Atterberg Limit Tests (LL and PL)

Summary

In this video, Dave Whinger from Missouri S&T's geotechnical labs demonstrates the laboratory procedures for conducting the Atterberg limit tests, which include the liquid limit and plastic limit tests. These tests are crucial for classifying the fine-grained portion of soil and have practical applications in geotechnical engineering. The video showcases how to perform these tests on a silt sample from the Mississippi River Valley, which has been modified with bentonite clay to enhance plasticity. The liquid limit is determined by the moisture content at which soil transitions from a viscous fluid to a plastic putty-like consistency, measured by the number of blows required to close a groove in the soil sample. The plastic limit is identified when the soil begins to crumble when rolled into a 3mm thread. The video guides viewers through the necessary equipment, calibration, and step-by-step testing process.

Takeaways

• 🧪 The video discusses laboratory procedures for performing Atterberg limit tests, specifically the liquid limit and plastic limit tests, which are crucial for classifying the fine grain portion of soil.
• 🏗️ Atterberg limits are index tests used in geotechnical engineering for soil description, classification, and correlating to engineering properties like shear strength.
• 📏 The liquid limit is determined by the moisture content at which soil transitions from behaving like a viscous fluid to a plastic putty, defined by the number of blows required to close a groove in the soil pat.
• 🛠️ For the liquid limit test, essential lab equipment includes the CAG Grande apparatus, grooving tool, moisture content cans, water bottle, mixing bowl, spatula, mortar, and pestle.
• 🔍 The plastic limit is identified as the moisture content where soil changes from a plastic putty to a brittle solid, determined by rolling soil into a thread until it crumbles at 3mm diameter.
• 📈 To produce a flow curve, four liquid limit tests are required at specific blow count ranges, and the results are plotted to determine the liquid limit through linear regression.
• 🌡️ Moisture content determination is a critical step, involving weighing soil samples before and after drying to ascertain the water content affecting soil behavior.
• 🔄 The process involves iterative testing and adjustment of soil moisture to achieve the desired blow counts for accurate liquid limit determination.
• ⚖️ Accurate calibration of the CAG Grande apparatus is necessary to ensure consistent and reliable test results.
• 📑 The lab documents, including the handout, ASM standards, and data sheets, are available on Blackboard for reference, guiding the execution and recording of the tests.

Q & A

What are the primary purposes of the Atterberg limit tests?

The Atterberg limit tests, including the liquid limit and plastic limit tests, are used to classify the fine-grained portion of soil and provide insights into how the soil will behave under certain conditions.

What is the significance of the liquid limit in geotechnical engineering?

The liquid limit is significant in geotechnical engineering as it represents the moisture content at which a soil transitions from behaving like a viscous fluid to a plastic substance, typically measured by the number of blows required to close a groove in the soil sample.

What is the plastic limit in the context of soil classification?

The plastic limit is the moisture content at which a soil starts to crumble when rolled into a thread of 3mm diameter, indicating the transition from plastic to brittle behavior.

What is the practical application of Atterberg limits in geotechnical engineering?

The Atterberg limits are used for soil description, quantitative soil classification, and correlating with engineering properties such as shear strength.

What type of soil is used in the described laboratory procedure?

The soil used in the laboratory procedure is a silt from the Mississippi River Valley, which has been mechanically pulverized and passed through a No. 40 sieve to remove large particles, with bentonite clay added to increase plasticity.

What equipment is necessary to perform a liquid limit test according to the script?

The equipment needed for a liquid limit test includes the Casagrande apparatus, grooving tool, moisture content cans, water bottle, mixing bowl, spatula, mortar and pestle, and a scale.

How should the soil be prepared before conducting the liquid limit test?

The soil should be mixed with water until it appears uniform and has a creamy surface, which may take up to 20 minutes of proper blending.

What is the procedure for calibrating the Casagrande apparatus?

The Casagrande apparatus is calibrated by placing the grooving tool underneath the cup and adjusting the thumb screw to ensure the cam just contacts the cup without lifting it, using the 10mm block on the grooving tool.

How are the blow counts determined during the liquid limit test?

The blow counts are determined by rotating the handle of the Casagrande apparatus at 120 revolutions per minute and counting the number of blows required for the groove to close to 13mm.

What is the process for conducting the plastic limit test as described in the script?

