Lab report soil mechanics

Lebanese American University

Byblos Campus

School of Engineering

Department of Civil Engineering

CIE 445 Soil Mechanics Lab

Lab Report 2

Sieve Analysis & Atterberg Limits

Supervised By: Eng. Omar El Masri

Elena Abboud - 201102974

Jennifer Hanna - 201101545

Stephanie Kehdy - 201104635

Joe Karam - 201102480

Nader Halabi - 201101471

Roy Fares - 201100567

Date of submission: 24/10/2013

CIE 445 Lab Report 2

Table of content

s

Introduction..................................................................................................................................................3

List of Equipment........................................................................................................................................3

Theory of the experiment.............................................................................................................................4

Experimental Procedure...............................................................................................................................4

Data Collected.............................................................................................................................................5

Liquid Limit.............................................................................................................................................5Plastic Limit.............................................................................................................................................6Sieve Analysis..........................................................................................................................................7

Discussion and Interpretation......................................................................................................................8

Question 2................................................................................................................................................8Question 4................................................................................................................................................9Question 5................................................................................................................................................9Question 6..............................................................................................................................................10Question 7..............................................................................................................................................11

Error Analysis............................................................................................................................................11

Conclusion.................................................................................................................................................11

References..................................................................................................................................................11

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List of figures and tables

Figure 1: Sieve Analysis Curve...................................................................................................................7Figure 2: Plot of Water content (%) vs. Number of blows (log).................................................................9Figure 3: Water content (%) vs. Number of blows......................................................................................9Figure 4: Cumulative particle size distribution plot on a semi log graph..................................................10

Table 1: Liquid Limit Data..........................................................................................................................5Table 2: Plastic Limit Data..........................................................................................................................6Table 3: Sieve Analysis Data.......................................................................................................................7

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Introduction

Soil consistence provides a means of describing the degree and kind of cohesion and adhesion between the soil particles as related to the resistance of the soil to deform or rupture. In other words, it is defined as the ease to which a soil can be deformed. Hence, consistency largely depends on soil minerals and water content. The smaller the size particle with high water content, the more the consistency (fine soils are more consistent). The consistency of soils is evaluated according to Atterberg limits that represent the limits of water content that are used to define soil behavior. Based on astm D4318, atterberg limits include three different tests:

1.Liquid Limit (LL) is defined as the moisture content at which soil begins to behave as a liquid material and begins to flow. ( 15<Number of blows<35)

2.Plastic Limit (PL) is defined as the moisture content at which soil begins to behave as a plastic material.

3.Shrinkage Limit (SL) is defined as the moisture content at which no further volume change occurs with further reduction in moisture content.

In addition, based on astm D2487, sieve analysis of soils will help classifying the soils into groups by determining the particle sizes characteristics and distribution. The size distribution is often of critical importance to the way the material performs in use.

List of Equipment

Liquid Limit

4 moisture cans Balance Dry soil Sieve N 40 Water in a plastic squeeze bottle Pan Casagrande cup Spatula Grooving tool Paper towel Oven Porcelain evaporating dish

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Plastic Limit

Moist soil Paper towel Glass plate Balance 3 moisture cans spatula Plastic squeeze bottle Oven Porcelain evaporating dish

Sieve Analysis

Sieves N(4,10,20,40,60,100,140,200) Bottom pan Cover Mechanical sieve shaker Balance

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Theory of the experiment

In general, the Atterberg Limits and the Sieve Analysis tests both target the classification of soils for usage in engineering applications. This classification is very important for determining the possible use of the available soil in different applications such as roads, dams, foundations…etc. depending on characteristics specific to each class (drainage, workability, productivity, availability, strength, compactibility, shrink-swell, compressibility, shear strength…etc.). Atterberg Limits include the liquid limit (LL) which is the moisture content at the transition point from liquid to plastic state, and the plastic limit (PL) which is the moisture content at the transition point from plastic to semi-solid state. Two of the experiments at hand aim to determine the LL and PL respectively.

The first utilizes the Casagrande cup and defines the liquid limit as water content which is required to close a distance ½ in along the bottom of a groove drawn in the soil sample after 25 blows. If the water content is too low then the number of blows required to close the gap will be too high (>35) and if it is too high then required number of blows will be too low (<25). As a result of the experiment water content is calculated for each trial (Wc= (M2-M3)/(M3-M1) * 100), the number of blows is recorded, and a curve representing the water content relative to the number of blows is plotted. In theory, the LL is intersection point of this curve with the flow curve drawn on the same graph.

