The modulus of elasticity of leda clay from field measurements

The construction of the Ottawa Sewage Treatment Plant provided an opportunity to measure bottom heave in two large excavations in clay. With guages installed prior to excavation, elastic heave, swelling, and heave due to pile driving were measured in an excavation 31.5 ft. deep. Using a Poisson's ratio of 0.4, the modulus of elasticity determined from field measurements compared favourably with the initial tangent modulus from the best unconfined compression strength tests. In the other excavation a drop in the ground water table produced an elastic settlement that exceeded the elastic heave resulting from unloading by excavation.La construction d'une usine d'\ue9puration des eaux \ue0 Ottawa nous a fourni une occasion de mesurer les soul\ue8vements du fond de deux fouilles d'importance dans l'argile L\ue9da. Avant le d\ue9but de l'\ue9xcavation, des jauges furent install\ue9es pour mesurer le soul\ue8vement d\ufb \ue0 la d\ue9formation \ue9lastique, au gonflement et au battage des pieux au fond d'une fouille de 31.5 pieds de profondeur. Le module d'\ue9lasticit\ue9 calcul\ue9 \ue0 partir des mesures sur le terrain et du coefficient de Poisson de 0.4 est comparable au module donn\ue9 par la tangent \ue0 la partie initiale de la courbe contrainte- d\ue9formation obtenue par les meilleurs essais en compression simple. Dans l'autre fouille, un affaissement de la nappe phr\ue9atique a produit un tassement \ue9lastique de plus grande amplitude que le soul\ue8vement d\ufb \ue0 l'excavation.Peer reviewed: NoNRC publication: Ye

Instructions for Wiring the Roscoe Earth Pressure Cell

Peer reviewed: NoNRC publication: Ye

Measurement of Mud Creek Bridge Foundation Movements

Peer reviewed: NoNRC publication: Ye

Temperature controlled humid storage room

The design of a soil sample storage room that has been in operation since 1954 is described. The room provides a storage environment with a constant temperature of 55 degrees F and relative humidities of 90 to 97 percent. It is of wood frame construction, lined with copper sheeting, forming a watertight interior. The desired temperature and humidities are obtained by running water down the walls of the room and circulating it through a heat exchanger. The preparation of samples for storage and the effect of storage times on soils are discussed.L'auteur d\ue9crit la conception d'une salle d'entreposage d'\ue9chantillons de sol exploit\ue9e depuis 1954. On y maintient une temp\ue9rature constante de 55 degr\ue9s F et l'humidit\ue9 relative est de 90 \ue0 97 pour cent. Il s'agit d'une construction \ue0 ossature de bois, rev\ueatue de t\uf4les de cuivre qui assurent un int\ue9rieur \ue9tanche. On obtient la temp\ue9rature et l'humidit\ue9 souhait\ue9es en laissant couler de l'eau le long des murs et en la faisant recirculer par un \ue9changeur de chaleur. L'auteur traite de la pr\ue9paration des \ue9chantillons pour l'entreposage et de l'effet du temps d'entreposage sur ceux-ci.Peer reviewed: NoNRC publication: Ye

Field observations of negative skin friction loads on long piles in marine clay

Two 270-ft. long end bearing pipe piles filled with reinforced concrete and a 160-ft. long hollow steel pipe friction pile driven through a 30-ft. high highway embankment founded on compressible marine clay at Berthierville, Quebec, Canada, were intrumented to measure the build-up of negative skin friction loads due to consolidation of the foundation soil. The observations indicate that skin friction is related to the effective stresses in the soil. The paper is a progress report of observations made in the field to the end of 1969.Dans le but de mesurer l'accroissement du frottement lat\ue9ral n\ue9gitif provenant de la consolidation d'une argile marine de fondation \ue0 Berthierville, Qu\ue9bec, Canada, on a instrument\ue9 deux pieux de 270 pi. r\ue9sistant par la pointe (tubes remplis de b\ue9ton arm\ue9) et un pieu flottant de 160 pi. (tube vide) enfonc\ue9s dans le remblai d'une chauss\ue9e de 30 pi. de hauteur appuy\ue9 sur l'argile marine. Ces mesures indiquent qu'il y a une relation entre le frottement lat\ue9ral et les contraintes effectives dans les sols. Cet article est un rapport int\ue9rimaire sur les observations sur place portant jusqu'\ue0 la fin de l'ann\ue9e 1969.Peer reviewed: NoNRC publication: Ye

