New data are presented from internal measurements in direct shear tests on sand. An interpretation is given for the plane strain angle of friction and the angle of dilation of sand in a direct shear test. The direct shear angle of friction deduced from the conventional analysis is shown to underestimate the frictional shearing resistance of sand by about 20%. Results are presented from direct shear tests on reinforced samples and these are fitted by a limit equilibrium analysis in which all the parameters are independently measured. Plastic incremental strains cause dilation in dense sand and dominate the deformation with increasing stress ratio. The rate of increase of the reinforcement force in shearing sand is shown to depend on the angle of dilation. The maximum bond angle of friction between sand and the rough surface of reinforcement is also determined by plastic deformation in the sand. A theoretical analysis for the bond is supported by the test results which show that the maximum bond angle of friction for rough reinforcement equals the direct shear angle of friction. Thus the modiied direct shear test is a good way to measure bond strength parameters for design.
The incorporation of the fatty acids in fish and olive oil into the colonic mucosa of patients with inflammatory bowel disease was examined during 12 weeks' dietary supplementation with the oils, and the influence on colonic mucosal prostaglandin and thromboxane generation was measured. With a dietary supplement of 18 g fish oil daily, concentrations of the major polyunsaturated fatty acids in fish oil, eicosapentaenoic acid and docosahexaenoic acid, were significantly raised in mucosal lipids. The first time these were measured, after three weeks' supplementation, the mean increases in eicosapentaenoic and docosahexaenoic acid were seven fold and 1.5 fold respectively, and these increases were maintained during the 12 week study. Arachidonic acid values fell throughout the study and this reduction was significant at 12 weeks. Mucosal prostaglandin E2 (PGE2), thromboxane B2, and 6-keto prostaglandin F,,, synthesis were suppressed, and this reached significance (p<005) at three and 12 weeks for PGE2 and at 12 weeks for thromboxane B2.
Experimental data from unreinforced direct shear tests on sand are presented to show the influence of the boundary conditions on the test measurements. The data and the theoretical considerations of the loading in the test show that a symmetrical direct shear test arrangement is preferable. A new method of analysis for the direct shear test is introduced based on the relationship between the sand shearing resistance and dilatancy. The analysis provides an independent check on the conventional analyses and on the consistency of the data from direct shear tests. The conclusion is that the symmetrical direct shear test is an effective method for the measurement of the plane strain and direct shear angles of friction for sand and the angle of dilation, at the density and stress level tested. The measured plane strain shearing resistance corresponds closely with the minimum value with respect to strength anisotropy. A simple modification for the standard laboratory direct shear apparatus and suggestions for the analysis of standard test data are recommended. L'article présente des données expérimentales obtenues à partir d'essais de cisaillement direct non-renforés pour démontrer l'influence exercée par les conditions limites sur les mesures effectuées au tours des essais. Ces données et des considérations théoriques du chargement dans l'essai indiquent qu'une disposition symétrique est préférable pour l'essai de cisaillement direct. On introduit une nouvelle méthode analytique pour l'essai de cisaillement direct, basée sur la relation entre la résistance au cisaillement du sable et la dilatance. Cette analyse fournit un contrôle indépendant des analyses conventionnelles et de l'uniformité des données des essais de cisaillement direct. On en conclut que l'essai de cisaillement direct symétrique représente une méthode effective pour la mesure de la déformation plane et des angles de frottement de cisaillement directs pour le sable et l'angle de dilatance à la densité et au niveau des contraintes de l'essai. La résistance au cisaillement mesurée sous déformation plane correspond pratiquement à la valeur minimale de la résistance anisotrope. On recommande une modification très simple de l'appareil normal utilisé pour les essais de cisaillement direct en laboratoire, tout en faisant des suggestions pour l'analyse des données des essais normaux.
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