Passive Force Behavior for Skewed Bridge Abutments During Combined Lateral and Rotational Loading

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General Information
Study Number: TPF-5(542)
Former Study Number: TPF-5(264)
Lead Organization: Utah Department of Transportation
Solicitation Number: 1608
Partners: CA, ID, NY, SC, UT, WA
Status: Cleared by FHWA
Est. Completion Date: Dec 31, 2027
Contract/Other Number:
Last Updated: Oct 08, 2024
Contract End Date:
Financial Summary
Contract Amount:
Suggested Contribution: $40,000.00
Total Commitments Received: $385,000.00
100% SP&R Approval: Approved
Contact Information
Lead Study Contact(s): David Stevens
davidstevens@utah.gov
Phone: 801-589-8340
FHWA Technical Liaison(s): Jennifer Nicks
jennifer.nicks@dot.gov
Phone: 202- 493-3075
Organization Year Commitments Technical Contact Name Funding Contact Name
California Department of Transportation 2025 $150,000.00 Kyungtae Kim Sang Le
Idaho Department of Transportation 2025 $40,000.00 Darren LaMay Amanda Laib
New York State Department of Transportation 2025 $40,000.00 Hailee Dances Gail Carpenter
South Carolina Department of Transportation 2024 $20,000.00 Nicholas Harman Terry Swygert
South Carolina Department of Transportation 2025 $20,000.00 Nicholas Harman Terry Swygert
Utah Department of Transportation 2024 $75,000.00 Darin Sjoblom David Stevens
Utah Department of Transportation 2025 $0.00 Darin Sjoblom David Stevens
Washington State Department of Transportation 2025 $20,000.00 Andrew Fiske Mustafa Mohamedali
Washington State Department of Transportation 2026 $20,000.00 Andrew Fiske Mustafa Mohamedali

Study Description

As part of pooled fund study TPF-5(264), led by UDOT and supported by FHWA and a few other state DOTs, large-scale passive force-deflection tests were performed on a simulated bridge abutment to investigate the effect of skew angle on passive force behavior. Tests were conducted at abutment skew angles of 0°, 15°, 30°, and 45° with a backwall that was 11 ft wide and 5.5 ft tall. Backfills included sand and sandy gravel compacted to 95% of the modified Proctor maximum dry unit weight. Test results indicate that the passive force decreases significantly as the abutment skew angle increases to 45° relative to non-skewed walls. The results also indicate that the reduced passive force for a skewed abutment, Pp(skew), can be predicted using a simple reduction factor, Rskew, multiplied by the passive force for a non-skewed abutment with the same roadway width. The skew reduction factor was relatively consistent for all soil types, wingwall styles, and backfill width-to-height ratios investigated. The Phase II part of the previous study included testing of additional backfill materials and an inclined loading (push-and-rotate) condition for a 30° skew angle. No significant effect on the passive force skew reduction factor was observed in the inclined loading testing that involved relatively small rotation.

Based on the previous study results, the skew reduction factor has already been implemented in the Caltrans Seismic Design Criteria, along with geotechnical guidelines for Oregon DOT and UDOT. However, as designers have started applying this approach, several questions have arisen. For example, in most of the field abutment tests, the simulated bridge abutment was forced to move longitudinally into the backfill soil.  In contrast, during earthquake loadings, the abutment has been observed to rotate. Although this rotation angle is quite small, it can lead to a significant difference in longitudinal displacement from the edges of the abutment from rotation. This would be expected to lead to a triangular distribution of pressure on the backwall of the abutment. Designers want to know (1) if the skew reduction factors remain the same when rotation is involved, and (2) if it is necessary to distribute the passive force non-uniformly along the backwall of the abutment.

Objectives

The objective of this new study is to assist with the calibration of numerical models by conducting a series of large-scale skewed abutment, passive force-displacement tests with enough abutment offset from rotation to evaluate the skew reduction factor and backwall pressure distribution. The maximum rotation and displacement would be larger than in the previous testing. As availability allows, the tests would be conducted at the same Salt Lake Airport test site used in the previous study.

Scope of Work

Planned tasks for this new study are as follows:

  1. Analysis of the existing abutment to determine acceptable rotation and loading scheme,
  2. Performance of large-scale skew abutment tests,
  3. Analysis of test results including determination of passive force reduction factors,
  4. Comparison with longitudinal test results and modifications,
  5. Supplemental numerical analysis of parameters affecting results,
  6. Preparation of interim and final reports, and
  7. Dissemination of results, including presentations at AASHTO committee meetings.

