Figure 16-7.-Ribbon test.diameter is moistened with water. This sample shouldbe just wet enough that the soil does not stick to yourfingers upon remolding or just below the sticky limit.For testing, the sample is then placed in the palm ofthe hand and shaken vigorously. This is usually done byjarring the hand on the table or some other firm objector by jarring it against the other hand. The soil is said tohave given a reaction to this test if, when it is shaken,water comes to the surface of the sample producing asmooth, shiny appearance. This appearance isfrequently described as livery (fig. 16-8).The sample is then squeezed between the thumb andforefinger of the other hand. As this is done, the surfacewater quickly disappears and the surface becomes dull.The sample becomes firm, resisting deformation, andcracks occur as pressure is continued. Finally the samplecrumbles like a brittle material.The vibration caused by shaking the soil sampletends to reorient the soil grains, decrease the voids, andforce water, which had been within these voids, to thesurface. Pressing the sample between the fingers tendsto disarrange the soil grains and increase the voidspaces. The water is then drawn into the soil. If the watercontent is still adequate, shaking the broken piecesFigure 16-8.-Livery appearance produced by wet-shaking test.causes them to liquefy again and flow together, and thecomplete cycle may be repeated. This process can occuronly when the solid grains are bulky in shape andnoncohesive in character. Very fine sands and silts fallinto this category and are readily identified by thewet-shaking test. Since it is rare that fine sands and siltsoccur without some amount of clay mixed with them,there are varying degrees of reaction to this test. Even asmall amount of clay tends to retard this reaction greatly.Some of the descriptive terms applied to the differentrates of reaction to this test are as follows:. SUDDEN OR RAPID. A rapid reaction to theshaking test is typical of nonplastic, fine sands and silts.A material known as rock flour that falls into the silt-sizeranges also gives this type of reaction.. SLUGGISH OR SLOW. A sluggish reactionindicates slight plasticity such as might be found froma test of some organic or inorganic silts or siltscontaining a small amount of clay. Even a slight contentof colloidal clay imparts some plasticity and materiallyslows up the reaction to the shaking test. Extremely slowor no reaction is typical of all inorganic clays and of thehighly plastic organic clays.. NO REACTION. Obtaining no reaction at all tothis test does not indicate a complete absence of silt orfine sand.ODOR TESTOrganic soils of the OL and OH groups usually havea distinctive, musty, slightly offensive odor. Withexperience, you can use this odor as an aid in identifyingthese groups. This odor is especially apparent from freshsamples. The odor gradually reduces when exposed to16-19
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