytical method was developed to estimate the pipe response when subject to axial frictional loads arising from soil movements, which accounts for these factors and the nonlinear stress-strain response of the pipe material. For a known relative axial soil displacement, the approach provides a convenient way to determine the axial force, strain, and length along which the friction is mobilized. The proposed analytical solution was used to model the response of five large-scale field pipe pullout tests. It is shown that the analytical solution is capable of effectively forming a framework to relate pipe displacement, pullout resistance, strain, and mobilized length. The findings also highlight the significance and need to account for soil dilation effects in describing the soil–pipe interaction in extensible plastic pipes. [ABSTRACT FROM AUTHOR]

It is commonly assumed that within inundated sand the Skempton B value and P-wave velocity decrease with decrease in saturation. In centrifuge tests a common saturation procedure is to inundate the specimen with carbon dioxide while under a vacuum and then slowly introduce the viscous pore fluid. The B value and related saturation is difficult to measure in centrifuge models and P-wave velocity—saturation correlations have been used for this purpose. A laboratory emulation of centrifuge saturation procedures was made using a triaxial cell with top and bottom bender elements and a viscous methyl cellulose–water pore fluid. Contrary to expectations, the laboratory tests showed high P-wave velocities indicative of full saturation when B values were low. Numerical modeling of the laboratory tests indicated that if air bubbles within the pore fluid are numerous and closely spaced then there is a good correlation between saturation, B value, and P-wave velocity. However if the air bubbles are larger and only present in some of the pores then the P-wave velocity is not a good indicator of B value and average saturation. The laboratory tests also showed that placing the specimen under backpressure for several days increased saturation and related B values. It is suggested that this common laboratory procedure should be considered for saturating centrifuge test specimens. [ABSTRACT FROM AUTHOR]

The performance of pipeline systems during earthquakes is a critical consideration in seismically active areas. Unique approaches to quantitative estimation of regional seismic vulnerability were developed for a seismic vulnerability assessment and upgrading program of a 500-km-long natural gas pipeline system in British Columbia, Canada. Liquefaction-induced lateral spreading was characterized in a probabilistic manner and generic pipeline configurations were modeled using finite elements. These approaches, developed during the early part of this 10-year program, are more robust than typical approaches currently used to assess energy pipeline systems. The methodology deployed within a GIS environment provided rational means of distinguishing between seismically vulnerable sites, and facilitated the prioritization of remedial works. While ground improvement or pipeline retrofit measures were appropriate for upgrading most of the vulnerable sites, replacement of pipeline segments using horizontal directional drilling to avoid liquefiable zones were required for others. [ABSTRACT FROM AUTHOR]