In Task 2, lateral load tests will be performed on the simulated bridge abutment with skew angles of 0°, 15°, 30°, and 45° relative to the direction of loading. The backfill will consist of concrete sand compacted to 95% of the modified Proctor maximum dry unit weight to provide direct comparisons with the previous tests performed with longitudinal loading. The passive force provided by the backfill will be determined by loading the abutment before and after compacting backfill behind the abutment. As with previous tests, the applied lateral force, abutment displacement and rotation, pressure on the backwall, vertical and horizontal movement of the backfill, and location of the failure surfaces in the backfill will be measured.

Comments

The Utah Department of Transportation (UDOT) will be the lead agency for this study, with Darin Sjoblom (dsjoblom@utah.gov) as the UDOT Champion. We intend to hire a firm or university as the prime consultant through qualifications-based selection in the UDOT General Engineering Services Pool, Research Work Discipline, after sufficient funds are committed by study partner agencies.

The study is planned to begin in the winter/spring of 2025, with study completion expected in two or three years’ time.

The minimum partner commitment expected for the study is $20,000 per year in FFY 2024 and 2025. If partner agencies would like to contribute lower amounts or shift the contributions to FFY 2025 and 2026, we are open to discussing these options. Reach out to the Lead Study Contact above as needed.

The 100% SPR approval (match waiver) has been approved.

Subjects: Bridges, Other Structures, and Hydraulics and Hydrology Soils, Geology, and Foundations

Documents Attached
Title File/Link Document Category Document Type Privacy Document Date Download
2024 3rd Quarter 2024 3rd quarter FHWA rpt_TPF-5(542).pdf Progress Report Quarterly Progress Report Public 2024-10-29
Acceptance Letter TPF-5(542) Acceptance Letter TPF5542 signed.pdf Memorandum Lead State Acceptance Memorandum Public 2024-09-12
Documents Attached
Title File/Link Document Category Document Type Privacy Document Date Download
SPR-B Match Waiver Memorandum #1608 #1608 Match Waiver Approval Memorandum Signed.pdf Memorandum SPR Match Waiver Approval Memorandum Public 2024-08-06

Passive Force Behavior for Skewed Bridge Abutments During Combined Lateral and Rotational Loading

General Information
Study Number: TPF-5(542)
Lead Organization: Utah Department of Transportation
Solicitation Number: 1608
Partners: CA, ID, NY, SC, UT, WA
Status: Cleared by FHWA
Est. Completion Date: Dec 31, 2027
Contract/Other Number:
Last Updated: Oct 08, 2024
Contract End Date:
Financial Summary
Contract Amount:
Total Commitments Received: $385,000.00
100% SP&R Approval:
Contact Information
Lead Study Contact(s): David Stevens
davidstevens@utah.gov
Phone: 801-589-8340
FHWA Technical Liaison(s): Jennifer Nicks
jennifer.nicks@dot.gov
Phone: 202- 493-3075
Commitments by Organizations
Organization Year Commitments Technical Contact Name Funding Contact Name Contact Number Email Address
California Department of Transportation 2025 $150,000.00 Kyungtae Kim Sang Le (916)701-3998 sang.le@dot.ca.gov
Idaho Department of Transportation 2025 $40,000.00 Darren LaMay Amanda Laib 208-334-8181 amanda.laib@itd.idaho.gov
New York State Department of Transportation 2025 $40,000.00 Hailee Dances Gail Carpenter 518-457-8083 Gail.Carpenter@dot.ny.gov
South Carolina Department of Transportation 2024 $20,000.00 Nicholas Harman Terry Swygert 803-737-6691 SwygertTL@scdot.org
South Carolina Department of Transportation 2025 $20,000.00 Nicholas Harman Terry Swygert 803-737-6691 SwygertTL@scdot.org
Utah Department of Transportation 2024 $75,000.00 Darin Sjoblom David Stevens 801-589-8340 davidstevens@utah.gov
Utah Department of Transportation 2025 $0.00 Darin Sjoblom David Stevens 801-589-8340 davidstevens@utah.gov
Washington State Department of Transportation 2025 $20,000.00 Andrew Fiske Mustafa Mohamedali 360-704-6307 Mustafa.Mohamedali@wsdot.wa.gov
Washington State Department of Transportation 2026 $20,000.00 Andrew Fiske Mustafa Mohamedali 360-704-6307 Mustafa.Mohamedali@wsdot.wa.gov

