A six-inch diameter underdrain pipe with perforations oriented downward is embedded within a compacted subgrade trench filled with three-eighths-inch pea gravel per specifications. The trench measures one foot six inches wide at the base with one-to-one side slopes and a minimum six-inch gravel clearance below the pipe. A layer of planting soil per soil plans rests directly above the gravel bed beneath the finished grade. The underdrain connects directly to the site drainage system.
Finished Grade Compacted Subgrade 3 8 " Pea Gravel, See Specifications 1'-6" 6" 6" 1 1 1 1 Min. Planting Soil, See Soil Plans Connect Underdrains to Drainage Note: 6" Diameter Underdrain- Perforations Down
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