Phases of Bored Cast In-Situ Pile Construction

Complete Practical Guide for Civil & Geotechnical Engineers

Table of Contents

1. Introduction
2. Phase 1 – Pile Boring
3. Phase 2 – Reinforcement Cage Lowering
4. Phase 3 – Flushing
5. Phase 4 – Pile Concreting
6. Quality Control
7. Safety
8. FAQ

Introduction

Bored Cast In-Situ piles are one of the most widely adopted deep foundation systems for bridges, high-rise buildings, metro projects, marine structures and industrial foundations. Unlike driven piles, these piles are constructed by drilling a borehole and subsequently placing reinforcement and concrete inside the bore.

Phase 1 – Pile Boring

Equipment Required

• Rotary Hydraulic Rig
• Kelly Bar
• Drilling Bucket
• Auger
• Chisel
• Tremie Pipe
• Bentonite Plant
• Desander Unit

Construction Procedure

1. Mobilize drilling rig at the marked pile location.
2. Establish two perpendicular reference lines.
3. Carry out initial boring up to about 2 m.
4. Install temporary guide casing.
5. Check casing verticality and pile center.
6. Continue boring using bentonite slurry wherever required.
7. Maintain bentonite density between 1.05 and 1.10 g/cc.
8. Maintain Marsh Cone viscosity between 30–40 seconds.
9. Maintain pH between 9.5 and 12.
10. Circulate slurry continuously.
11. Recycle slurry through settling tanks and desander.
12. Measure bore depth using sounding chain.
13. Record bore log.

Important: The borehole should remain stable throughout drilling. Slurry properties shall be checked at regular intervals.

Phase 2 – Reinforcement Cage Lowering

1. Fabricate reinforcement cage as per approved drawing.
2. Inspect cage dimensions and welding.
3. Provide concrete cover blocks.
4. Lift cage using suitable crane.
5. Lower cage carefully inside bore.
6. Large cages should be lowered in segments and welded.
7. Verify final cage level.

Phase 3 – Flushing

Flushing removes loose sediments accumulated at the base of the borehole.

1. Insert 200 mm diameter tremie pipe.
2. Maintain 75–100 mm clearance above pile base.
3. Pump bentonite through tremie.
4. Continue flushing until inflow and outflow slurry become similar.
5. Ensure clean founding stratum before concreting.

Phase 4 – Pile Concreting

1. Check slurry density near bottom.
2. Collect slurry samples.
3. Attach funnel to tremie.
4. Maintain slump between 150–200 mm.
5. Provide initial concrete plug.
6. Maintain continuous concreting.
7. Keep tremie embedded in fresh concrete.
8. Avoid interruption.
9. Concrete at least 300 mm above cut-off level.
10. Clean tremie after completion.

Quality Control Checklist

Item	Requirement
Verticality	Within permissible tolerance
Bore Diameter	As per design
Depth	As per drawing
Bentonite Density	1.05–1.10 g/cc
Marsh Cone	30–40 sec
Slump	150–200 mm
Tremie Embedment	Always inside concrete

Safety Precautions

• Barricade drilling area.
• Use PPE.
• Inspect lifting equipment.
• Prevent personnel from standing below suspended cage.
• Provide proper lighting during night work.

Frequently Asked Questions

Why is bentonite used?

To stabilize borehole walls and prevent collapse.

Why is flushing required?

To remove loose sediments before concreting.

Why should tremie remain embedded?

To prevent segregation and contamination of concrete.

Conclusion

Proper execution of the four construction phases—pile boring, reinforcement cage lowering, flushing, and tremie concreting—ensures high-quality bored cast in-situ piles with adequate structural performance and durability. Quality control and inspection at every stage are essential for successful foundation construction.

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About the Author

Digitech Education
Prepared by Mohan Dangi (Gold Medalist, M.Tech Geotechnical Engineering, NIT Warangal) for civil engineering professionals and students.

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