Showing papers in "Canadian Geotechnical Journal in 1997"

Seventeenth Canadian Geotechnical Colloquium: The effect of cohesion loss and stress path on brittle rock strength

Abstract: Stress-strain curves for brittle rocks show three characteristic stress levels: crack initiation, long-term strength, and peak strength. Damage-controlled testing at low confining stresses has shown that the long-term and peak strengths are sensitive to the amount of induced damage, i.e., the greater the amount of damage, the lower the long-term and peak strengths. These tests also showed that the brittle-failure process is characterized by a loss of cohesion as friction is mobilized. Excavation of a circular test tunnel in massive brittle rock resulted in failure around the tunnel. The back-calculated strength for the failed rock around the tunnel is approximately one-half of that measured in laboratory tests. Crack-induced damage of Lac du Bonnet granite, both in the laboratory and in situ, begins when the load exceeds approximately one-third of the unconfined compressive strength. However, the stress level associated with failure is a function of loading path. In the laboratory, where the loading path monotonically increases, the ultimate strength of an unconfined sample is 225 MPa. Numerical studies suggest that in situ the loading path around the tunnel is more complex, involving stress increase and decrease and stress rotation. For this loading path, failure initiates at a stress between 100 and 120 MPa. Conventional frictional failure criteria did not adequately predict the extent of brittle failure measured around the circular tunnel. The results from the damage-controlled laboratory tests and the microseismic monitoring carried out during tunnel construction indicate a constant-deviatoric-stress criterion is a reliable indicator for predicting the onset of damage. This criterion was also found to give a reasonable prediction for the maximum depth of failure around the test tunnel. The fundamental assumption in the constant-deviatoric-stress criterion is that at low confining stresses, such as those which occur around underground openings, the brittle-failure process is dominated by cohesion loss.

Effects of nonplastic fines on static liquefaction of sands

Abstract: Des essais triaxiaux en compression non draines ont ete effectues sur des echantillons reconstitues de sable du Nevada et d'Ottawa, avec variation systematique de la teneur en fines (particules inferieures a 0,074 mm) afin d'evaluer l'effet de la fraction fine sur le potentiel de liquefaction statique lors d'un chargement monotonique. Les fines etaient non-plastiques. Les resultats indiquent clairement que la presence de fines peut augmenter considerablement le potentiel de liquefaction statique des quatre sables propres etudies lorsqu'on utilise la technique du montage a sec avec un entonnoir. Les fines semblent creer dans le sol une structure particulaire tres compressible ce qui accroit ainsi le potentiel de liquefaction alors meme que la densite augmente. Accroitre la teneur en fines d'un sable propre peut aboutir a l'augmentation du potentiel de liquefaction jusqu'a un seuil maximum pour lequel les fines dominent le comportement non draine du sol. A ce point la, le potentiel de liquefaction tend a devenir constant vis-a-vis de l'indice de densite. On a trouve que la liquefaction statique complete pouvait intervenir a un indice de densite superieur a 60% pour des teneurs en fines elevees.

Pile capacity by direct CPT and CPTu methods applied to 102 case histories

Abstract: Six methods to determine axial pile capacity directly from cone penetration test (CPT) data are presented, discussed, and compared. Five of the methods are CPT methods that apply total stress and a filtered arithmetic average of cone resistance. One is a recently developed method, CPTu, that considers pore-water pressure and applies an unfiltered geometric average of cone resistance. To determine unit shaft resistance, the new method uses a new soil profiling chart based on CPTu data. The six methods are applied to 102 case histories combining CPTu data and capacities obtained in static loading tests in compression and tension. The pile capacities range from 80 to 8000 kN. The soil profiles range from soft to stiff clay, medium to dense sand, and mixtures of clay, silt, and sand. The pile embedment lengths range from 5 to 67 m and the pile diameters range from 200 to 900 mm. The new CPTu method for determining pile capacity demonstrates better agreement with the capacity determined in a static loading test and less scatter than by CPT methods.