Mud creek bridge foundation movements

A 400 ft (122 m) long, five-span concrete bridge over Mud Creek, supported on end bearing steel piles, was instrumented to measure horizontal movements of its foundations. Fifteen years of observations show that the abutments and piers have moved downslope and rocked back and forth through a small vertical angle about their bases. The net convergence of the abutments is about 4 cm. The horizontal movements were caused by soil creep in the marine clays of the steep valley slopes. The change in verticality of the piers was attributed to the expansion and the contraction of the bridge deck due to seasonal temperature variations. The steel end bearing batter piles were ineffective in maintaining the piers and abutments in their original positions.Le pont sur le Mud Creek, d'une longueur de 400 pieds (122 m), et constitu\ue9 de cinq trav\ue9es en b\ue9ton support\ue9es sur des pieux d'acier \ue0 r\ue9sistance en pointe, a \ue9t\ue9 instrument\ue9 pour mesurer les mouvements horizontaux de sa fondation. Quinze ann\ue9es d'observations montrent que les cul\ue9es et les piles ont subit une translation vers le bas talus et de faibles rotations autour de leur base vers l'avant ou l'arri\ue8re. La convergence nette des cul\ue9es est de 4 cm. Les d\ue9placements horizontaux ont \ue9t\ue9 caus\ue9s par le fluage de l'argile marine dans les talus raides de la vall\ue9e. Le changement de vericalit\ue9 des piles a \ue9t\ue9 attribu\ue9 \ue0 l'expansion et la contraction du tablier du pont par suite des variations saisonni\ue8res de temp\ue9rature. Les pieux en acier inclin\ue9s, \ue0 r\ue9sistance en pointe, se sont av\ue9r\ue9s incapables de maintenir le piles et les cul\ue9es dans leur positions originales.Peer reviewed: NoNRC publication: Ye

Bearing capacity of clays for tower silos

Canadian farmers are building larger and higher tower silos than they did in the past, following the modern trend for larger engineering structures. These large tower silos represent a substantial expenditure, and in an effort to reduce costs the foundations are often compromised. When silos were smaller there were generally no problems. However, with larger structures the applied loads often approach the bearing capacity of the foundation soils. This has led to excessive settlements, dangerous tilting, and frequently, complete failure. Silos must have foundations designed for the bearing capacity of the soil and with an adequate factor of safety if the structures are to perform as desired. A method for determining the allowable bearing capacity based on soil tests, and some suggested improvements in the design of foundations are given.Peer reviewed: NoNRC publication: Ye

Soil shrinkage damages shallow foundations at Ottawa, Canada

Fine-grained soils are often very sensitive to moisture content changes. Shrinkage due to removal of water tends to become permanent if the clay particles are randomly oriented, which is the case in the Leda clay deposits of the Ottawa-St. Lawrence river valleys. A survey of residential buildings in Ottawa revealed a wide range of damage intensity, such as settlement cracks. Wood frame construction resisted damage much better than brick buildings. Paved streets and sewers tend to drain away surface water causing lowering of the ground water table. Buildings on clay soils in Ottawa show greater settlement on the sides facing paved streets. Large trees cause severe settlement in buildings and damage to streets and sidewalks. By removing water through root systems they cause a local drying and shrinking of the soil resulting in non-uniform settlement and cracking in the roadway. Minimization of the movements, due to trees, on such soils as Leda clay, can be influenced by frequent watering to prevent drying out. Trees should not be planted close to structures and foundations should be at a depth where seasonal moisture changes are small.Fr\ue9quemment, les sols \ue0 grains fins sont sensibles aux fluctuations de la teneur en humidit\ue9. La contraction provoqu\ue9e par le retrait de l'eau a tendance \ue0 devenir permanente si les particules d'argile sont orient\ue9es au hasard. Une \ue9tude de constructions r\ue9sidentielles d'Ottawa a mis en \ue9vidence divers degr\ue9s de gravit\ue9 dans les dommages, soit par exemple les fissures de tassement. Les habitations \ue0 ossature de bois ont beaucoup mieux r\ue9sist\ue9 aux dommages que les b\ue2timents de brique. Les rues asphalt\ue9 es et les \ue9gouts favorisent l'\ue9coulement des eaux de surface, provoquant un abaissement du niveau de la nappe phr\ue9 atique. Les b\ue2timents d'Ottawa reposant sur des sols argileux subissent un tassement plus marqu\ue9 sur les c\uf4t\ue9s faisant face aux rues asphalt\ue9es. Les gros arbres provoquent de forts tassements des b\ue2timents et des d\ue9g\ue2ts aux rues et aux trottoirs; en tirant l'eau par leur syst\ue8me radiculoaire, il provoquent un ass\ue8chement localis\ue9 et un retrait du sol qui entra\ueenent un tassement irr\ue9gulier et la fissuration de la chauss\ue9e. Il est possible de favoriser la r\ue9duction des mouvements provoqu\ue9s par les arbres sur les terrains tels que les argiles Leda en proc\ue9dant \ue0 de fr\ue9 quents arrosages pour pr\ue9venir l'ass\ue8chement. Les arbres ne devraient pas \ueatre plant\ue9s pr\ue8s des b\ue2timents et les fondations devraient \ueatre implant\ue9es \ue0 une profondeur o\uf9 les fluctuations d'humidit\ue9 saisonni\ue8res sont n\ue9gligeables.Peer reviewed: NoNRC publication: Ye