HEATING MAIN MONTAGE INSTRUCTIONS CV4.04
10. BACKFILLING OF THE TRENCH
Place pipes on compressed sand foundation, keeping track of spacing between pipes and
spacing from trench sides – see 2
nd
section. Place compensation pillows according to
designed specification (documentation).
Remove from the trench temporary supports and any other objects.
Fill up the trench by adding layers gradually. Before adding following layer, first compact
previous one. Maximal thickness of one layer if non mechanical compaction is performed –
150 mm, if mechanical then 300 mm.
Depending from designed thermal deformation compensation method, available 2 (two)
trench backfilling versions:
1) fill up the trench when pipes are in cold state;
2) previously loading (heating) pipes before filling of the trench.
1
st
version First, cover pipes from the sides and gap between the pipes, until level of layer
doesn’t reach 100 mm above pipes. Use sand that does not contain any rocks, metal
pieces, floral leftovers, soil and stone pieces. Perform non-mechanical compaction. Place
caution tape at the designed depth (not less than 100 mm about preinsulated pipes) and
secure it by covering with sand.
For preinsulated pipes with diameter
≥
200 mm is recommended to place caution tape
above every pipe, heating and return. If preinsulated pipe diameter is <200 mm – place
one caution tape above both of the pipes. The rest of the trench fills with earlier digged out
soil. Mechanical compaction can be performed after trench filling is 200 mm above
preinsulated pipe.
If compensators or fixed anchors are used then no special backfilling demands are
required.
2
nd
version
In section where thermal pressure is
present, compact that area with sand up to
the center of preinsulated pipes (see
drawing). Mechanical compaction is not
allowed.
Heating main needs to be completely filled
up and compacted after the designed
temperature is reached.
If heating main is planned to be pressurized using base compensator, then cover pipes
and compress the trench while pipes are in cold condition; ends need to be left free where
thermal deformation compensation is predicted – compensator and heating main turns
within 60°÷90°. When heating main is heated up to t he designed pre-pressurized
temperature and base compensator finished working then weld the compensator out from
the pipe line. Fill and compact remaining part of the pipe line while keeping pre-
pressurized temperature.
After filling up of the trench perform environmental improvements to the area where
pipeline is buried: plant trees or other green plants, street or sidewalk restoration, etc.
10.1.
Ground level
