I Am A Geotechnical Engineer!
Lesson 10 of 15
Objective: Students become aware of the engineering process through inquiry, data collection and core samples of soil
I open up the lesson today with Layers of the Earth Slide Show. This introduces students to the concepts of the layers of the Earth so they can understand the role of the lithosphere and its relationship to the whole Earth.
I explain before I begin the slide show that the layers are like a hard boiled egg. The core is a lot like the yolk and that the mantles are the white. I bring up the second page of the slide show as we talk about the Earth from the center out. I explain about the pressure that the liquid layers put on the solid layers and that the lithosphere sort of "floats" on top of the asthenosphere.
I then open up the last slide as I use explicit instruction, pronouncing and explaining each vocabulary word as I point to the layers of the lithosphere. I explain that bedrock is solid and located deep down, explaining that "core samples" help us understand the layers of the Earth's lithosphere. Core samples reveal much about what minerals are present, what types of soil as well as the best places to locate a building or structure. I ask them to sketch the last slide in the right side of their science notebooks and have them list the vocabulary words and note any questions they have about the lithosphere at this point.
One student shares that they wonder if the bedrock is the same all over the Earth. Great question! I explain that it is not, but that it is basically made up of igneous rock, such as basalt. I use the website, Facts About Bedrock, scanning as students bookmark it on their iPads for silent read time. This resource helps them compile more non fiction science reading that will connect more understanding to weathering.
As I close up this portion of the lesson, I ask them how determining what layers are under our feet helps us understand what can be build in that spot? They respond with ideas about how bridges need the right spot so that it holds up. One student mentions the TarPul from the literature in one of our recent lessons. That lesson laid a foundation for understanding what geotechnical engineering was about and they were ready to move onto the investigation.
I ask them if they would like to be geotechnical engineers today?
Taking Core Samples
Materials and Set Up the Day Before:
- 2 plastic containers that measure about 8"x5"x4", labeled A & B.
- One package of wet type oasis that is used for fresh flowers.
- A cup and a half of sand and topsoil that layers up about an inch,
- 2 red cans of play dough, 2 green cans. (Mixed, they produce brownish colored clay.) Or about 4 cups of flour/salt homemade play dough mixed with red and green food coloring to make it look like brownish clay. (Homemade clay is basically 1 c. salt, 1 c. flour & 1c water + more to make a play dough consistency. Keep kneading it until it is like clay. I added several drops of red and green food coloring and kept mixing until it was brown. You can adjust the color so that it is different than the topsoil color.)
- 3/4" plastic tubes that are cut 8" long. You need two for each partner or group of 3.
- Paper plates and paper towels.
Container A: Soak the oasis and then slice it to 1" thick and place on the bottom, filling up all the gaps. You can push it around so it fills in. Then place the clay on top of that and layer it to be 3/4 to 1 inch. Then, pour sand on top, followed by a layer of topsoil. Both should be a couple inches deep.
Container B: Omit the oasis and layer with clay, sand and soil. Each container will take about 6-8 samples.
Students partner up by choice. I pass out the Core Sampling Worksheet so that my students know exactly what to do and we read the directions together. I instruct the class on how to take a core sample. Students get busy taking turns taking samples. Those who waited for the core (rather than doing the sampling) take one sample back and begin sketching and measuring. As they fill out their sheets, I rove the classroom and ask them what the difference is between the two samples. They can easily see that the Sample A contains the bedrock and the sketches are accurate. They measure each layer to the nearest cm. It is hard to find the layers on some samples.
When their work is done, they dump the contents on the paper plate to observe it with a hand lens. I had set up a microscope for them to view a sample of soil under the microscope, for another perspective. We discuss if soil is alive or dead. The discussion turns into a small debate. Most students think soil is dead. Another argues that soil sprouts seeds, so it must be alive.
They begin to answer the questions on the back of the sheet. I rove around asking students which core sample will prove to be a better site for a building structure? They agree that they thought the one with the bedrock was more stable.
As we clean up, we reflect on how this model core sample helped us see what taking a core sample from a real site would be like.