Liquid Limit and Plastic Limit Tests _ Lab Experiments

11/29/2017

Liquid Limit and Plastic Limit Tests | Lab experiments

Liquid Limit and Plastic Limit Tests

TABLE OF CONTENTS __________________________________________________ PAGE

INTRODUCTION

2

OBJECTIVE

2

APPARA APPARATUS TUS LIQUID LIMIT TEST PLASTIC LIMIT TEST

3 5

PROCEDURES LIQUID LIMIT TEST PLASTIC LIMIT TEST

3 5

CALCULATION

7

RESULTS

8

CONCLU CONCLUSION SION

9

REFERE REFERENCES NCES

9

· ·

· ·

LIQUID AND PLASTIC LIMITS TEST

INTRODUCTION http://civilengineeringlaboratory.blogspot.com/2012/02/liquid-limit-and-plastic-limit-tests.html

1/8

11/29/2017


Consistency of Soil – Atterberg Limits In the early 1990s, a Swedish scientist named Atterberg developed a method to describe the consistency of fine-grained soils with varying moisture contents. Atterberg limits are defined as the water corresponding to different behaviour conditions of fine-grained soil (silts and clays). The four states of consistency in Atterberg limits are liquid, plastic, semisolid and solid. The dividing line between liquid and plastic states is the liquid limit; the dividing line between plastic and semisolid states is the shrinkage limit. If a soil in the liquid state is gradually dried out, it wills past through the liquid limit, plastic state, plastic limit, semisolid state and shrinkage limit and reach the solid stage. The liquid, plastic and shrinkage limits are therefore quantified in terms of the water content at which a soil changes from the liquid to the plastic state. The difference between the liquid limit and plastic limit is the plasticity index . Because the liquid limit and plastic limit are the two most commonly used Atterberg limits, the following discussion is limited to the test procedures and calculation for these two laboratory tests. The liquid limit is that moisture content at which a soil changes from the liquid state to the plastic state. It along with the plastic limit provides a means of soil classification as well as being useful in determining other soil properties. As explained, plastic limit is the dividing line between the plastic and semisolid states. From a physical standpoint, it is the water content at which the soil will begin to crumble when rolled in small threads.

OBJECTIVE 1.

To determine the liquid limit of a soil.

2.

To determine the liquid limit of a soil.

LIQUID LIMIT TEST APPARATUS 1.

Cone penetrometer

2.

Flat glass plate

3.

Metal cups

4.

Spatula

5. Containers 6.

Distilled water

PROCEDURE Fall-cone Method 1.

Check the apparatus so that : a.

Mass of falling cone assembly to 0.1g.

b. Stem falls freely when released. c.

Tip of cone can be felt through gauge when brushed with finger.

http://civilengineeringlaboratory.blogspot.com/2012/02/liquid-limit-and-plastic-limit-tests.html

2/8

11/29/2017

2.


Mix the soil (paste with the spatulas for at least 10 minutes, distilled water must be added in successive stages to give a cone penetration of about 15mm and mix well in. Note : Through mixing and kneading is the most important feature of the test and must never be overlooked.

3.

Press the soil paste against the side of the cup to avoid trapping air. Press more paste well into the bottom of the cup, without an air pocket. The small spatula is convenient for these operations. The top surface is finally smoothed off level with the rim using the straight edge.

4.

Adjust the tip of the cone with a few millimetres of the surface of the soil in the cup. Hold the cone, press the release button and adjust the height of the cone so that the tip just touches the soil surface.

5.

Lower the stem of the dial gauge to make contact with the top of the cone shaft. Record the reading of the dial gauge to the nearest 0.1mm (R1). Alternatively if the pointer is mounted on a friction sleeve, adjust the pointer to read zero.

6.

Set the timer to 5 second and then press the button and release it immediately. Automatic re-locking of the stem is indicated by a click. The apparatus must remain steady and must not be jerked.

7.

Record the dial reading to the nearest 0.1mm (R2). Record the difference between R1 and R2 as the cone penetration. If the pointer was initially set to read zero, the reading R2 gives the cone penetration directly.

8.

Lift out the cone and clean it carefully. Avoid touching the sliding stem. Add a little more wet soil to the cup, without entrapping air, smooth off and repeat procedure (5), (6) and (7).

9.

Two consecutive penetrations should be within 0.5mm or three within 1mm.

