Untitled - Future Pipe Industries

Figure 23: Pipe pig
• Preliminary deflection measurement (Recommended) :
This measurement should be taken when backfill reaches 12” above pipe crown. At this stage the measured deflection should
be zero or slightly negative (not less than -2%). A slight negative deflection means the pipe vertical ID has increased slightly
from the compaction forces coming from good side backfill compaction.
If a positive deflection is measured at this stage it indicates inadequate compaction in the pipe zone, and improvements in
the quality of installation and compaction effort are required. Depending on final depth of cover it may be advisable to
remove the backfill to about 1/3 of the pipe ID from the trench bottom, and to re-compact the backfill in stages up to the top
of the pipe zone. After this rectification, the preliminary deflection should be measured again. If the backfill compaction has
been done properly then a slight negative deflection should be observed.
• Initial deflection measurement (Required)
This measurement should be done immediately after backfilling reaches the final grade and after all temporary sheeting has
been withdrawn and all de-watering systems (e.g. well points) have been turned off for two days. The maximum initial deflection
should not exceed the following limits:
Table 11
If the initial deflection exceeds the above limits, the Contractor should re-excavate the trench (by hand from 1 foot above pipe
crown), remove the pipe zone backfill and start backfilling the pipe once more, paying attention to the pipe haunches and
backfilling in appropriate lifts to reach the required compaction density. Alternatively if the deflection only slightly exceeds
the above limits, the pipeline section deflection may be monitored over the following 6 months period with monthly deflection
measurement. If deflections at the end of the 6 months do not exceed 5 %, the pipeline section may be considered as
accepted. Any section whose deflection has exceeded 5 % must be excavated and re-backfilled.
Any recently installed pipe exhibiting deflections equal or greater than 9% (7% for pipes SN 72 psi) must be replaced. Such
pipe must not be re-installed nor incorporated in any permanent works on site.
• Final deflection measurement (optional)
Soils Groups
1 2 3 4
Blow counts (N) (ASTM D 1586 >8 6-8 3-5 2
Cohesive soils Stiff Medium Soft Very Soft
Granular soils S. Compact Loose Loose V. Loose
max. initial deflection 3% 3% 2.50% 2%
Good native soils >>>Poor native soils
This measurement should be done 6 months after the initial test is done, in cases where the initial deflection readings have
exceed the limits shown in table 10 above and have not been rectified. The deflection reading at this stage can be considered
the long term deflection and should not exceed 5% ( 6 % for water pipe). Pipes exhibiting deflections in excess of these
values should be re-excavated and re-backfilled with properly compacted backfill material.
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