Passive force-displacement relationships have been developed based on lateral load tests on pile caps/abutments aligned perpendicular to the soil backfill. However, many bridge abutments are constructed at a skew relative to the backfill. The orientation of the skew appears to cause the abutment to slide past the backfill and leads to torsion on the bent. This becomes an important consideration for integral abutments subject to thermal expansion. In addition, post-earthquake reconnaissance studies in Chile and numerical analysis suggest that bridges with skewed abutments are likely to experience more damage in seismic events. No large scale tests have been performed on skewed abutments to this point to help designers better analyze this behavior, but limited small scale tests and computer analyses indicate that the ultimate passive force may decrease as skew angle increases. No design procedures are currently available to define how the passive resistance would change for variations in skew angle. This research study would conduct large scale field tests to evaluate the effect of abutment skew on passive force. Regarding Phase II: Controlled Low-Strength Materials (CLSM) (a.k.a. flowable fill, cellular concrete, etc.) are increasingly being used as backfill materials instead of compacted granular fills due to their ease of placement. Although CLSM backfill can accelerate the bridge construction process, there is currently no basis for selecting design parameters for this material. Some study partners requested research field testing of CLSM as abutment backfill to better understand passive resistance, with and without skew, and seismic performance.

Objectives for Phase I of this study include: 1. Determine passive force-displacement curves for skewed abutments with and without wingwalls from large scale tests. 2. Provide comparisons of behavior of skewed abutments with that of normal abutments. 3. Evaluate the effect of wingwalls on response. 4. Develop design procedures for calculating passive force-displacement curves for skewed abutments. Objectives for Phase II of this study include: 1. Define bridge abutment passive force-deflection relationships for CLSM backfill from large-scale testing. 2. Determine the influence of skew angle on the resistance of CLSM backfills. 3. Determine the effect of rotation during passive force development and the reduction in passive force for skewed abutments. 4. Develop design procedures to account for the observed passive force-deflection relationships for CLSM backfills. 5. Investigate the effect of rotation on passive force reduction factors defined previously for longitudinal loading only.

Phase I tasks for this study include: I-1. Perform literature review to collect available data and analysis regarding skewed abutment performance. I-2. Perform laboratory passive force-deflection tests on 2 ft high wall with skew angles of 0º, 15º, 30º and 45º. I-3. Perform field passive force-deflection tests on 5.5 ft high abutment with skew angles of 0º, 15º, and 30º and transverse wingwalls. I-4. Perform field passive force-deflection tests on 5.5 ft high abutment with skew angles of 0º, 15º, 30º and MSE wingwalls. I-5. Calibrate computer model to results of physical model tests and conduct parametric studies. I-6. Prepare a final report that documents the entire research effort and disseminate results. (Tasks 7 - 12 added April 2013) I-7. Perform additional field passive force-deflection tests on 5.5 ft high abutment with a skew angle of 45º with and without MSE wingwalls. I-8. Perform field passive force-deflection tests on 3.0 ft high unconfined backfill with skew angles of 0º and 30º. I-9. Perform field passive force-deflection tests on 5.5 ft high pile cap with concrete wingwalls and skew angles of 0º and 45º. I-10. Perform field passive force-deflection tests on 3.5 ft high unconfined gravel backfill with skew angles of 0º and 30º. I-11. Perform field passive force-deflection tests on 3.5 ft high GRS gravel backfill with skew angles of 0º and 30º. I-12. Present the results of the study at TRB and AASHTO meetings. Phase II tasks for this study include: (added July 2016) II-1. Conduct literature review to define typical characteristics of CLSM backfill II-2. Perform lab-scale passive force test with CLSM II-3. Conduct large-scale passive force field tests with CLSM II-4. Perform large-scale passive force tests with rotation and longitudinal displacement II-5. Validate or calibrate computer models II-6. Develop simplified design models to simulate observed performance II-7. Prepare final report with design examples for typical cases II-8. Disseminate results and work with sponsors and AASHTO to implement findings into future codes

The Principal Investigator for this study will be Dr. Kyle Rollins of Brigham Young University. Dr. Rollins has extensive experience with lateral passive force tests on abutments and pile caps. He has been the Principal Investigator on previous passive force pooled fund studies led by the Utah Department of Transportation. In addition he has a 6 ft high pile cap in the field which can be adapted to skewed abutment testing with MSE wing walls. Lab testing is planned to begin in the spring of 2012, followed by conducting of field tests and other project tasks. The minimum partner commitment expected is $20,000.