Pile foundations for bridges with integral abutments must resist lateral loads produced by earthquakes and thermal expansion or contraction. Increasingly, right-of-way constraints are also leading to vertical mechanically stabilized earth (MSE) walls at abutment faces. Currently, there is relatively little guidance for engineers in assessing the lateral resistance of piles located close to these MSE walls. As a result, some designers assume that the soil provides no resistance whatsoever which leads to larger pile diameters and increased foundation cost. Other designers locate the abutment piles six to eight pile diameters behind a wall face to minimize the interaction and use conventional design approaches. However, this approach increases the bridge span and the cost of the bridge structure. Still other designers position the pile close to the wall face and reduce the lateral pile resistance using engineering judgment. However, the appropriate reduction factor to use as a function of pile spacing is not well defined. Recent testing conducted by Rollins et al (2013) and Pierson et al (2008) indicate that lateral resistance decreases substantially as pile spacing from the wall decreases; however, reinforcing can reduce this effect. Rollins et al also found that p-multipliers defined as a function normalized spacing and reinforcement length seemed to provide reasonable agreement with measured pile response. Furthermore, Rollins et al found that the tensile force in the reinforcements owing to the lateral load on the pile could be estimated for design purposes using a correlation with pile load, spacing behind the wall, and distance transverse from the pile load. Although the tests to date provide a framework for understanding the mechanisms involved and likely design approaches, the available data is too limited to make firm design recommendations. To improve our understanding of pile-MSE wall interaction, we propose to construct a test embankment approximately 80 ft long and 20 ft tall where it will be possible to conduct a number of lateral pile load tests on different pile types behind an MSE wall with both strip and grid type steel reinforcements. Additional contributions to the project will consist of in-kind donations from various contractors and material suppliers.

Objectives for this study include the following, all aimed at improving our understanding of pile-MSE wall interaction: 1. Measure reduced lateral pile resistance vs. displacement curves for circular, square, and H piles behind an MSE wall with steel strips and grid reinforcement. 2. Measure the increase and distribution of tensile force in the MSE reinforcement induced by lateral pile loading. 3. Measure effect of special pile head geometry (e.g. corrugated pipe sleeves, double plastic sheeting) on lateral pile resistance. 4. Develop design rules (e.g. p-multipliers) to account for reduced pile resistance as a function of spacing and reinforcement. 5. Develop equation to predict reinforcement force induced by pile loading. 6. Develop design equations to account for pile shape and pile head geometry.

Tasks for this study include: 1. Instrument test piles and reinforcements. 2. Drive test piles and construct dedicated MSE wall to height of 15 ft, away from the highway right-of-way and in coordination with contractors and suppliers. 3. Perform lateral load tests on single piles with 15 ft high MSE wall. 4. Reduce data and develop report on the testing for the 15 ft high wall. 5. Determine p-multipliers and reinforcement force equations for 15 ft high wall test results. 6. Perform lateral load tests on single piles with 20 ft high MSE wall. 7. Reduce data and develop report on the testing for the 20 ft high wall. 8. Determine p-multipliers and reinforcement force equations for 20 ft high wall test results. 9. Develop design recommendations to account for pile sleeves and plastic sheeting effects. 10. Prepare final report with recommendations based on all tests. 11. Hold Technical Advisory Committee (TAC) meetings. 12. Present results of the study at AASHTO, TRB, and ASCE meetings to help with implementation of design methods into code.

The Principal Investigator for this study is Dr. Kyle Rollins of Brigham Young University. Dr. Rollins has extensive experience with lateral load tests on piles. He was the Principal Investigator on the Utah Department of Transportation's recent study of three bridge sites where piles were tested at variable spacings behind MSE walls. Construction at the dedicated wall site is planned to begin in the winter/spring of 2014, 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.