Benefits of Lightweight Geotech Fill for Bridge Embankments
Lightweight aggregates, like expanded shale, clay and slate (ESCS), support soil stabilization and foundation design for a wide range of construction projects. While the material’s lightweight nature and high internal friction angle can benefit parking garages, water treatment plants and more, it also contributes specific engineering advantages to bridge construction.
ESCS can be incorporated in almost all aspects of concrete bridge design, from bridge decks to foundations. Lightweight aggregate can also play an important role in soil amendments that improve the performance and durability of bridge abutments, embankments and other supporting structures. As such it can solve site-specific constraints as well as contribute to more efficient construction in general, supporting civil and structural engineers, DOTs and other project stakeholders as they build new or repair existing bridges.
Soil stabilization for improved approaches
ESCS lightweight aggregate is made by expanding raw materials in a rotary kiln at approximately 2000 degrees Fahrenheit (F). During the firing, the material develops air bubbles that remain as a network of unconnected voids after the aggregates have cooled. These voids reduce density, support free-draining soils, and contribute to a higher internal friction angle than conventional aggregates—up to 45 degrees.
These physical characteristics support soil stabilization for bridge approaches in areas with soft soils. Projects with these soil types routinely see settlement that causes asphalt and roadway failure. Using ESCS as a soil amendment material in these locations can create more stable bridge approaches and longer lasting infrastructure, which can decrease the total cost of ownership over a bridge’s service life.
These benefits were central to the repair and improvement of a North Carolina bridge approach. ESCS represented a cost-effective means of stabilizing the alluvial muck that was underneath the bridge embankments.
Soil amendments with lightweight geotechnical fill supports retaining wall performance
Because ESCS has a lower density and higher internal friction angle than other conventional fills, it can improve the efficacy of mechanically stabilized earth (MSE). Their lighter weight reduces the dead load exerted on retaining walls. The benefit here is twofold: either standard retaining walls can then support more additional weight or engineers can specify smaller systems, which can lead to reductions in material cost and challenges to fill placing logistics. In addition, the high internal friction angle contributes to lower lateral earth pressure forces.
These two benefits can help engineers more readily plan for present and increasing traffic loads. This supports infrastructure that is more resilient and future-proof than previously possible.
Lightweight aggregate’s physical characteristics solve concurrent challenges
Although each of the above examples isolates the way ESCS soil amendments contribute to improved bridge abutments, approaches, and embankments, it is important to note that often these considerations overlap to create complex challenges in bridge design. In these instances, ESCS can be a cost-effective solution to site-specific issues that intersect.
For example, the Charter Oak bridge repair project in Hartford, Conn., used ESCS lightweight aggregates to solve several soil stabilization challenges. The material stiffened the clay soils and reduced impact on neighboring sewer systems. Further, because the bridge was located along a wharf, ESCS supported bulkheads and piling systems for a safer wharf and boat launch.
To learn more about the soil mechanics of lightweight geotechnical fill and how it can support your next bridge project, peruse the Expanded Shale, Clay, and Slate Institute’s (ESCSI) library of technical documents.