Geosynthetic clay liner (GCL) : chemical compatibility by hydraulic conductivity testing and factors impacting its performance

Abstract: On rapporte ici les resultats d'essais de gonflement sous confinement, d'essais de consolidation et de conductivite hydraulique effectues sur une membrane argile-geosynthetique (MAG) aiguilletee. On a examine les effets du liquide de percolation (eau distillee, solutions aqueuses salines avec des concentrations en NaCl de 0,01 et 2,0 M, lixiviat synthetique de type dechets municipaux), ainsi que les effets de la contrainte statique, du liquide hydratant et du degre d'hydratation de la bentonite a l'instant de l'application de la pression de confinement. L'augmentation de la concentration en sel de la solution et la diminution de la pression de confinement ont entraine une augmentation de la conductivite hydraulique. On a aussi montre que des concentrations en sel elevees dans le liquide hydratant augmentent la conductivite hydraulique. Les MAG soumises a des solutions de NaCl a des concentrations de 0,6 et 2,0 M etaient plus permeables que les MAG initialement hydratees a l'eau. Le liquide hydratant n'etait pas un facteur aussi critique pour des circulations de fluide a 0,1 M NaCl. On a egalement constate l'importance du degre d'hydratation de la bentonite lors de l'application de la pression de confinement, ce qui souligne les avantages hydrauliques qu'il y a a maximiser la contrainte verticale avant l'hydratation de la membrane. Les essais effectues avec le lixiviat synthetique ont donne des resultats comparables a ceux obtenus avec les solutions salines entre 0,2 et 0,8 M NaCl. On discute finalement les consequences pratiques de ces essais.

Static liquefaction of very loose sands

Abstract: On presente les resultats d'une etude experimentale menee sur deux sables differents. Des essais triaxiaux en compression, draines et non draines, ont ete effectues sur du sable du Nevada a quatre indices de densite initiaux differents, soient 12, 22, 31 et 42%. Des essais semblables ont ete faits sur du sable d'Ottawa a un indice de densite initial de 0%. Tous les essais ont suivi un chargement monotonique. A ces faibles densites on a obtenu un comportement anormal du materiau. Les essais triaxiaux en compression non draines ont abouti a une liquefaction statique complete (pression de confinement effective nulle et difference de contrainte nulle) sous des pressions de confinement faibles. Lorsqu'on augmente les pressions de confinement, les chemins de contraintes effectives indiquent une augmentation de la resistance a la liquefaction par une tendance plus marquee a la dilatance. Ceci est contraire au comportement normal d'un sol, ou augmenter la contrainte de confinement conduit a une attenuation de la dilatance. La presence de fines dans le sol (particules inferieures a 0,074 mm) a ete identifiee comme etant la cause probable de ce comportement. On a emis l'hypothese que les fines et les particules plus grosses creaient une structure granulaire ayant une compressibilite anormalement elevee a des pressions de confinement faibles. Les essais draines ont revele des contractions volumiques importantes qui en conditions non drainees se traduisent par des pressions interstitielles suffisamment elevees pour produire une liquefaction statique complete. Le comportement anormal peut se lire sur les angles de frottement draine aux faibles indices de densite qui augmentent d'abord avec la pression de confinement puis diminuent en suivant un processus normal.

The effect of soil suction on evaporative fluxes from soil surfaces

Abstract: This paper presents a theoretical approach in which a Dalton-type mass transfer equation is used to predict the evaporative fluxes from nonvegetated soil surfaces. Soil evaporation tests were conducted in the laboratory on three different soil samples of Beaver Creek sand, Custom silt, and Regina clay. The soil surfaces were saturated and allowed to evaporate to a completely air-dried state. The actual evaporation rate for each soil surface was measured along with the potential evaporation rate for an adjacent water surface. The ratio of actual evaporation to potential evaporation or normalized soil evaporation was then evaluated with respect to drying time, soil-water content, and soil suction. The value of the normalized soil evaporation was found to be approximately equal to unity for all soils until the total suction in the soil surfaces reached approximately 3000 kPa. The rate of actual soil evaporation was observed to decline when the total suction exceeded 3000 kPa. A relationship between the actual evaporation rate and total suction was found to exist for all three soil types which appears to be unique and independent of soil texture, drying time, and water content.

