2 Specific Gravity Test

Introduction

The specific gravity (Gs)of a material is the ratio of the mass of a unit volume of soil solids at a specific temperature to the mass of an equal volume of gas-free distilled water at the same temperature. The specific gravity of soil is usually reported at 20°C.

$G_s(\text{at T} ^o C)= \frac{\text{Wt. of a given volume of the material at T }^o C}{\text{Wt. of the same volume of water at T}^o  C}$

Practical Application

  • The specific gravity of soil solid is used in calculating the phase relationships of soils, such as the void ratio and the degree of saturation.
  • The specific gravity of soil solids is used to calculate the density of the soil solids.

Objective

The objective of this experiment is:

  • To determine the specific gravity of soil solid at 20°C using a pycnometer.

Equipment

  • Volumetric flask (500 ml) with a stopper that has a pipe hole.
  • Thermometer graduated with a division of 0.1°C.
  • Balance sensitive to 0.01 g.
  • Distilled water.
  • Entrapped air removal apparatus
    • Hot plate or Bunsen burner that is capable of maintaining a temperature high enough to boil water
    • Vacuum system, vacuum pump, or water aspirator
  • Evaporating dishes
  • Spatula
  • Drying oven

Method

  1. Clean and dry the volumetric flask.
  2. Carefully fill the flask with de-aired, distilled water up to the 500 ml mark (The bottom of the meniscus should be at the 500 ml mark).
    One person on the left side is holding a plastic spray bottle in his hand. Another person standing on right side is holding a glass flask. The person on the left side is pouring water into the flask using the spray bottle.
    Figure 2.1: Fill the flask with distilled water
  3. Measure the mass of the flask and the water W1.
    A round bottom glass flask in placed upon a weight scale to measure the weight. The glass flask is filled with water.
    Figure 2.2: Measuring the weight of pycnometer filled with water
  4. Insert the thermometer into the flask with the water to determine the water’s temperature (T= T1°C.)
    A person is standing on the left side of the image. He is holding a black colored thermometer. The stick of the thermometer is placed into a glass flask to measure the temperature of water. Thermometer shows 25 degrees Celsius.
    Figure 2.3: Temperature of the water during the test
  5. Put approximately 100 grams of air-dried soil into an evaporating dish.
    A ceramic bowl is placed over a weighing scale to measure the weight of soil. The scale is showing a value of 100.0 gram.
    Figure 2.4: Weighing the soil samples
  6. For cohesive soil, add de-aired and distilled water to the soil and mix it until it forms a smooth paste. Soak it for one-half to one hour in the evaporating dish. (This step is not necessary for granular, i.e., non-cohesive soils.)
  7. Transfer the soil (if granular) or the soil paste (if cohesive) into the volumetric flask.
    A funnel is placed into a glass flask filled with water. A person is pouring loose soil into the flask through the funnel.
    Figure 2.5: Placing the sample in a pycnometer
  8. Add distilled water to the volumetric flask containing the soil or soil paste until it is about two-thirds full.
    A person holding a plastic squeeze bottle. He is filling a glass flask with water. The flask has some soil at the bottom.
    Figure 2.6: Filling the rest of the pycnometer with water
  9. Remove the air from the soil-water mixture by applying a vacuum pump or an aspirator until all of the entrapped air has been removed. Notice that this is an extremely important step, as most errors in the results of the test are due to entrapped air that has not been removed.
  10. Add de-aired, distilled water to the volumetric flask until the bottom of the meniscus touches the 500 ml mark. Dry the outside of the flask and the inside of the neck above the meniscus.
  11. Determine the combined mass of the bottle plus soil plus water (W2).
    A glass flask filled with soil and water is placed over a weighing scale.
    Figure 2.6: Taking the final weight of pycnometer filled with water and soil sample (after theapplication of vacuum)
  12. Pour the soil and water into an evaporating dish. Use a plastic squeeze bottle to wash the inside of the flask, making sure that no soil is left inside.
  13. Put the evaporating dish into an oven to dry it to a constant weight.
  14. Determine the mass of the dry soil in the evaporating dish (Ws).

Video Materials

Lecture Video

A PowerPoint presentation is created to understand the background and method of this experiment.

Demonstration Video

A short video is executed to demonstrate the experiment procedure and sample calculation.

Results and Discussions

Sample Data Sheet

\begin{tabular}{|c|c|c|c|} \hline Sample No. & 1 & 2 & 3 \\ \hline Mass of flask + water filled to mark,$W_1$ (g) & 683 & 659.7 & 675 \\ \hline Mass of flask + soil + water filled to mark,$W_2$ (g) & 745.1 & 722 & 737 \\ \hline Mass of dry soil, $W_s$ (g) & 100 & 100 & 100 \\ \hline Water temperature, $T_1 (^o$C) & 23 & 24 & 23.5 \\ \hline Temperature correction factor, A (from table) & & & \\ \hline Specific gravity, $G_s$ & & & \\ \hline \end{tabular}

Sample Calculation

For Sample no. 1,

Mass of flask + water filled to mark, W1(g)=683 gm
Mass of flask + soil + water filled to mark, W2(g)= 745.1 gm
Mass of dry soil, Ws(g)=100 gm
Water Temperature, T1(°C)= 23°C
Temperature Correction Factor, A (from Table)=0.9993
Specific Gravity, $G_s=\frac{W_s}{W_1+W_s-W_2}\times A=2.64$

Blank Date Sheet

\begin{tabular}{|c|c|c|c|} \hline Sample No. & 1 & 2 & 3 \\ \hline Mass of flask + water filled to mark,$W_1$ (g) & \hspace{1cm} & \hspace{1cm} & \hspace{1cm} \\ \hline Mass of flask + soil + water filled to mark,$W_2$ (g) & & & \\ \hline Mass of dry soil, $W_s$ (g) & & & \\ \hline Water Temperature, $T_1 (^o$C) & & & \\ \hline Temperature Correction Factor, A (from Table) & & & \\ \hline Specific Gravity, $G_s$ & & & \\ \hline \end{tabular}

Report

Use the template provided to prepare your lab report for this experiment. Your report should include the following:

  • Objective of the test
  • Applications of the test
  • Apparatus used
  • Test procedures (optional)
  • Analysis of test results – Complete the table provided and show one sample calculation
  • Summary and conclusions – Comment on the specific gravity of the given soil sample
  • Average specific gravity at 20°C should be reported to the nearest 0.01.

License

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Properties and Behavior of Soil - Online Lab Manual by MD Sahadat Hossain, Ph.D., P.E.; Md Azijul Islam; Faria Fahim Badhon; and Tanvir Imtiaz is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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