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NEES Teaching Demonstration: Soil Liquefaction

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Abstract

Students will be able to observe soil liquefaction and its potential effects on adjacent structures and infrastructure. This demonstration will need to be made age-appropriate by the lesson that is built around it. Several suggestions are listed below.            

Introduction

The introduction to the lesson will develop the path your lesson takes. This demonstration could be used in lessons on several topics, including liquefaction, soil improvement techniques (i.e., dynamic compaction, vibro-compaction, vibro-replacement, vibratory probe, aggregate piers, soil mixing, jet grouting, and controlled fill), structural improvements (i.e., earthquake drains, deep pile foundations, and post-tensioned slab foundations) , liquefaction-induced landslides (and landslide-generated tsunami), soils and water tables, pore pressure, shear stress, soil bearing capacity, system equilibrium, earthquakes, effects of liquefaction on structures and infrastructure, and engineering career field.

Earthquake Engineering Component

Structural earthquake engineering is an iterative process that strives to improve structural response to earthquake-induced forces. Earthquakes can cause walls to crack, foundations to move or settle, utilities to rupture and even entire buildings to collapse. In an effort to protect the public and avoid structural damage engineers incorporate into their structural designs techniques that withstand these incredible forces. Some examples include cross bracing, tapered profiles, base isolation and tuned mass damping. In all cases engineers contrive an idea, test it, and then, based on its performance, re-engineer the structure until the desired outcome is achieved.

Learning Objectives and Standards

Links to the National Science Standards and to individual State Science Standards are available by using this link: http://nees.org/education/for-teachers/k12-teachers#standards Students may be able to (grade level dependent):

  • Identify the factors that make soils susceptible to liquefaction.(Knowledge)
  • Identify the factors that make structures in liquefied soil susceptible to damage.(Knowledge)
  • Explain why engineers need to understand earthquakes.(Comprehension)
  • Predict methods to improve and re-engineer the structure or soil profile to better resist damage.(Application)
  • Identify cause-effect relationships between earthquakes,liquefaction and structures.(Analysis)
  • Describe how you would apply what you have learned to a)new building & b) an old building.(Synthesis)
  • Summarize in a journal a record of observations and conclusions.(Evaluation)

Material List

  • Transparent container (like a clear plastic storage bin)
  • Sand (play sand works well, but any sandy soil can be made to work)
  • Water
  • Stone, brick, or paver (used to replicate a structure atop the soil)
  • Shake table or other surface enabling replication of earthquake shaking.
  • OPTIONAL: Empty pill bottle or other lightweight, buoyant item (used to replicate underground utilities or storage tanks in liquefied soil)
  • OPTIONAL: Accelerometer from Quake Catcher Network (QCN) linked to a computer and QCN software (see link to QCN below).

Procedure

Optionally, see instructions at nees.org/education on how to assemble a shake table for the following activity. Sliding the liquefaction bin on a smooth surface works well too. Construct and liquefy the soil:

  1. Place the sand or sandy soil in the transparent bin or tub.
  2. Saturate the soil replicating a high water table. Take care not to over saturate to the point that there is standing water on the surface of the soil prior to liquefaction. Mixing or stirring the soil during incremental water placement will help to control saturation. If the soil does become oversaturated, simply scoop some water out, or allow it to stand long enough for the water evaporate.

  1. OPTIONAL: insert the empty pill bottle (with cap in place) inside the saturated soil. When the soil is liquefied the bottle will float to the surface demonstrating that utility lines and underground tanks are susceptible to liquefaction-caused damage as well.
  2. Place the paver, brick, stone, or other token structure on the soil surface. It may add to the observation to show the students that you can press down on the structure and it does not sink. The soil is able to bear the surcharge.

(Red lines were drawn with marker to improve perception of the settlement.)

  1. Place the tub on the shake table, or other shaking surface available, and gently shake the tub back and forth. As the soil liquefies the structure will partially sink. (Additional shaking may be required to allow the optional pill bottle to emerge.)

(See Activity Extensions below for explanation on why the building on the left did not sink)

  1. OPTIONAL: There are several follow-on experiments that you can do with the students following their observation of the liquefaction. These are listed below under Activity Extensions.
  2. OPTIONAL: Attach the QCN accelerometer to the shake table for students to observe the accelerations being applied to the soil.

Links and Resources

Assessment

Pre Activity Assessment

  • Have students write their observations of the soil and its ability to hold the structure. It may be beneficial to allow each student to press down on the structure to feel the strength of the soil.
  • Have students make predictions based on their preliminary observations and write them in a notebook.

Activity Embedded Assessment

  • Have students observe the behavior of the soil as it liquefies and the differences with the observations they made prior to liquefaction; have students write their observations.
  • Invite students to comment on what they are observing, draw conclusions, and innovate with new ideas that might help to reduce the liquefaction. You may choose to test the innovative ideas to see how well they work, or don't work.

Post Activity Assessment

  • If any activity extensions (below) are demonstrated, have students make comparisons with the behavior of the soil before and after each technique used to mitigate liquefaction.
  • Invite students to comment on why these techniques are important. Have them record their reflections in a notebook.

Extensions

  • This activity could be extended by adding mitigation techniques used by engineers in follow-on demonstrations. Some techniques will not be feasible in a classroom setting. Some are feasible, however, such as soil mixing and deep pile foundations (see photo below).
  • Soil mixing could be accomplished by having available additional types of soil and gravel that the students can mix into the tub. Some sand should be removed by scooping and then gravel or clay-based soils can be added and mixed with the sand.
  • Deep pile foundationscan be demonstrated with some prior preparation as well. See the photo below showing how drilled slots, wood dowels, and Gorilla glue have produced a rudimentary mock-up of a pile foundation. The piles should be measured to be long enough to extend from the bottom of the brick or paver, while sitting on the soil surface, to the bottom of the tub. This way the dowels bear on top of the tub bottom. Take care while shaking to not become too vigorous or the structure may tip over when the soil liquefies (if the brick or paver is tall slender). This does not happen in real applications because the piles extend far beneath the liquefied zone and are often "socketed" into bedrock providing stability to the structure. However, in the tub essentially all of the soil is liquefied and the piles are not connected to the bottom.

  • Additionally, USGS, Center for Engineering Strong Motion Data (www.strongmotioncenter.org), EERI, NEHRP, and NEES are excellent inquiry sources for the students to explore answers to questions, current global seismic activity, or other as desired.

Scaling

  • This demonstration can be tailored to the learning level of the students by the complexity of the principles drawn upon for discussion and reflection (i.e. water tables vs. shear stress).
  • This demonstration could be made more difficult and interactive by putting the students into small teams. After liquefaction is demonstrated each team would be charged to devise a way to reduce its effects on the structure. Depending on the grade level examples could be provided for them in class (lower grades) or the students could be given an inquiry-based assignment (higher grades) to investigate current methods used, decide which they will use, and then implement their idea. One day could be targeted for all teams to have their design ready to demonstrate in class. Discussions could naturally follow what is observed in each teams design and a report could be assigned capturing the students observations, research, and reflections.

Cite this work

Researchers should cite this work as follows:

  • Jason Lloyd; NEES EOT (2011), "NEES Teaching Demonstration: Soil Liquefaction," http://nees.org/resources/2942.

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