Prediction for swelling characteristics of compacted bentonite

Abstract: Compacted bentonites are attracting greater attention as back-filling (buffer) materials for high-level nuclear waste repositories For this purpose, it is very important to quantitatively evaluate

Assessment of the hazard from rock fall on a highway

Abstract: Rock falls can cause delays, damage, injury, and death to highway users. In 1982, a rock fell on a vehicle in the Argilite Cut on British Columbia (B.C.) Highway 99 killing a woman and disabling her father. The father successfully sued the provincial Ministry of Transportation and Highways for damages. The Supreme Court of Canada found that the Ministry could readily foresee the risk that harm might befall users of the highway if it were not reasonably maintained and that maintenance could be found to extend to the prevention of injury from falling rock. A risk analysis methodology can assess the probability of loss of life due to rock fall. Rock fall impact-mark mapping supplemented by documented rock fall records was used to establish a rock fall frequency. The risk of rock fall on this highway in 1982 can be compared with accepted societal risks. For the Argillite Cut, the probabilities of death of a one time user and a daily commuter on the highway were 6 X 10-8 and 3X10-5 per year, respectively. The annual probability of a rock fall causing a death in the exposed population was 8 X 10-2 in the Argillite Cut. This was higher than the level of risk now commonly accepted in some industries and large engineering projects. (A)

A idealized framework for the analysis of cohesive soils undergoing desiccation

Abstract: The authors wish to thank the discussers for their interest in the work on crack formation in clays during drying. The model presented by the authors holds for soils with a high clay content in which desiccation cracks form while the soil is still saturated. This was the case for the Saint-Alban clay for which cracks appeared for a suction of about 23 kPa, 18 hours after the soil surface was exposed to evaporation. Only the onset of cracking was modelled, and crack depth is approximated with linear elastic fracture mechanics in mode I, i.e., opening of the crack. Further crack propagation occurs with the ongoing evaporation leading eventually to the formation of secondary and even tertiary cracks if the soil is restrained in all directions. Furthermore, these cracks, depending on soil type, may be initiated in an unsaturated soil. Hence, we agree that the model must then also consider unsaturated soil mechanics. Owing to differential behaviour between a relatively dryer surface layer and soil at a higher moisture content with increasing depth, secondary crack propagation may also be controlled, in some cases, by shear failure at the crack tip. As stated by the discussers, the cracking problem is complex and the subject received little attention so far.

Desiccation of a sensitive clay: field experimental observations

Abstract: An excavation with three different levels was exposed to continuous evaporation during 35 days in order to observe and document the formation of shrinkage cracks in an intact and weathered sensitive marine clay. Desiccation of the intact Saint-Alban clay under restrained conditions, at an average evaporation rate of 0.018 cm/h and an initial moisture content of 103%, produced visible primary cracks after 17 h with an average spacing of 20 to 24 cm. Secondary cracks within each original polygon appeared after about 70 h of evaporation. Subhorizontal cracks at a depth of 6 to 8 cm were also created owing to differential strains induced by differential shrinkage of the soil polygons. Further evaporation resulted in the formation of a new set of vertical cracks after about 150 h of evaporation in the soil below the subhorizontal shear plane. The shrinkage-induced volume change associated with these different sets of cracks produced polygons with a protuberance at their bottom part indicating that the depth of crack propagation below the subhorizontal shear plane was about 3 to 4 cm. In weathered clay at an initial moisture content of about 50%, the average spacing was 10 to 12 cm, indicating that spacing between primary cracks is related to soil type. In the cohesionless topsoil, no cracks were observed.

The relationship between the probability of landslide occurrence and rainfall

Abstract: A study of rainfall and the number of landslides is presented using 5 min rainfall records for all rainfall gauges in Hong Kong Island over a 10 year period. The results indicate that rainfall of 1-12 h duration is important in predicting the number of landslides, and that antecedent rainfall also has some influence. Analysis of the data gives general threshold rainfall values causing isolated landslides. Models predicting the number of landslides from rainfall near a specific rain gauge are developed. Rainfall for a 1 in 100 year event is calculated and utilized in the prediction of the number of landslides caused by such a storm event over the area of Hong Kong Island. Thus, the number of landslides for a substantial area, versus annual exceedance probability, can be approximately predicted using only rainfall data and records of landsliding. This approach can be utilized wherever landslide and detailed rainfall and landsliding records are, or can be, kept.

Slope stability analysis by the upper bound approach: fundamentals and methods

Abstract: A new method for stability analysis in soils and rocks is presented, based on the upper bound theorem of classical plasticity. The sliding mass is divided into a small number of discrete blocks, with linear interfaces between blocks and either linear or curved bases to individual blocks. By equating the work done by external loads and body forces to the energy dissipated in shearing, either a safety factor or a disturbance factor may be calculated. The rigorous theoretical background is established, from which it may be demonstrated that for several well-defined classical slope problems the equations for the multi-block solution reduce to the published closed-form solutions. Powerful optimization routines are provided in the computer program EMU to search for the critical failure mechanism giving the lowest factor of safety. Several examples are given to demonstrate that, for problems where the exact answers are known, the new method produces accurate values of safety factor and predictions of failure mechanism. Applications to practical problems have shown that the new method is as simple as the conventional limit equilibrium methods for practitioners.

