Students measure the permeability of different types of soils, compare results and realize the importance of size, voids and density in permeability response.
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- Measure the values of permeability in soils, k, through a basic laboratory model.
- Describe water flow in soils.
- Outline the applications of water flow models in practice engineering.
- Identify variables affecting permeability, such as particle size, porosity and compaction.
- permeameter device (can build your own using transparent containers, see Figure 1)
- 3 soil samples with varying permeability (such as gravel, sand, silt, and clay)
- LEGO MINDSTORMS NXT Brick available for $299.95 at http://shop.lego.com/en-US/NXT-Intelligent-Brick-9841?CMP=AFC-BP6648365778&HQS=9841
- LEGO Ultrasonic Sensor available for $29.95 at https://shop.education.lego.com/legoed/education/EV3/EV3+Ultrasonic+Sensor/45504&isSimpleSearch=false
- paper and markers
- 3 two-liter soda bottles
- graduated jar
- small piece of stockings
- rubber band
- projector for the Soil Permeability Presentation
|permeability or coefficient of permeability:||A measure of the soil's ability to allow water to flow through its pore spaces.|
|groundwater:||Water located below the land surface that occupies the voids of the soil.|
|mechatronic components:||Combined tools that comprise mechanics, electronics and robotics fields in order to design and manufacture useful products.|
|soil:||Natural body consisting of three phases: mineral-water-air. Soil is derived from rocks that have been altered by various chemical mechanical and environmental processes. Different soils include gravel, sand, silt, and clay.|
|soil voids/pores:||The spaces between soil particles, which may be filled with liquids (especially water), or gases (especially air).|
|saturation:||When all voids of a particular soil are full of water.|
|permeameter:||A device used to calculate the coefficient of permeability.|
|earth dam:||Massive manmade water barrier used to store water for supply and/or power purposes.|
|landslide:||Natural disaster which consists of a wide range of ground movement.|
|aquifer:||Underground water storage which lies between two low-permeability layers.|
|ultrasonic sensor:||A sensor used to detect proximity of objects by using dual (transmitter-receiver) ultrasonic signal.|
|sensor:||A device that detects or senses a signal, which is a form of energy.|
|ultrasonic signal:||A signal that measures a sound wave by timing how long it takes for the sound to bounce off objects.|
Before the Activity
- Construct at least one permeameter device. The more soil permeability devices you create for the classroom, the more tests can be conducted simultaneously. See Figure 1 for the set-up. Make a basic permeameter device using transparent plastic or acrylic comprised of two main parts: the upper part where the water is poured; and the lower part where the soil sample to be tested is placed. Attach a flexible tube and a valve to the lower end of the device. Your permeameter device does not have to be identical to the one shown in the activity photographs. However, losses of water must be avoided, and flow continuity from top to bottom of the chamber should be guaranteed.
- Make copies of the Soil Permeability Pre-Evaluation, Soil Permeability Datasheet and Soil Permeability Post-Evaluation, one each per student.
With the Students
- Write the following terms on the classroom board and ask students to think about what they mean: soil, groundwater, voids and saturation.
- Explain how the permeameter device works, and use it with a natural soil sample (collected from outside). Demonstrate how water flows through the permeameter.
- Ask students how fast they think water will flow through three different soil types such as gravel, clay and sand.
- Divide the class into groups of five students each.
- Have students collect three samples of different soils (such as clay, sand and gravel).
- Help student groups each make three funnels by cutting three two-litter soda bottles to pour the soil sample inside (see Figure 3). Do not allow students to do this step. The three soda bottles will be used to test the permeability of the three different soil samples.
- Pour enough soil material to cover about ¾ of the bottle funnel. Have students pack down the soil with their hands, but have them try not to overly compact the specimen.
- Prevent losing materials by using a piece of stocking and a rubber band to cover the bottle mouth.
- Use a graduated jar to collect the exiting water. Use a watch or clock to measure the time it takes to fill the collection jar.
- Instruct students to use their Soil Permeability Datasheets as they gather and record their results. Students and teachers should look for the time it takes the water level on the jar to change between two known marks.
- Fill the lower permeameter chamber with soil. If only one chamber is being used, test one soil sample at a time.
- Fill the upper chamber with water. Next, open the valve, and allow water to flow through the soil. Wait until all air bubbles disappear, indicating that the soil sample is fully saturated.
- Close the valve and point out the initial and final water level marks on the chambers to students. Explain that the students will be looking for the time it takes for the water level to change between the two water level marks on the permeameter chamber.
- Once the test is ready to run, open the valve again and simultaneously starting timing.
- Close the valve again and stop timing when the lower water mark is reached. Have students record the results on their datasheets.
- Help students to estimate the water flow by dividing the distance of water level change by the time. Explain to students that this calculated value is proportional to the soil permeability.
- Repeat steps 13 through 16 while an ultrasonic sensor is connected to both the NXT brick and the upper cap of the water cell, as shown in Figure 2. Use the LEGO MINDSTORMS code shown in Figure 4 to read the water levels and time this process. This code allows both the ultrasonic sensor and the timer to read values in real time. In other words, during the permeability tests, the NXT screen will show the water distance and time measurements simultaneously. Once the test is ready to run, open the valve and simultaneously press the orange button of the NXT-LEGO brick to start measuring. Stop NTX bricks when the water level reaches the lower mark, and it will automatically report the distance between both water levels, as well as the time it took the water to reach lower level. Again, the more permeameters the classroom has, the more tests can be conducted at the same time. If only one device is available, conduct the tests while students observe, record data and respond to targeted questions.
- Conduct this test for all the soil samples tested in Part 2 of this activity.
Activity Embedded Assessment
- What is permeability? (Answer: The measurement of water's ability to flow through soil.)
- Why is permeability important in construction and engineering? (Answer: When a civil engineer is focused on earth structures design, water behavior becomes important. The presence of water, in most cases, provides additional forces that can destabilize a building site. Engineers often need to identify the presence of ground water, calculate the water pressure that it provides to the element under construction, and accurately predict the water flow around their construction plan. In that sense, measuring water flow can help to design more durable and cost-efficient structures.)
- What is the ground water table? (Answer: Water located below the land surface that occupies the voids of the soil.)
- Where does rainfall water go after it lands on a soil surface? (Answer: Part of it slides down through the land surface, and depending on the permeability of the soil media, the remaining part infiltrates down into the soil mass.)
- Why does groundwater travel slower than a river? (Answer: Because groundwater travels through less void space than an open channel, such as a river.)
- List at least three cases where permeability is used in civil engineering. (Answer: 1. Building a dam. The main goal of a dam is to retain water behind it, so engineers choose low permeability areas for dams. 2. Deep excavations. The lack of knowledge about groundwater position and permeability may cause severe damage to an open excavation, and even worse to personnel inside the trench. 3. The design of filters for drainage. The best way to control groundwater inside land slopes and excavations is to organize and correctly drain the water out of these elements)
- Why do you think data collected from a test is more accurate if sensors and mechatronics tools are used? (Answer: Because mechatronics tools minimize errors that human beings make while reading results.)
- What elements influence the value of permeability? (Answer: Soil particles, voids between grains, and type of fluid.)
Eduardo Suescun, Ryan Cain, Russ Holstein, Magued Iskander
© 2012 by Regents of the University of Colorado; original © 2012 Polytechnic Institute of New York University
AMPS GK-12 Program, Polytechnic Institute of New York University
Last modified: February 27, 2015