In this article, we will discuss the method statement of pile cap in detail.
A pile cap is a thick concrete foundation that sits on concrete or timber piles driven into the porous or unstable ground to provide a stable foundation. It usually forms part of the foundation of a building or structure, or it is the uppermost portion of a pile that secures the piles in position and receives and distributes superstructure loads.
Table of Contents
Method Statement of Pile Cap
1. Equipment
Excavator
Dumpers
Batching Plant
Transit Mixers Truck/trailer
Welding Generator
Concrete Vibrators
Jackhammers
Air Compressor Crane
Dewatering Pump
As per site condition, above mentioned equipment can be increased or decreased.
2. Procedure
a. Survey
Before excavation, the pile cap area shall be marked on the ground after conducting a survey concerning control points. After excavation, the pit levels shall be verified for correctness to the drawings and recorded.
Longitudinal and transverse centerlines shall be marked outside the pit for reference for cross-verifying the pile.
The pile shift shall be recorded by marking the theoretical coordinates of the pile on the ground, and a circle equivalent to the pile diameter shall be drawn, and the shift of the actual pile will be measured from the theoretical edges of the pile.
The as-built details of the piles shall be recorded jointly. Based on the shifted location of the pile top, the pile cap / Portland Concrete Cement (PCC) layout shall be marked to ensure a minimal 150 mm offset from the outer edge of the pile. After laying of PCC, the layout of the pile cap shall be marked on it with reference to the reference points to facilitate tying of rebar and erection of shuttering.
b. Excavation
Shoring shall be provided contingent upon the stability of the soil found in the area. Shoring shall be done with the aid of old steel plates and props. At road locations, the pit shall be excavated to the dimensions giving working space all around the pile cap to facilitate the fixing of steel & erection of shuttering as detailed in the drawings.
The last 300 mm excavation shall be carried out manually & leveling course shall be laid down within 36 hrs after concluding the excavation of the last 200 mm depth.
A sump shall be provided at the comer of the pit to pump out underground water about 750 mm deep from the PCC bottom.
Also, an earthen drain of about 200 mm in width, if required, shall be provided all around the pile cap dimension & it shall be connected with a sump to drain off excess rainwater/seepage water to ensure that the water table will at least 300 mm below the lowest level of the excavation before laying PCC. Means of vehicles/loaders shall then dispose of the excavated earth.
c. Removal of Laitance
After excavation, the laitance of the piles shall be cleared by using pneumatic jackhammers seven days after casting the pile or manually three days after casting the pile. After striping, the top of the pile shall project 50 mm into the pile cap, and reinforcements of the pile shall be entirely anchored in the pile cap as per clause 709.5.2 of IRC: 78:2000.
The debris of fractured concrete shall be removed from the pit and disposed of to approve dumping sites. Exposed bars shall be straightened & cleaned correctly with a wire brush.
d. PCC
After leveling the bottom of the planter, sprinkle some water to keep the soil moist. PCC of Mix M15 or specified in the drawing shall be mixed at the centralized batching facility at the casting yard and transported to the site in transit mixers.
The concrete shall directly pour through chutes from three locations, spread, and leveled manually to the specified thickness indicated in the drawing.
PCC edges shall be projected 100 mm more than the pile cap as detailed in the drawing to facilitate the fixing of formwork, and levels of PCC shall be jointly checked & verified. The PCC shall be cured by showering with water.
e. Reinforcement
a) Fabrication
BBS shall be prepared per the “Approved for Construction” drawings for reinforcement fabrication.
The Reinforcement shall be cut using cutting machinery or manually as required and bent at the rebar yard. The re-bars shall either be transported to the location in a trailer/vehicle or cutting bending may be done at the site depending upon the situation.
b) Fixing of Rebars
The re-bars shall be manually fixed into their position, as shown in the good for construction drawing. Reinforcement of the pile cap shall be lapped with the pile reinforcement. Cover blocks of the same grade of concrete in which these are to be embedded shall be provided at a spacing of about 2.0 m c/c to ensure uniform cover as specified in the drawing and tied together with GI binding wire.
