Exercise 8: Soil Compaction

CE337, Section 006, Team 3

Experimental data acquired on April 16, 2015 by:

John Fisher (Role A)

Colin Crist (Role B)

Maria Baldonieri (Role C)

Yuhao Luo (Role C)

Submittal Date: May 4, 2015

The Pennsylvania State University

Department of Civil and Environmental Engineering

ii

ABSTRACT

The objective of this laboratory exercise was to determine the optimum moisture content and

maximum dry density of a soil specimen using the standard proctor compaction test. This test was

performed using a compaction mold that was filled with soil and then compacted three times using

the standard proctor hammer. In this test, the water content of the soil sample was incrementally

increased. The soil was compacted into a constant volume and then massed. The water provides

lubrication for the movement of soil particles. The maximum dry density of a soil is achieved with

very high moisture content, where almost all of the air is driven out and the soil is at its densest

compaction state. Further moisture will over saturate the soil where the soil particles are not

touching each other, and are instead separated by water molecules. The optimum moisture content

is the water to soil ratio at which maximum dry density can be achieved. Among the groups

conducting this experiment, the average optimum moisture content is about 14%. The average

maximum dry density of the soil among the groups is about 1.9 grams per cubic centimeter. In

civil engineering practices, these two numbers would be used to determine the appropriate soil

compaction conditions for an individual project.

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TABLE OF CONTENTS

Page

ABSTRACT ......................................................................................................... ii

TABLE OF CONTENTS..................................................................................... iii

LIST OF TABLES .............................................................................................. iv

LIST OF FIGURES ............................................................................................. iv

INTRODUCTION ................................................................................................ 1

THEORETICAL BACKGROUND ...................................................................... 2

METHODS AND MATERIALS .......................................................................... 4

RESULTS AND DISCUSSION ........................................................................... 5

CONCLUSIONS AND RECOMMENDATIONS ................................................ 8

REFERENCES ..................................................................................................... 9

iv

LIST OF TABLES

Page

Table 1: Results from Groups……………………………………………………………6

Table 2: Statistics of Data………………………………………………………………...6

v

LIST OF FIGURES

Page

Figure 1: Soil compaction mold and Proctor Hammer used in this experiment………............1

Figure 2: Dry Density vs. Moisture Content w/ Zero-air-voids curve…………………………7

1

INTRODUCTION

In this experiment, a soil compaction test was completed. This test slowly adds water to a certain

amount of soil to see when the Optimum Moisture Content (OMC) has been met. This experiment

is done in the field to ensure that buildings or foundations are being built on properly compacted

soil. From sewer systems, roads and walkways, to skyscrapers, soil compaction is a necessity in

construction. In the civil and architectural engineering fields, knowledge of soil compaction is

essential for any project. In the experiment, there reaches a time when the more water that is

added, the less the soil can be compacted. To fulfill this experiment, a sample 3150 grams of soil

was used and mixed with first, 315 grams of water, and then 95 grams of water each time the

experiment was completed. In order to compact the soil, a compaction mold and standard Proctor

Hammer were used. To find the moisture content, a sample of soil from each step was gathered,

massed out, and placed in an oven to dry overnight. The sample was then massed out the next day.

Figure 1: Soil compaction mold and Proctor Hammer used in this experiment.

2

THEORETICAL BACKGROUND

The specific propose of the proctor compaction test is to determine the maximum dry density and

optimum moisture content of a soil. It is at the maximum dry density that a soil can achieve

maximum soil compaction in the field. This data can then be used by an engineer to adjust the

moisture content to achieve the maximum dry density of a soil to be used in a construction project.

The motivation for R. R. Proctor to develop this test was to determine a solution for the in situ

behaviors of clay and ground soils that cause them to be unsuitable for construction. Proctor

wanted to find the practical maximum density of soils and not just a theoretical maximum density,

so he created the soil compaction test. It was found that in a controlled environment (or within a

control volume), the soil could be compacted to the point where the air could be completely

removed, simulating the effects of a soil in situ conditions. This theoretical maximum dry density,

where there are zero air voids, can be calculated by

𝛾𝑑(𝑚𝑎𝑥 𝑡ℎ𝑒𝑜𝑟𝑦) =𝛾𝑤

(𝑤(%)

100+

1

𝐺𝑠)

Where:

𝛾𝑤 = 𝑢𝑛𝑖𝑡 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟

𝐺𝑠 = 𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑔𝑟𝑎𝑣𝑖𝑡𝑦 = 2.65 w(%) = water content

𝑤(%) = 𝑚𝑜𝑖𝑠𝑡𝑢𝑟𝑒 𝑐𝑜𝑛𝑡𝑒𝑛𝑡 =𝑊𝑤

𝑊𝑠

Where:

𝑊𝑤 = 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟

𝑊𝑤 = 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑠𝑜𝑖𝑙

3

In this experiment, the practical dry densities could be determined by simply measuring the

weight of the soil before and after compaction, calculating the moisture content, and furthermore,

calculating the dry density. This dry density can be calculated by

𝛾𝑑 =𝛾

1 +𝑤(%)

100

Where:

𝛾 = 𝑚𝑜𝑖𝑠𝑡 𝑢𝑛𝑖𝑡 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑠𝑜𝑖𝑙 w(%) = moisture content

With the improvement of compaction equipment, the original Proctor test had to be modified to

account for higher dry densities. In 1958, the modified Proctor compaction test was developed as

an ASTM standard and used worldwide. (Davis 2008)

4

METHODS AND MATERIALS

In this experiment, methods of compaction of soil were used to calculate the optimum moisture

content and to prove that at a certain water content, the compaction decreases. The method of

compaction used in this experiment is the Proctor Method of compaction. In this method, a

compaction mold and a standard 5.5 pound Proctor hammer were used along with a pre-massed

soil sample that passes through sieve no. 4, a scale, moisture cans, water, a large flat pan for

mixing, a jack and a drying oven.