The PL experiment utilizes manual rolling for the determination of the plastic limit which is defined as the water content at which the soil crumbles when rolled into threads of 1/8 in diameter. This experiment (like the previous) depends on trial and error and is based upon the testing of three samples to obtain three results which can be averaged for better accuracy. This average value of the three water contents obtained is used as the PL. The same soil is used for both experiments; therefore, the liquid and plastic limits are now both determined and can be used in order to determine the plasticity index (PI) which is calculated by subtracting the plastic limit from the liquid limit ( PI=LL-PL). In general, there are ranges for the PI which determine the degree of plasticity of the soil: 1-5: slightly plastic 5-10: low plasticity 10-20: medium plasticity 20-40: high plasticity >40: very high plasticity

Atterberg Limits are mainly used for the classification of fine-grained soils; however, to classify regular soils (coarse) the process of Sieve Analysis is used utilizing standard sieves of different sizes and mechanical shakers. This process results in the determination of the mass percentage of each grain size of the soil sample (mass retained on each sieve) to the total mass of the sample after shaking through a set of sieves with progressively smaller openings. This results in a gradation table and associated curve showing the percentage of different sizes inside the sample tested.

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Of course, when the classification of a soil sample is required, the first question that arises is what standard to use. The most commonly used standards for classification of soils are the American Association of State Highway and Transportation Officials System (AASHTO) and The Unified Soil Classification System (USCS). The planned usage for the soil sample we have is the main factor which allows us to determine what standard to use. The AASHTO, just like its name suggests, classifies soils for usage only in transportation systems and facilities (rural roads, urban roads, highways, freeways…etc.). It utilizes a group classification system (A-1, A-2, A-3…) which classifies soils depending on their quality for use in different types of transportation systems. Each soil sample tested is assigned a group index (GI) which is calculated according to an equation:

GI= (F200 – 35) [0.2 +0.005(LL-40)] + 0.01(F200 - 15) (PI-10) where F200 is the percentage passing the No. 200 sieve.

And for groups A-2-6 and A-2-7:

GI= 0.01(F200 - 15) (PI-10)

However, the USCS which is a unified system is used for all engineering structures (foundations, dams, residential buildings…etc.), unlike the transportation specific AASHTO. It classifies the soils according to a grouping system depending on different parameters that specify the type of soil and assigns it a symbol which indicates this type (GW, CL, GC…). This symbol is assigned using an organized naming system and is used to determine the properties associated with this type of soil to help us determine the possibility of its usage in the planned structure and whether it requires any type of treatment before application or initiation of construction project.

Experimental Procedure

Liquid Limit

1. Weight four different moisture cans using the digital balance and record the data (M1)2. Weight 250g of an air dry soil sample passing sieve no.4 and place it in a porcelain evaporating

dish 3. Pour distilled water from the plastic squeeze on the soil sample and mix them until the soil

transforms into a uniform paste4. Regulate the height of the Casagrandre cup to around 8 mm according to ASTM D43185. Insert a portion of the plate in the calibrated Casagrande cup6. Smooth the surface of the cup by the help of a spatula in a way that the maximum depth of the

sample does not exceed 8 mm until the soil becomes flattened with the bottom lip of the cup7. Using a grooving tool, cut a groove along the centerline of the soil sample placed on the

Casagrande cup. The grove should be perpendicular to the cup at all points of contact

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8. Zero the number of blows instrument recording. Roll the crank of the cup at a rate of 2 blows/second until the groove closes for about 2 inch and record the number of blows

9. If the number of blows was either below 15 or above 35, the soil should either be hydrated (by adding water) or dried (by the use of paper towels and the oven) then repeat the steps 5 through 8

10. If the number of blows was between 15 and 35, remove a portion from the cup perpendicularly and across the close groove

11. Place the sample in one of the moisture sample and weight it by the use of a digital balance 12. Record the sample13. Steps 5 through 12 should be executed four times in order to obtain four different sample for

which two have a number of blows between 15 and 25 and two have a number of blows between 25 and 35

14. Place the four moisture cans containing the soil samples in a large pan and place the pan in the oven for the samples to dry

15. Remove the samples the next day from the oven, weight the mass of the moisture cans with the sample, and record the data

