Test Method For Liquid Limit, Plastic Limit, And Plasticity Index

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Test Method For Liquid Limit, Plastic Limit, And Plasticity Index

Transcript Of Test Method For Liquid Limit, Plastic Limit, And Plasticity Index

TEST METHOD FOR LIQUID LIMIT, PLASTIC LIMIT, AND PLASTICITY INDEX
GEOTECHNICAL TEST METHOD GTM-7
Revision #2
AUGUST 2015

GEOTECHNICAL TEST METHOD: TEST METHOD FOR LIQUID LIMIT, PLASTIC LIMIT, AND PLASTICITY INDEX
GTM-7 Revision #2
STATE OF NEW YORK DEPARTMENT OF TRANSPORTATION GEOTECHNICAL ENGINEERING BUREAU

EB 15-025

AUGUST 2015
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TABLE OF CONTENTS
I. INTRODUCTION................................................................................................................3
II. LIQUID LIMIT TEST PROCEDURE .................................................................................4 1. Scope........................................................................................................................4 2. Definition .................................................................................................................4 3. Apparatus .................................................................................................................4
MECHANICAL METHOD .................................................................................................5
4. Preparation of Test Sample ......................................................................................5 5. Adjustment of Mechanical Device...........................................................................6 6. Procedure .................................................................................................................6 7. Calculations..............................................................................................................9 8. Preparation of the Flow Curve .................................................................................9 9. Liquid Limit Determination .....................................................................................9
ONE-POINT METHOD ......................................................................................................9
10. Apparatus .................................................................................................................9 11. Preparation of Test Sample ......................................................................................9 12. Adjustment of Mechanical Device...........................................................................9 13. Procedure ...............................................................................................................10 14. Calculations............................................................................................................10
III.. PLASTIC LIMIT TEST .....................................................................................................11 1. Scope......................................................................................................................11 2. Definition ...............................................................................................................11 3. Apparatus ...............................................................................................................11 4. Preparation of Test Sample ....................................................................................12 5. Procedure ...............................................................................................................12 6. Calculations............................................................................................................13
IV. PLASTICITY INDEX........................................................................................................15 1. Definition ...............................................................................................................15 2. Calculations............................................................................................................15 3. Comments ..............................................................................................................15

APPENDIX ....................................................................................................................................16 A. Mechanical Liquid Limit Device ........................................................................ A-1 Diagrams Illustrating Liquid Limit Test ............................................................. A-2 Diagrams Illustrating Plastic Limit Test ............................................................. A-3 B. SM 309 Forms......................................................................................................B-1 C. Example: Use of SM 309 Forms..........................................................................C-1

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I. INTRODUCTION
The following moisture conditions - liquid limit, plastic limit, along with shrinkage limit are referred to as the "Atterberg Limits", after the originator of the test procedures.

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Atterberg Limits and Indices
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II. LIQUID LIMIT TEST PROCEDURE
1. SCOPE
1.1 This section describes the laboratory procedure for determining the liquid limit of soils using the device specified in Section 3.8, securing the results of at least three trials, and the plotting of a flow curve. Provision is also made for a one point method requiring the calculation of the liquid limit value from data obtained from a single trial.
The method described herein is based upon AASHTO Designation T89 which has been modified for New York State Department of Transportation use.
2. DEFINITION
2.1 The liquid limit of a soil is the moisture content, expressed as a percentage of the weight of the oven-dried soil, at the boundary between the liquid and plastic states of consistency. The moisture content at this boundary is arbitrarily defined as the water content at which two halves of a soil cake will flow together, for a distance of ½ in. (12.7 mm) along the bottom of a groove of standard dimensions separating the two halves, when the cup of a standard liquid limit apparatus is dropped 25 times from a height of 0.3937 in. (10 mm) at the rate of two drops/second.
3. APPARATUS
3.1 Porcelain evaporating dishes or similar mixing dishes approximately 4½ in. (114 mm) in diameter.
3.2 Pulverizing apparatus - mortar and rubber-covered pestle.
3.3 U.S. No. 40 (0.425 mm) sieve.
3.4 Spatula, about 3 in. (75 mm) long and approximately ¾ in. (19 mm) wide.
3.5 Balance sensitive to 0.01 g.
3.6 Watering bottle, with distilled, demineralized or tap water.
3.7 Drying tares with covers, such as metal cans with lids, which will prevent moisture loss. The tares and covers should be marked and weighed as matched pairs.
3.8 Mechanical Liquid Limit Device(s)
3.8.1 Manually operated - consisting of a brass cup and carriage, constructed according to the plan and dimensions shown in Figure 1.