10. Take a moisture content sample of about 10g from the area penetrated by the cone using the tip of a small spatula. Placed in a numbered moisture content container, which is weighed, oven dried and weighed as in the standard moisture content procedure in experiment 1. 11. The soil remaining in the cup is remixed with the rest of the sample on the glass plate together with a little more distilled water, until a uniform softer consistency is obtained. 12. Penetration range of the soil sample should be within 15 – 25mm. Repeat the procedure (3) – (10) with different volume of water to get at least 4 points evenly spaced. 13. The moisture content of the soil from each penetration reading is calculated from wet and dry weighing as in the moisture content test. Each cone penetration (mm) is plotted as ordinate, against the corresponding moisture content (%) as abscissa, both to the linear scales. The best straight line fitting these points is drawn. 14. From the graph, the moisture content corresponding to a cone penetration of 20mm is read off to the nearest 0.1%. The result is reported to the nearest whole number as the liquid limit (cone test).

PLASTIC LIMIT TEST APPARATUS 1.

Glass plate

2. A separate glass plate for rolling of threads 3. Spatulas 4. Moisture content apparatus


3/8

11/29/2017


PROCEDURE 1.

Take about 20g of the prepaid soil paste and spread it on glass mixing plate so that it can partially dry. Mix occasionally to avoid local drying out.

2.

When the soil is plastic enough, it is well kneaded and then shaped into a ball. Mould the ball between the fingers and roll between the palms of the hands so that the warmth of he hands slowly dries it.

3.

When slight cracks begin to appear on the surface, divide the ball into two portions each of about 10g. Further divide each into four equal parts, but keep each set of four parts together.

4.

One of the parts is kneaded by the fingers to equalize the distribution of moisture and then formed into a thread about 6mm diameter, using the first finger and thumb of each hand.

5.

Roll the thread between the fingers of the one hand and the surface of the glass plate by uniform pressure. The pressure should reduce the diameter of the thread from 6mm to about 3mm after between five and ten back-andforth movements of the hand. Note : It is important to maintain a uniform rolling pressure throughout; do not reduce pressure as the thread approaches 3mm diameters.

6.

Dry the soil further by moulding between the fingers again, not by continued rolling which gives a dried crust. From it into a thread and roll out again as before, repeat this procedure until the thread crumbles when it has been rolled to 3mm diameter.

7.

Crumbling of the thread include falling apart in small pieces; breaking into a number of short pieces tapered towards the ends; longitudinal splitting from the ends towards the middle and then falling apart. Note : Crumbling must be the result of the decreasing moisture content only, and not due to mechanical breakdown caused by excessive pressure or oblique rolling or detachment of an excessive length beyond the width of the hand.

8.

As soon as the crumbling stage is reached, gather the crumbled threads and place them into a weighed moisture content container. Replace the lid immediately.

9.

Repeat procedure (4) – (8) for other pieces of soil and place in the same container. Weigh the container and soil as soon as possible, dry in the oven overnight, cool and weigh dry, as in the standard moisture content procedure.

10. Repeat procedure (4) – (9) on the other set of four portions of the soil, using a second moisture content container. 11. Calculate the moisture content of the soil in each of the two containers. Take the average of the two results. If they differ by more than 0.5% moisture content, the test should be repeated. 12. The average moisture content referred to above is expressed to the nearest whole number and reported as plastic limit (w1) of the soil. The method of the preparation of the soil is reported and so is the percentage of material passing the 425µm sieve if it was sieved. The result is usually reported on the same sheet as the liquid limit test. 13. The difference between the liquid limit and the plastic limit is calculated to give the plasticity index ( I p ) of the soil : I p= W L – W P The value is also reported to the nearest whole number. If it is possible to perform the plastic limit test, the soil is reported as non-plastic (NP). This also applies if the plastic limit is equal to or greater than the liquid limit : the http://civilengineeringlaboratory.blogspot.com/2012/02/liquid-limit-and-plastic-limit-tests.html

4/8

11/29/2017


latter can occur in same soils with a high mica content (Tubey and Webster, 1978).

CALCULATION

LIQUID LIMIT TEST Fall-cone Method

PLASTIC LIMIT TEST


5/8

11/29/2017


RESULT


6/8

11/29/2017

i.


Fall-cone method Liquid Limit = 50.3%when the penetration is equal to 20mm.

ii.

Plastic Limit Plastic limit = [ 24.14+22.78+21.05+24.74+26.14+20.83+23.81 ] / 7 = 23.36 = 23

iii.

Plastic index Plastic index = Liquid Limit – Plastic Limit = 50 – 23 = 27

CONCLUCION


7/8

11/29/2017


Figure 1Plasticity Chart After we have done the experiment (Liquid Limit and Plastic Limit Tests), we found that the plastic index of the soil is equal to 27 and the liquid limit of the soil is equal to 50.3 ( obtained from fall-cone method ). From the chart we found that the type of soil was falling under Inorganic silts of compressibility and organic silts.


8/8

Liquid Limit and Plastic Limit Tests _ Lab Experiments

Recommend Documents