SCREWS. Manipulate the screws to adjust theheight to which the cup is lifted. The point on thecup that comes into contact with the anvil of themachine should be exactly 1 cm above the anvil(the upper surface of the hard-rubber base of themachine). Check the adjustment by turning thecrank at a rate of two drops per second. Youshould hear a slight click when the adjustment iscorrect.Steps in the test procedure are as follows:1. From the prepared test material, take asample that weighs about 100 g and place a por-tion in the cup above the spot where the cup restson the base. Squeeze the sample and spread it withas few strokes of the spatula as possible, takingcare to prevent the air bubbles from gettingtrapped within the mass. With the spatula, levelthe soil as you trim it to a depth of 1 cm at thepoint of maximum depth. Divide the soil in thecup by making a groove with the grooving toolalong the center line of the cam follower or hookthat holds the cup. When you make the groove,hold the cup in your left hand with the hook up-ward, and draw the grooving tool, beveled edgeforward, through the material downward awayfrom the hook. With some soils (especiallysandy soils and soils containing organic matter),it is not possible to draw the grooving tool throughthe specimen without tearing the sides of thegroove. In such cases, make the groove witha spatula, using the tool only for final shaping.When made correctly, the groove is wedge-shapedin section; it is open at the bottom for a dis-tance equal to the width of the tip of the groovingtool.2. Attach the cup to the carriage and turn thecrank at a rate of two revolutions per second.Count the blows as you continue to turn the crankuntil the two halves of the soil cake come into con-tact at the bottom of the groove along a distanceof about 1/2 in. (fig. 15-35). Record the numberof blows required to close the groove in thismanner.After you record the number of blows, re-move the cup from the testing device. Remixand regroove the sample. Place the cup againin the testing device and repeat the test. Ifthe number of blows on the second test dif-fers from the number on the first by one orless, record both numbers on the data sheetand consider the test finished. If the number ofblows on the second test differs by more than one,repeat the test until three successive tests give areasonably consistent sequence. The average ofthe three is taken as the number required for theclosure.3. Remove a slice of soil approximately thewidth of the spatula (say about 10 g), extendingfrom the edge of the soil cake at right angles toFigure 15-35.-Liquid limit test.15-31
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