Soil Liquefaction and Pore Pressure Testing

ISEF Category: Engineering Technology: Statics and Dynamics

Subcategory: Civil Engineering  ·  Difficulty: Advanced  ·  Setup: University Lab  ·  Time: Full Year

The Hook

During an earthquake, sand can briefly act like a liquid. That can make buildings sink, tilt, or fail fast. You can model that effect in a box, measure the pressure inside the sand, and compare your data with an engineering method used in practice.

What Is It?

Soil liquefaction happens when loose, wet sand loses strength because shaking raises water pressure between the grains. Think of the sand like a crowd standing on a dance floor. When the floor shakes, people cannot keep steady contact, so the group behaves less like a solid and more like a fluid.

In your project, you would make a small sand box, saturate it with water, and vibrate it with a speaker or similar shaker. At the same time, you would measure pore pressure, which means the pressure of water inside the spaces between sand grains. If that pressure rises enough, the sand grains stop bearing as much load, and the material can start to flow or settle.

The Seed–Idriss simplified procedure is a classic engineering method for estimating liquefaction risk from soil and shaking conditions. Your job is to see how well a small-scale model matches that prediction. That gives you a real bridge between lab measurements and field design.

Why This Is a Good Topic

This is a strong science fair topic because you can change one clear variable at a time, like sand density, water content, or shaking strength, and measure a real physical response. The question matters in earthquake engineering, land stability, and foundation design. You also get to compare your own data with a standard method, which makes the project more than a simple demo.

Research Questions

• How does sand packing density affect the shaking level needed for liquefaction onset?
• What is the effect of grain size on the rate of pore-pressure buildup during vibration?
• Does increasing water saturation lower the vibration threshold for liquefaction onset?
• To what extent does shaking frequency change the peak pore pressure in saturated sand?
• Which sensor placement pattern gives the most consistent pore-pressure readings in the sand box?
• How does the measured liquefaction threshold compare with the Seed–Idriss simplified procedure for the same soil conditions?

Basic Materials

• Clear rigid box or acrylic container for the sand bed.
• Clean sand with known grain size range.
• Water supply and measuring pitcher.
• Vibrating speaker, subwoofer, or small shaker platform.
• Signal source such as a phone, tablet, or function generator.
• BMP280 barometric sensors, sealed in latex or thin flexible waterproof film.
• Microcontroller such as Arduino or Raspberry Pi Pico.
• Breadboard, jumper wires, and connector cables.
• Digital kitchen scale with 0.1 g accuracy.
• Ruler or caliper for bed depth and packing checks.
• Smartphone or camera for recording surface motion.
• Notebook or spreadsheet for recording trial conditions.

Advanced Materials

• Geotechnical triaxial or resonant column access for comparison data.
• Accelerometer or vibration sensor for input calibration.
• Differential pressure sensor or high-accuracy pore-pressure transducer.
• Data acquisition system with multi-channel logging.
• Load cell for measuring transmitted force or settlement.
• Sieve set for controlled grain-size separation.
• Deaired water setup to reduce trapped air in saturation tests.
• Image analysis setup for surface displacement tracking.

Software & Tools

• Arduino IDE: Uploads code to log sensor data from the BMP280 setup.
• Python: Cleans time-series data and plots pore pressure against vibration input.
• ImageJ: Tracks surface motion or settlement from video frames.
• Google Sheets: Organizes trial conditions, sensor readings, and summary statistics.
• PubMed: Helps you find review articles on soil liquefaction and pore-pressure response.

Experiment Steps

1. Define the liquefaction signal you will measure, such as a sharp rise in pore pressure, surface settlement, or loss of shear resistance.
2. Choose one soil variable to change first, then hold every other condition steady so your comparison stays clean.
3. Plan how you will calibrate your vibration input, because speaker motion without calibration makes results hard to compare.
4. Build a sensor layout that lets you compare pore pressure at more than one depth or position in the sand bed.
5. Design controls that separate true liquefaction behavior from simple water sloshing or loose packing collapse.
6. Set up your analysis so you can compare your measured threshold with the Seed–Idriss prediction using the same soil description inputs.

Common Pitfalls

• Letting air bubbles stay trapped around the BMP280 sensors, which blocks true pore-pressure contact with the sand water.
• Using sand with mixed grain sizes across trials, which changes packing behavior and hides the effect you meant to test.
• Driving the box at an unmeasured vibration level, which makes each trial impossible to compare.
• Calling any surface slump liquefaction, which can confuse settlement from grain rearrangement with true pore-pressure failure.
• Skipping a soil calibration step for the Seed–Idriss comparison, which makes your model and prediction use different assumptions.

What Makes This Competitive

A stronger project does more than show that shaking wet sand moves. It measures a real response with calibrated sensors, compares multiple soil conditions, and tests whether a standard engineering prediction matches the small-scale data. You can push the work further by using depth-resolved pressure data, cleaner statistics, and a careful uncertainty analysis. That turns your project into an engineering study, not just a demonstration.

Project Variations

• Test different sand grain sizes, from fine to coarse, to see how particle size shifts liquefaction onset.
• Compare fresh water saturation with salt water saturation to study whether fluid properties change pore-pressure buildup.
• Replace the speaker-driven shaker with a controllable motorized platform and compare how vibration waveform changes the threshold.

Learn More

• USGS earthquake hazards resources: Search the USGS site for liquefaction, ground failure, and soil behavior pages.
• NOAA National Centers for Environmental Information: Find earthquake and ground-motion background material in the NOAA data and education sections.
• MIT OpenCourseWare, soil mechanics courses: Search for lectures on effective stress, pore pressure, and soil behavior.
• PubMed: Search review articles on liquefaction, pore pressure, and saturated granular media.
• ASCE Library: Look for peer-reviewed papers on laboratory liquefaction tests and simplified prediction methods.