The plastic limit test involves rolling a soil sample into a thread until it reaches a 3mm diameter, at which point the soil should crumble. Samples are then collected for moisture content determination to find the average moisture content at the point of crumbling.

How many liquid limit tests must be conducted to produce a flow curve, and what are the required blow count ranges for these tests?

Four liquid limit tests must be conducted, with one test each between blow counts of 15-20, 20-25, 25-30, and 30-35.

Outlines

00:00

🧪 Introduction to the Casagrande Limit Test

Dave Whinger from the Missouri S&T Geotechnical Labs introduces the Casagrande limit test, which includes both the liquid limit and plastic limit tests. These tests are essential for classifying the fine-grained portion of soil and have practical applications in geotechnical engineering, such as soil description, quantitative soil classification, and correlation to engineering properties like shear strength. The video demonstrates how to conduct these tests according to ASTM specifications using a silt sample from the Mississippi River Valley. The liquid limit is defined as the moisture content at which soil transitions from a viscous fluid to a plastic substance, like peanut butter. This is operationally defined by the water content at which a groove in the soil sample requires 25 blows to close at a 13 mm distance using the Casagrande apparatus. The necessary lab equipment includes the Casagrande device, grooving tool, moisture content cans, water bottle, mixing bowl, spatula, mortar and pestle, and a scale. The plastic limit is the moisture content at which the soil transitions from a plastic to a brittle state. The video outlines the required equipment for the plastic limit test, which includes a glass plate, a 3 mm diameter rod, and additional cans for moisture content determination.

05:00

🔬 Conducting the Liquid and Plastic Limit Tests

The video script details the process of conducting the liquid limit test, which involves preparing the soil sample by adding water and mixing until it appears uniform and creamy. The weight of the soil is recorded for moisture content determination. The Casagrande apparatus is calibrated using a grooving tool with a 10 mm block to ensure accurate test results. The soil is placed in the cup and a standardized groove is made. The number of blows required to close the groove at 13 mm is counted, with adjustments made to the soil's moisture content as needed to achieve tests within specific blow count ranges. The plastic limit test involves rolling a soil sample into a thread until it reaches a 3 mm diameter. The soil is dried and rolled until it crumbles at this diameter, at which point samples are collected for moisture content determination. The average of these moisture contents is calculated to find the plastic limit. The script also mentions that the lab documents, including the handout, standards, and data sheets, can be found on Blackboard in PDF format.

Keywords

💡Aberg Limit Test

The Aberg Limit Test, as mentioned in the script, is a set of laboratory procedures used to classify the fine-grained portion of soil. This test includes both the liquid limit and plastic limit tests, which are crucial in geotechnical engineering for soil description, classification, and understanding engineering properties such as shear strength. The script describes how these tests help to indicate how a soil will behave under certain conditions, which is vital for engineering applications.

💡Liquid Limit

The liquid limit is a concept defined by the moisture content at which soil transitions from acting as a viscous fluid to behaving like a plastic putty. In the script, it is described as the water content where a groove in a soil pat made by the Casagrande apparatus requires 25 blows to close at a distance of 13 mm. This parameter is essential for understanding soil plasticity and is determined through the liquid limit test as demonstrated in the video.

💡Plastic Limit

The plastic limit refers to the moisture content at which a soil begins to act less like a plastic putty and more like a brittle solid. In the context of the video, it is determined by rolling a soil sample into a thread until it crumbles at a diameter of 3mm, indicating the soil's transition from plastic to brittle behavior. This test is important for understanding the soil's workability and its engineering properties.

💡Casagrande Apparatus

The Casagrande apparatus, also known as the standard liquid limit device, is a laboratory tool used in the liquid limit test. As described in the script, it is used to determine the number of blows required to close a groove in a soil pat, which aids in determining the liquid limit. The apparatus is a critical component in the laboratory procedures for soil classification.

💡Moisture Content

Moisture content is a key factor in soil behavior and is central to both the liquid and plastic limit tests. The script outlines the process of determining moisture content by weighing soil samples before and after drying them in an oven. Accurate moisture content measurement is essential for conducting the Aberg limit tests and understanding soil's engineering properties.

💡Shear Strength

Shear strength is an engineering property of soil that describes its resistance to deformation and failure under shear stress. The script mentions that Aberg limits, including liquid and plastic limits, correlate to shear strength, which is a critical factor in geotechnical engineering for designing foundations and retaining structures.

