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Mother Nature is always throwing us challenges, and I enjoy finding the best way to overcome them. A problem that we often encounter in Texas is sulfate-rich soil that does not work well with lime. Lime is a stabilizer frequently used to improve the soil’s strength and stability. Without a stabilizer such as lime, soil can shrink or swell with changes in weather or moisture. However, adding lime to sulfate-rich soil can create minerals such as ettringite, which results in swelling and heaving. This can damage the infrastructure, shorten its effective life expectancy, and requires costly repairs.
This is the situation that we encountered working in Denison, Texas, at the US75 and FM503 interchange, in a region that is known to have sulfate-rich soil. TxDOT initiated a project to reconstruct and reconfigure the interchange to better accommodate traffic coming down off of the main lanes onto the frontage road. We needed to account for a substantial elevation change respective to the length of the exit ramp. It was imperative that we have a firm foundation for the reconstructed roadway. The initial thought was to stabilize the subgrade soil with lime. The presence of sulfate-rich soils precluded this solution.
We examined a number of options, and found a better solution was a Full-Depth Reclamation (FDR) process in which we used materials from the existing roadway to create a new stabilized base by adding cement. Conserving existing materials has both economic and environmental benefits, allowing us to recycle valuable resources and eliminate the need to haul away old materials.
The project savings were approximately 2 days in construction and about $50,000. More importantly, it avoided potential future maintenance problems that are associated with the correction of heaving pavement and would require its removal and replacement.
In the end, this project was successful because we carefully examined the options and developed the right plan from the beginning. The resulting infrastructure is built for sustained high performance for roadway users.
Read more about the project here: US 75 Case Study