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Measuring Corrosion Conditions in Mechanically Stabilized Earth Walls
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2021-08-01
[PDF-5.65 MB]
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Edition:July 2018–March 2020
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Abstract:KDOT extensively utilizes mechanically stabilized earth (MSE) walls, typically with coarse aggregate backfill. Previous projects K-TRAN: KSU-15-6 and K-TRAN: KU-15-5 tested the aggregate material from MSE walls under construction. KU identified that several of the clean aggregate samples contained some fines, likely from crushing of the aggregate, and two of the walls contained over 10% fines. Aggregate backfill is specified because it allows for free drainage, limiting the pore water pressure buildup behind the wall. There is the potential for these fines to migrate towards the base of the wall over time. This migration of fines would not only increase the potential for water retention, but it would also increase the localized corrosion potential of the backfill. This joint project measured the backfill corrosion conditions of 12 MSE walls selected by KDOT. Walls were surveyed using a variety of non-destructive resistivity arrays and by cutting through the wall face, sampling the backfill, and inspecting reinforcing strap conditions. Multiple walls with potentially corrosive backfills (low resistivity) were identified, and several walls had reinforcement with visible corrosion in progress. The resistivity survey method and the physical sampling method were generally consistent in identifying backfills with low resistivity. The results support the potential of using a modified four-electrode electrical resistivity measurement to identify corrosive environments in MSE walls. If used by KDOT, this will improve KDOT’s geotechnical asset management of MSE walls. Results from the physical testing of backfills showed that the finest fraction of the backfill (D10) was strongly correlated with low resistivity values, particularly with the sand backfills. High chloride concentrations were also measured in the three samples with the lowest resistivity. These results support the current recommendation that the percentage of fines (material smaller than the #200 sieve) be limited to a maximum of 5%, and encourages the consideration of an additional specification that the percentage passing the #100 sieve be limited to 10%.
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