2. INTRODUCTION
Pile caps are thick reinforced concrete mat which rest on top of
the concrete or timber piles (driven or bored and cast-in-situ) to
provide stability to the foundation. The main objective of constructing
the pile caps is to distribute the load of column(s), which is generally
huge for large constructions, to the under lying piles. A similar type of
foundation to the pile caps are Raft Foundation. In case of Raft, which is
a thick and wide spread RCC slab directly resting at the base of
foundation, loads from columns get directly transported to the soil
strata through the Raft. Raft can only be used for stable hard soil layer
capable to carry huge load without failure. Otherwise Pile and Pile caps
are generally used.
FUNCTION OF PILE CAP
1. To distribute a single load coming from the column to the piles
equally.
2. To laterally stabilize the pile thus increasing the overall
efficiency of the pile group
3. To provide the necessary combined resistance stresses set up
by the super structure and/or the ground movement.
3. Typical arrangements of piles in pile groups:
Typical shape of pile caps for different number of
piles:
4. MAIN FEATURES OF PILE CAPS
Minimum grade of concrete that can be used in construction
of piles and pile caps is M25. A complete pile cap can be
casted monolithically in case of smaller pile like for 2-3 piles.
For larger pile caps than those casting is done in layers.
Reinforcement bars of columns are embedded into the pile
caps up to their development lengths.
After casting is done pile caps are cured for 28 days and the
shuttering is removed. The adjacent soil is compacted and
leveled using compactor.
When number of piles in a group is too high, pile caps are
constructed in the form of raft instead of constructing small
pile caps.
Reinforcement caging for a pile cap with 7 piles underneath
5. PILE CAP CONSTRUCTION AFTER PILES ARE
COMPLETE:
After the completion of DMC piling, the piles are kept for 28
days for curing and the reinforcement bars of the piles are
kept well above the ground level so that they can be easily
traced later.
The surveyor determines the level up to which the soil is to
be excavated to construct pile caps.
The soil is excavated according to that predetermined level
and the upper portions of the piles are then chipped off with
ordinary hammer and jack-hammer. The necessity of this
chipping off of the upper portions of the piles is to get well
compacted concrete piles beneath the pile caps. If the pile
heads were not chipped off, there may have some voids
present in piles below the caps leaving them of little
strength.
The upper portion of piles after excavation up to desired level
6. Chipping off of the upper ends of the piles
As per design and detailing, the depth of the pile caps are
assured and reinforcement is provided. Sufficient clear cover
is provided using concrete cubes of required dimension,
passing them through the steel bars in definite intervals.
The form work is then completed and concreting is done
monolithically or in layers depending upon the size, depth
and reinforcement density of the pile caps.
7. BATCHING
PLANT
PROJECT SITE
TCS (TATA CONSULTANCY SERVICE) IT-SEZ PARK
DLF, NEWTOWN, RAJARHAT, KOLKATA,
WESTBENGAL
JOINT VENTURE PROJECT OF L&T AND SPCL
8. INTRODUCTION
A batching plant is a mechanical system that efficiently mixes and
prepares concrete of desired strength and quality. Cement, coarse
aggregates, sand, water are mixed according to design specifications,
fly ash, admixtures etc are added if required. The whole process is done
mechanically.
Schematic diagram of a concrete batching plant.
9. Types of batching plant
On the basis of amount of concrete prepared by the plant in unit
time the plants are classified. At the project site the plant in work was
CP30 or Concrete Plant 30. It means that the plant can ideally produce
30 m3
concrete in an hour. There is also CP60 type of plants that are
usually used. It produces 60 m3
concrete in an hour, or 1 m3
concrete in
a minute. So these are also called M1 plants.
COMMON PARTS OF A BTACHING PLANT
CEMENT SILO: These store the cement. There is usually
more than one silo used for a plant to store different kinds
of cements. These are large cylindrical structure with
tapered bottom end connected to the screw conveyor.
SCREW CONVEYOR: this is used to carry the cement from
the silo to the pan mixer.
HOPPER: this is where the front end loader dumps the
aggregates.
BELT CONVEYEOR: this carries the aggregates from hopper
to the aggregates bin.
AGGREGATE STORAGE BIN: These are the conical bins that
temporarily store the aggregates, both coarse and fine and
supply them to the skip bucket.
PNEUMATIC CYLINDER AND DISCHARGE GATE: These are
attached with computerized censors and discharge exact
amount of aggregate into the skip bucket as per mix design
specification.
10. SKIP BUCKET: it carries the aggregate from storage bin to
the pan mixer.
SKIP BUCKET AND DISCHARGE GATES
PAN MIXER: this is where the concrete is prepared by
mixing all its ingredients. And when the concrete is ready
they discharge the ready concrete into the transit mixer.
ADMIXTUER CHAMBER: admixtures are stored here and
those are conveyed to the pan mixers.
ADMIXTURE CHAMBER
11. CEMENT FEEDING PUMP: these are used to feed the silo
with cement from the cement storage rooms.
DUST COLLECTOR: this is a chamber that, through a pipe
and pump, collects the harmful cement dust from the
storage room.
DUST COLLECTOR
CONTROL ROOM: this is, from where the whole procedure
is controlled. Computer software is made by the plant
manufactures that also controls the concrete preparation
process. If in case there is any problem the procedures can
be controlled manually too.
SOFTWARE AIDED CONTRLON
WATER VAT: this is a vat located near the plant from where
required amount of water is supplied to the pan mixer
through a pump.
13. CONCLUSION TO THE PORJECT
At the project site the plant was aided by one 180kVA and
one 125kVA power generators. Naphtha-base “sikamant-3008NS”
admixtures were being used. For concrete of higher strength (higher
grade than M50) PC-base admixtures are used. The mixing arms inside
the pan mixer are powered by 30Hp motor. Correction shits were
prepared on daily basis to check deviation in strength of concrete due
to variable moisture content of sand.
