Hands-on Activity Engineering a Solution to Study Soil Mechanics

Learning Objectives

After this activity, students should be able to:

• Explain why soil is important to development.
• Understand how soil characteristics are affected by plant roots.
• Develop lab notes including drawings and quantitative data.
• Draw conclusions based on observations and data collected.

Educational Standards

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.

NGSS: Next Generation Science Standards - Science

International Technology and Engineering Educators Association - Technology

State Standards

Materials List

Each student needs:

• safety eyeglasses
• protective gloves
• Lab Notes Graphic Organizer
• Presentation Rubric

Each group needs:

• a plant in a transparent container
• note: it should be far enough into the growth phase that roots can be clearly observed
• container with only soil
• mist spray bottles with measurements on the bottle
• clear ruler (in cm)

To share with the entire class:

• weights to act as a force on top of the tested soil
• metric weight set (two sets recommended; available at Learning Resources or other online sources)
• PocketLab with pressure sensor (PocketLab and pressure sensor available online; activity can be modified to use a different tactile pressure sensor)
• fertilizer (for one group)
• herbicide (for one group)

Worksheets and Attachments

Pre-Req Knowledge

Students should have an understanding of the parts of a plant before beginning this activity.

Introduction/Motivation

(Before the introduction: Make sure the plants that will be used for your experiment have grown enough to have developed root structures.)

As we’ve been learning about ecosystems, we study the importance of each link in the food chain and each chain in the web. We also discuss the effect of changes in the environment and ecosystem on all living things that exist within it. Humans are a part of that system and there are many people who study ways for us to grow and develop in each ecosystem.

• What are some jobs that people have that help people understand the environment in which we live?
• Did you know that there are engineers that also help people learn how to best build structures that will safely fit within our environments? There are agricultural engineers, environmental engineers, and civil engineers.
• What do you think are some challenges that these environmental professionals face in their jobs?

How many of you have either tried to build with blocks in a room with thick carpet or built a sandcastle too close to the water? What happened to your structures?

This is a problem that engineers called civil engineers, specifically geotechnical engineers, face in their daily job as they study the ground on which structures, such as buildings, bridges, tunnels, roads and more, will be built.

For the next couple of weeks, we are a team of geotechnical engineers hired to investigate ways to affect a soil’s strength so that it is stiffer and can withstand an increased amount of weight compared a control soil sample.

[Close by showing students the plants they will be working with and have them hypothesize how they will be able to work with the soil samples and change mechanical properties of the soil. Have them write down some of their ideas in their lab notebooks.]

Procedure

Background
Understanding soil science is vital in many industries and careers. Beyond agriculture, soil science is important for ecologists, etymologists, biologists, botanists, environmental protection agencies who study and manage soil erosion, city planners, landscapers, civil and mechanical engineers, etc. There are many facets to soil science ranging from studying the various types of soil and how they were formed, the chemical and biological make-up of soils, soil fertility, the physical properties of soil, and more. Each of these areas of soil science plays a role in understanding how land is utilized, managed, and protected.

In this activity, we are studying soil mechanics, specifically soil stiffness and bearing capacity. The difference between stiffness and hardness. Stiffness is a material’s ability to return to its original form after a force is applied to it. Hardness is the ability for a material to resist deformation. Since we are working with a soft material, we are investigating its stiffness, rather than its hardness. Studies have shown that managing water levels and utilizing the right type of plants can help improve soil stiffness increase its ability to support weight and counter act the effects of soil erosion.

We will apply a force to soil and use a PocketLab to measure how changing characteristics of the soil changes the soil stiffness. We will measure this by utilizing the PocketLab tactile pressure sensor and a set of weights. The pressure sensor will be placed on top of the soil and the weights will be placed on top of the sensor. The PocketLab will measure the amount of force the weights are able to exert on the pressure sensor, which is being supported by the soil. The weaker the soil, the lower amount of pressure the weights will be able to exert on the sensor.

 
Procedure

Before the Activity Part 1 – Initial data collection and first treatment:

• Set up plant and soil pots at each group/table.
• For this activity, student groups each have one potted tomato plant and one soil only pot.
• Student groups will be:
• Control group – no chemicals, regular amount of watering
• Regular amount of water with herbicides
• Regular amount of water with fertilizer
• No water group
• Overwater group (water twice as much as the control amount)
• Have stackable weights, PocketLab, and pressure sensor accessible for data collection.
• Distribute safety googles and gloves as necessary.

With the Students

1. Describe what each student group will be responsible for testing.

• Group A will be the control group.
• Explain to students what a control group is – The control group is a group in an experiment that does not receive any testing or treatments. (The control group can be managed by the teacher.)
• Test group B will give their soil twice as much water as the other groups.
• Test group C will provide same amount of water as the control group and will also spray herbicides on the soil.
• Test group D will provide the same amount of water as the control, and it will contain fertilizer.
• Test group E will not provide any water for their soil.

2. Discuss with students how they will complete their initial lab report. Explain to students the importance of taking detailed lab notes that anyone can look at and follow. It is also important that they are clear so that they understand what information they were trying to record when they go to look back at it too.

