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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]

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]