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Plastic Limit

1. Weight three empty moisture cans and record the data2. Separate around 20g of the moist soil before initiating the liquid limit experiment to be aside to

dry on a paper towel

3. Divide this soil sample into three equal proportions4. Squeeze each sample on the palm of your hand with your fingers until ellipsoidal shapes are

obtained5. Roll one of the three samples at a rate of 80 strokes/minute on a glass plate using the palm of

your hand until its diameter becomes around 1/8 inch. 6. A 1/8 inch diameter is reached when the specimen starts showing signs of crumbling. At that

moment, stop the rolling and kneading.7. Collect the small crumbled pieces and place it in the moisture can8. Weight the moisture can with sample and record the data (M2)9. Repeat steps 5 through 8 for the two remaining samples10. Place the three moisture can in a large pan and place it in the oven11. Collect all the moisture cans from the pan the next day from the oven 12. Weight each moisture can with the soil samples and record the data (M3)

Sieve Analysis

1. Weight about 500g soil sample passing sieve no.4 and record the data as Mt to the nearest 0.1g2. Collect sieves no. 4, 10, 20, 30, 40, 100, 140, 200 and the pan3. Weight each of the empty sieves collected using a digital balance and record the data4. Stack the sieves from the largest opening to the smallest which least to a stack of sieves in the

following order: sieves no. 4, 10, 20, 30, 40, 100, 140, 200 and at the end the pan5. Place the soil into the top sieve and cover6. Place the stack full of the soil samples into the mechanical sieve shaker and turn the shaker for

about 8 minutes7. Turn off the shaker and collect each sieve and the pan8. Weight each sieve as well as the pan with the soil sample on top with a digital balance and

record the data

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Data Collected

Liquid Limit

Test No. 1 2 3 4Can No. 1 2 3 4

Mass of can, M₁ (g) 1.7 1.68 1.7 1.68

Mass of can + moist soil, M₂

(g)36.79 47 41.87 39.84

Mass of can + dry soil M₃ (g) 30.12 39.41 34.78 33.04

Water Content, W

(%)23 20 21 22

Number of blows 16 34 27 23

Table 1: Liquid Limit Data

Sample Calculation

In order to determine the Liquid Limit (LL), first we must determine the Water Content W (%) and round it to the nearest whole number

W =M 2−¿ M 3

M 3−M 1× 100¿

For Can #1:

W =36.79−30.1230.12−1.7

×100=23 %

Then after calculating the Water Content for the rest of the cans, we plot W (%) vs. Number of blows, as seen in question 2

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Plastic Limit

Test No. 1 2 3 AverageCan No. 1 2 3

Mass of can, M₁ (g) 1.68 1.67 1.7

Mass of can + moist soil, M₂

(g)7.14 7.68 9.69

Mass of can + dry soil M₃ (g) 6.29 6.72 7.56

Plastic Limit 18 19 36 25

Table 2: Plastic Limit Data

Sample Calculation

In order to calculate the Plastic Limit (PL) we use the following formula and round the answer to the nearest whole number, then average the answers of all 3 cans:

PL=M 2−¿ M 3

M3−M 1× 100¿

For can #1:

PL (can¿1 )=7.14−6.296.29−1.68

×100=18 %

The total Plastic Limit is calculated by averaging all the answers:

PL=PL (¿1 )+PL (¿2 )+PL(¿3)

3

PL=18+19+363

=25 %

Now that we have LL and PL we can calculate the Plastic Index:

PI=¿−PL=21.5−25<0

Note: The liquid limit is calculated afterwards in the discussion section, but we have used it here to facilitate calculationSince PI<0, this soil is non plastic. Or this could be due to errors in the experiment, explained later.

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In Order to facilitate our work and continue with our interpretation of the experiment, we shall disregard the value of 36, hence the plastic limit of our experiment turns out to be: 18.5%, Hence PI=3

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Sieve Analysis

M⫟ = 500.83 g

Sieve No.Sieve

Opening, D(mm)

Mass of Sieve (g)

Mass of sieve and retained soil (g)

Mass of retained soil

on each sieve, Mn (g)

% of mass retained on each sieve,

Rn

Cumulative %

retained, ΣRn

% finer, 100-ΣRn

4 4.75 474.26 475.21 0.95 0.190 0.190 99.81010 2 706.17 1001.18 295.01 58.931 59.121 40.87920 0.85 617.43 696.08 78.65 15.711 74.832 25.16830 0.6 605.86 624.13 18.27 3.650 78.482 21.51840 0.425 572.64 588.57 15.93 3.182 81.664 18.336

100 0.26 515.75 564.81 49.06 9.800 91.464 8.536140 0.106 511.86 535.41 23.55 4.704 96.169 3.831200 0.075 300.83 315.07 14.24 2.845 99.013 0.987Pan 280.63 285.57 4.94 0.987 100.000 0.000

500.6 100

Table 3: Sieve Analysis Data

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Discussion and Interpretation

Question 2

10 10018

19

20

21

22

23

24

Water content (%) vs. Number of blows(log)

Figure 1: Plot of Water content (%) vs. Number of blows (log)

In order to measure the Liquid limit, it is better to use a non logarithmic scale.

