Atterburg Limits Lab Report (Lab Report 1)

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Report on

Atterberg Limits: Soil Mechanic Lab Report

ENCE 444 - Experimental Methods in

Geotechnical Structural Engineering

Submitted to

Mr. Bora Cetin, ENCE 444 Teaching Assistant Department of Civil & Environmental Engineering

University of Maryland, College Park

by

Victor Evans Mohammed Muqtader

William Friedman Sergio Adantor

Laboratory Date(s): September 8, 2010 Report Date: September 15, 2010

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COVER PAGE . . . 1

TABLE OF CONTENTS . . . 2

I. INTRODUCTION . . . . 3

II. THEORETICAL BACKGROUND & PURPOSE . . . 3

1. Background . . . 3

III. EXPERIMENTAL PRCEDURE . . . 5

1. Multi-point Liquid Limit Test . . . 5

2. Deviation from ASTM & Error Considerations . . . 7

3. Plastic Limit Test . . . 8

4. Deviation from ASTM & Error Considerations . . . . 9

5. One point Liquid Limit Test . . . 9

6. Deviation from ASTM & Error Considerations . . . . 9

IV. RESULTS & ANALYSIS . . . 10

1. Results . . . 10

2. Accuracy Assessment . . . 10

V. CONCLUSIONS . . . . 12

VI. REFERENCES . . . . 13

VII. APPENDIX . . . . 14

1. Graph & Charts . . . 14

2. General Equations. . . 15

3. Laboratory Data . . . 16

4. Tables . . . 18

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The purpose of this report is to analyze tests performed in the laboratory to establish the Atterberg Limits of various soil samples. The Atterberg limits can be used to distinguish the soil between silt and clay, in multiple categories, as well as the boundaries between each states of soil (solid, semi-solid, plastic, and liquid) and thereby the change in the soil’s behavior. The standardized method for performing these tests is described in ASTM Standard D 4318. The objective of this test is to derive the Plastic and Liquid Limit from the results and thereby classify the composition of the soil. By varying the composition of various soil samples, the effect that the composition has on the Atterberg Limits could be determined as well. Understanding the plasticity of the soil is of vital importance, as in any project, plasticity will affect the workability and shear strength of the soil.

Theoretical Background & Purpose

Background

The Atterberg Limits determines the plastic limits (PL), the water content where soil starts to exhibit plastic behavior, and the liquid limits (LL), where the water content of a soil changes from plastic to liquid behavior. These limits are used to determine the consistency of a soil composition at various water content values, and are important for the classification of the soils. The theory behind the test is that the closer a soil sample is to its liquid form, the fewer the number of drops will be required to close up the groove in the Liquid Limit Device. The actual Liquid Limit is the water content when 25 drops are needed to close the groove.

Two methods of calculating the Liquid Limit are performed and verified against each other to derive an accurate measurement. The One-Point Liquid Limit Test, which attain the number of blows (N), through one iterative usage of the Liquid Limit Device. The theoretical model

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is then used to find the Liquid Limit. The other method used is the Multipoint Liquid Limit Test, which required several iterations of use of the Liquid Limit Device. The water content at 25 drops is then interpolated from the regression model formed by the data collected. The Multipoint Liquid Limit Test is generally more accurate than the One-Point Liquid Limit Test because it accounts for several trials of the test, but if there is an outlier, the data may be skewed and the model may be inaccurate. Typical values for the Multipoint Liquid Limit Test are 30 to 40 drops in the first trial, 25 to 30 blows in the second trial, and 15 to 20 blows in the third trial.

The Plastic Limit of the samples is found by rolling smaller specimens repeatedly until the specimen breaks at 3.18mm diameter. The water content at this point is the Plastic Limit of the specimen. The theory behind the test is that as the specimen is rolled down, some of the water in the soil specimen dissipates until the specimen breaks off. Since soil in its plastic state deforms without cracking, the point when the specimen does crack determines the moisture content just gone below its plastic limit.

