10/28/2022 0 Comments Plastic limit testA little extra of the soil mixture shall be added to the cup and mixed with the soil in the cup.The number of drops required to cause the groove close for the length of 12 mm shall be recorded.This length shall be measured with the end of the grooving tool or a ruler.The cup shall be fitted and dropped by turning the crank at the rate of two revolutions per second until the two halves of the soil cake come in contact with bottom of the groove along a distance of about 12 mm (see Note 4).In case where grooving tool, Type A does not give a clear groove as in sandy soils, grooving tool Type B or Type C (see Note 3) should be used.The soil in the cup shall be decided by firm strokes of the grooving tool along the diameter through the centre line of the cam follower so that a clean, sharp groove of the proper dimensions is formed (see Note 2).(Diagram Illustrating Liquid Limit Test), with as few strokes of the spatula as possible and at the same time trimmed to a depth of one centimetre at the point of maximum thickness, returning the excess soil to the dish. A portion of the paste shall be placed in the cup above the spot where the cup rests on the base, squeezed down and spread into position shown in Fig. The soil should then be re-mixed thoroughly before the test.In the case of clayey soils, the soil paste shall be left to stand for a sufficient time (24 hours) so as to ensure uniform distribution of moisture throughout the soil mass (see Note 1).The pastes hall have a consistency that will require 30 to 35 drops of the cup to cause the required closure of the standard groove.of the soil sample passing through 425-micron IS Sieve shall be mixed thoroughly with distilled water in the evaporating dish or on the flat glass to form a uniform paste. Note: - If evenness of the base is not maintained in course of time, the base of the liquid limit device should be changed. The adjustment plate shall then be secured by tightening the screw. Using the gauge on the handle of the grooving tool or a separate gauge and by means of the adjustment plate of the mechanical liquid limit device, the height through which the cup is lifted and dropped shall be adjusted so that the point on the cup which comes in contact with base falls through exactly one centimetre for one revolution of the handle.The grooving tool shall also be inspected to determine that it is clean and dry. The liquid limit device shall be inspected to determine that it is clean, dry and in good working order, that the cup falls freely and it does not have too much side play at its hinge.If this is done and stones are present, only the material passing 425-micron IS Sieve shall be used for the test this can be obtained by rubbing the wet soil through the sieve until a sufficient quantity of the size passing 425-micron IS Sieve is obtained. The test record shall state that soil in the natural condition was used. When soils are tested in the natural condition, the results will usually differ from those obtained with air-dried samples. Note - When no stones are present in the soil and practically all of the soil passes 425-micron IS Sieve, there is sometimes a practice of testing samples without previously preparing them. shall be taken from the thoroughly mixed portion of material passing through 425-micron IS Sieve obtained in accordance with IS : 2720 (Part I)-1983
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