Synopsis This Paper describes both the design and principles of operation of a new ring shear apparatus, and its application to the measurement of the residual strength of undisturbed and remoulded samples. As the test results differ significantly from those obtained in multiple reversal direct shear box tests, a critical examination is made of all possible sources of error in both measurement and interpretation. The results of tests on five soils, blue London Clay, brown London Clay, Weald Clay, a Norwegian clay and the Cucaracha Shale from Panama, are presented and discussed in relation to other published residual strength data from tests on these materials. The factors controlling the brittleness of soils tested under drained conditions are examined. Cet article décrit à la fois la conception et les principes d'opération d'un nouvel appareil de mesure du cisaillement circulaire par torsion, et de son application à la mesure des résistances résiduelles d'échantillons non pertubés et remoulés. Comme les résultats des essais diffèrent d'une manière significative de ceux obtenus lors d'essais multiples effectés dans une boîte de cisaillement renversé direct, on donne une analyse critique de toutes les sources d'erreurs possibles à la fois dans les mesures et dans leur interprétation. Les résultats d'essais sur cina sols: arsdle bleu de Londres, argile brun de Londrks, argile de Weald, argile Norvégien et schiste Cucaracha de Panama, sont présentés et discutés par rapport aux autres résultats d'essais de résistance résiduelle publiés sur ces matériaux. On examine les facteurs qui contrôlent la fragilité de ces sols dans des conditions de drainage.
The Norwegian Geotechnical Institute has recently developed a light inspection vane borer for field determination of the undrained shear strength in clay. The range of the instrument is from 0 to 2 tons/ft2 (0 to 20 tons/m2). It is primarily intended for use in trenches and excavations at a depth not influenced by drying and excavation procedure.
Once it had been shown that high-activity silica, even in comparatively small additions, improves the aging resistance of latex vulcanizates by many times, and that also an effect similar to that of a coactivator is set up by the interaction of high-activity silica with age resistors, ultra-accelerators and atmospheric oxygen in latex mixtures, a like effect was to be expected in sulfur-free latex vulcanizates crosslinked by thiuram compounds. In order to get comparable data it was necessary in the first place to get sulfur-free latex mixtures giving vulcanizates with starting properties in the same order of value as those of latex vulcanizates with the classical sulfur recipe. In addition it was necessary also to develop stocks from which threads could be extruded by the well-known two-stage method, since the investigations mentioned at the beginning were carried out exclusively on vulcanized threads, which lend themselves particularly well to determinations of tensile strength, elongation at break and tensile stress. Above all an attempt was made to manage with vulcanization temperatures below 100° C. To make this possible a thiuram compound active at relatively low temperatures had to be used. Here we had the opportunity of using DPTT (dipentamethylenethiuram tetrasulfide, Tetrone A), which the manufacturers (Du Pont) designate, alone among their thiuram accelerators, as “very active”, and which J. Willums referred to in a German journal as far back as 1944.
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