About the research
Poor drainage is by far the most common cause of poor performance for earth retention systems. Poor performance includes burdensome serviceability problems that can progress to outright failure of the earth retention system if not addressed.
A common method for improving earth retaining wall drainage is to include weep holes, which relieve water pressure by creating a controlled seepage path through the retaining wall face. Maintainable drains are a more reliable means of promoting retaining wall drainage than traditional weep holes, which are likely to become clogged during the lifespan of the wall.
To evaluate performance of retaining walls with maintainable drains, the researchers constructed and tested two physical model retaining walls in the large-scale geotechnical modeling laboratory at the University of Missouri. The first wall retained a silty sand backfill, and the second wall retained a fine sand backfill. For each wall, a series of tests was conducted with varying drain type (maintainable and conventional weep), drain size (diameters of 2 in., 4 in., and 6 in.), and drain spacing. For each test, a constant height of water was impounded behind the wall backfill while measuring drain outflow and backfill pore pressure.
The research team created three-dimensional (3D) finite element models to evaluate the results of the physical models. The researchers created additional models to evaluate the effect of facial drainage features on a generic retaining wall.
The research team then developed design criteria for maintainable conical drains that penetrate the wall backfill, as well as for drains that do not penetrate the wall backfill, including conventional weep holes. The design criteria are general and do not address all situations, including situations when permittivity controls affect outflow, backfill is not compatible with the drain geotextile, or multiple rows of drains are used.
The final report documents the project’s research methodology, results, and interpretation. The interpretation culminated in the development of the team’s Design Guide for Maintainable Drains, which is included as the Appendix to the report.
Midwest Transportation Center
Skyline Steel LLC ($17,000.00)
Contract Number: DTRT13-G-UTC37