• Students will complete boxes a-d in graphic organizer for each plant.
• Then, they will use the stackable weights to measure the original stiffness of the soil (See Figure 1).
• Place the pressure sensor on top of the soil. Make sure that the cord is placed in a way that doesn’t interfere with the sensor’s freedom of movement.
• Begin recoding on the PocketLab app and video record as well, if possible.
• Place the first 1000 g weight on the pressure sensor. Wait for the reading to stabilize and have students record the result in box E of the lab notes.
• Add a second 1000 g weight to the stack, repeat measurement process and have students record the result in box e of the lab notes.
• Stacking weights one by one as opposed to placing them all down at once simulates constructing layers/floors of a building and provides clear data points from the pressure sensor.
• Add a third 1000 g weight to the stack, repeat measurement process, and have students record the result in box e of the lab notes.
• Students can then use the clear ruler to measure the depth of the indentation made in the soil by the weights, if any, and can also record that in box e (as shown in Figure 2 below).
• Students should also write a short description of what they just did in box F.
• Once students have taken their initial readings, they should administer the prescribed soil treatment and then document that in box f as well.

3. Once students are done with their data collection and treatments, they should return their plants to a sunny location.

Before the Activity Part 2 – Continued treatments and data collection

• Make sure that spray bottles, safety goggles, and gloves are accessible.
• Sensors should be available when data collection is conducted.

With the Students

1. Daily prescribed treatments are given as applies to each plant – make sure that the control and groups C and D are not over watered, that amount of water is the same and that group A gets twice as much water.
2. At the end of each week, students will repeat the measurement process using the pressure sensor.

• Students will complete steps #2 through #3 from Activity Part 1 for as long as necessary in order to determine a conclusion about treatment results – recommended data measurements taken once a week for 4 weeks.
• Students can also take pictures of experiment progress to use in their final presentations.

Before the Activity Part 3 – Data Analysis and presentation of information

• Students should have all their digital data/records and lab notebooks.

With the Students

1. Have students work in their groups to combine analyze their data and determine the meaning of their results. Students can input their pressure sensor data and measurements into an excel spreadsheet and create a bar graph with the data.  (See sample graph in Figure 3).

   

2. Ask guiding questions such as:

• What happened to the soil as you conducted your experiment? 
• Did the way it looked or feel change?
• Did its weight-bearing capacity change over time? If yes, how?
• Could it hold more weight or less weight?
• At what weight limits did the ‘building’ begin to sink?  How deep did it sink each time?
• What happened to your plant during the experiment?
• Do you think the changes in the plant effected the changes in the soil?  If so, how do you know?  (If the change in the plant affected the soil, then there should be a difference in the results between the soil with a plant and the soil without the plant.)
• Do you think your treatment helped or hurt your soil stiffness?
• How do you think your treatment may affect development? How do you think your treatment might affect the environment?
• Were there any problems, accidents, or mistakes that happened while you were collecting data that might have affected your results? If so, what happened and why do you think it happened?

3. Students will compile their results in a digital presentation medium of their choice, such as PowerPoint.
4. Findings can be presented to class and/or other classes as well.

Vocabulary/Definitions

civil engineer: Someone who designs and constructs anything that has to do with development and structure such as buildings, roads, bridges, tunnels, airports, and more.

control: The group in an experiment that does not receive any testing or treatments and is used as a measure to compare to the other groups that receive treatment or testing.

geotechnical engineer: A specific type of civil engineer that examines how the Earth beneath a structure will affect how it is built and how the Earth can be utilized in building structures.

soil: The top layer of the Earth’s surface that is made up of a variety of organic matter, rocks and minerals, water, and air.

stiffness: The ability of a material to return to its original form after a force is applied to it.

to bear weight: The ability of something to hold up a certain amount of weight.

Assessment

Pre-Activity Assessment

Pre-Quiz: Have students conduct the Pre/Post-Quiz.

Activity Embedded Assessment

Graphic organizer: See Lab Notebook Graphic Organizer (Use to monitor student observations and check for understanding)

Post-Activity Assessment

Rubric: See the Presentation Rubric.

Post-Quiz: Have students re-take the Pre/Post-Quiz.

Safety Issues

• All students should wear protective eyewear when watering plants. Students using fertilizer and/or herbicides should also wear protective gloves.

Troubleshooting Tips

• Depending on the time of year this experiment needs to be conducted, the teacher may need to plant the seeds ahead of time, so the plants are fully grown by the time the experiment is to be conducted. Tomato plants don’t have to be used for this experiment. However, the plant chosen should have an extensive root system.

Activity Extensions

• Add an erosion element to the project by using a box/container that can allow the soil slide away or erode over time. One container can have only soil and the other can have soil with plants.
• Have students construct buildings on the tested soil.
• Conduct similar experiment with different types of plants and/or soil.

Additional Multimedia Support

“Loose Soil.” Discovery Education, Discovery Channel, 2003, app.discoveryeducation.com/learn/videos/1ea89801-8c15-4d04-a187-cd7641201d86.

References

Copyright

Contributors

Supporting Program

Acknowledgements

This curriculum was developed under the National Science Foundation EEC grant no. 1711543. However, these contents do not necessarily represent the policies of the NSF, and you should not assume endorsements by the federal government.