Physical Modeling and Development of Design Criteria for Maintainable Drains for Earth Retention Systems-Paper

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The study evaluates maintainable drains for reducing water pressure behind retaining walls and develops design criteria for their size and spacing. The drains are installed through the wall face into the backfill; their removable, geotextile-filtered inserts allow cleaning or replacement. Conventional weep holes were also evaluated.<br /><br />Researchers tested large-scale physical models with silty sand and fine sand backfill, measuring drain outflow and pore pressures under a maintained water level. Three-dimensional finite element models were calibrated against the test results and then used to assess full-scale wall configurations.<br /><br />Both physical and numerical results showed that facial drains reduce water pressure. Backfill hydraulic conductivity strongly affected the volume of seepage, but had comparatively little effect on drawdown. Drawdown depended more on geometry, including drain diameter, spacing, and whether the drain extended into the backfill. In the fine sand tests, larger drains generally produced greater outflow and drawdown. Conical maintainable drains also outperformed weep holes in some configurations, particularly at larger diameters.<br /><br />The proposed design criteria specify allowable drain spacing based on groundwater height above the drain and drain diameter. Drains that penetrate the backfill can generally be spaced farther apart than drains that do not; conventional weep holes use the closer-spacing criteria. Spacing is capped at 30 ft, and several size-and-spacing combinations may meet the criteria.<br /><br />The criteria are intended as general guidance, not a substitute for project-specific analysis. They do not address multiple drain rows, incompatible filter and backfill materials, or cases where geotextile permittivity controls flow.

Keywords

maintainable drains

retaining walls

water pressure reduction

drain spacing

drain diameter

weep holes

geotextile filter

backfill seepage

finite element modeling

groundwater drawdown