Heat and mass transfer in unsaturated soils during freezing

Abstract: This paper presents an approach for predicting heat and mass transfer in freezing unsaturated soil when frost heave does not occur. The theoretical formulation uses soil-freezing and soil-water characteristic curve data to combine the heat and mass transfer relationships into a single equation for freezing or frozen regions of the soil. Numerical simulations were compared with the results of freezing tests for a closed system of fine silica flour where large moisture redistribution occurred without frost heave. Accurate predictions of ice content and water content were obtained using a single permeability versus suction function with no impedance factor. The permeability function was obtained using a recently developed method for predicting permeability functions for unsaturated soils using the soil-water characteristic curve. (A)

Bearing capacity of plane-strain footings on layered soils

Abstract: A study has been carried out of the bearing capacity of sand layers overlying clay soils for the case where the thickness of the sand layer is comparable to the width of a rigid foundation placed on the soil surface. A review of previous work is given and a discussion is presented of the dimensionless groups that govern the behaviour of this type of foundation. A parametric study is carried out using both finite element and finite difference methods. This study is based on the use of soil parameters obtained from an assessment of the range of values that might be expected to be appropriate for full-scale structures. The results of the parametric study are used to illustrate the mechanics of the system and also to develop charts that may be used directly in design. In particular, the results illustrate that the shear strength of the clay has an important influence on the mechanisms of load spread within the fill. Resume : Lion a rOalisO une Otude sur la capacitO portante de couches de sable reposant sur des sols argileux pour le cas oo liOpaisseur de la couche de sable est comparable ‡ la largeur diune fondation rigide posOe sur la surface du sol. Lion prOsente une revue des travaux antOrieurs et une discussion sur les groupes sans dimension qui rOgissent le comportement de ce type de fondation. Une Otude paramOtrique est rOalisOe en utilisant les mOthodes tant des OlOments finis que des diffOrences finies. Cette Otude est fondOe sur liutilisation des paramtres de sols obtenus en partant de liOvaluation de la plage des valeurs que lion pourrait siattendre ‡ trouver dans des structures ‡ pleine Ochelle. Les rOsultats de liOtude paramOtrique ont OtO utilisOs pour illustrer le mOcanisme du systme et aussi pour dOvelopper des abaques qui peuvent Œtre utilisOes directement dans la conception. En particulier, les rOsultats illustrent que la rOsistance au cisaillement de liargile a une influence importante sur les mOcanismes de rOpartition de la charge ‡ liintOrieur du remblai. Mots clOs : capacitO portante, sols multicouches, analyse numOrique. (Traduit par la rOdaction)

Reliability analysis of reinforced embankments on soft ground

Abstract: L'on a formule un modele de stabilite a l'equilibre limite de remblais sur sols mous, et propose une procedure pratique d'evaluation de la fiabilite. Le modele peut tenir compte d'une fissure de traction dans le remblai, d'armature en tension a la base du remblai, et d'un profil non lineaire de resistance au ciaillement non draine dans le sol mou. La procedure d'evaluation de la fiabilite proposee decoule d'une perspective ellipsoidale intuitivement evidente. Elle genere le meme indice de fiabilite que la methode courante de fiabilite de premier ordre (FORM), mais elle est plus pratique et plus transparente parce que la recherche automatisee sur le chiffrier est dans l'espace originale des variables. La methode proposee manipule des correlations sans transformation orthogonale de la matrice de covariance. La versatilite de la methode proposee est demontree dans un exemple de remblai arme qui a 12 variables aleatoires, incluant 6 valeurs de resistance autocorrelees, et une fonction de performance qui est non explicite a cause de la necessite de rechercher la surface critique de glissement et d'integrer numeriquement la resistance au cisaillement en fonction de la profondeur. La probabilite de rupture se compare bien avec la simulation de Monte-Carlo. L'on discute egalement de la conception basee sur la fiabilite, et l'on fait des comparaisons avec des histoires de cas. La facilite d'execution, la clarte du concept et la versatilite de la methode proposee devraient favoriser un usage plus etendu de l'analyse et de la conception basees sur la fiabilite, plus rationnelles que l'approche conventionnelle du coefficient de securite.

