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.

Objectives for 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.

Tasks for this study include: 1. Perform literature review to collect available data and analysis regarding skewed abutment performance. 2. Perform passive force-deflection tests on 2 ft high wall in lab with skew angles of 0º, 15º, 30º and 45º. 3. 3. Perform passive force-deflection tests on 3.5 and 5.5 ft high walls in field with skew angles of 0º, 15º, and 30º. 4. Calibrate computer model to results of physical model tests and conduct parametric studies. 5. Develop a simplified design procedure for predicting passive resistance-displacement considering skew angle. 6. Submit a final report that documents the entire research effort.

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.