Several soil samples were used in this experiment. One was entirely made up of

kaolinite. The other 3 had successively greater amounts of sand introduced. Kaolinite is a clay mineral with typically high Plastic and Liquid Limits, and so the introduction of the sand into the sample would presumably decrease these values.

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Multipoint Liquid Limit Test

The standard used for this test was ASTM D 4318: Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils. The purpose of this test is to determine the boundary between plastic and viscous fluid state of the fine-grained soil. The

equipments used for the test included: Liquid Limit Device, porcelain (evaporating) dish, flat grooving tool with gage, eight drying cans, balance, glass plate, and a spatula.

Prior to the laboratory proceedings, the class was divided into four groups. The specimen properties for each group as shown below:

TABLE 1.

Specimen Properties for each group

Amount of Soil Mixture (g) Water Increment (%) Amount of Initial Water (%) Percentage of sand (g) Percentage of Kaolinite (g) Group 1 100 3 52 0 100 Group 2 100 2 45 10 90 Group 3 100 2 42 20 80 Group 4 100 2 38 30 70

The testing procedures as well as the calibration of apparatus prior to each testing proceed as follows:

1. Four groups prepared the 100 g of soil mixture with different initial water, sand,

and kaolinite contents on the porcelain dish. Assuming that the soil was

previously passed through a No.40 sieve, air-dried, and then pulverized, the soil was thoroughly mixed with the amount of water specified to each group. Mix until the specimen appears as a smooth homogeneous paste.

2. While the specimen was being mixed, four of the eight drying cans were weighed

and the respective weights were recorded on the data sheet. The liquid limit apparatus was also calibrated during this time, by checking the height of the drop

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of the cup. The block on the end of the grooving tool was used to calibrate the 10 mm gap between the point where cup contacts the base and the base of the liquid limit apparatus.

3. Using a spatula, portion of the prepared soil was placed in the cup of the liquid

limit apparatus. Alternating between squeezing and spreading, we squeezed the soil down with the spatula to eliminate any air voids and spread the soil into the cup to the depth of 10 mm at its deepest point. Subsequently, we tapered the top of the soil into a smooth horizontal surface. The unused soil was kept in the porcelain dish.

4. Using the tip of the grooving tool, straight clean groove was made right down the

center of the cup. Extreme cautions were taken as to preserve the

perpendicularity of the grooving tool to the surface of the cup and to prevent the sliding of the soil relative to the surface of the cup as the groove was created.

5. Proceeding by making sure that the base of the apparatus below the cup and the

underside of the cup is clean of soil, the crank of the liquid limit apparatus was cranked at an approximate rate of two drops per second. While one individual cranked the apparatus, other observed and counted the number of drops, N, it took to make the two halves of the soil pat come in contact at the bottom of the groove.

6. In the situation where the number of drops, N, exceeded 100, the entire soil

specimen was removed out of the liquid limit apparatus without recording the number of drops. It was then remixed in the porcelain dish with 2% additional water content to decrease the number of drops required to close the groove. Otherwise, the numbers of drops were recorded on the data sheet.

7. For every successful trial, a slice of soil, approximately the size of the spatula,

from the edge to edge of the soil pat, was removed. This includes the soil on both sides of where the groove came into contact. The extracted soil specimen was then placed into a drying can, weighed, and oven dried at 105 degrees Celsius

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for 24 hours to determine the water content of the soil in accordance with ASTM Test Method D 2216.

8. The remaining soil in the cup of the liquid limit apparatus was returned into the

porcelain dish. The cup is detached from the liquid limit apparatus, and along with the grooving tool and spatula, it was washed and dried in preparation for the next trial. While the apparatus is being cleaned, the entire soil specimen was remixed with specified amounts of additional water. The soil specimen was carefully mixed until the paste reached a smooth homogeneous state. The cup is reattached to the liquid limit apparatus and recalibrated in the methods described in step 4.

