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ROLL OR THREAD TEST - 14071_396
BITE OR GRIT TEST - 14071_398

Engineering Aid 2 - Intermediate Structural engineering guide book
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Figure 16-7.-Ribbon test. diameter is moistened with water. This sample should be just wet enough that the soil does not stick to your fingers upon remolding or just below the sticky limit. For testing, the sample is then placed in the palm of the hand and shaken vigorously. This is usually 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 if, when it is shaken, water comes to the surface of the sample producing a smooth,   shiny   appearance.   This   appearance   is frequently  described  as  livery  (fig.  16-8). The sample is then squeezed between the thumb and forefinger of the other hand. As this is done, the surface water  quickly  disappears  and  the  surface  becomes  dull. The  sample  becomes  firm,  resisting  deformation,  and cracks occur as pressure is continued. Finally the sample crumbles like a brittle material. The vibration caused by shaking 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  void spaces. The water is then drawn into the soil. If the water content is still adequate, shaking the broken pieces Figure 16-8.-Livery appearance produced by wet-shaking test. causes them to liquefy again and flow together, and the complete cycle may be repeated. This process can occur only when the solid grains are bulky in shape and noncohesive in character. 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 tends to retard this reaction greatly. 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. A material known as rock flour that falls into the silt-size ranges also gives this type of reaction. .  SLUGGISH  OR  SLOW.  A  sluggish  reaction indicates slight plasticity such as might be found from a  test  of  some  organic  or  inorganic  silts  or  silts containing a small amount of clay. Even a slight content of colloidal clay imparts some plasticity and materially slows up the reaction to the shaking test. Extremely slow or no reaction is typical of all inorganic clays and of the highly plastic organic clays. . NO REACTION. Obtaining no reaction at all to this test does not indicate a complete absence of silt or fine  sand. ODOR TEST Organic soils of the OL and OH groups usually have a  distinctive,  musty,  slightly  offensive  odor.  With experience, you can use this odor as an aid in identifying these groups. This odor is especially apparent from fresh samples.  The  odor  gradually  reduces  when  exposed  to 16-19







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