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. Unfortunately, there are no design methods available to predict the reduction in pile resistance or the increase in force on the walls for these conditions. In addition, little guidance is available regarding the spacing behind the wall necessary to eliminate these effects. The data base of load tests is limited to three recent test series in Utah and one test series with block wall/geogrids in Kansas. Testing in the recent Utah study shows significant decrease in lateral resistance and increases in reinforcement force as piles are placed closer to the MSE wall. Placing piles further from the wall increases bridge cost. Additional field testing at a dedicated wall site with single and group piles is necessary to define performance.

Objectives for this study include: 1. Determine reduced lateral pile resistance vs. distance behind MSE wall for single and group piles from dedicated full-scale testing. 2. Determine the increase in wall force due to lateral load on the pile. 3. Develop design rules (p-multipliers, etc.) to account for reduced pile resistance. 4. Develop equations to predict increased force on MSE reinforcement due to lateral pile loading.

Tasks for this study include: 1. Construct dedicated MSE wall(s) away from the highway right-of-way, in coordination with contractors and suppliers. 2. Conduct lateral load tests on single piles and pile groups at dedicated MSE wall(s). 3. Perform parametric studies with a calibrated numerical model. 4. Develop design procedures to predict reduced pile resistance and increased wall pressures based on the results of the testing program and the parametric studies. 5. Submit a final report that documents the entire research effort. 6. Make presentations at AASHTO bridge engineers committee meetings to implement design methods into code.

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 Utah Department of Transportation's active study of three bridge sites where piles have been tested at variable spacings behind the MSE walls. Construction at the dedicated wall site is planned to begin in the spring of 2013, followed by conducting of field tests and other project tasks. The dedicated wall site will allow the research team to have improved control over wall construction and pile layout, test variables, and the testing schedule. The minimum partner commitment expected is $20,000.