💡Silt

Silt is a fine-grained soil particle that is being tested in the video. The script specifies that the silt used is from the Mississippi River Valley and has been mechanically pulverized and passed through a No. 40 sieve to remove large particles. This silt is used to demonstrate the Aberg limit tests, highlighting its importance in geotechnical analysis.

💡Bonite Clay

Bonite clay is added to the soil sample to increase its plasticity, as mentioned in the script. This addition is made to ensure that the soil has the necessary properties for the laboratory tests, specifically to enhance the soil's behavior during the liquid and plastic limit tests.

💡Grooving Tool

The grooving tool is used to create a standardized groove in the soil pat for the liquid limit test. As described in the script, the tool has shoulders that should just scrape the surface of the soil pat, ensuring a consistent test procedure. The grooving tool is an essential part of the Casagrande apparatus setup.

💡Flow Curve

The flow curve is a graphical representation of the relationship between moisture content and the number of blows required to close a groove in the soil pat. The script explains that four liquid limit tests must be conducted at different blow counts to plot this curve. The curve is used to determine the liquid limit through linear regression, which is a crucial step in the Aberg limit test analysis.

💡Linear Regression

Linear regression is a statistical method used to establish a relationship between two variables, in this case, moisture content and blow counts. The script mentions that a linear regression can be established through the data points obtained from the liquid limit tests, allowing for the interpolation of the liquid limit from the flow curve.

Highlights

Introduction to laboratory procedures for performing an Atterberg limit test, including liquid limit and plastic limit tests.

Explanation of Atterberg limits' role in classifying the fine grain portion of soil and their practical applications in geotechnical engineering.

Description of the soil sample used for the test, which is a silt from the Mississippi River Valley, mechanically pulverized and passed through a No. 40 sieve.

Mention of the addition of bentonite clay to the soil to increase its plasticity for the lab experiment.

Definition of the liquid limit as the moisture content at which soil transitions from a viscous fluid to a plastic putty-like consistency.

Description of the CAG Grande apparatus and its use in determining the number of blows required to close a groove in the soil pat.

List of lab devices needed for the liquid limit test, including the CAG Grande apparatus, grooving tool, moisture content cans, and other equipment.

Procedure for calibrating the CAG Grande apparatus to ensure accurate test results.

Instructions on preparing the soil sample for the liquid limit test, including mixing and determining uniformity.

Process of conducting the liquid limit test, including creating a groove and counting the number of blows to close it.

Guidelines for adjusting the soil's moisture content based on the number of blows and the required test range.

Explanation of how to plot the moisture content versus blow counts to determine the liquid limit from the flowchart.

Definition of the plastic limit as the moisture content at which soil transitions from a plastic putty to a brittle solid.

List of equipment needed for the plastic limit test, including a glass plate, a 3mm diameter rod, and moisture content cans.

Procedure for conducting the plastic limit test, which involves rolling the soil into a thread until it crumbles at 3mm diameter.

Instructions for collecting and determining the moisture content of the crumbling soil to find the plastic limit.

Emphasis on the importance of repeating the plastic limit test to obtain enough samples for accurate moisture content measurements.