Dynamic nonlinear analysis of pile foundations using finite element method in the time domain

Abstract: A quasi-three-dimensional method of analysis is presented for the nonlinear dynamic analysis of single piles and pile groups. The analysis is performed in the time domain using strain-dependent moduli and damping, yielding at failure, and a no-tension cutoff. The analysis has been incorporated into the computer program PILE-3D and has been validated using data from centrifuge tests on a single pile and a 2 X 2 pile group under simulated earthquake loading. Analyses of the centrifuge tests demonstrated a significant reduction in soil moduli around the piles during strong shaking and a corresponding reduction in pile stiffnesses. The time-dependent shear modulus distribution in soil around the pile is obtained as part of the output. This allows the time variation of dynamic impedances of pile foundationsduring shaking to be established and allows a realistic assessment of thesingle-valued stiffnesses and damping factors usually incorporated into commercial structural analysis programs for the seismic analysis of pile-supported structures. The analysis also demonstrates the importance of inertial interaction between foundation and structure. (A)

Use of the tensile strength of water for the direct measurement of high soil suction

Abstract: Discussions The authors express their appreciation for the additional information provided by the Discussers on the subject of the tensile strength of water. This is a new subject area to the geotechnical literature and one that initially appears to go counter to the basic physics related to the behaviour of water. The test results and findings of the ongoing research pro gram on this subject, at Imperial College, U.K., have proven to be extremely valuable in better understanding the behaviour of water that has been conditioned through the use of pressurization process. The Discussers have pointed out that the sustainable tension in the direct measurement, high suction probe appears to be related to the air entry value of the ceramic. All of the tests performed by the authors were performed using a 1500 kPa ceramic. The maximum sustainable tension appeared to be limited by the ceramic; however, a repeated cavitation of the sensor appeared to reduce the maximum sustainable tension. Also, different ceramics with the same air entry value (i.e., 1500 kPa) often produced a different response both in terms of magnitude and response pattern. For example, in one case, it was not possible to sustain a maximum tension in excess of 300 kPa, no matter what attempts were made to pressurize and saturate the system. Even with the use of 10 000 kPa, the maximum sustainable tension could not be increased, no matter what attempts were made to saturate the system. The experience of the authors was that the 24 h pressurization period did not provide much advantage over the 12 h or even the 6 h pressurization period. The Discussers have emphasized the benefit of having a small water compartment. The authors found it difficult to determine the exact amount of water in the compartment, but a space ranging from 0.1 to 0.3 mm would appear to be favorable. Further studies, over a long period of time — under both field and in situ conditions — will prove extremely valuable in encouraging the direct measurement of high tensions in the water phase (i.e., high soil suctions). The Imperial College Suction Probe, as well as other probes, are indeed a welcome device in the application of unsaturated soil mechanics to geotechnical engineering.

Analysis of CANLEX liquefaction embankments: prototype and centrifuge models

Abstract: Un objectif principal du projet canadien d'etude de la liquefaction (Canadian Liquefaction Experiment, CANLEX) etait de verifier les procedures d'analyse pour la prediction des phenomenes de liquefaction. A cette fin, deux cas de chargement ont ete realises: un chargement sur le terrain comprenant un remblai construit sur une couche de fondation de sable lâche, et un essai au centrifuge realise sur un modele de la structure prototype. Tant l'essai sur le terrain que l'essai au centrifuge ont ete planifies de facon a induire une rupture par liquefaction statique. Les caracteristiques mecaniques fondamentales de la couche de fondation ont ete determinees dans des essais en laboratoire sur des elements (triaxiaux et cisaillement simple). Ces caracteristiques ont ete d'abord obtenues sur un element en utilisant un modele de comportement contrainte-deformation elasto-plastique. Le prototype et les structures a l'echelle ont alors ete modelises comme un ensemble de tels elements. Le drainage etait un facteur tres important durant le chargement et etait directement incorpore dans la procedure de l'analyse. Les resultats predits concordent bien tant avec l'essai au centrifuge qu'avec les mesures sur le terrain.