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3.8.2 Electrically operated - a motorized device equipped to produce the rise and rate of drops of the brass cup as described in Sections 5.2 and 6.4 of this procedure, respectively. The cup and the critical dimensions of the device shall conform to those shown in Figure 1 of Appendix A. The device shall be calibrated to give the same liquid limit value as obtained with the manually operated device.
3.9 Grooving Tool and Gauge - a combined grooving tool and gauge conforming to the dimensions shown in Figure 1.
3.10 Oven - a thermostatically controlled drying oven capable of maintaining temperatures of 230±9° F (110±5° C).
3.11 Desiccator - a container, usually of glass, fitted with an airtight cover, and containing at the bottom a desiccating agent such as calcium chloride. The device prevents the sample from absorbing moisture from the air while being cooled for weighing.

MECHANICAL METHOD

4. PREPARATION OF TEST SAMPLE
4.1 It is preferable that soils used for liquid limit determination be in their natural or moist state, because drying may alter the natural characteristics of some soils. Organic soils in particular undergo changes as a result of oven-drying or even extended air-drying. Other soils containing clay may agglomerate, lose absorbed water which is not completely regained on rewetting, or be subject to some chemical change.
4.2 If it is determined that the soil is organic or fine-grained, containing no plus No. 40 (0.425 mm) material, the liquid limit shall be run on the sample in its natural state (see 6.1 Procedure).
4.3 If the soil contains sand or larger size particles, provision must be made to separate the minus No. 40 (0.425 mm) material for testing despite the possibility that drying may alter the characteristics of some soils. The fine fraction of granular soil is normally free of organic matter or contains a minimal amount which does not affect the liquid and plastic limit results.
The soil shall be thoroughly dried in an oven at a temperature not exceeding 230±9° F (110±5° C). The pulverizing apparatus and the No. 40 (0.425 mm) sieve shall then be utilized for separation of the minus No. 40 (0.425 mm) fraction. Care should be

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exercised to insure that the pulverizing apparatus does not reduce the natural size of the individual grains. If the sample contains brittle particles, the pulverizing operation shall be done carefully and with just enough pressure to free the finer material adhering to the coarser particles. The ground soil shall then be separated into two fractions by means of the No. 40 (0.425 mm) sieve. The plus No. 40 (0.425 mm) component shall be reground as before. When repeated grinding produces only a minimal quantity of minus No. 40 (0.425 mm) soil, the material retained on the No. 40 (0.425 mm) sieve shall be discarded and further pulverization of this fraction should be suspended.

4.4 The material passing the No. 40 (0.425 mm) sieve obtained from the grinding and sieving operations described above shall be thoroughly mixed together and set aside for use in performing the physical tests. Approximately 0.3 lb. (150 g) would generally suffice for the liquid limit test.

5. ADJUSTMENT OF MECHANICAL DEVICE

5.1 Inspect the liquid limit device to determine that it is in proper adjustment prior to each use, each day. Check the drop of the brass cup. See that the pin connecting the cup is not worn excessively to permit side play, that the screws connecting the cup to the hanger arm are tight, and that a groove has not been worn in the cup through long usage. Inspect the grooving tool to determine that the critical dimensions are as shown in Figure 1. Replace grooving tool tips that become worn. Replace cup when it becomes grooved by wear from the grooving tool.

5.2 By means of the gauge on the handle of the grooving tool and the adjustment plate H, Figure 1, adjust the height to which the cup C is lifted so that the point on the cup that comes in contact with the base is exactly 0.3937 in. (10 mm) above the base. Secure the adjustment plate H by tightening the screws, I. With the gauge still in place, check the adjustment by revolving the crank rapidly several times. If the adjustment is correct, a slight ringing sound will be heard when the cam strikes the cam follower. If the cup is raised off the gauge or no sound is heard, further adjustments are required.

6. PROCEDURE

6.1 If the soil is organic or fine-grained containing no plus No. 40 (0.425 mm) material, and is in its natural state, proceed without adding water. Chopping, stirring and kneading may be necessary to attain a uniform consistency. Then proceed as described in Sections 6.3 through 6.9 below.

6.2
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The soil sample prepared under 4.3 shall be placed in an evaporating dish, covered, and cured, and then thoroughly mixed with the addition of distilled, demineralized or tap water by alternately and repeatedly stirring, cutting and kneading with a spatula. If needed, further additions of water shall be made in increments of 1 to 3 mL; each increment of water shall be thoroughly mixed with the soil. The cup of
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6.3 6.4
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the liquid limit device should not be used for mixing soil and water. Add sufficient water to produce a consistency that will require 25 to 35 drops of the cup to cause closure.

