SummaryStudents determine the mass and volume of soil samples and calculate the density of the soils. They use this information to determine the suitability of the soil to support a building foundation.
Geotechnical engineers use measurements such as soil density to determine the constituents of soil. One major soil constituent is sand. Sand with a small of amount of silt has been found to offer the best foundation support for a house, building or road.
Ability to define and calculate density.
After this activity, students should be able to:
- Explain the soil density of sand, silt and clay.
- Develop proficiency in measuring volume and mass using a triple-beam balance and graduated cylinder.
- Calculate density.
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Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.
All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).
In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.
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Each group needs:
- 150 mL isopropyl alcohol
- 2 plastic pipettes
- dishwashing liquid in a dropper bottle
- 100 mL graduated cylinder
- 3 plastic sandwich bags, each containing at least 5.5 g. of three different soil samples (gather from different locations so you have a range of sandy, silty and clay-type samples; if necessary, purchase soil at a plant nursery or home improvement center)
- weigh paper (or small paper cups; see Troubleshooting Tips section)
- triple-beam balance
- plastic spoon
- paper towels
- lab apron
- Lab Worksheet
We learned from our lesson that clays in soils cause the soils to swell with increasing moisture content and shrink with decreasing moisture content. Remember that this shrink/swell potential results in damage to the foundation of homes and roads. We talked about one test that geotechnical engineers use to determine the constituents of soil, called bulk density.
Today you are going to act as the geotechnical engineers on a project! You will measure the bulk density of three soil samples to determine if they offer sufficient foundational support for an office building. As you are going through this activity, keep in mind that sandy soil has the greatest bulk density of all soil components, and that sandy soil with a small quantity of silt provides the greatest structural support for foundations.
density: Mass per unit volume of a substance.
geotechnical engineer: A branch of civil engineering concerned with the engineering behavior of earth materials; geotechnical engineering includes investigating existing subsurface conditions and materials; determining the physical/mechanical and chemical properties that are relevant to the project considered, assessing risks posed by site conditions; designing earthworks and structure foundations and monitoring site conditions, earthwork and foundation construction.
mass: The amount of matter in an object.
volume: The amount of space occupied by a three-dimensional object or region of space, expressed in cubic units.
Before the Activity
- Gather soil samples from three separate locations. Be sure to gather enough soil so groups each have 5.5 g of each sample for the lab experiment. If time allows, collect the samples as a class so that students can experience some geotechnical engineering fieldwork! Simply pick three different areas around the school grounds that you think might have varying soil contents.
- Gather the rest of the materials, and make copies of the Lab Worksheet.
With the Students: Pre and Post Lab
- Have students complete the four math problems (provided in the Assessment section) to make sure they are fluent in density calculations.
- Show students Table 1 (also found on the lab worksheet) and explain that not every soil sample they test as geotechnical engineers will have the same density. Some soils are better for supporting foundations than others.
- Divide the class into groups of two to three students each. (If not using the lab worksheet, instruct students to prepare a blank data table in their lab notebooks, like that shown in Figure 1.) Have student teams conduct the lab by going through the steps below (also provided on the lab worksheet).
- Conclude with a class discussion to review results and draw conclusions. Use the questions provided in the Assessment section.
With the Students: Lab Instructions
- Place a piece of weigh paper on the pan of the triple-beam balance.
- Set the balance to read 0.
- Place 5.0 g. of soil onto the weigh paper using a plastic spoon.
- Record in your data table the soil weight.
- Wash off the plastic spoon with water and dry it completely with a paper towel. Carefully pour 50 mL of isopropyl alcohol into a 100 mL graduated cylinder. Use a plastic pipette to remove or add isopropyl alcohol, as needed.
- Record in the data table the volume of the isopropyl alcohol added to the 100 mL cylinder.
- Fill the two plastic pipettes with isopropyl alcohol from the graduated cylinder.
- Add 1 drop of dishwashing detergent to the isopropyl alcohol in the graduated cylinder.
- Place the funnel in the top of the graduated cylinder.
- Transfer the soil on the weigh paper to the graduated cylinder.
- Use the liquid in the plastic pipettes to wash any soil sticking to the funnel or sides of the graduated cylinder into the liquid in the graduated cylinder.
- Gently tap the bottom of the graduated cylinder on the tabletop to remove any bubbles from the liquid and help settle the soil to the bottom of the graduated cylinder.
- Let the soil completely settle to the bottom of the graduated cylinder.
- Read the volume of the isopropyl alcohol and the soil and record it in the data table.
- Calculate the density of the soil sample and record it in the data table. Show your calculations.
- Repeat these steps for two other soil samples.
- Isopropyl alcohol is flammable and a hazard to skin and eyes, so make sure students use gloves and eye protection. Also do not use this chemical around open flames.
Make sure to have students clean and dry their graduated cylinders prior to the lab.
You may want to have students weigh the soil into small paper (Dixie) cups instead of on weigh paper to help prevent loss of soil during transfer to the graduated cylinders.
Density Calculations: Before starting the lab work, have students individually solve the following four problems, as a way to make sure they understand how to calculate density.
- Calculate the density of a cube with sides of 3 cm, 3 cm and 4 cm and a mass of 24 grams. (Answer: d = m/v = (24)/(3x3x4) = .67 g/cm3)
- Determine the mass of a soil with a density of 1.7 g/mL and a volume of 55 mL. (Answer: m = d x v = 1.7 x 55 = 93.5 g)
- Determine the volume of a soil sample that has a mass of 10 g. and a density of 1.3 g/mL. (Answer: v = m/d = 10/1.3 = 7.7 mL)
- The density of a soil sample is 1.5 g/mL. If this sample was halved how would the density of the sample change? (Answer: d = m/v Because mass and density are directly proportional, when the mass is cut in half, so is the density. Therefore, density is .75 g/mL.)
Concluding Discussion: As you are reviewing results, ask students the following questions and discuss as a class.
- What are the bulk densities of your soil samples?
- Based on the density calculations of the three soil samples, can you determine the major constituents of your soil samples? What are they? How do you know? (Look to see that students compare their data to the numbers provided in Table 1 to determine the major constituents of their soil samples.)
- Which of your soil samples would provide the best support for the foundation of an office building? Why? (Look to see that students are answering this question by remembering that sandy soil has the greatest bulk density of all soil components, and that sandy soil with a small quantity of silt provides the greatest structural support for foundations. Therefore, students should be recommending the site that had the soil with the greatest bulk density.)
Birkeland, P.W. Soils and Geomorphology. New York, NY: Oxford University Press, 1984. pp. 14-15.
Blake, G.R. and K.H. Hartge. 1986. Bulk Density, in A. Klute, ed. Methods of Soil Analysis, Part I. Physical and Mineralogical Methods: Agronomy Monograph No. 9. (second edition), pp. 363-375.
Branwyn, Gareth. Forensics Lab 5.2: Examine the Physical Characteristics of Soil. Posted August 16, 2009. Make Magazine. Accessed July 14, 2010. (Information on determining soil density and settling time) http://makezine.com/laboratory-52-examine-the-physical/
Holtz, R. and Kovacs, W. An Introduction to Geotechnical Engineering, Prentice-Hall, Inc., 1981. ISBN 0-13-484394-0
ContributorsSherry L. Wright; Marissa H. Forbes
Copyright© 2013 by Regents of the University of Colorado; original © 2010 University of Texas
Supporting ProgramResearch Experience for Teachers (RET) Program, University of Texas at Arlington
The contents of this digital library curriculum were created through the University of Texas at Arlington's College of Engineering NSF RET grant. However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.
Last modified: March 24, 2018