Study Description

Study Description

As part of pooled fund study TPF-5(264), led by UDOT and supported by FHWA and a few other state DOTs, large-scale passive force-deflection tests were performed on a simulated bridge abutment to investigate the effect of skew angle on passive force behavior. Tests were conducted at abutment skew angles of 0°, 15°, 30°, and 45° with a backwall that was 11 ft wide and 5.5 ft tall. Backfills included sand and sandy gravel compacted to 95% of the modified Proctor maximum dry unit weight. Test results indicate that the passive force decreases significantly as the abutment skew angle increases to 45° relative to non-skewed walls. The results also indicate that the reduced passive force for a skewed abutment, Pp(skew), can be predicted using a simple reduction factor, Rskew, multiplied by the passive force for a non-skewed abutment with the same roadway width. The skew reduction factor was relatively consistent for all soil types, wingwall styles, and backfill width-to-height ratios investigated. The Phase II part of the previous study included testing of additional backfill materials and an inclined loading (push-and-rotate) condition for a 30° skew angle. No significant effect on the passive force skew reduction factor was observed in the inclined loading testing that involved relatively small rotation.

Based on the previous study results, the skew reduction factor has already been implemented in the Caltrans Seismic Design Criteria, along with geotechnical guidelines for Oregon DOT and UDOT. However, as designers have started applying this approach, several questions have arisen. For example, in most of the field abutment tests, the simulated bridge abutment was forced to move longitudinally into the backfill soil.  In contrast, during earthquake loadings, the abutment has been observed to rotate. Although this rotation angle is quite small, it can lead to a significant difference in longitudinal displacement from the edges of the abutment from rotation. This would be expected to lead to a triangular distribution of pressure on the backwall of the abutment. Designers want to know (1) if the skew reduction factors remain the same when rotation is involved, and (2) if it is necessary to distribute the passive force non-uniformly along the backwall of the abutment.

Objectives

The objective of this new study is to assist with the calibration of numerical models by conducting a series of large-scale skewed abutment, passive force-displacement tests with enough abutment offset from rotation to evaluate the skew reduction factor and backwall pressure distribution. The maximum rotation and displacement would be larger than in the previous testing. As availability allows, the tests would be conducted at the same Salt Lake Airport test site used in the previous study.

Scope of Work

Planned tasks for this new study are as follows:

  1. Analysis of the existing abutment to determine acceptable rotation and loading scheme,
  2. Performance of large-scale skew abutment tests,
  3. Analysis of test results including determination of passive force reduction factors,
  4. Comparison with longitudinal test results and modifications,
  5. Supplemental numerical analysis of parameters affecting results,
  6. Preparation of interim and final reports, and
  7. Dissemination of results, including presentations at AASHTO committee meetings.

In Task 2, lateral load tests will be performed on the simulated bridge abutment with skew angles of 0°, 15°, 30°, and 45° relative to the direction of loading. The backfill will consist of concrete sand compacted to 95% of the modified Proctor maximum dry unit weight to provide direct comparisons with the previous tests performed with longitudinal loading. The passive force provided by the backfill will be determined by loading the abutment before and after compacting backfill behind the abutment. As with previous tests, the applied lateral force, abutment displacement and rotation, pressure on the backwall, vertical and horizontal movement of the backfill, and location of the failure surfaces in the backfill will be measured.

Comments

The Utah Department of Transportation (UDOT) will be the lead agency for this study, with Darin Sjoblom (dsjoblom@utah.gov) as the UDOT Champion. We intend to hire a firm or university as the prime consultant through qualifications-based selection in the UDOT General Engineering Services Pool, Research Work Discipline, after sufficient funds are committed by study partner agencies.

The study is planned to begin in the winter/spring of 2025, with study completion expected in two or three years’ time.

The minimum partner commitment expected for the study is $20,000 per year in FFY 2024 and 2025. If partner agencies would like to contribute lower amounts or shift the contributions to FFY 2025 and 2026, we are open to discussing these options. Reach out to the Lead Study Contact above as needed.

The 100% SPR approval (match waiver) has been approved.

Subjects: Bridges, Other Structures, and Hydraulics and Hydrology Soils, Geology, and Foundations

Title File/Link Type Private
2024 3rd Quarter 2024 3rd quarter FHWA rpt_TPF-5(542).pdf Progress Report Public
Acceptance Letter TPF-5(542) Acceptance Letter TPF5542 signed.pdf Memorandum Public
Title File/Link Type Private
SPR-B Match Waiver Memorandum #1608 #1608 Match Waiver Approval Memorandum Signed.pdf Memorandum Public

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