7/29/2019 Drainage Pipe and Metal Culve - Method Statement
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1. Scope of Works
This section covers the work in connection with excavation,
laying and
backfilling of prefabricated concrete, rectangular and metal
pipe culverts as
well as extending existing culverts.
2. Reference Documents
Specifications General Specifications for Roads and Bridge
Works, Republic of
Uganda. Volume III A section 2200
Tender Dossier: Volume IV Section 7.1 (Special Specifications)
Manufactured Items Prefabricated Concrete pipe culverts
Prefabricated rectangular concrete culverts Corrugated metal pipe
culverts Quality Control Plan: 110.199/QCP/003
Contract Drawings
3. Plant Requirements
Excavator or TLB 7 ton crane truck Watercart 75-90 Bomag Wacker
Rammers
7/29/2019 Drainage Pipe and Metal Culve - Method Statement
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4. MethodologyEnsure that all materials that will be
incorporated into the permanent works have been
approved by the Engineer prior to commencement of the works.
Construction of drainage
will be done in half widths and after completion of the fill
layers. Surveyor to check and set
out for culverts giving line and invert level by means of
profiles and traveler.
As a general rule, prefabricated culverts shall be constructed
under trenched conditions.
The only exceptions to this rule will normally be thelarger size
of metal culverts and in some instances the larger portal or
rectangular culverts
or, where the Engineer considers it advisable under the certain
local or climatic conditions
that prefabricated culverts be constructed ahead of the fill.
Culverts shall be constructed
under embankment conditions only where shown on the Drawings or
on written authority of
the Engineer.
After setting out excavation will commence to the correct line
and level and width. The
bedding of the culverts consists ofaClass A bedding. Therefore
the bottom of the trench
will be compacted with a pedestrian roller but not tested. The
surveyor will then provide
steel pegs with invert levels marked at each end inside the
trench.
Cast a Class 15/40 MPa concrete blinding layer below the lowest
part of the pipe as
indicated on the Drawings and allow to harden. Using an
excavator, placing of the culverts
will commence. The culverts shall be laid hard up against each
other so as to obtain tight
joints. In the case of butt-edged pipes, the joints shall be
externally wrapped with two
layers of 340g/m2 type Hessian which has previously been soaked
in bituminous emulsion.
The wrapping shall be at least 150mm wide, and the pipes shall
first be primed with a coat
of 60% bituminous emulsion before wrapping with the Hessian. The
inside of the pipe shall
be smooth with no displaced joints. All pipes shall be laid true
to line and level.
Place a stop ends at inlet and outlet of pipes, then pour a
class of 15/40 MPa concrete to
encase the pipe culverts as indicated on the Drawings. A poker
vibrator will be used tovibrate the concrete as it is poured around
the pipe. Concrete casing shall be cast in one
continuous operation until completed.
The next day backfilling will commence. Where the excavated
material is not of adequate
quality, selected material shall be imported for this use.
Whereby culverts are not encased
in concrete, backfilling shall be carried out simultaneously and
equally on both sides on the
culvert to avoid unequal material forces, and in layers not more
than 150 mm in thickness.
Backfilling will continue until the required maximum and minimum
as indicated on the
Drawings. The gravel will be compacted to 95% MOD AASTHO and
each layer will be tested.
