Lesson 2/Learning Event 4
Silty Soils
The silt grains are so much smaller than sand grains that they do not feel nearly so harsh between the
teeth, and are not particularly gritty although their presence is still easily detected.
Clayey Soils
The clay grains are not at all gritty, but feel smooth and powdery like flour between the teeth. Dry
lumps of clayey soils will stick when lightly touched with the tongue.
WET SHAKING TEST
Like all the other tests described in this part the wet shaking test is performed only on the material
passing the #40 sieve. For this test, enough material to form a ball of material about 3/4 inch in diameter
is moistened with water. This sample should be just wet enough that the soil will not stick to the fingers
upon remolding or just below the sticky limit.
Place the soil in the palm of the hand and shake vigorously. This is done by jarring the hand on the table
or some other firm object, or by jarring it against the other hand. The soil is said to have given a
reaction to this test when, on shaking, water comes to the surface of the sample producing a smooth,
shiny appearance. This appearance is frequently described as "livery." Then, squeeze the sample
between the thumb and forefinger of the other hand. The surface water will quickly disappear and the
surface will become dull. The material will become firm and resist deformation. Cracks will occur as
pressure is continued, with the sample finally crumbling like a brittle material. The vibration caused by
the shaking of the soil sample tends to reorient the soil grains, decrease the voids, and force water,
which had been within these voids, to the surface. Pressing the sample between the fingers tends to
disarrange the soil grains and increase the voids space, and the water is drawn into the soil. If the water
content is still adequate, shaking the broken pieces will cause them to liquefy again and flow together,
and the complete cycle may be repeated. This process can occur only when the soil grains are bulky and
noncohesive.
Typical Reactions
Very fine sands and silts fall into this category and are readily identified by the wet shaking test. Since
it is rare that fine sands and silts occur without some amount of clay mixed with them, there are varying
degrees of reaction to this test. Even a small amount of clay will tend to greatly retard this reaction.
Some of the descriptive terms applied to the different rates of reaction to this test are as follows:
Sudden or Rapid. A rapid reaction to the shaking test is typical of nonplastic, fine sands, and
silts.
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