Bridge abutment piles are frequently surrounded by mechanically stabilized earth (MSE) walls rather than a soil slope. Piles near MSE walls must be designed for lateral loads from earthquakes and thermal expansion/contraction. In the TPF-5(272) Phase 1 study involving several state DOTs, a series of 31 tests on free-head piles provided p-multipliers as a function of pile spacing which can be used to account for reduced lateral soil resistance due to the presence of an MSE wall. Equations were also developed to compute the induced force developed in the reinforcements by the lateral pile loading. However, a number of questions came up when the results of the Phase 1 study were presented to engineers and those responsible for code changes. These issues involve (a) the effect of cyclic loading when previous testing was monotonic, (b) the effect of pile head fixity because previous tests were on free-head piles while most abutment piles are “fixed-head”, (c) the effect of pile group loading when previous tests were for single piles, and (d) the effect of pile diameter on the p-multiplier and induced force equations because previous tests were all for piles about 12 inches in diameter.

To provide closure relative to the outstanding issues described above, a series of additional tests will be conducted as a Phase 2 follow-up to the original test series.

The Phase 1 study included construction of a dedicated MSE wall site in Utah with instrumented piles behind the 20-ft high wall. Prior to the Phase 2 testing, the top 6.5 ft of backfill behind the MSE wall will be excavated, new instrumented reinforcements will be placed, and the backfill will be re-compacted. Tasks for this Phase 2 study include: 1. Conduct cyclic lateral pile load testing. 2. Conduct fixed-head lateral pile load testing. 3. Conduct lateral pile load testing of larger-diameter piles (18- or 24-inch diameter), to be newly placed between cut-off existing piles. 4. Conduct lateral pile load testing of a pile group. 5. Analyze the Phase 2 lateral pile load testing results, compare these with the Phase 1 results, and update the design procedures and numerical model from Phase 1 as applicable. 6. Submit a final report that documents the Phase 2 research effort. 7. Make presentations at AASHTO bridge engineers’ committee meetings and TRB events to aid in national efforts to implement the study results.

The Principal Investigator for this study will be Dr. Kyle Rollins of Brigham Young University. Dr. Rollins has extensive experience with lateral load tests on piles. He is the Principal Investigator on the TPF-5(272) Phase 1 study. Conducting of the Phase 2 field tests at the dedicated wall site is planned for the summer of 2018. The minimum partner commitment expected for Phase 2 is $20,000. This could consist of $20,000 for FY2018 or FY2019, or the amount may be split between the two years. We will be requesting the 100% SP&R Approval from FHWA.