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South Dakota Department of Transportation
Project Synopsis
SD1996-02


Title: Integral Abutment Bridge End Treatment
Project Researcher: Vernon Schaefer, SDSU
Project Manager: Dan Strand
Research Period: -
Status:
Cost: $0.00

Problem Statement:Voids under bridge approach slabs damage the approach system resulting in decreased life expectancy, increased maintenance costs for repair and stabilization, and rider discomfort due to bumps in the approach system. In 1990, SDDOT initiated a research project entitled "Void Development Under Bridge Approaches", SD90-03, that studied void development under both integral and non-integral abutment bridges. The study showed a high correlation between void development and integral abutment structures. Based on results of field and scale model studies, it was determined that the mechanism of void development under approach slabs is thermally-induced movements of integral abutments tied to bridge beams. The integral abutment movements create voids by the cumulative effects of bridge end backfill deformation as passive failure of the material occurs, backfill densifies as a result of particle breakage, and the embankment bulges as the backfill deforms. Several recommendations resulted from this study. To lessen the initial cost of the backfill, geometric design and material gradation changes were recommended and adopted. A recommendation was made to modify approach slab reinforcement design to redistribute internal stresses to avoid approach slab cracking. Finally, recommendations were made regarding when to perform maintenance. The report stated that these recommendations were intended to reduce construction and maintenance costs. However, the report also stated that the development of voids under approach slabs is an inherent problem of integral abutment bridge designs.

Because study SD90-03 determined the mechanism that causes voids, the Department needs to change its design to accommodate this mechanism. A likely bridge end backfill design alternative is the Wyoming Department of Transportations (WYDOT) which uses a fabric reinforced soil wall. This design incorporates the construction of a vertical void behind the abutment wall to accommodate the abutment movement without causing the backfill to experience lateral pressures.

The feasibility of using other materials for bridge end backfill designs to accommodate the abutment movement should also be investigated. These materials should either be able to create a vertical void behind the abutment or exhibit engineering properties that will alleviate lateral pressures. Rubber chips from discarded tires and expanded polystyrene blocks are examples of materials which may warrant investigation.

Findings:

Research Objectives:
1  To design, construct, monitor, and evaluate an actual bridge end backfill using a fabric reinforced soil wall similar to that used by WYDOT.
2  To determine the feasibility of using other materials as a bridge end backfill material.

Research Tasks:
1  Review and summarize literature regarding bridge end backfill designs that attempt to prevent void development beneath the approach slab.
2  Interview WYDOT geotechnical, design, field, and research personnel to better understand all aspects of their fabric reinforced soil bridge end backfill design.
3  Work with SDDOT to adapt WYDOT's backfill design to SDDOT's bridge geometry. A bridge to be constructed in 1996 will be selected by Department personnel for use in this study.
4  Submit for approval an instrumentation plan to monitor movements in the abutments, embankments, fabric reinforced soil walls, approach slabs, and sleeper slabs. The plan should include ways to monitor voids behind the abutment walls and beneath the
5  Observe the construction of the bridge ends, documenting sequences and construction problems.
6  Monitor the performance of the bridge ends for a period of two years after construction.
7  Review other possible materials that can be used in bridge end backfill designs to alleviate the effects of thermally-induced stresses (i.e. - expanded polystyrene blocks, rubber chips from discarded tires).
8  In conjunction with SDDOT, develop a backfill design which utilizes the material with the greatest potential determined in Task 7.
9  For the Brookings DOT model abutment, submit for approval an instrumentation plan to monitor movements in the abutment, approach slab, and sleeper slab for the design developed in Task 8. Also, the plan should include ways to monitor any deformatio
10  Using the SDDOT model integral abutment at the Brookings DOT Maintenance Yard, construct a bridge end using the backfill design and instrumentation plan developed in Tasks 8 and 9, documenting construction sequences and problems. This should be cons
11  Using accelerated testing, monitor and evaluate the bridge end model.
12  Compare the costs of SDDOT's present bridge end backfill design and performance to that constructed in Task 5. Also, for the model abutment constructed in Task 10, estimate the costs associated with the backfill design and performance as if it were
13  Compare the costs of SDDOT's present bridge end backfill design and performance to that constructed in Task 5. Also, for the model abutment constructed in Task 10, estimate the costs associated with the backfill design and performance as if it were
14  Submit an executive summary and a final report that incorporates the interim report and results of the full evaluation period.
15  Present findings and conclusions to SDDOT Research Review Board upon completion of the project.

Documents Available:
SD0996_02_Final_Report.pdf

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