15 20 25 30 3518

19

20

21

22

23

24

W (%) vs Number of Blows

Figure 2: Water content (%) vs. Number of blows

From the curve we can deduce that LL= 21.5%

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Question 3

This part was already done previously, we have found out that:

PL= 18.5%

PI= 3

Question 4

In order to determine the type of our fine grained soil by the use of the Casagrende chart found in ASTM D 2487-06 we need to determine PI, the plasticity index, and the liquid limit known as LL. According to the previous calculations, PI was found to be equal to 3 and LL was found to be equal to 21.5. The Casagrande chart indicates that for a PI=3 and LL=21.5, the fine-grained soil can be classified as ML or OL. M stands for Silt, O stands for Organic, and L stands for Low Plasticity.

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Question 5

0.1 1 100.000

20.000

40.000

60.000

80.000

100.000

120.000

%Cumulative vs. Sieve size (log)

Figure 3: Cumulative particle size distribution plot on a semi log graph

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Question 6

1 100.000

20.000

40.000

60.000

80.000

100.000

120.000

% Passing Vs. Sieve size (log)

Figure 4: Sieve Analysis Curve

From the curve above we can determine: D : ₆₀ The sieve opening at which we have 60% passing = 2.86 mmD₁₀: The sieve opening at which we have 10% passing = 0.175 mmD₃₀: The sieve opening at which we have 30% passing = 1.15 mm

Cu= D₆₀D₁₀

= 2.860.175

=16.343

Cc=(D ₃₀) ²

(D ₆₀∗D ₁₀)=2.642

Cu > 4 and 1< Cc < 3 therefore the soil is well graded.

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Question 7

In order to use the USCS flow charts we need to calculate the PI of the soil sample, the distribution of the particle sizes among the soil, the coefficient of uniformity, and the coefficient of curvature. The following properties have all been measured and calculated. Since more than 50% of the soil was retained on No.200 sieve, the flow chart for Classifying Coarse grained Soils should be used. The chart proceeds in the following way:

Hence, the soil is well graded sand according to USCS flow charts.

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Error Analysis

No experiment is ever made without errors. This time our error led to a major error in the output of the experiment, leading to a negative plasticity index thus ruining our whole interpretation of the classification of the soil. However, the errors are mainly due to:

Sieve Analysis:

Mass determination in this experiment might now be as accurate as needed, mainly due to soil separation through phases. However this error is very minor and the results retrieved are very close to perfect.

Liquid Limit

The soil placed on the cup isn’t exactly 8mm thick, it was made using an approximation The cutting of the centerline wasn’t exactly precise The rate of blows wasn’t exactly at about 2 blows/second The closure of the centerline wasn’t exactly at about 0.5 in There was a little bit of soil moist remaining in the cup before the complete removal of soil We have also added a little too much water at the beginning and then put the soil in the oven in

order for it to dry up. This might have caused some distortion of the real result.

Plastic Limit

The shape at the beginning isn’t quite ellipsoidal because we have gotten it using our hand, which isn’t quite accurate.

The rate isn’t quite accurate (80 strokes per minute) When we have reached a diameter of 1/8 in, we might not have completely reached it, because it

was mainly due to eye inspection Using the screw to have a diameter, wasn’t quite precise and accurate

Note: All these errors have summed up to lead to a negative plasticity index which have discarded some results of the whole experiment.

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Conclusion

In our experiment we have basically a couple of conclusions that we got:

The liquid limit of our soil was 21.5%, the plastic limit turned out to be 18.5%, and the Plasticity index hence equal to 3.

Based on the Casagrende chart, the fine-grained soil can be classified as ML or OL. M stands for Silt, O stands for Organic, and L stands for Low Plasticity.

Based on the sieve Analysis, we have concluded that our soil is well-graded. According to USCS flow charts, we can also conclude that our soil is well graded.

References

Eng. Omar El Masri, Handout 2ASTM D 422-63 (Reapproved 2007)ASTM D 2487-06ASTM D 4318 - 05

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Lab report soil mechanics