Lab Report #1: Specific Gravity of Soils and Moisture Content
This experiment aimed to determine the specific gravity of a soil sample using a pycnometer. The specific gravity is generally needed to perform additional testing of the soil. The soil sample was put in a pycnometer, which was then filled with water, taking care to eliminate air bubbles. The mass of the pycnometer when filled with water and soil, Mpws, was determined and then the temperature of the soil-and-water mixture was measured. The soiland-water mixture was poured onto a pan and then dried in an oven to determine the mass of solids, Ms. With the temperature of the soil-and-water mixture known, the mass of the pycnometer when filled with water, Mpw, was found from the calibration of the pycnometer. Using the acquired data, the specific gravity of soil was computed. The procedure was repeated for the second trial. The soil sample was found to have a specific gravity of 2.521.
Submitted by: Joanna M. Gamboa
Groupmates: Arsenio Esteves Jr. Romano Guerrero Juarez Robin James Enclona Christopher Erick Cruz Ellaine Mary Paglicauan
Date Performed: June 25, 2012 Date Submitted: July 6, 2012 1
I. Objectives This experiment was performed to determine the specific gravity of soil solids that pass the No. 4 sieve by means of a water pycnometer. Given that the specimen is moist, its moisture content is determined first.
II. Materials 1. Pycnometer (volumetric flask), with a capacity of 250 mL 2. Balance (with accuracy to 0.01 g) 3. Drying Oven 4. Thermometer 5. Hot Plate or Stove 6. No. 4 Sieve (4.75 mm) 7. Moisture Can 8. Funnel
III. Methodology
Since the soil sample was moist, a portion was placed in a moisture can and the weight, Wcws, was determined and recorded
The specimen was oven-dried and its weight, Wcs, was determined and recorded
The moisture content was calculated, ω=
Wcws - Wcs × 100% Wcs - Wc
Using the moisture content, the range of wet masses for specific gravity specimen was calculated, Wws = 45.96 ± 10.21
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The pycnometer was cleaned and dried and its weight, Wp, was determined and recorded
The pycnometer was filled with water up to calibration mark, and the weight of the pycnometer and water, Wpw, is determined and recorded
The calibration temperature, Ti, was determined and recorded to the nearest 0.01°C
The density of water at calibration temperature, ρw,i, was determined using Ti and Table 1
The calibrated volume of the pycnometer, Vp, was calculated, Vp =
Wpw,i - Wp ρw,i
The soil sample (45 g) was transferred into the empty pycnometer using the funnel
Water was added until the water level is 1/3 to 1/2 of the depth of the main body of the pycnometer. The water was agitated until a slurry is formed
Heat the pycnometer on the stove and let it boil for 15 minutes. The slurry is agitated regularly to prevent any soil from sticking or drying onto the glass
The mixture was cooled until its temperature reached Ti
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Water was added up to the calibration mark and the weight of the pycnometer, water and soil, Wpws, was determined and recorded
The test temperature, Tx, was determined and recorded to the nearest 0.01°C
The weight of the pycnometer and water at the test temperature, Wpw,x, was calculated, Wpw,x = Mp - Vp ∙ ρw,x
The weight of a pan, Wd, was determined and recorded. The entire slurry was transferred into the pan and was oven-dried for at least 16 hrs
The specimen was cooled and the weight of the pan and soil, Wds, was determined and recorded
The weight of the dry soil, Ws, was calculated, Ws = Wds - Wd
The correction factor, K, was determined using Tx and Table 1
The specific gravity of the soil at 20°C, G20, is calculated, G20 =
KWs Wpw,x - Wpws - Ws
Figure 1. Flow Chart of Experimental Procedure 4
Table 1. Density of Water and Temperature Coefficient (K) for Various Temperatures Temperature (°C) 27.0 .1 .2 .3 .4 .5 .6 .7 .8 .9 29.0 .1 .2 .3 .4 .5 .6 .7 .8 .9
Density (g/mL)
Temperature Coefficient (K)
