pounds per cubic foot (pcf) to between 55 and 60 pcf, compacted, and by increasing the internal stability/shear strength of the soil to be between 40 and 46 degrees (compared to gravel’s 33 to 40 degrees). These qualities helped reduce the lateral load forces exerted on MSE walls in a Connecticut section of I-95. One goal for this project was to increase the load accommodations from 40,000 vehicles per day from its original 1958 design to its current capacity—an excess of 140,000 vehicles per day. By utilizing over 100,000 cubic yards of ESCS, this rehabilitation project helped create a resilient section of a well-traveled portion of the interstate without having to build additional support systems for the MSE structures. However, soil stabilization and improving the structural performance of MSE walls are not mutually exclusive. To alleviate congestion at an interchange between I-10, Bluebonnet Boulevard and Siegen Lane, the Louisiana Department of Transportation and Development (LaDOTD) sought to create a robust and intricate interchange. While an MSE retaining wall seemed to be a promising solution, the project’s geotechnical consultant discovered that due to the low bearing capacity of the area soils, the critical height for these walls would be around 22 feet. Building above this height with normal weight backfill would result in unacceptable settlements—a major challenge given some of the proposed walls approached heights of nearly 40 feet. ESCS lightweight aggregate reduced the structure’s vertical pressure on the soil, allowing the walls to reach the proposed heights without substantial risk. Reduced pressure on buried pipelines In addition to contributing to resilient roadways, ESCS can also benefit adjacent infrastructure systems including water, sewage and gas pipelines. When looking at these systems alone, ESCS can be a cost- effective alternative to expensive pile and cradle systems as well as sideline risks of conventional fills sloughing off and allowing pipelines to settle and crack. The key to the benefits is the material’s lightweight nature as it reduces pressure on the pipes and the materials under them. As such, ESCS lightweight aggregate can be a solution for road rehabilitation projects that sit on top of underground pipelines. For example, the Indiana Department of Transportation (INDOT) constructed 3 new lanes along the southbound US Highway 31 in central Indiana. While the task was simple on the surface, the Panhandle Eastern Pipeline Company had buried gas lines approximately 33 feet below the project site. To help alleviate increased vertical load issues, INDOT replaced the in-place soil with ESCS lightweight aggregate. Likewise, designers of a major interchange in Birmingham, Ala., used ESCS to reduce the weight exerted on a buried concrete box culvert. This drainage system is 20 feet underground and needed a significant amount of fill materials to bring it up to grade. Due to ESCS lightweight aggregates’ density and high angle of internal friction, the
material significantly reduced the vertical pressure the nearly 2,500- foot drainage system would need to withstand, alleviating concerns that the project may crack the culvert.
ESCS lightweight aggregates reduce lateral forces on steep slopes Credit: Courtesy of ESCSI
Looking below to improve the surface While most people’s experience of roads ends with the pavement that touches their vehicle’s tires, a key consideration for long-term resiliency is what’s under the street. The soil beneath the nation’s roads should resist settling due to increased traffic loads, higher water handling demands resulting from the increased frequency of severe weather events and other causes of settlement. Because ESCS lightweight aggregates weigh nearly half as much as conventional fills and have a high angle of internal friction, they can reduce vertical and lateral pressures to enhance the stability of soils and MSE walls. Further, because it is chemically inert and free draining, this material can withstand the demands of projects in areas prone to flooding and heavy rainfall. As the referenced case studies demonstrate, the benefits of ESCS are not merely theoretical. Departments of Transportation across the country have been using this material for years because it provides long-term value to infrastructure projects. As the industry nears the next ASCE report card, ESCS could be an efficient means for improving the nation’s grade in road, water and energy infrastructure.
JODY WALL, P.E., LEED AP has been involved in many lightweight innovations since joining Stalite 23 years ago. Jody served as Chairman of the Board of the Expanded Shale Clay and Slate Association, Chairman of ASTM Sub- committee C9.21, Chairman of the National Concrete Masonry Association- Acceptable Workmanship Committee and Chairman of Board of Directors of the Southeast Concrete Masonry Association. Jody’s areas of interest include energy efficiency, structural design and production optimization.
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AUGUST 2023 csengineermag.com
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