Summary An analysis is made of a large number of tests for workability as measured by the compacting factor, in order to determine how workability is related to the grading and shape of aggregate, the mix proportions and the water/cement ratio. An index is developed which takes account of the influence of particle size on workability, and largely overcomes the limitations of the fineness modulus and surface area coefficients. Similarly, an angularity index is introduced which is based on a test on the aggregate and is shown to take account of its shape. The relation between workability and mix proportions is assessed. It is established that a proportion of the water, equivalent to a water/cement ratio of about 0·25, is required to wet the cement, and that any additional water may be regarded as available to make the mix workable. An approximate relation is given for the calculation of compacting factors, and a worked example illustrates the use of this relation for mix design.
Synopsis The article describes a soil investigation and loading tests which were made on bored and driven concrete piles in London clay to study their bearing capacity and settlement. It was found that the shearing strength of the fissured clay decreased rapidly with time after sampling, due to opening of the fissures which could not be closed sufficiently by large triaxial pressures. Water from concrete of bored piles installed in an unlined auger borehole softens the clay and this softening could not be avoided except by an unworkable dry mix. Whilst the point resistance can be based on the natural shearing strength, the skin friction of these bored piles is closely given by the fully softened strength. On the other hand, the skin friction of concrete piles driven into stiff to hard clay seems to have an upper limit of 2,000 lb. per square foot. At a factor of safety of 3 against shearing failure, the settlement of widely spaced bored and driven piles in London clay is unlikely to be greater than 1 inch. L'article déit un examen du sol et des essais de charge faits sur des pieux de béton, forés et enfoncés, dans l'argile de Londres, afin d'en examiner la charge limite et le tassement. On a trouvé que la résistance au cisaillement de l'argile fissurée après le prélèvement d'échantillons diminue rapidement en fonction du temps, par suite de l'ouverture de fissures qu'on n'a pu suffisamment refermer moyennant une grande pression triaxiale. L'eau provenant du béton des pieux foré dans un sondage non-cuvelé ramollit l'argile, et l'on n'a pu éviter ce ramollissement qu'en employant un mélange trop sec pour en permettre l'utilisation. Alors que la résistance à un point donné peut être basée sur la résistance spécifique au cisaillement, le frottement superficiel de ces pieux forés est donné avec une bonne approximation par la résistance dans l'état ramolli. Par contre, le frottement superflciel de pieux de béton enfoncés dans une argile tenace ou dure semble avoir une limite supéieure de 2,000 livres par pied caré. Avec un facteur de sécurité de 3 centre une rupture par cisaillement, l'affaissement de pieux largement éartés, forés ou enfoncés dans l'argile de Londres, ne dépassera probablement pas un pouce.
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