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
ABSTRACT ii 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.
TABLE OF CONTENTS iii 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
LIST OF TABLES iv Page Table 1: Results from Groups 6 Table 2: Statistics of Data...6
LIST OF FIGURES v 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
INTRODUCTION 1 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.
THEORETICAL BACKGROUND 2 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 Where: γ w = unit weight of water G s = specific gravity = 2.65 w(%) = water content γ d(max theory) = γ w ( w(%) 100 + 1 G s ) Where: W w = weight of water W w = weight of soil w(%) = moisture content = W w W s
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 γ d = 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)
METHODS AND MATERIALS 4 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: γ d = γ 1 + w(%) 100
RESULTS AND DISCUSSION 5 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)
Table 1: Results from Groups 6 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% Table 2: Statistics of Data 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 σ= N 1 (x i μ) 2 N CV=σ/μ Max. Dry density: where μ= N 1 x i N 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
Figure 2: Dry Density vs. Moisture Content w/ Zero-air-voids curve 7
CONCLUSIONS AND RECOMMENDATIONS 8 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.
REFERENCES 9 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.