Untitled - Future Pipe Industries

Figure 4: Pipes in the same trench
Where pipes of the same or different diameters are installed in the same trench, a minimum spacing equal to (ND pipe ‘a’
+ ND pipe ‘b’)/4, but not smaller than 12”, is required.
3.4: Trench depth
3.4.1: Minimum trench depth
Generally the burial depth of pipe is specified by the design Engineer. A minimum clear cover above pipes (H min) shall
always be observed as follows for all stiffness classes.
• 2.0‘ with no traffic loads
• 3.3‘ with AASHTO H-20 traffic (4’ for SN 18 psi pipe & all Type IV installations)
• 5.0‘ with BS 153 HA traffics & ISO HT-60, 3 axle trucks loads.
• 5.0‘ for road compaction equipment up to 18 Tons (vibrated roller compacter)
• 10‘ for Cooper E-80 Railroad loadings (12’ for SN 18 psi pipe).
Note: Minimum cover restrictions may be reduced with special installations such as concrete encasement, concrete protection
slabs, casings, or other provisions to carry the surface load. In case of high ground water table, a minimum cover depth
equal to 80 % of the pipe diameter of granular compacted soil must be provided to prevent pipes from floating. Always insure
that this minimum cover is available before turning off dewatering systems.
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