Why Some Roads Are Made of Styrofoam

Summary

This video explores the issue of bumps that often occur at the transition between roads and bridges, a common problem due to differences in how embankments and bridges settle over time. The video discusses various lightweight fill materials, such as expanded shale, foamed glass aggregate, and EPS foam, which are used to reduce the load on soft soils and prevent settlement. The video also highlights the advantages and challenges of using these materials in construction, emphasizing the importance of innovative solutions in civil engineering.

Takeaways

• 🌉 The bump often experienced when driving on or off a bridge is a common issue affecting nearly a quarter of US bridges and is caused by differential settlement between the bridge and the embankment.
• 🚧 Engineers have developed various ground modification techniques to manage the weight of structures on soft soils, with one approach being the use of lightweight fills to reduce the load on the ground.
• 🌲 Wood fibers are a type of lightweight fill that can last up to 50 years before decaying, offering a robust solution for reducing the weight of embankments.
• 🔥 Shredded tires have been successfully used as a lightweight fill in New York, reusing waste material and avoiding issues like spontaneous combustion seen in other states.
• 🏗️ Expanded shale and clay aggregates, as well as foamed glass aggregate, are manufactured lightweight fills that are created by heating materials to form tiny bubbles, reducing their density.
• 🛑 Retaining walls often require the use of lightweight fills to reduce the lateral pressure exerted by the backfill, which can be significant and proportional to the wall's height and the material's density.
• 🚧 The use of lightweight fill in the Port Canaveral expansion project saved approximately $3 million by reducing the size of the required piles and simplifying the structure.
• 🏗️ Cellular concrete, or lightweight concrete, can be pumped directly into place, speeding up construction and reducing the need for heavy equipment, making it suitable for difficult or time-consuming projects.
• 📦 Expanded polystyrene foam, or geofoam, is a lightweight fill material that is easy to handle and place but must be used with caution due to its buoyancy, susceptibility to wind, and reaction to fuel.
• 🌿 Lightweight fills like geofoam are used in various construction projects worldwide, contributing to cost-effective and long-lasting infrastructure, often without the drivers' awareness.

Q & A

What is the common issue faced by drivers when transitioning onto or off of a bridge?

The common issue is hitting a bump in the road, which can be dangerous and expensive to fix. This bump is often caused by the differential settlement between the bridge and the embankment.

Why do bridges and embankments settle differently?

Bridges and embankments settle differently because they are structurally distinct. Bridges are relatively lightweight and supported on a rigid foundation, while embankments are essentially heavy piles of soil that can cause the ground to settle, especially on soft soils.

What is one simple solution engineers have proposed to mitigate the settlement of embankments?

One simple solution is to make embankments less heavy by using lightweight fills, which reduces the load on the foundation and can help prevent the formation of bumps at bridge transitions.

What are some examples of materials used as lightweight fills in embankments?

Examples of lightweight fill materials include wood fibers, shredded tires, expanded shale and clay aggregates, foamed glass aggregate, cellular concrete, and expanded polystyrene foam (EPS or geofoam).

How do lightweight fills benefit retaining walls?

Lightweight fills reduce lateral pressure on retaining walls, which can simplify the design and construction of these walls, and potentially reduce the size of the required structural elements.

What is the advantage of using cellular concrete as a lightweight fill?

Cellular concrete can be pumped directly to where it needs to be, speeding up construction and eliminating the need for heavy equipment. It is also strong enough to handle traffic loads without imposing excessive weight.

What are the potential drawbacks of using expanded polystyrene foam (EPS) in embankments?

EPS foam may not be suitable for areas with standing water or high groundwater due to buoyancy issues, it is affected by wind due to its light weight, and it can be susceptible to damage from fuel spills due to its solubility in fuel.

How does the use of lightweight fills impact the cost and effectiveness of infrastructure projects?

While lightweight fills can be more expensive than traditional materials, they can save money on infrastructure projects by reducing the size and complexity of structural elements, thus making the infrastructure more cost-effective and long-lasting.

What is the significance of the graph that the geotechnical engineer provides in the hypothetical situation?

The graph represents the settlement of the embankment over time and is used to determine how long the embankment must settle before paving the road and opening the bridge, which is crucial for planning construction timelines and minimizing disruptions.

Why might a transportation engineer consider using lightweight fills for a new highway bridge project?

A transportation engineer might consider using lightweight fills to reduce the settlement time of the embankments, allowing for a quicker construction process and less disruption to the existing traffic and community.