Desiccation of a sensitive clay: application of the model CRACK

Abstract: Field data obtained during the desiccation of an intact clay were used to assess the performance of a model enabling the prediction of depth and spacing of primary shrinkage cracks. The model requires several input parameters such as the soil-water characteristic curve to predict the evolution of the suction profile with time, the tensile strength of the soil to define the conditions at crack initiation, and the fracture toughness to calculate ultimate crack depth. Predictions of suctions at crack initiation, time of crack initiation, and depth of crack propagation were reasonable using laboratory determined values of these soil properties obtained from undisturbed samples. Field data suggest that neighbouring cracks form where the computed relief stresses reach 80 to 88% of the tensile strength of the soil.

Bearing capacity of unpaved roads

Abstract: Elastic layer theories may be valid for relatively stiff pavement materials and pavements subjected to low traffic stresses; however, the assumption of linear elastic behavior is not suitable for thin pavements and unpaved roads consisting of untreated granular bases over cohesive subgrades. The behavior of such pavements, even at low traffic stresses, is markedly nonlinear. Pavement design methods based on a bearing capacity theory are more applicable to roads with thin pavements. This paper outlines an ultimate strength method of designing low-volume roads. A procedure for determining the ultimate loads in layered systems, incorporating the effect of matric suction, is also presented. Existing empirical relationships that account for traffic loading are utilized in the proposed design procedure. Resume : Les thOories de couches Olastiques peuvent Œtre relativement valides pour les matOriaux de pavage et les pavages soumis ‡ de faibles contraintes de trafic; cependant, lihypothse de comportement Olastique linOaire ne convient pas ‡ des pavages minces et ‡ des routes non pavOes constituOes de fondations granulaires non traitOes reposant sur des infrastructures cohOrentes. Le comportement de tels pavages, mŒme sous de faibles contraintes de trafic, est nettement non linOaire. Les mOthodes de conception de pavages basOes sur la thOorie de capacitO portante siappliquent mieux aux routes avec des pavages minces. Cet article expose une mOthode de rOsistance ultime pour concevoir des routes ‡ faible volume de trafic. Lion prOsente une procOdure pour dOterminer les charges ultimes dans des systmes ‡ plusieurs couches, incorporant lieffet de succion matricielle. Des relations empiriques existantes qui tiennent compte des charges de trafic sont utilisOes dans cette procOdure de conception. Mots clOs : capacitO portante, routes non pavOes, thOorie non linOaire, rOsistance ultime. (Traduit par la rOdaction)

Skin friction on large-diameter piles socketed into rock

Abstract: Dans cet article sont discutes les resultats de cinq essais de charge axiale sur des pieux de grand diametre ancres dans la roche. Les pieux ont ete realises dans un site italien ou l'on a differentes formations rocheuses a une profondeur moderee au-dessous de terrains granulaires plus superficiels. Les ancrages ont ete effectues sur des roches ayant differentes caracteristiques de resistance, telles que marbre, calcaire, gypse et diabase. La reponse statique des pieux sous charge s'est revelee etre dependante de la resistance de la roche, de la longueur de l'ancrage et de la portion de pieu dans les terrains. Un modele de calcul est utilise dans cet article afin d'evaluer le frottement lateral a l'interface pieu-roche. Ce modele, base sur les fonctions de transfert de type hyperbolique, permet d'effectuer aisement des analyses a posteriori. En suivant les approches de type empirique, les parametres du modele sont d'abord caracterises sur la base des donnees fournies par les essais in situ et de laboratoire. Les parametres sont ensuite modifies en comparant les deplacements reels des tetes des pieux avec ceux fournis par le modele de calcul. Les valeurs finales de frottement limite ainsi calculees s'averent sensiblement plus basses que celles qu'on trouve dans la litterature.

Landslides: risk perception and acceptance

Abstract: The quantification of risk is gaining importance in many fields, including geotechnical engineering. Landslide risk management systems are gradually maturing in various countries. Following a review of acceptable risks and the psychology of risk perception, a study of landslide risk perception in Australia and Hong Kong is detailed. The general views of those surveyed on landsliding, issues of land development regulation and remedial costs, a comparison of landsliding to other hazards, cognitive structures, the perception of a quantified annual loss of life frequency, a ranking of various landslide situations to each other, and acceptable probabilities of landsliding for loss of life and property damage were obtained, analysed, and discussed.

Zeta potential and electroosmotic permeability of clay soils

Abstract: L'on etudie les permeabilites electro-osmotiques de six sols argileux et leurs potentiels zeta calcules en partant de la double couche Stern-Gouy. L'on trouve que la permeabilite electro-osmotique est proportionnelle au potentiel zeta, en accord avec le modele electrocinetique de Helmholtz-Smoluchowski communement accepte, a la condition de prendre en compte le caractere tortueux des capillaires du sol et une coupure du potentiel zeta. La technique presentee dans cette etude peut etre utilisee pour evaluer l'efficacite du procede electro-osmotique sur un sol d'un site specifique pour obtenir certaines proprietes du sol en partant du laboratoire.

