More Than a Soil Amendment: The Many Uses of Lightweight Aggregate

As a geotechnical fill, lightweight aggregates, such as expanded shale, clay and slate (ESCS), can aid in soil stabilization, subgrade improvements, thermal insulation, bridge abutment design and other geotechnical engineering challenges. The material has half the unit weight of conventional aggregates and a predictably high internal friction angle. It is also free draining, durable and chemically inert.

But what do these qualities lend projects that quarried materials do not? And how can geotechnical engineers use ESCS lightweight aggregates to realize projects that may be unfeasible with other backfills?

Minimize Loads on Structures Under Roads and Bridges

Because ESCS can weigh nearly half that of conventional fills, it can reduce settlement under densely packed roadways as well as minimize deadloads on underground structures, such as storm water drainage systems. With this in mind, geotechnical engineering teams have used ESCS to support bridge abutments, retaining walls and other aspects of infrastructure without overcomplicating their design. This is especially relevant when there is a need to accommodate greater traffic frequency than when a road was originally constructed.

In fact, these and other considerations led the engineering teams for the 11th Street Bridges in Washington, D.C., to use ESCS to preserve historic storm drainage outfall structures. The team used lightweight aggregate to add up to 20 feet of free-draining geotechnical fill, resulting in in a load condition that was acceptable without modification to the structures.

Soil Remediation That Maintains Free Drainage

ESCS does more than protect stormwater drainage systems. This material can also contribute to stormwater management itself. As a chemically inert, water and acid insoluble and free-draining material, ESCS lightweight aggregate can promote the quick filtration and drainage of rainwater. As such, it has been readily used in flood-prone areas to promote drainage and sideline the need to plan additional onsite structures.

For example, lightweight aggregate played a vital role during phase 1 improvements of Central Regional Wastewater System in Dallas, Texas. In addition to its lower density, ESCS could also withstand the area’s heavy rainfall during May and October without settlement. As a result, weather never hindered the geotechnical fill operations due to the free draining characteristic of the material.

Reduce Bulkhead Material Costs in Waterfront Construction

Lightweight aggregate can also be essential to cost-effective waterfront development. Its predictably high internal friction angle and lower density can reduce lateral earth pressures. As a result, it can lessen the material and strength requirements of pile and foundation systems, which may contribute to a more structurally efficient design for waterfront construction such as piers and bridge foundations.

The geotechnical engineers for the Port Canaveral expansion used ESCS’s capabilities to create a wharf for a new cruise terminal. The lightweight aggregates reduced material requirements for the bulkhead materials. This not only allowed the project to move forward efficiently, but also supported a design that fit within the projected cost of the expansion.

Minimize Lateral Loads on Bridge Abutments and Walls

In addition to waterfront projects, ESCS as a lightweight fill can solve geotechnical engineering challenges in bridge abutment and retaining wall construction. As noted above, given the lightweight nature and stability of ESCS, the material can reduce forces acting on these structures, especially when they are larger than average.

The geotechnical engineering teams for a parking garage in Charlotte, N.C., used lightweight aggregate to support a new parking garage built adjacent to a local elementary school. The three-story structure was situated along an embankment that required backfill to stay level with the neighboring school yard. ESCS reduced the forces acting on the parking garage while also allowing self-drainage—all to reduce moisture from accumulating along the wall.

Solving Geotechnical Engineering Challenges One Truckload at a Time

The combination of ESCS lightweight aggregates’ physical and chemical properties make it an ideal geotechnical fill for a variety of projects. Further, ESCS can ease construction logistics. No specialty contractor is required for fill placement of ESCS lightweight aggregates. It also requires fewer shipping loads due to its lightweight nature. Both aspects allow general contractors greater control over their construction schedules. As such, ESCS can solve onsite geotechnical engineering challenges in projects ranging from bridge abutments to bluff stabilization.