9. Steps 5, 7, and 8 is then repeated for at least two additional trials, until the number of drops, N, required for a closure of groove falls below 25 drops.

10.After 24 hour of oven-drying, the sample was taken out of the oven and

immediately measured for its weight and water content.

WN(%) = WwWs Eq. 2

Deviations from ASTM & Error Considerations:

Following descriptions are of steps and procedures which have or could have deviated from the ASTM standards and thereby producing an erroneous result.

– Tap water was used instead of distilled water when mixing with the soil.

– Addition of water content inaccuracy due to small samples and scale precision. – Width, depth, and characteristic of the groove are not according to ASTM. – Soil specimen was not homogeneously mixed.

– Handle of the liquid limit apparatus was cranked too fast or too slowly.

– Soil specimen in the porcelain dish wasn’t covered with a wet towel to preserve the accurate moisture content.

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Plastic Limit Test

1. After the 1st successful trial, a slice of soil, approximately the size of spatula, was

removed from the edge to edge of the cup, including the soil on both sides of where the groove came into contact. This soil specimen was air dried to reduce the water content to a consistency at which it can be rolled without sticking to the hands or glass plate.

2. The soil specimen is formed into an ellipsoidal mass and rolled between the palm

of the hands and the glass plate. Sufficient pressure and uniformity was applied into the rolling of the mass at an approximate rate of 80 strokes per minutes.

3. The specimen was rolled into a thread with a uniform diameter of 3.18mm. When

the specimen doesn’t crumble at this point, the soil specimens was collected, knead into an ellipsoidal mass, and re-rolled again until the thread crumbled before reaching 3.18mm in diameter.

4. Crumbled threads were gathered together and placed into a drying can, holding

at least 6 g of soil. It was then weighed and placed into the oven at 105 degrees Celsius for 24 hours to determine the water content of the soil in accordance with ASTM Test Method D 2216.

5. After 24 hour of oven-drying, the sample was taken out of the oven and immediately measured for its weight and water content.

WN(%) = WwWs Eq. 2

– Tap water was used instead of distilled water when mixing with the soil. – Improper technique in rolling thread

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– Thread not uniformly 3.18mm in diameter. – Moisture content of the sample is too small – Air drying of the sample before weighing.

One-point Liquid Limit Test

1. After the last trial, which the liquid limit was achieved after 24 blows on the liquid

limit apparatus, a slice of soil, approximately the size of spatula, was removed from the edge to edge of the cup, including the soil on both sides of where the groove came into contact.

2. The extracted soil specimen was then placed into a drying can, weighed, and oven dried at 105 degrees Celsius for 24 hours to determine the water content of the soil in accordance with ASTM Test Method D 2216.

3. After 24 hour of oven-drying, the sample was taken out of the oven and immediately measured for its weight and water content.

WN(%) = WwWs Eq. 2

(See ‘Deviations from ASTM & error considerations’ on page 7 & 8)

Results & Analysis

Results

Completing the liquid limit test on the various group samples, using the procedure aforementioned, the water content to number of blows is shown in Table 2. A general trend of all group samples that becomes evident is that the water content is inversely proportional to the number of blows. A deviation to note is Group 1’s 303 N.

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TABLE 2.

Water Content (W), Number of Blows (N) for each group

G1 G2 G3 G4 W(%) N W(%) N W(%) N W(%) N 52.7 303 45.6 49 43.8 42 40 61 53.3 59 51.5 57 43.1 32 42 54 61.8 32 50.7 30 45.6 28 45 29 63.4 21 50.9 18 48.7 24 48 21

In order to find the liquid limit, two methods were employed, multipoint method and one-point method. For one-point method, a single pair of water content and number of drops was plugged into Equation 2, yielding an approximate liquid limit. For multi-point method, four pairs of water content and number of drops were put on a scatter plot, fit with a regression line, and then interpolated the 25th_{drop to find the liquid limit. The}

following results are shown in Graph 1 below.