Note 1 -

Allow ample time for mixing and curing since variations can cause erroneous test results. Some soils are slow to absorb water. Therefore it is possible to add the increments of water so fast that a false liquid limit value is obtained. This is particularly true when the liquid limit of a clay soil is obtained from one determination as in the one-point method.

A sufficient quantity of the soil mixture obtained under 6.1 or 6.2 shall be placed in the cup above the spot where the cup rests on the base and shall then be squeezed and spread into the position shown in Figure 2 (Appendix A), with as few strokes of the spatula as possible. Care should be taken to prevent the entrapment of air bubbles within the mass. With the spatula, level the soil and at the same time trim it to a depth of 0.3937 in. (10 mm) at the point of maximum thickness. Return the excess soil to the evaporating dish.

The soil in the cup shall be divided equally by a firm stroke of the grooving tool along the diameter through the centerline of the cam follower so that a clean, sharp groove of the proper dimensions will be formed. To avoid tearing of the sides of the groove or slipping of the soil cake on the cup, up to six strokes, from front to back, or from back to front counting as one stroke, shall be permitted. The depth of the groove should be increased with each stroke and only the last stroke should scrape the bottom of the cup.

Lift and drop the cup by turning the crank, F, at the rate of 2 rps, until the two halves of the sample flow together and come in contact at the bottom of the groove along a distance of ½ in. (12.7 mm). Record the number of drops (blows) required to close the groove this distance. A valid test is one in which 15 to 35 blows are required to close the groove.

Note 2 -

Some soils tend to slide on the surface of the cup, at a lesser number of blows than 15, instead of flowing. If this occurs more water should be added and the sample remixed, then the mixture placed in the cup, a groove cut with the grooving tool, and 6.4 repeated. If soil continues to slide on the cup at a lesser number of blows than 15, the test is not applicable and a note should be made that the liquid limit could not be determined.

Note 3 -

It is possible to check on the number of drops of the cup required to close the groove. This is done by immediately remixing the soil, redoing the groove and then checking the number of drops necessary to close the ½ in. (12.7 mm) groove. If this is done at once, the operator should be able to close the groove with the same number of drops. If there is a wide deviation in the number of drops, it would indicate that the soil has either

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not been properly mixed or sufficiently cured. Then remixing is necessary and the test should be redone.
6.5 A sample of the soil is now taken to determine its moisture content. Remove a slice of soil approximately the width of the spatula, extending from edge to edge of the soil cake at right angles to the groove and including that portion of the groove in which the soil flowed together. Place in a moisture tight tared container. Weigh to the nearest 0.01 g and record.
6.6 The soil remaining in the cup shall be transferred to the mixing dish. The cup and grooving tool shall then be washed and dried in preparation for the next trial.
6.7 The foregoing operations shall be repeated for at least two different determinations on the soil sample to which sufficient water has been added (see 6.8 for wet natural soil) to change the soil to a fluid state, and then a more fluid state. The object of this procedure is to obtain samples of such consistency that at least one determination will be made in each of the following range of drops: 25-35, 20-30, 15-25, so the range in the three determinations is at least 10 drops. The number of drops required to close the groove should be above and below 25.
6.8 The test shall proceed from the drier to the wetter condition of the soil. However, when the soil in its natural state (see 6.1) is of such consistency that closure occurs at less than 25 drops (sample wet), the process must be reversed so as to obtain determinations in each of the aforementioned range of drops (see 6.7). Drying of the soil shall be accomplished by a combination of air-drying and manipulation by kneading. In no case shall dried soil be added to the natural soil being tested.
6.9 Oven-dry all the soil samples in the tared, uncovered containers to constant weight at 230±9° F (110±5° C), place samples in a desiccator (1) and allow to cool. Replace the covers on the containers, and weigh before hygroscopic moisture can be absorbed. Weigh (2) to the nearest 0.01 g and record. The loss in weight of the soil in each tare, due to drying, is recorded as the weight of water.
(1) A desiccator is used to cool the dried soil samples before weighing. The hot samples, if placed immediately on the balance, cause convection currents in the air which can cause serious weighing errors. Weigh within 15 minutes, at which time the samples should be cool.
(2) Always weigh on the same balance previously used.

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SoilCupGrooveWaterLimit