1 OBJECTIVE
To define the operations involved during
foundation construction and the procedures for each activity to ensure
compliance with the technical specification and safety to plant and personnel.
2 ACTIVITIES
The activities comprise:
·
Site
preparation (Item 3)
·
Setting
out (Item 4)
·
Excavation
(Item 5)
·
Blinding
Concrete (where necessary) (Item 6)
·
Stub
setting (Item 7)
·
Reinforcement
work (Item 8)
·
Formwork
(Item 9)
·
Mixing,
pouring and compaction of concrete (Item 10)
·
Formwork
removal (Item 11)
·
Concrete
curing (Item 12)
·
Backfilling
(Item 13)
·
Site
Cleanup and Erosion Control (Item 14)
3 SITE PREPARATION
Permitted area of working
The permitted area of working shall be verified.
Condition of work site
The work site shall be cleared of all
materials and obstruction that may impede the site activities.
Leveling
The
works of final Leveling should be getting approval by supervisor
Center Peg
The center peg shall be checked to
ensure it is in place and suitably protected
4 SETTING OUT
Center Peg
The Center peg together with
adjacent line pegs shall be used as the reference for all setting out at site.
5 EXCAVATION
Depth of excavation
The depths of the pit
excavations shall be referred to the center peg and recorded on the Inspection Worksheet.
Excavation shall be executed manually or by the use of an excavator.
Shoring and Shuttering
Shoring and Shuttering shall
be used where there is any possibility of collapse of the excavation.
Pumping
Should water be encountered
in the excavation suitable pumps shall be used. Manual de-watering shall only
be employed where the quantity of water ingress is minimal.
Foundation Type Verification
The foundation type
identified in the approved foudation class and the approved drawing shall be the basis of starting the excavation.
Excavation Check
When excavation is completed,
the levels of the excavated pits will be checked and entered in the Inspection
Worksheet.
6 BLINDING CONCRETE
Blinding concrete shall be laid , necessary to provide a clean and level working
surface. The thickness of the blinding layer shall be in accordance with the
approved foundation drawings.
7 STUB SETTING
All setting dimensions (back to back,
diagonals and levels) shall be measured using theodolites and calibrated steel
measuring tapes. The stubs will be set individually as follows.
Stub setting dimensions
Identify the required stub
setting dimensions for the tower type, body and leg extensions and, where
appropriate, chimney extension. The required values shall be entered on the
worksheet.
Precast block
The precast block shall be
placed over the working point and the dimension and level at the base
confirmed. The block shall be cast with the same approved design mix with a
size of 200 x 200 x 100mm.
Placement of Stub
Placing the first stub within the
excavation on the precast block and anchor the top of the stub employing the
stub supports. The stub supports are provided with means of fine adjustment
(turnbuckle) to facilitate the positioning of the stub to the correct location
(levels, rake and horizontal dimensions).
8 REINFORCEMENT WORK
All reinforcement bars shall
be strictly as per the sizes in the approved drawing. All bent reinforcement
shall be fabricated in the store yards and transported to site.. During
placement the following shall be adhered to :
All reinforcement shall be
cleaned of foreign material (mud, etc.) prior to placement.
The spacing between the bars
is as per the foundation drawing.
Precast concrete cover blocks
are to be utilized at all locations to ensure a minimum concrete cover of 50 mm
is obtained.
All reinforcement bars are to
be secured employing binding wires. The pad reinforcing shall be provided with
adequate supports to prevent sagging.
9 FORMWORK
Wooden formwork will be
employed with firm connections at the corners to prevent mortar from flowing
out of the base portion. The thickness of form work shall be suitable for the
intended purpose and of such a size to prevent any sagging that might result in
the specified concrete cover being infringed at any point.
10 MIXING, POURING AND COMPACTION OF CONCRETE
General
·
All
the materials such as fine and coarse aggregates, water, and cement required
concrete would be inspected for use prior to commencement.
These checks are to be
recorded in the Foundation Inspection Worksheet.
·
Prior
to commencement of concreting activities the following shall be available on
site:
Mixer in good working order;
Vibrator ;
Water (required quantity);
Fine Aggregate (required
quantity);
Coarse Aggregate (required
quantity);
Cement (required quantity)
and protection for the same;
Aggregate measuring boxes,
Slump cone and accessories;
Required test cube moulds and
accessories;
Dewatering pumps (if
necessary for the site).
Storage of materials
All materials employed for
the concrete shall be from approved sources only.