Lateral earth pressures behind rotating walls

Abstract: Classical earth pressure theories are valid strictly for retaining walls subject to uniform free translation. Practically all retaining walls rotate, and movements of the wall could be restricted, particularly under working conditions. The lateral earth pressure on the wall often deviates from the fully active Coulomb value. There is a need for predicting the lateral earth pressure at any wall displacement behind a rotating wall. The finite element method (FEM) is capable of providing valid solutions of lateral pressures for different wall movements, but a simple alternative method has its practical value. This paper presents a simple analysis method using a modified Coulomb's solution of active pressure. The deformation pattern and the associated mobilization of shearing resistance in the soil as affected by the wall movement are considered in a simplified manner. Comparisons of calculated results with solutions from FEM and observations from model tests show that the method can provide a good prediction of lateral pressures for walls rotating about the base when proper distributions of mobilized shearing resistance and wall friction are used. For walls rotating about the top, the prediction is fair due to arching and the difference between assumed and observed rupture mechanisms.

Dynamic elastic analysis of pile foundations using finite element method in the frequency domain

Abstract: A quasi-three-dimensional finite element method of analysis is proposed for the dynamic response analysis of pile foundations that is computationally feasible for practical applications. The method uses a simplified three-dimensional wave equation for describing the dynamic response of the soil. The response of the pile foundation is computed directly without having to use pile-soil-pile interaction factors. The quasi-three-dimensional solution greatly reduces the computational time for the direct analysis of pile groups. The method is presented here for an elastic response so that itcan be validated against existing more exact elastic solutions and low-amplitude field vibration tests. The method is extended to nonlinear dynamicresponse analysis in an accompanying paper. (A)

Electokinetic dewatering of clay slurries as engineered soil covers

Abstract: Le courant continu produit le mouvement des particules d'argile en suspension dans l'eau. Au moment de la formation de la structure du sol, le courant produit en plus le mouvement de l'eau a l'interieur du squelette du sol. Les phenomenes sont connus comme etant de l'electrocinetique. Cette etude examine la faisabilite de l'utilisation de la technique d'extraction d'eau par electrocinetique pour fabriquer des couvertures de sols pour la prevention du drainage des acides sur les sites miniers. L'on discute les aspects tels que la vitesse de sedimentation, la permeabilite electro-osmotique, les reactions electrochimiques, le renversement de la polarite, le courant intermittent, la duree de traitement, la qualite de l'eau recueillie, et la consommation d'energie. Les resultats demontrent que le traitement electrocinetique reduit les teneurs en eau de deux boues d'argile naturelle a leurs limites de liquidite en moins de 30 h. La consommation d'energie de l'extraction d'eau par electrocinetique est regie par les proprietes du sol et le temps de traitement.

Measurement of evaporative fluxes from candidate cover soils

Abstract: Pour certaines applications en genie geotechnique, par exemple la conception de couvertures en sol pouvant retenir l'humidite et reduire les effluents acides contenus dans les dechets miniers, il est necessaire de connaitre avec precision la vitesse d'evaporation a l'interface sol-atmosphere de facon a evaluer la teneur en eau de la couverture pendant les periodes seches. Dans la presente etude, on a mesure les vitesses reelles d'evaporation pour un sable grossier, un sable fin, une argile et un sol de surface, dans des conditions de laboratoire controlees. Les resultats ont montre dans tous les cas trois phases d'evaporation typiques des sols. Dans la phase I (phase a vitesse constante) les vitesses observees pour les sables fins et grossiers sont semblables a la vitesse d'evaporation potentielle ou maximale mesuree pour une surface d'eau libre. L'argile compactee et le sol de surface ont montre des vitesses d'evaporation initiales legerement plus basses, probablement a cause de leur conductivite hydraulique non saturee plus faible. Les teneurs en eau mesurees dans les colonnes de sol ont indique que les fronts d'assechement penetraient dans le profil au fur et a mesure que l'evaporation progressait, jusqu'a la fin de la phase II (premiere phase de decroissance de la vitesse) pour laquelle la vitesse d'evaporation etait faible. Pendant la phase III, deuxieme phase de decroissance de la vitesse, les profils de teneur en eau etaient a peu pres uniformes dans les sables et le sol de surface. Dans l'argile, cependant, le front d'assechement etait toujours present. L'utilite d'une mesure des flux d'evaporation est demontree par l'analyse d'une couverture de sol au-dessus de dechets miniers.

