The Power of Seismic Refraction

Return to Blog

At Berg Construction, we are fortunate to have a team of people with diverse skill sets that allow us to approach our projects with innovation. One of our standout capabilities is our expertise in seismic refraction, a geophysical method that allows us to accurately analyze subsurface conditions and enhance the efficiency and safety of our projects. With a dedicated staff geologist serving as our Director of Geotechnology, we are among the few companies in the Northeast equipped with the programs and expertise to utilize this technology effectively.

Understanding Seismic Refraction

Seismic refraction is the oldest geophysical technology still in use today. Its origins date back to World War I, but it became established as a prospecting method in the 1920s and 30s due to its successes in the Gulf region of the United States. This method was initially used for oil exploration, enabling the detection of salt domes in the United States, mapping large structures in Iran, and discovering oil fields in the Algerian Sahara.

The primary advantage of seismic refraction is its non-invasive nature. It allows us to get a ‘snapshot’ of what lies beneath the surface without the need for drilling or heavy equipment. This is particularly useful in our industry, where understanding subsurface conditions can significantly impact project planning and execution.

How Seismic Refraction Works

The seismic refraction process involves several key steps and equipment:

  1. Geophones Setup: We deploy 24 geophones, typically in grounding groups of 12, placed in a straight line with equal spacing, usually three feet apart. These geophones are connected to a receiver.
  2. Generating Seismic Waves: A seismic wave is generated by striking an aluminum plate on the ground with a heavy striking tool. This ‘hammer’ like tool is equipped with a trigger that is wired to the receiver, signaling the release of the sound wave.
  3. Recording Data: The geophones record the arrival times of the seismic waves at different locations. By measuring these arrival times, we can calculate the speed of the seismic waves through various subsurface materials.
  4. Interpreting Density Changes: Seismic waves travel at speeds proportional to the density of the material they pass through. When the density changes, the velocity of the waves changes, which is detected by observing the changes in arrival times recorded by the geophones.
  5. Software Analysis: The collected data is processed using specialized software to generate density maps of the subsurface materials. These maps provide insights into the composition and structure of the geological layers.

Field Operations and Challenges

Our geotechnical surveys typically involve multiple soundings, usually between seven and eight, at different locations. This is because the subsurface in our region is highly diverse, with varying geology, including rocks and soils. The complexity of the subsurface requires careful planning and interpretation to ensure accurate results.

Applications in Earthmoving and Construction

Seismic refraction data is incredibly valuable in assessing the rippability of the ground by earthmoving equipment. Manufacturers like Caterpillar, Komatsu, and John Deere rate the rippability of their machines based on the seismic velocity of the materials. This information helps us determine the most suitable equipment for different types of materials, ultimately improving efficiency and reducing costs.

For instance, understanding the subsurface conditions can prevent unexpected encounters with rock layers that could slow down production. By using seismic refraction, we can identify whether explosives are necessary or if there is a more cost-effective solution.

Benefits for Project Planning

Utilizing seismic refraction in project planning offers numerous benefits:

    • Risk Reduction: By gaining a clear understanding of the subsurface conditions, we can reduce uncertainties that might impact project costs and timelines.
    • Cost-Effectiveness: Knowing the subsurface conditions helps avoid unnecessary excavation or the use of explosives, potentially saving significant expenses.
    • Environmental Friendliness: This technology generates essential data without disturbing the environment, making it an eco-friendly option for subsurface exploration.

 

Comparison With Other Technologies

Seismic refraction complements other geophysical methods like ground-penetrating radar (GPR). While GPR is useful for detecting objects like pipes underground, seismic refraction provides detailed information about the geological structure and density of materials. Together, these technologies offer a comprehensive understanding of subsurface conditions.

Practical Example

Consider a scenario where a company is evaluating a piece of land for potential development. Without disturbing the site, we can use seismic refraction to gather crucial subsurface information. This non-invasive approach helps in making informed decisions about land purchases, minimizing risks and costs associated with unforeseen ground conditions..

Conclusion

Seismic refraction is a versatile and effective technique that continues to be integral to modern geophysical exploration and engineering projects. Its ability to provide valuable insights into subsurface conditions makes it a critical tool in our industry specifically because it enables us to anticipate and address potential challenges before they arise, ensuring smoother and more efficient project execution. By leveraging this technology, we help our clients make informed decisions, manage risks, and optimize project outcomes.

To learn more about our capabilities, read our Services.