0.99652 0.99649 0.99646 0.99643 0.99410 0.99638 0.99635 0.99632 0.99629 0.99627 0.99595 0.99592 0.99589 0.99586 0.99583 0.99580 0.99577 0.99574 0.99571 0.99568
0.99831 0.99828 0.99825 0.99822 0.99820 0.99817 0.99814 0.99811 0.99808 0.99806 0.99774 0.99771 0.99768 0.99765 0.99762 0.99759 0.99756 0.99753 0.99750 0.99747
Temperature (°C) 28.0 .1 .2 .3 .4 .5 .6 .7 .8 .9 30.0 .1 .2 .3 .4 .5 .6 .7 .8 .9
IV. Data and Results Wcws = 50.94 g Wcs = 50.06 g Wc = 8.87 g
ω=
Wcws - Wcs 50.94 g - 50.06 g ×100% = ×100% Wcs - Wc 50.06 g - 8.87 g
ω = 2.136%
Wp = 82.67 g Wpw,i = 330.44 g Ti = 28.5 °C
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Density (g/mL)
Temperature Coefficient (K)
0.99624 0.99621 0.99618 0.99615 0.99612 0.99609 0.99607 0.99604 0.99601 0.99598 0.99565 0.99562 0.99559 0.99556 0.99553 0.99550 0.99547 0.99544 0.99541 0.99538
0.99803 0.99800 0.99797 0.99794 0.99791 0.99788 0.99785 0.99783 0.99780 0.99777 0.99744 0.99741 0.99738 0.99735 0.99732 0.99729 0.99726 0.99723 0.99720 0.99716
Vp =
Wpw,i - Wp 330.44 g - 82.67 g = g ρw,i 0.99609 mL
Vp = 248.743 mL
Table 2. Experimental data and results of Specific Weight Determination Trial No.:
1
2
Wpws (g)
357.37
356.66
Tx (°C)
28.5
28
330.440
330.477
Wd (g)
134.60
124.33
Wds (g)
178.89
167.97
Ws (g)
44.29
43.64
K
0.99788
0.99803
2.546
2.495
Mass of pycnometer + water at Tx,
Wpw,x = Wp + Vp ∙ρw,x
Specific gravity of soil, 𝐺20 =
𝐾𝑊𝑠 𝑊𝑝𝑤 ,𝑥 − 𝑊𝑝𝑤𝑠 − 𝑊𝑠
V. Analysis and Discussions The difference between the two values of specific gravity is 0.051, which is greater than the acceptable range, 0.03. This renders the test results unusable. This discrepancy is due to the loss of soil solids in the second trial while removing water that exceeded the calibration mark. Another factor that affected the precision of the results was the presence of air bubbles in the soil-and-water mixture. Despite letting the slurry boil for an appropriate amount of time, air bubbles in the slurry were not entirely removed. Additional air was also introduced while adding water up to the calibration mark. The presence of air bubbles decreased the value of Wpws, thus decreasing the value of the specific gravity. The average of the calculated values of specific gravity, 2.521, does not fall into any of the ranges listed in Table 3. The value, however, indicates that the soil sample is composed mainly of halloysite, an aluminosilicate clay mineral. 6
Table 3. Expected Values for Specific Gravity Type of Soil
Gs
Sand
2.65-2.67
Silty sand
2.67-2.70
Inorganic clay
2.70-2.80
Soils with mica or iron
2.75-3.00
Organic soils
Variable, but may be under 2.00
Also, given that the initial weight of the soil sample is 45 g and the moisture content is 2.14%, the expected value of Ws is 44.06 or lower, considering losses. However the actual value of Ws in the first trial is 44.29. This implies that either the specimen wasn’t oven-dried for the sufficient amount of time, or additional soil solids were introduced during the course of the experiment. Since the specimen was oven-dried for more than 16 hours, 19 hours exactly, the cause is the latter. Other factors that may have caused errors in the experiment include nonuniform temperature of the soil-and-water mixture and imprecise weights due to unclean equipment.
VI. Conclusions and Recommendations The calculated specific gravity of the soil sample is 2.521. A more efficient method of removing air bubbles should be developed, as the presence of air bubbles causes the greatest error. More care should be given in adding water to the soiland-water mixture, to prevent additional air to be entrapped. Also, more time should be allotted for letting the specimen reach thermal equilibrium.
VII. References 1.
ASTM D854-10. Standard Test Methods for Specific Gravity of Soil Solids by Water Pycnometer.
2.
Liu, Cheng and Jack B. Evett. Soil Properties: Testing, Measurement, and Evaluation. 5th Ed. New Jersey: Prentice-Hall, 2003.
3.
Braja M. Das. Principles of Geotechnical Engineering. 4th Ed. Boston: PWS, 1998.
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