·
All
bags of cement shall be stored on site in a correct and proper manner; they
shall be protected from rain and surface water;
·
Aggregates
shall be placed on a waterproof sheet and covered to protect against dust and
heating by the sun. The fine and coarse aggregate stacks shall be kept
physically separated.
·
If
the coarse aggregates contain any foreign material (mud, excess, fines, etc,)
they shall be washed prior to use. Fine aggregates found to contain foreign
material shall be rejected
Mixing of concrete
·
The
mix quantities shall, at all times, be strictly in accordance with the approved
design mix quantities.
·
Volume
employing boxes of approved sizes shall measure all aggregates. The boxes shall
not be overfilled. After filling the box the contents shall be flush with the
top edges of the box sides to ensure the correct quantity in each box.
·
The
quantity of water added shall be reduced from the design volume depending on
the moisture content of the aggregates.
·
The
aggregates together with the cement shall be first added to the mixer without
water and mixed for a minimum of one minute or as long as is necessary to
ensure a homogeneous mix. When a homogeneous mix has been obtained the water
then shall be added after which the mixing shall continue for not less than 1
minute
·
Concrete
cubes shall be taken as follows:
All cubes shall be cast in an
approved manner. This shall comprise filling the mold in three equal layers
each being tamped 25 times with a 25 mm² tamp rod. After casting, the upper
(exposed) surface of the cube shall be indented with the cube identification
details comprising
Date
Section & Tower Number
Leg
Location (chimney / pad)
·
The
cubes shall, at the end of the working day and after setting has taken place,
be transported to the designated testing location where they will be stored and
cured under controlled conditions.
·
Cubes
taken from the chimney and pad / pyramid shall be tested at 28 days. However,
at the initial stages of construction extra cubes will be taken and tested at 7
as required to ensure acceptable quality standards are achieved.
Placement of Concrete
Proper care will be taken to
transfer the concrete from the mixer to the pit to avoid segregation of the
constituent materials. The following shall be adhered to:
·
The
maximum free-fall height shall not be more than 1.5 m. To ensure this chutes
shall be employed. Chutes shall be employed for pouring into the chimney
formwork.
·
After
and during pouring
the concrete shall be continuously vibrated to ensure proper compaction. Vibration
shall not be used as a means of repositioning the placed concrete.
·
Construction
joints shall be avoided as far as possible. Where this is unavoidable adequate
bond between the old and new shall be ensured by chipping the old concrete
surfaces to a rough surface. Immediately before placing the new concrete the
surface shall be cleaned and all loose particles removed. The cleaned surface
shall be primed with a layer approximately 15 mm thick of a wet mix comprising
cement and fine sand in equal proportions.
·
Immediately
after placement of the base and chimney concrete the setting dimensions will be
checked and adjusted provided concrete setting has not yet taken place.
·
11 FORMWORK REMOVAL
·
The
formworks will be carefully removed a minimum of 24 hours after casting.
·
12 CONCRETE CURING
·
Immediately
after the removal of the formwork all concrete exposed surfaces shall be
protected by the application of jute covers or equivalent which shall be kept
moist during the entire curing period.
·
Curing
shall be continuous for a minimum of 3 days after removal of the formwork or
until back filling commences.
13 BACKFILLING
·
Backfilling
shall be performed up to and restore the original contours of the site.
·
Backfilling
of the excavation shall not commence until a minimum of 24 hours after formwork
removal.
·
Backfilling
shall not commence until the concreting works have been inspected and approved
by PT. DSSP
and his representatives THIS IS AN INSPECTION HOLD POINT and shall be recorded
in the Inspection Worksheet.
·
Prior
to the commencement of backfilling all temporary timbering, shuttering, etc.,
and all decomposable or perishable material shall be removed from the
excavations.
·
Organic
matter, silt and oversize rocks shall not be employed as backfill material.
·
After
backfilling for all four legs is completed the stub setting dimensions and
levels will be rechecked and the results entered in the Inspection Worksheet.
·
The
stub supports will be removed after the foundation works have been finally
accepted.
14 SITE CLEANUP AND EROSION CONTROL
·
After
completion of all foundation and earthing activities the site shall be cleaned
of all surplus excavated material and construction materials.
·
The
work site shall be reinstated, wherever possible, to the original ground
contours.
·
The
site shall be checked to ensure the foundations are not exposed to possible
erosion problems from either natural surface water drainage and or that
resulting from the construction activities. If erosion is considered to be a
possible problem the matter shall be referred to the PT. DSSP supervising engineer who
shall determine what remedial measures are necessary. If erosion control
measures are deemed necessary a proposal shall be submitted to PT DSSP for approval giving the
following information:
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