Performance of collapsible bridge approach backfill with geosynthetic drainage and reinforcement

Laboratory tests involving a one-fourth scale bridge abutment, approach pavement, four different backfill materials, horizontal layers of geotextile reinforcement, and vertical geocomposite drainage systems were performed to experimentally evaluate approach backfill and subdrain performance of bridges in Iowa. The results from these tests included measurements of void development from collapse-induced volume change in the backfill, approach pavement settlement, and drainage capacity. Based on 14 different tests, it was determined that horizontal layers of geotextile reinforcement in the backfill or the use of open-graded clean gravel backfill can reduce void development under the approach pavements. From a subsurface drainage capacity standpoint, the incorporation of vertical geocomposite drainage products can increase the drainage capacity by over 10 times compared with sandy backfill materials. The findings in the paper suggest relatively low-cost changes that could improve field performance of bridge approach pavement systems.