On the physicochemical aspects of compacted clay compressibility

Abstract: L'on etudie les effets du systeme argile-eau-electrolyte, et de la temperature sur la compressibilite du sol due a la consolidation primaire et la compression secondaire. La methode utilisee pour l'alteration du complexe d'echange a fourni une seule espece de cation (Na + , Ca ++ , ou K + ) pour dominer le complexe d'echange, soit plus de 87% du total des cations echangeables presents dans le complexe d'echange. Le complexe d'echange domine par le potassium (K + ) a produit des changements fondamentaux dans le comportement du sol teste: par rapport au sol non traite, le sol traite au potassium a subi une diminution de 66 a 13% de I p , de 10,5 a 1,7% du gonflement libre, et une augmentation par un facteur 10 du coefficient de permeabilite. L'on trouve que l'indice de compression vierge (C c ) est fortement relie au poids volumique sec du sol et peut etre modelise en consequence avec precision. La temperature affecte de facon significative le comportement du sol non traite; le coefficient de permeabilite mesure a ete augmente d'environ 100% pour un changement de temperature de 26 a 40°C, alors que la temperature n'a quasiment pas d'influence sur le sol traite au potassium.

Seabed instability due to flow liquefaction in the Fraser River delta

Abstract: Les ruptures par liquefaction de depots de sables lâches peuvent representer une menace importante pour les structures cotieres. On a evalue, a partir des concepts d'etats stationnaires, les contributions possibles de divers mecanismes de declenchement lors d'une rupture par liquefaction qui a eu lieu en 1985 a l'embouchure du chenal principal de la riviere Fraser. Parmi les mecanismes qui ont pu declencher le glissement par liquefaction en 1985, on a etudie la sedimentation, les vagues de surface et les marees basses. L'analyse montre qu'une sedimentation rapide genere des contraintes de cisaillement dans la pente mais ne pourrait pas faire demarrer des ruptures par liquefaction. Lorsqu'on evalue l'effet des vagues de surface et leur capacite a causer des glissements de type coulee profonde, on trouve qu'il ne s'accumule pas de pressions interstitielles significatives dues aux vagues de surface pouvant exister dans la region. Les marees basses ne peuvent pas non plus declencher de rupture dans des sables submerges et completement satures. L'apparition de gaz provoque cependant la desaturation des sediments ce qui peut induire des pressions interstitielles residuelles pendant les marees basses. On emet donc l'hypothese que c'est la combinaison de sediments lâches, de faibles quantites de gaz et de marees basses qui favorise les ruptures par coulees liquefiees dans le delta. Ces ruptures conduisent a des glissements regressifs.

The modified block punch index test

Abstract: The block punch index test, requiring only a small cylindrical disc sample, has been developed during the last decade and provides a practical index in assessing the strength of intact rock. In this study, earlier developments in the block punch index test are reviewed and a method for sample size correction is described. Analysis of the results, obtained from 23 different rocks, reveals that size correction in the block punch index test is indispensable. A strong correlation was found between the block punch index and the uniaxial compressive strength and strength anisotropy. Utilization of the block punch index as an input parameter in rock mass classification was also suggested. Resume : Developpe au cours de dix dernieres annees, le «block punch index test,» qui necessite des petits echantillons, procure des indexes pratiques a l'evaluation de la resistance de la roche entacte. D'autre part, il est indispensable de tenir compte de l'effet de dimension, tres importante pour cette experience. Ce petit travail essaie d'elaborer une methode a obtenir une facteur corrective pour l'echantillon ainsi que des graphiques et des nomogrammes correspondants pour diminuer l'influence de l'effet de dimension, tout en evaluant de developpement du «block punch index test.» Le donnes obtenus a la suite des analyses faites sur 23 differentes roches nous prouvent que l'adaptation du processus de l'effet de dimension au cours de «block punch index test» est indispensable. La correlation elevee a ete determinee au milieu du «block punch index» et la resistance a la compression uniaxiale et l'enisotropie de resistance. L'utilisation du «block punch index» comme une parametre donnee a la classification des roches en masse a ete aussi consideree.