Soil Classification Lab 1

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Soil Classification

12-336 Soil Mechanics Lab

By

Russell Markosky, Erin Persson, Samantha Sanstrom, Clare Svrisko, and

Kristi Wong

Department of Civil and Environmental Engineering

Carnegie Mellon University

Pittsburgh, PA 15213

October 1, 2014


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Abstract


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Table of Contents

Abstract ........................................................................................................................................................ ii

1.0 Introduction ................................................................................................................. 1

2.0 Materials and Methods ................................................................................................ 1

3.0 Results ......................................................................................................................... 3

4.0 Summary and Conclusions ............................................................................................ 3

Appendix A Data Sheets .......................................................................................................................... A-1


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1.0 INTRODUCTION

One of the most important aspects of any Civil or Environmental Engineering project is the soil

beneath it; it is essential for the engineer to know what types of soils the structures will be built on and

what the properties of those soils are. This knowledge allows one to predict the behavior of the soil

under certain conditions, and therefore determine what kind of structure would be sustainable on that

plot of land. Without this information, projects can experience catastrophic failure, potentially incurring

millions of dollars of damage, impairment of infrastructure, and even loss of life.

The purpose of this lab was to perform ASTM standard tests in order to determine the classification

of two sample soils; properties such as liquid limit, plastic limit, and grain size were the main data

required in order to do this using a United Soil Classification System (USCS) chart. To determine the

liquid and plastic limit of the first soil sample, this lab utilized the Atterberg limit test, which is composed

of a liquid limit determination component and a plastic limit determination component. For the second

soil sample, which aimed to test the grain sizes of the sample, the sieve test was used. The percent finer

values that were derived from this test were then used run through the USCS chart to classify the

soil. Because of these tests and the USCS chart, both soil samples were able to be correctly identified.

2.0 MATERIALS AND METHODS

Before any procedure involving the soil under question could begin, it was necessary to label 10 metal

containers and weigh them, since they were the vehicles by which the soil sample would be transferred

into the oven in order for it to dry so the amount of moisture in the soil could be measured after an

ASTM-specified time limit. The first part of this lab had the objective of finding the plastic limit and liquid

limit of a soil using Atterberg limits so it could ultimately be classified. In order to determine the plastic

limit, a small sample of the given soil was taken and rolled on a piece of marble with one of the group

members hands; the sample was rolled into a small worm, until its diameter achieved a size of about

3 millimeters. The sample was then picked up and draped over the group members finger in order to

determine how much it deformedif both ends of the worm draped gracefully over the finger, the

procedure of making the worm was repeated. This continued until the process of physically rolling the

worm became impossible because it became too cracked and fell apart. At this point, the segment of the

worm with a decent amount of cracks in it was put into one of the labeled containers and weighed.

Then, the sample and the can were placed into the oven. After more than 24 hours passed, the sample

was taken out of the oven and weighed again. The difference between the two weights represents the


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mass of the moisture that was present in the soil and allows the calculation for water content to be

performed. This process involving the creation of the worm and weighing it both before and after it

was put in the oven was repeated four more times in order to get an average mass of moisture per

sample of soil.

The second part of the Atterberg limits tests focused on the liquid limit of the soil. In order to determine

the liquid limit of a soil, an amount of soil was placed into an Atterberg device and smoothed down so

its surface in the bowl was relatively smooth. Then, using a 1 centimeter-wide groove, an indentation

was made straight down the middle of the sample in the bowl so that there was a gap between two

sides of the same sample of soil. Then, the crank of the Atterberg machine was turned by a group

member until the gap between the two sides of the soil started to decrease; once the two sides of the

soil touched at any point, the cranking of the machine stopped and the number of hits the bowl made

was recorded. Then, the part of the soil sample that came together was scooped out and placed into

one of the same kind of container that was previously used for the plastic limit determination portion of

the experiment. This small sample was then also placed in the oven. This process was repeated four

times; after each smaller sample was placed in the oven, more water was added to the bowl containing

the whole sample of soil to be tested, and the soil was mixed in order to incorporate all the water into it.

Once the five samples had been in the oven for over 24 hours, they were all removed and weighed

individually; this allowed the determination for the mass of moisture and water content to be made.

Once the water content was determined, the values for each iteration of the experiment were plotted

with respect to the number of blows it took the Atterberg device to make the soil sample converge. This

graph was utilized to find the liquid limit of the soil.

