Excavation, Placement and Compaction Technical Requirements in Subkha Areas
“Minimum trench width from the bottom to 300 mm above the top of the pipe shall be as follows:
Type of Pipe Nom. Size (mm) Min. Width (mm)
Thermoplastic 90 & under 300
Thermoplastic 110 & over O.D. + 300
RTR 250 & under O.D. + 300
RTR 300 – 600 2 x O.D.
RTR Over 600 O.D. + 600
Cast Iron All O.D. + 400
Ductile Iron All O.D. + 400″
“Depth of trench shall be dug deep enough to provide a cover above the top of the pipe as listed below, and a ground bed of at least 150 mm from the bottom of the pipe.
Type of Pipe Nom. Size (mm) & Service Min. Cover (mm)
Thermoplastic Sewers, gravity flow 900
Thermoplastic Press. pipe under 100mm 600
Thermoplastic Press. pipe 100mm & larger 900
Thermoplastic irrigation, under 90 mm size 300 *
Thermoplastic irrigation, 90 mm & larger 600
RTR Under 150 mm 600
RTR 150mm and larger 900
Cast Iron soil Typical 900
Ductile Iron Typical 900
* 600 mm under paved roads”
- In Sabkha areas, the base support layer shall consist of 150mm deep of Class B crushed stone. (Alternatively, a double layer of sandbags may be used for a base support layer, with approval from the Chairman of Plumbing and Utilities Standards Committee).
- Base support layers of crushed stone base shall be compacted to at least 95% per ASTM D698.
- Clean sand bedding layers shall be 150mm thick and free of debris or rocks.
- A non-woven geotextile with a minimum unit weight of 100 g/sq. m shall be placed prior to placing the clean sand, to avoid sand filtration into the crushed stone base.
- Clean sand layer shall be compacted to at least 70% relative density per ASTM D4253/4254 or 95% relative compaction per ASTM D698 whichever gives a higher density.
- Frequency of Testing shall be as follows: Road base & subbase, One test for every 2000ft2 (180m2) of each lift; Backfill for trenches, One test for every 50 linear feet (15 meters) of each lift; General fill shall have one test performed for every 5000ft2 (460m2) of each lift.