What Were the White Pockets Found Beneath the Highway

[MikePhua]

Uncovering a Forgotten Road Stabilization Technique
During a full-depth reconstruction of an aging highway in Wyoming, a crew encountered something unexpected beneath layers of asphalt overlays—hundreds of evenly spaced, perfectly round pockets filled with a dense, snowball-like white paste. These pockets were approximately 10 inches in diameter and extended nearly 18 inches deep. They appeared in a consistent pattern every five feet across a two-mile stretch of road, suggesting a deliberate engineering intervention rather than random geological phenomena.
The material was soft, moldable, and adhesive enough to stick to passing equipment when thrown. It was unlike any standard base or subgrade material typically found beneath roadways. The discovery prompted speculation about its origin and purpose, especially since even seasoned state engineers were unfamiliar with it.
Bentonite and Its Role in Subgrade Stabilization
The most plausible explanation for the white substance is bentonite—a naturally occurring clay composed primarily of montmorillonite. Bentonite is known for its high water absorption capacity and swelling behavior, making it useful in geotechnical applications where moisture control is critical.
Terminology annotation:

• Bentonite: A type of absorbent clay used in drilling, sealing, and soil stabilization.
  
• Subgrade: The native soil layer beneath a road’s base and surface layers.
  
• Overlay: An additional layer of asphalt applied over existing pavement to restore surface integrity.
  

In swampy or unstable areas, bentonite may be drilled into the subgrade in powder form to wick moisture away from the roadbed. Once hydrated, it forms a gel-like matrix that can reduce water migration and improve load-bearing capacity. This technique was occasionally used in the mid-20th century, particularly in regions with problematic soils and limited access to modern geotextiles.
Historical Precedents and Engineering Experiments
In the 1990s, Kennecott Copper faced a crisis with its tailings retention dike near Salt Lake City. The dike was saturated and at risk of collapse, threatening nearby infrastructure. Engineers drilled hundreds of vertical shafts and filled them with synthetic filter media and bentonite-like compounds to stabilize the structure. The method proved effective, and the dike remains intact decades later.
This precedent supports the theory that bentonite or a similar absorbent material was used beneath the Wyoming highway to mitigate moisture-related failures. The consistent spacing and depth of the pockets suggest a grid-based stabilization strategy, possibly intended to prevent frost heave or subgrade pumping.
Alternative Theories and Soil Nailing
Another possibility is that the white pockets were part of a soil nailing system. Soil nailing involves inserting reinforcing elements—typically steel bars or synthetic materials—into the ground to stabilize slopes or weak soils. While traditionally used in vertical applications, horizontal soil nails have been deployed in roadbeds to bridge unstable sections.
In this case, the pockets may have housed absorbent capsules or anchors designed to interact with the surrounding soil. However, the absence of structural remnants like rebar or casing makes this theory less likely than bentonite injection.
Modern Comparisons and Evolving Practices
Today, road engineers rely on geotextile fabrics, lime stabilization, and cement-treated bases to address moisture and instability. These materials offer predictable performance and are easier to install and inspect. Yet, the bentonite method—though largely forgotten—was a creative solution in its time.
Recommendations for modern subgrade stabilization include:

• Using woven geotextiles to separate base from subgrade
  
• Applying lime or fly ash to chemically stabilize clay soils
  
• Installing underdrain systems to redirect groundwater
  
• Conducting cone penetration tests (CPT) to assess soil strength
  

In 50 years, future crews may uncover today’s geosynthetics and wonder about their purpose, just as this crew puzzled over the white pockets beneath the Wyoming highway.
Conclusion
The mysterious white pockets discovered during road reconstruction were likely remnants of a bentonite-based stabilization experiment, designed to combat moisture and improve subgrade performance. Though unconventional by today’s standards, such methods reflect the ingenuity of past engineers working with limited resources and evolving knowledge. As infrastructure ages and layers of history are peeled back, these buried innovations remind us that every road tells a story—sometimes in clay.