After fixing the pile cap rebar, the pier shaft rebar shall be erected. This rebar shall be supported by erecting a suitable staging structure across the width of the pile cap. The rebar cage shall be checked per the checklist in the QA manual, and RFI for inspection shall be raised with IE.
The rebar, chairs, spacers & laps shall be jointly checked after cage placing. Sufficient chairs and spacers shall be provided to maintain the cage in its proper position. After receiving the clearance, shuttering balance work will be taken up. Pier dowels shall be held in position rigidly to prevent them from buckling.
f. Shuttering
Shuttering fabricated as per approved drawings shall be placed at locations as per the pile cap dimensions shown in the good-for-construction drawing. Reinforcement shall be fixed as per the drawing and marking of the layout on PCC for the pile cap. After concluding the fixing of the rebar cage, shuttering shall be erected & fixed on the layout drawn on PCC.
Before fixing, the shuttering area shall be cleaned with a wire brush & approved shuttering lubricant shall be applied on the concrete face. After fixing of shuttering, it shall be checked as per the QA checklist, and RFI to be raised for inspection of IE.
To prevent leakages from joints, rubber strips/foam strips shall be provided at the joints of shuttering plates. Right-side supports/bracings/tie bars shall be provided to resist the lateral pressure of green concrete during pouring.
g. Concreting
The required (M-35) grade concrete shall be produced per the approved concrete design mix from the centralized batching facility and transported by transit mixers to the pouring location. Before pouring concrete, the 80 mm to 130 mm slump shall be checked at the pouring position.
A pump /placer boom or direct chutes shall deposit the concrete. Concrete placement commences from one end to another in a cascading manner till completion. The falling height of the concrete should not be more than 1.5 m. The concrete shall be vibrated using 60 mm / 40 mm diameter needle vibrators. Concrete slabs shall be taken to test compressive strength as per IRC 21 at the pouring location.
Concreting should be done so that the next layer of concrete should be laid before an initial set of concrete of the previous layer to avoid cold joints. Regular tamping shall be done during & after concreting operation.
h. Curing
The definite date shall be inscribed on the concrete surface to ensure curing up to the specified duration after the casting date.
The ponding procedure shall cure the concrete. Bunds of cement mortar of lean mix shall be built after the concrete attains the final setting time after concrete casting; these bunds shall be filled with water from the approved source.
The sides of the pile cap shall be covered with a Hessian cloth till backfilling is begun. Further, curing is ensured by maintaining the backfill moist with water.
i. Backfilling
Immediately after de-shuttering, the concrete surface shall be checked jointly and get the approval for backfilling. Backfilling with local earth available or excavated material shall be carried out in strata of 250 mm (compacted thickness).(as per MORT&H clause no – 304.3.7)
The compaction shall be done with the help of suitable equipment, such as a rammer or plate vibrator, after necessary watering to attain a density not less than the required field density.
j. Miscellaneous Works
After backfilling, the damaged roads, if any, shall be repaired promptly, preferably within 15 days of backfilling as per specification before removing the barricades; the whole area shall be cleaned after completion of work.
Safety:
All safety precautions shall be followed per the safety manual submitted.
Further, the preparatory works shall also be carried out as per diversion plans separately submitted for construction activities in urban areas.
1. A width of approximately 8.00 m (outside to outside of barricading) shall be barricaded along the road to construct pile capping. This can be increased at a specific location with the prior sanction of the Engineer.
2. Suitable reflectors, blinkers, diversion board, painting of barricade, etc. shall be done to caution the road users and for their safety. Working space shall be well illuminated during work at night.
3. All site personnel shall wear headgear, safety shoes, and other safety devices as required.
Proper precautions and safety provisions shall be used for activities like welding, handling of reinforcement, fixing of formwork, electrically operated equipment, etc.
tag: Method Statement of Pile Cap