Pile Cap Construction Methodology

Methodology for Pile Cap

Before commencement of excavation, the pile cap area shall be marked on the ground with reference to approved control points and drawings.

After excavation, pit levels shall be checked and recorded as per approved drawings.
Longitudinal and transverse center lines shall be marked outside the excavation pit for reference and cross-checking of pile positions.
Pile shift shall be recorded by marking theoretical pile coordinates and comparing actual pile positions.
A circle equivalent to pile diameter shall be drawn to measure pile deviation.
As-built details of piles shall be jointly recorded.
Based on pile location, PCC and pile cap layout shall be marked ensuring minimum 150 mm offset from pile edge.
After laying PCC, pile cap layout shall be transferred on PCC surface to facilitate reinforcement fixing and shuttering erection.

Excavation shall be carried out as per approved drawings and required dimensions.

Shoring arrangements shall be provided depending on soil stability conditions.
Steel plates and props shall be used for shoring wherever required.
Excavation dimensions shall provide sufficient working space around pile cap.
Last 300 mm excavation shall be carried out manually.
Levelling course shall be laid within 36 hours after completion of final excavation.
A sump of approximately 750 mm depth below PCC level shall be provided for dewatering.
Earthen drains shall be provided around excavation if required to divert rainwater and seepage water.
Water table shall be maintained at least 300 mm below excavation level before PCC laying.
Excavated earth shall be disposed using dumpers/loaders at approved dumping locations.

Pile head laitance shall be removed after pile casting to expose sound concrete.

Pneumatic jack hammers may be used after 7 days of pile casting.
Manual chipping may be carried out after 3 days of pile casting.
Pile top shall project minimum 50 mm into pile cap as per IRC:78 Clause 709.5.2.
Pile reinforcement shall be fully anchored into pile cap.
Broken concrete debris shall be removed and disposed at approved locations.
Exposed reinforcement bars shall be cleaned and straightened using wire brush.

After levelling the foundation surface, PCC shall be laid as per approved drawings.

Foundation surface shall be watered before PCC placement.
PCC of M15 grade or specified grade shall be produced in batching plant and transported using transit mixers.
Concrete shall be poured through chutes and levelled manually.
PCC shall extend at least 100 mm beyond pile cap edges to facilitate shuttering.
PCC levels shall be jointly checked and verified.
PCC curing shall be carried out by sprinkling water.

Reinforcement shall be fixed manually as per approved drawings.
Pile reinforcement shall be lapped with pile cap reinforcement.
Cover blocks of same grade concrete shall be provided at approximately 2 m c/c spacing.
Bars shall be tied using GI binding wire.
Pier shaft reinforcement shall be erected after fixing pile cap reinforcement.
Suitable staging frames shall be used for supporting pier reinforcement cages.
Reinforcement cage inspection shall be carried out jointly with AE as per IRC SP:112 checklist.
Sufficient chairs and spacers shall be provided to maintain cage position and cover.
Pier dowels shall be fixed rigidly to prevent buckling or displacement.

Shuttering shall be fabricated and erected as per approved drawings.

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Shuttering locations shall be marked based on pile cap layout over PCC.
Shuttering surfaces shall be cleaned with wire brush before erection.
Approved shuttering oil shall be applied before fixing.
Rubber strips or foam strips shall be provided at joints to prevent slurry leakage.
Adequate side supports, bracings, and tie bars shall be provided to resist concrete pressure.
Shuttering alignment, dimensions, and supports shall be checked before concreting.

Concrete of approved grade shall be produced at batching plant and transported using transit mixers.

Slump shall be checked at pouring location and maintained between 80 mm and 130 mm.
Concrete shall be placed using concrete pump, placer boom, or chutes.
Concrete placement shall proceed continuously from one end to another.
Free fall of concrete shall not exceed 1.5 m.
Concrete shall be compacted using 40 mm / 60 mm needle vibrators.
Concrete cubes shall be cast for compressive strength testing as per IRC:21.
Successive layers shall be placed before initial setting of previous layer to avoid cold joints.
Regular tamping and vibration shall be ensured throughout concreting operations.

Date of casting shall be marked on concrete surface to monitor curing duration.

Concrete curing shall be carried out using ponding method.
Bunds shall be prepared using lean cement mortar after initial setting.
Bunds shall be filled continuously with water from approved source.
Pile cap sides shall be covered with wet hessian cloth until backfilling starts.
Backfill soil shall also be kept moist to continue curing effect.

Backfilling shall commence after de-shuttering and joint inspection approval.

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Backfilling shall be carried out using approved excavated material or local soil.
Soil shall be placed in layers not exceeding 150 mm compacted thickness.
Compaction shall be carried out using mechanical tampers, rammers, or plate compactors.
Watering shall be done as required to achieve proper compaction.
Compacted density shall not be less than pre-excavation field density.

Proper barricading and caution boards shall be provided around excavation areas.
Workers shall wear PPE including helmets, gloves, safety shoes, reflective jackets, and safety belts.
Dewatering arrangements shall be maintained during excavation activities.
All lifting equipment and machinery shall be inspected before use.
Safe access ladders and working platforms shall be provided inside excavation pits.
Night work areas shall be properly illuminated.