Untitled - Future Pipe Industries

4.0: Backfilling and installation selection
The installation type and choice of pipe bedding and backfill material is normally specified by the design Engineer, based
on the specified pipe stiffness class (SN), maximum burial depth, vacuum requirements, and native soil conditions.
4.1: Acceptable pipe foundation, bedding and pipe zone backfill materials
The following materials are generally acceptable for the pipe foundation, bedding and pipe zone backfill depending on the
selected installation type.
A) Crushed stones & rock
B) Gravel
C) Clean sand
D) Mixed Sand
E) Excavated granular material
F) Cement stabilized sand (sand - cement mixture)
** Not recommended in high water table installations.
A & B) Clean; single grade or well graded gravel and crushed rock/stones containing less than 15% sands and less than 5%
fines, are an excellent backfill material. These materials are essentially self-compacting and the required density is generally
achieved when dumped (maximum 12”lifts) with only light compaction required after the pipe haunches have been filled. In
cases of high ground water table in the trench zone where the possibility of migration with native soils exist, a suitable geotextile
filter membrane (e.g. Terram® ) should be used to line the trench bottom and sides up to the top of the pipe zone. If
geotextile filter membrane is required, but unavailable, then clean sand should be used as the backfill material.
(Unified soils classification: GW, crushed rock)
Note: See section 4.3 on native soil migration
C) Clean sand containing less than 5% fines, is good backfill material. Compacted to 90% standard proctor density, using
hand tamping or plate vibrators (recommended). Maintain moisture content near optimum to minimize compaction effort.
Place and compact in 12” maximum layers.
(Unified soil classification per ASTM D2487: SW, SP)
D) Mixed sand containing less than 12% fines is good backfill material. Compacted to 90% standard proctor density, using
hand tamping or plate vibrators (recommended). Maintain moisture content near optimum to minimize compaction effort.
Place and compact in 8” maximum layers.
(Unified soil classification per ASTM D2487: SW, SP)
E) Excavated granular material containing more than 12% fines consisting basically of gravel with fines or sand with fines.
Compacted to 90 % standard proctor density, using hand tamping or plate vibrators (recommended). Maintain moisture content
near optimum to minimize compaction effort. Place and compact in 6” maximum layer.
(Unified soil classification per ASTM D2487: GM, GC, SM, SC)
F) Cement stabilized sand is a mixture of one sack of cement per one ton of clean sand. This backfill material provides excellent
support for pipe where native soil conditions are poor and would otherwise require a wide trench (up to 4 x DN) excavation,
or a higher stiffness pipe. This mixture can be obtained dry, from ready-mix concrete suppliers. It should be placed in
the foundation, bedding, haunches and pipe zone backfill in maximum 8” lifts. Each lift should be wetted with water and
compacted with plate vibrators before the cement sets.
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