United States Department of Transportation
i
Estimating Soil Pressure Against Unyielding Surfaces
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2022-08-01
[PDF-11.96 MB]
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Edition:Final Report 02/01/2018 – 10/31/2022
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Abstract:This report focuses on the earth pressures that develop when two MSE walls are tied together, creating an unyielding condition. During the research an extensive literature review was completed that included current design practices and standards, and construction and quality control procedures. This ensured the constructed wall configurations adhered to the FDOT’s standard specifications for road and bridge construction and complied with the AASHTO Design code. This also ensured proper construction and sequencing took place to provide structures that were representative of the practice. For the research, two relative compaction efforts were investigated, 95% and 103% of the backfill soil’s optimum dry density. During construction, earth pressure coefficients were derived for each compacted soil lift for each state of soil density. Once construction was complete, a reaction frame loading system was utilized to induce controlled incremental surcharge loads, and earth pressure coefficients were derived for each incremental surcharge load applied. The final surcharge loads provided the necessary B/H = 0.3 for both compaction efforts to ensure the results were representative of the practice. From the derived earth pressure coefficients, it was observed that in an unyielding condition, the earth pressures move from a passive condition to either an active or at-rest condition as the soil height increases above the reinforcement level, which is different from conventional MSE wall design and construction. Consequently, a new equation was developed from the research that incorporates a variable friction angle (φ) based on the compaction effort for an unyielding condition, and FDOT design and construction requirements. When compared to the measured results, the new equation followed the trends of the data well.
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