Accuracy Assessments

Using the multipoint method is more accurate than the one-point method because it takes an average, while the latter does not. One-point method also requires the operator to judge when the test specimen is approximately at its liquid limit, therefore has a greater margin for errors. The percentage error was calculated using Equation 3 and the results were tabulated in Table 3. The range of error can be seen to be roughly between 0% - 3%. An obvious trend in percentage error to other factors, such as water content or clay to sand mixture, does not emerge. This randomness of percentage error could vary depending on which pair of numbers were used in the one-point method or due to various other human errors during the experiment. Another source of error can be the liquid limit derived from the multipoint method. This potential for error can be seen in Group 1’s outlier point (52.7,303) as shown in Graph 1. This outlier will cause a skewed regression model, and thus a false liquid limit.

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TABLE 3.

Error Calculation – Multipoint vs. One-Point Methods

MULTI-POINT ONE-POINT % ERROR

G1 60.1 62.0 3.2

G2 50.3 49.0 -2.7

G3 46.9 48.4 3.3

G4 46.7 47.0 0.7

The plastic limit for each soil sample was recorded after following the procedures aforementioned. The plasticity index, shown in Table 4, is the range between the liquid and plastic limits (Eq 4) and is dependent on the clay content, increasing with the amount of clay. A sample with a hundred percent clay should yield the highest plasticity index; however, Group 1’s plasticity index was 12.3, the third lowest. This number would inform that there was a miscalculation. The trend should show a decreasing plasticity index as the concentration of sand increases through the different group samples, yet it does not. This means that there were errors that were overlooked. Group 4’s plasticity index, being the lowest, makes logical sense because they had the lowest clay content.

Plasticity Index (PI) = Liquid Limit (WLL) – Plastic Limit (WPL) Eq. 4

TABLE 4:

Plasticity Index (PI)

PI WLL WPL

G1 12.3 60.1 47.8

G2 12.8 50.3 37.5

G3 18.7 46.9 28.2

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Using the plasticity index and liquid limit, the soils were classified using the Plasticity Chart shown in Graph 2. The four soil samples were comprised of kaolinite clay and fine sand. However, after being plotted, the samples were classified as low plasticity silt (ML) and high plasticity silt (MH). Looking at Table3.4- Atterberg Limits of Clay Minerals (Aydilek, pg 22) one can see that a hundred percent kaolinite has a plasticity index of 32 and liquid limit of 53 landing it as high plasticity clay (CH), however, Group 1’s data yields a soil classification of MH. This incoherency alludes to the fact that the experiential result has mistakes.

Conclusion

The objective of this laboratory was to determine and understand the Atterberg Limits of various samples of soil and how the soil composition can affect these limits. By using the Liquid Limit Test Device, and following ASTM D 4138, the Plastic and Liquid Limits of the samples were found. The two methods of testing for the Liquid Limit, One-Point and Multipoint, were found to have a sufficient error. The four specimens tested each had an increasingly larger portion of sand and thus a smaller portion of clay. It was expected that the Liquid Limit of the specimen would be reduced as the proportion of clay was reduced, and this expectation was confirmed from the testing. The Plastic Limits found also generally seemed to follow a trend of decreasing as the amount of clay was decreased. However, the resulting Plasticity Indexes did not seem to reflect typical clay properties as were expected, possibly due to various errors made in performing the tests.

References:

Aydilek, Ahmet. "Ence 444 Soil Composition." ENCE 444. Print.

ASTM Standard. Vol. D 4318 - 00. West Conshohocken,PA 19428: American Society for

Testing and Materials, 2000. Print. Standard Test Method for Liquid Limit, Plastic Limit, and Plasticity Index of Soils.

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Appendix

Graphs & Charts

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GRAPH 2: PLASTICITY CHART

General Equations

LL = WN(%) x (N/25)0.121 Eq. 1

WN (%) = water content

N = number of blows in liquid limit test.