In order to get the soil to the proper water content, initially, about 10% by mass of water was added

in 3 parts to ensure even distribution and mixing. The Proctor method consists of filling the mold

in 3 layers, and in between each layer, using the compaction hammer to administer 25 blows spread

about the surface area of the soil. The soil is then massed to complete the necessary calculations.

After the initial water content and first compaction, about 3% of water by mass is added. These

steps are repeated until the moist density of the soil decreases. Moist density can be found by

dividing the mass of the soil by the volume of the compaction mold.

After each compaction, a sample of the soil was taken and placed into a separate moisture can. It

was then placed into an oven in order to find the moisture content of the soil. From the water

content, the dry density of compaction can also be found by using the following formula:

𝛾𝑑 =𝛾

1 +𝑤(%)

100

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RESULTS AND DISCUSSION

The purpose of the exercise is to determine the optimum moisture content and maximum dry

density of a soil specimen. Figure 1 presents graphically the values obtained for the dry density of

the soil as shown in Table 3 after each run of the test. The zero-air-voids curve (presented in

orange) was created from the values calculated in Table 1. As expected, no part of the dry density

curve plots above the zero-air-voids curve. The results obtained are 1.86g/cm^3 for the maximum

dry density and 13.6% for the optimum moisture content (Figure 1). Based on the theory, there is

a critical point where the soil has maximum dry density. Increasing or decreasing the moisture

content from OMC would result in lower dry density. From our results, it is apparent that the goal

was successfully achieved. To be specific, the water acts as a lubricant to help soil particles move.

Decreasing the moisture content would result in a flocculated soil structure, and increasing it would

increase the pore space between particles. Thus, the dry density of the soil will be lower. The dry

density vs. moisture content curve obtained is not as obvious as what is suggested in the lab

manual, but the objective of this experiment is to determine the optimum moisture content and

maximum dry density of a soil specimen using the standard Proctor compaction test. There is

nothing new and unexpected. Besides the error that might be caused by the equipment, soil must

be air-dry in different condition by several groups. Also, when compacting soil, there may be

discrepancies. For this exercise, all groups followed the procedure strictly and received good

quality of data with no strength and weakness found. In comparison with the other results from

other groups, the values obtained are in the middle of the set of data. All the data seems to be good

quality, which means data collected from every group falls into the reasonable range. (Table 2)

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Table 1: Results from Groups

Table 2: Statistics of Data

σ= √∑ (𝑥𝑖−𝜇)2𝑁

1

𝑁 where μ=

∑ 𝑥𝑖𝑁1

𝑁

CV=σ/μ

Max. Dry density:

σ= {[(1.92-1.9005)2+ (1.84-1.9005)2+ (1.86-1.9005)2+(2.083-1.9005)2+2*(1.85-1.9005)2]1

6}0.5

σ=0.093902

CV=σ/μ=0.093902/1.9005=0.049409

OMC:

σ={[(0.1385-0.1431)2+(0.16-0.1431)2+(0.136-0.1431)2+(0.125-0.1431)2+(0.15-0.1431)2+(0.149-

0.1431)2]1

6}0.5

σ=0.012387

CV=σ/μ=0.012387/0.1431=0.086573

group1 group2 group3 group4 group5 group6

Max Dry densisty g/cm^3 1.92 1.84 1.86 2.083 1.85 1.85

Optimum Mositure content 13.85% 16% 13.60% 12.50% 15% 14.90%

Mean Median sd cv

Max Dry densisty g/cm^3 1.9005 1.855 0.093902 0.049409

Optimum Mositure content 14.31% 14.38% 0.012387 0.086573

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Figure 2: Dry Density vs. Moisture Content w/ Zero-air-voids curve

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CONCLUSIONS AND RECOMMENDATIONS

In conclusion, the average optimum moisture content for all groups in the class was approximately

14%. Group 3 calculated an optimum moisture content of 13.6% which falls into an acceptable

range compared to the average. The optimum moisture content is important because it corresponds

to the maximum compaction or soil density. The average maximum dry density of soil for all

groups in the class was about 1.9 grams per cubic centimeter. Group 3 calculated a maximum dry

density of 1.86 grams per cubic centimeter. This value also falls into an acceptable range compared

to the average. Group 3 recommends implementing a standard height of the hammer above the soil

to maximize consistency among the groups. Group 3 also recommends a standard height of each

lift for the soil to maximize consistent compaction. In order for the experiment to take less time,

group 3 recommends spraying Pam cooking spray on the soil compaction mold for easy removal

of the soil between runs of the test.

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REFERENCES

Davis, Tim (2008). Geotechnical Testing, Observation, and Documentation. 2nd edition. Reston,

Virginia: American Society of Civil Engineers, 25-26.

Palomino, A., N. Plaks, N. Ostadi, BT Adams, and C. Cartwright. "Exercise 8: Soil Compaction."

Civil Engineering Materials Laboratory Course Manual. By S. Iyer. 5th ed. N.p.:

Pennsylvania State University, n.d. 81-85. Print.