Transcripts

hello I'm Dave whinger with the Missouri

S&T geotechnical Labs today we will be

going over the laboratory procedures on

performing an adberg limit test these

tests include the liquid limit and the

plastic limit tests they are used to

classify the fine grain portion of a

soil the practical application of adberg

limits and geotechnical engineering incl

includ soil description quantitative

soil classification and correlations to

engineering properties such as Shear

strength the adberg limits are index

tests and they are designed to give an

idea or indicate how a soil will act

under certain conditions this short

video will demonstrate how to conduct a

liquid limit test and a plastic limit

test in accordance with ASM

specifications the soil that we will be

performing the limits tests with today

is a loial silt that comes from the

Mississippi River Valley this silt has

been mechanically pulverized and then

passed through a number 40 Civ to remove

all large particles for the purpose of

today's lab experiment bonite clay has

been added to increase the plasticity of

the

soil the liquid limit is defined by the

moisture content in which a soil begins

to act less as a viscous fluid and more

as a plastic putty like peanut butter by

convention this is defined as the water

content at which a groove cut into a

soil Pat in the CAG Grande apparatus

requires 25 blows to close at a distance

of 13 mm 1 half in the distance of this

tool handle we will need a few lab

devices to help us with this first we

will have the standard liquid limit

device also known as the cap CAG Grande

apparatus this will Aid Us in getting

the blow

counts next we will need the grooving

tool used to make a standardized Groove

in the soil Pat we will also need a

couple moisture content cans for

moisture content

determination we will need a water

bottle so we can add moisture to our

soil we will need a mixing boil Bowl to

prepare our soil in a spatula to mix our

soil a mortar and pestl to Crum crush

the soil if need be we will also need a

scale to record the weights of each

test the plastic limit is defined as the

moisture content at which a material

begins to act less like a plastic putty

and more like a brittle solid in order

to conduct the plastic limit test the

following will be required we will need

a glass plate to roll out our 3mm

threads on we will need a rod that is 3

mm in diameter to gauge when we get down

to 3

mm we'll need two cans to get moisture

content

in and we will also need a spatula to

spread and dry out our soil the

documents pertaining to today's lab can

be found on blackboard in PDF format the

documents include the lab handout the

ASM standards and the data sheets in

order to produce the flow curve four

liquid limit tests must be conducted one

test between the blow counts of 15 and

20 another between the blow counts of 20

and 25 a third between the blow counts

of 25 and 30 and finally one between 30

and

35 as the soil dries out the moisture

content is reduced this results and

stiffer soil to perform the liquid limit

test weigh out about 300 G of the

provided soil if the soil is clumpy you

can break it up in the morar and pestle

add water from the water bottle and mix

the soil until it appears uniform and

the surface looks creamy a proper

blending could take up to 20

minutes determine and record the weights

of the four te cans which will be used

later in the test for moisture content

determination the CAG Grande apparatus

is easily knocked out of calibration so

it is important to calibrate the device

often the grooving tool has a block on

the back of it that is exactly 10 mm

tall the fall height of the kasag Grande

cup calibrate the apparatus by placing

the grooving tool underneath the

cup rotate the handle so that the cam

just contacts the cup if the apparatus

is

calibrated the cam will just barely

touch the cup and it will not lift it up

the grooving tool loosen the set screw

on the top and adjust the thumb screw in

the back to raise or lower the

cup thoroughly clean and dry the

cup evenly spread a moderate amount of

soil into the cup to create a soil Pat

to be tested using the grooving tool

create a straight Groove through the

center of the soil Pat the shoulders of

the grooving tool should just scrape the

surface of the soil Pat if the shoulders

do not contact the soil Pat surface too

little soil has been placed in the cup

and the test should be restarted once

the groove has been made rotate the

handle at 12 120 revolutions per minute

two cycles per second and count the

number of blows it takes to close the

groove in the soil Pat 13 mm or 1/2 in

which is the width of the grooving tool

handle if if the number of blows Falls

between 15 and 20 scoop out some of the

soil and place in one of the pre-weighed

tear cans and record the new weight for

moisture content

determination place the can with the

soil in the oven and reway it again in

24

hours if the number of blows Falls below

15 mix the soil to dry it out clean dry

the cup and repeat the

test if the number of blows Falls above

20 add moisture to the soil mix it clean

and dry the cup and retest repeat the

procedure to get tests between 20 and 25

25 and 30 and 30 and 35 blows plot the

moisture content versus blow counts and

determine the liquid limit from the

flowchart with the moisture content

plotted in the vertical axis and the

blow counts plotted in the horizontal

axes in log scale a linear regression

can be established through the data and

the liquid limit can be

interpolated the plastic limit is the

average of the moisture content when the

soil starts to crumble when it is being

rolled into a 3mm Fred so you take a 25

to 30 G

sample spread it out on the plate to dry

it

out when it gets to a workable

State you can pick it up and start

working it in your

hand start rolling the soil into a

thread roll the soil until the diameter

of the thread is reduced to 3

mm the rod can be used as a gauge to

determine when the soil has reached 3 mm

in

diameter if the soil does not crumble

when rolled down to 3 mm further dry out

the soil and try

again once the soil crumbles at 3 mm

collect samples of the crumbling soil

and place them in pre-wed tear cans for

moisture content

determination repeat the test enough

times so that enough soil has been

obtained for two moisture content

samples of approximately 6 gam each

record the wet weights of the moisture

content samples and place in the oven

reway the samples again in 24 hours

the average of the two moisture contents

is the plastic limit