Finally, the last component of this experiment was to classify a sample of dry sand using sieves of

various numbers in order to separate the particles the sand contains by size. The sieve numbers used

were 4, 10, 20, 40, 100, 200, and a pan; each sieve was cleaned and weighed individually, then stacked

from bottom to top in increasing size/decreasing number so that the pan was on the bottom, the

number 200 sieve was on top of it, etc. The sample of soil was then weighed and that value was

recorded; then, the sample was dumped directly onto the number 4 sieve, stacked on top of all the

other sieves. The stack of sieves was then placed on a mechanical shaker and the stack was shaken for 5

minutes, which is an ample amount of time to ensure that all the grains of soil settle in their respective

sieves. Once this process was complete, the sieves were taken apart and each sieve, with all the settled


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soil, was massed individually. Those masses were recorded and the percent finer of the soil for each

sieve number was calculated and plotted on a graph (see Appendix A).

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RESULTS

Using two ASTM standard teststhe grain-size test and the Atterberg limits testthe classification

of two soil samples was achieved. To determine the liquid and plastic limit of a soil sample, the

Atterberg tests were used, and, based on the data that was collected, the water content of the sample

was determined; from this result, the liquid limit and plastic limit were obtained to be 30% and 22.62%,

respectively. The plasticity index, then, was found to be 7.38% and a USCS chart was used to determine

the composition of the soilit was classified to be fine-grained with a low compressibility, putting it in

the CL groupa clay with low plasticity.

The second soil specimen was determined through a mechanical grain size analysis. After

determining how much of the soil sample passed through each sieve in the test, the resulting percent

finer was used to classify the soil. Since over half of the soil specimen passed through the no. 4 sieve,

the sample is immediately classified as a sandy soil. From there, the values for the particle diameter of

the soil at percent finer values of 10%, 30%, and 60% (D10, D30, and D60, respectively) were extrapolated

from the graph. The ratio D60/D10and the value from the formula D302/(D60D10) were then calculated to

be 2.857 and 0.97, respectively. Because these values put the soil outside of the range for SW (well-

graded sand), the percent finer value for the soil passing through the 200 sieve was referenced, and

since that value was between 0 and 5% (at 1.36%), the soil was classified, through the process of

elimination, to be in the SP (poorly-graded sand) group. This classification is further proven by the fact

that, during the experiment, the majority of the sample ended up in the no. 10, no. 20, and no. 40

sieves, indicating that the sample is poorly-graded.

All data obtained and the resulting values and calculations, as well as the graphs that were plotted

with this data, can be found in Appendix A.

4.0 SUMMARY AND CONCLUSIONS

The objective of this lab was to classify the soils that were tested based on the United Soil

Classification System (USCS) once the data was obtained through the Sieve Analysis test and the


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Atterberg limits tests. The USCS chart was the final reference used once the calculations of the percent

finer, plastic limit, and liquid limit were completed; the chart allows one to determine the group a soil

belongs to based on the type of test that was performed on it and the way that soil behaved during

those tests. To classify these soils we need to find the liquid limit, plastic limit, and grain size. We used

the Atterberg test to find the liquid and plastic limit. To find the grain size of the soil, we used to sieve

test.

In order to classify the soil that was used in the Atterberg tests for liquid limit and plastic limit,

the data tables were completed using basic methods of algebra, thereby obtaining the numbers

required to calculate the limits. Once the water content of the liquid limit determination test was

plotted on the graph against the number of blows the Atterberg device took, the liquid limit was

determined by extrapolating from the grapha vertical line was drawn from x=25 blows, and the liquid

limit was determined by the water content value from the intersection of the two lines. The liquid limitwas found to be 30% at this point. To determine the plastic limit, the water content values of each trial

from the rolling test were averaged; the plastic limit was calculated to be 22.62%. From these values,

the plasticity index was found to be 7.38%, once the plastic limit was subtracted from the liquid limit.

Based on these values and referencing the chart with the knowledge of how the soil behaved during

these two tests, the sample was determined to be fine-grained with a low compressibility, which puts its

classification as CL, a clay with low plasticity.

For the second soil, which was tested using the ASTM Standard Sieve test, the percent finer of

each sieve was calculated using the data provided from the lab. Using the graph that was drawn based

on the performance of the soil as it passed through each sieve, the D60, D30, and D10values were

extrapolated and used to classify the soil; since its D60/D10value was 2.857 and its D302/(D10D60) value

was 0.97, this put the soil as poorly graded. Over half of the sample passed through the no. 4 sieve, and

less than 5% of the sample was finer than the 200 sieve, so the soil was determined to be in the SP

group. Ultimately, the objective of the lab was to use ASTM tests to determine soil classifications; this

was accomplished using the USCS standards.


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Appendix A

Data Sheets


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Documents

Soil Classification Lab 1