WN(%) = WwWs Eq. 2

Ww= weight of water

Ws= weight of solids

Error % = [One-Point Method, WLL - Multipoint Method, WLL ] / Multipoint Method, WLL Eq. 3

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Laboratory Data

Group

1

Liquid Limit Test

Can # Weight Of Can, W1 (g) Weight of Can + wet soil, W2 (g) Weight of Can + dry soil, W3 (g) Water Content (%) Number of Blowss (N) Liquid Limit One Point 2 9.6 18 15.1 52.73 303 71.3 3 9.5 16.4 14 53.33 59 59.2 4 9.3 14.8 12.7 61.76 32 63.6 5 9.8 26.3 19.9 63.37 21 62.0

Can # Weight Of Can, W1 (g) Weight of Can + wet soil, W2 (g) Weight of Can + dry soil, W3 (g) Water Content (%) 1 9.6 13 11.9 47.8

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Group 2

Can # Weight Of Can, W1 (g) Weight of Can + wet soil, W2 (g) Weight of Can + dry soil, W3 (g) Water Content (%) Number of Blowss (N) Liquid Limit One Point 2 9.6 17.9 15.3 45.61 49 49.5 3 9.8 20.1 16.6 51.47 57 56.9 6 9.9 20.3 16.8 50.72 30 51.9 5 9.3 17.3 14.6 50.94 18 49.0

Can # Weight Of Can, W1 (g) Weight of Can + wet soil, W2 (g) Weight of Can + dry soil, W3 (g) Water Content (%) 4 9.4 11.6 11 37.50 Group 3

Can # Weight Of Can, W1 (g) Weight of Can + wet soil, W2 (g) Weight of Can + dry soil, W3 (g) Water Conten t (%) Number of Blowss (N) Liquid Limit One Point A 9.6 22.4 18.5 43.82 42 46.7 B 9.8 19.1 16.3 43.08 32 44.4 C 9.7 22.8 18.7 45.56 28 46.2 E 9.8 21.1 17.4 48.68 24 48.4

Can # Weight Of Can, W1 (g) Weight of Can + wet soil, W2 (g) Weight of Can + dry soil, W3 (g) Water Conten t (%) D 9.7 14.7 13.6 28.2 Group 4

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Liquid Limit Test Can # Weight Of Can, W1 (g) Weight of Can + wet soil, W2 (g) Weight of Can + dry soil, W3 (g) Water Content (%) Number of Blowss (N) Liquid Limit One Point 28 10 24.6 20.8 40.00 61 44.6 35 9.6 21 18.1 42.00 54 46.1 11 10.4 18.4 16 45.00 29 45.8 37 9.8 23.8 19.2 48.00 21 47.0

Can # Weight Of Can, W1 (g) Weight of Can + wet soil, W2 (g) Weight of Can + dry soil, W3 (g) Water Content (%) 31 9.5 21.15 18.8 38.0 36 9.6 18.8 16.8 40

Tables

MOISTURE CONTENT & NUMBER OF BLOWS

G1 G2 G3 G4 W N W N W N W N 52.7 303 45.6 49 43.8 42 40 61 53.3 59 51.5 57 43.1 32 42 54 61.8 32 50.7 30 45.6 28 45 29 63.4 21 50.9 18 48.7 24 48 21

PLASTICITY INDEX (PI)

PI WLL WPL

G1 12.3 60.1 47.8 G2 12.8 50.3 37.5 G3 18.7 46.9 28.2

G4 8.7 46.7 38

ERROR CALCULATION - MULTI VS SINGLE POINT METHODS

MULTI-P SINGLE-P % ERROR RANGE

G1 60.1 71.3 62 18.7 3.2 15.5

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G4 46.7 47.0 44.6 0.7 -4.4 5.1 Amount of Soil Mixture (g) Water Increment (%) Amount of Initial Water (%) Percentage of sand (g) Percentage of Kaolinite (g) Group 1 100 3 52 0 100 Group 2 100 2 45 10 90 Group 3 100 2 42 20 80 Group 4 100 2 38 30 70