Trench or Open Ditch InstallationsNominal Minimum Minimum Min. Trench Diameter Thickness Cover Width D B C W 10" 4" 12" 26" 12" 5" 12" 28" 15" 5" 12" 31" 18" 6" 12" 36" 24" 6" 12" 42" 30" 6" 12" 50" 36" 6" 12" 57"
- Care during installation- Care should be taken to prevent damage to the pipe during the backfilling operation. Avoid dropping large clods or rocks directly on the pipe especially if the flexible pipe is being used. Impact loads of all types should be avoided until pipe is properly bedded.
- Bedding- Pipe should be bedded in gravel. However, selected soil backfill material may also be used with satisfactory results, provided it is compacted. The bedding material should be placed around the pipe to a depth at least 2" over the top of the pipe. When selected soil bedding material from the trench excavation is used, choose small, loose particles of soil that will flow around the pipe and minimize soil setting. Avoid large rocks that may damage the pipe or large clods of soil that cause voids and subsequent excessive settling.
- Depth of Cover- If vehicular traffic is expected over pipe, there should be a minimum of 12" of cover. Typical recommended gravel materials would be pea gravel, 6A stone, or pit-run coarse sand and gravel mixes.
- Proper Grade- The grade, or fall, on which pipe is laid is critical in that reversals in grade will greatly reduce the effectiveness of the system. Best drainage results are achieved with a continuous downhill fall, or grade, over the entire length of the drain line. A fall of 0.2 inches per 10 feet of length is generally considered adequate. Greater fall will promote more rapid drainage. I like a fall of 1 inch for 10 feet of length, but that is not always possible.
- Proper Selection of Materials- Choose your materials according to application. If absorption and drainage are required, perforated pipe should be used. If pipe serves only to move water away from an area (such as downspout run-offs, etc.), non-perforated pipe is best because it will not dissipate water into the surrounding area. Non-perforated pipe should also be used if the line runs close to trees where root penetration may be a problem. If the soil being drained is sandy or silty, then either a protective wrap, hay or gravel should be used to prevent the soils from entering and blocking the drainage line.
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