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Bored Pile Construction: Comprehensive Guide to Quality Control and Post-Grouting Techniques

Project Overview of Bored Piles

This project features a ±0.000 absolute elevation of 5.050, with natural ground elevation at -0.550. The excavation depth reaches 15.2 meters, extending to 17.05 meters in specific areas and 19.85 meters in elevator pits. The foundation piles consist of Φ700 and Φ800 bored cast-in-place piles, with the Φ800 piles requiring post-grouting.

Key specifications:

  • Φ700 piles penetrate 3 meters into the 10-2 strongly weathered breccia tuff bearing stratum

  • Φ800 piles either penetrate 5 meters into 10-2 stratum or 1 meter into 10-3 moderately weathered breccia tuff

  • Excavation dimensions: North side 158m, West side 211.7m, South side 178m, East side 271m

  • Total excavation area: 36,516m² with approximately 570,000m³ of earthwork

  • Base soil composition: silty clay with淤泥 quality

  • Foundation pit design safety rating: Grade I according to technical specifications

Quality Control for Bored Cast-in-Place Piles

Quality Requirements

  • Project target: Luban Award (China’s highest construction quality honor)

  • Pile quality standard: 98% must meet Class I pile standards

  • Zero tolerance for Class III piles

Construction Process Flow

1. Construction Preparation

  • Plan site access roads, considering all construction factors

  • Install water supply, power, and drainage systems

  • Configure mud pits, sedimentation tanks, and mud channels per layout

  • Install and test equipment (Drill rig model: PS-10)

  • Verify material certifications and conduct pre-construction testing

2. Survey Layout

  • Verify and protect all control points and benchmarks

  • Mark pile positions with steel nails and red paint triangles

  • Measurement protocols:

    • Protect all survey markers with visible identification

    • Verify positions through triple-check system (technician → supervisor → client)

    • Maintain complete measurement records

    • Tolerance: <±5mm control error, <20mm pile position deviation

3. Steel Casing Installation

  • Specifications:

    • Length ≥1.2m, thickness=5mm

    • Φ700 piles: 800mm inner diameter casing

    • Φ800 piles: 900mm inner diameter casing

  • Installation requirements:

    • Top elevation above the groundwater level

    • Verticality tolerance <1/200

    • Ovality ≤2cm

    • Full penetration welding for watertightness

    • Bottom embedded ≥0.2m into natural soil

    • Center deviation ≤20mm

4. Drilling Rig Positioning

  • Level the rig base using precision instruments

  • Center deviation <20mm

  • Four-direction leveling error <1/200

5. Mud Process

  • Natural mud formation based on geological conditions

  • Continuous monitoring and waste mud removal

6. Drilling Process

  • Optimize parameters (speed/pressure) for different strata

  • Implement skip drilling when pile spacing <4D (D = pile diameter)

  • Alternative: 36-hour interval between adjacent piles

  • Depth control:

    • Minimum: design depth

    • Maximum over-drilling: 30cm

  • Verticality tolerance: <1/100

  • Position deviation: <50mm

7. Hole Cleaning

Two-stage process:

  1. Primary cleaning: Using drilling tools (≥30 minutes)

  2. Secondary cleaning: Through the tremie pipe after rebar cage installation

  • Final sediment thickness: ≤100mm

  • Time between cleaning and concreting: ≤30 minutes

8. Rebar Cage Construction

Fabrication standards:

  • Segmented fabrication (9m standard lengths)

  • 50% staggered lap joints

  • Protection layer: 60/50mm (±20/-10mm tolerance)

  • Spiral ties: 50% spot welded in checkerboard pattern

  • Welding requirements:

    • Main bars: 10D single-side full weld

    • E43 rods for Grade I steel, E50 for Grades II/III

  • Installation controls:

    • Maximum 2-layer stacking

    • Verticality tolerance <1%

    • Center deviation ≤10mm

    • Elevation control using measuring rods

9. Underwater Concrete Placement

Material specifications:

  • Compressive piles: C40 concrete (underwater grade +2 levels)

  • Tension piles: C30 concrete (underwater grade +1 level)

  • Slump: 180-220mm

  • Initial set: 6-8 hours

Placement protocol:

  • Tremie pipe bottom clearance: 0.5m

  • Initial charge volume: ≥1.5m embedment

  • Continuous placement duration: ≤8 hours

  • Embedment depth: 2-6m during placement

  • Maximum lift per cycle: ≤10m

  • Overpour height: ≥2m

  • Bulking factor: 1.0-1.3

Quality controls:

  • Sampling: 150mm cubes @ 50m³ or 1 set/pile

  • Curing: 20±2°C @ 95% RH for 28 days

  • Night work restrictions: Use high-density mud for temporary hole sealing

10. Quality Assurance Measures

Critical control points:

  1. Survey accuracy (position/verticality)

  2. Mud properties (density/viscosity/sand content)

  3. Hole quality (verticality/diameter/depth/sediment)

  4. Rebar cage (connections/specs/spacing/accessories)

  5. Concrete (grade/mix/placement rate/slump)

Testing protocol:

  • Steel: 60T batches (tensile/bend tests)

  • Concrete: 50m³ batches (compression tests)

Post-Grouting Construction Methodology

1. Grout Pipe Installation

  • Material: Φ25×3.2mm steel pipes

  • Configuration: 2 pipes/pile (symmetrical)

  • Valve design:

    • 16×7mm one-way outlets

    • Rubber wrapping for sealing

    • 20-50cm embedment below the pile tip

Installation requirements:

  • Secure binding to main bars @1.5-2.0m intervals

  • Water pressure test after installation

  • Top protection with threaded caps

2. Water Fracturing Test

  • Timing: 7-8 hours after concreting

  • Parameters:

    • Volume: 0.2-0.6m³

    • Duration: 3-5 minutes

    • Pressure: 0.2-0.5MPa

3. Grouting Process

Equipment:

  • Grout pump: ≥6MPa capacity

  • Hoses: 10MPa rated, Φ25mm ID

Materials:

  • Cement: Fresh P.O 42.5

  • Mix ratio: 0.55-0.6 W/C

  • Filtration: ≤3mm mesh

Operation:

  • Initial pressure: Test pressure ×1

  • Final pressure: Test pressure ×2-3

  • Flow rate: 30-40L/40L/min

  • Balanced injection through both pipes

Termination criteria (whichever comes first):

  1. Design volume achieved OR

  2. Pressure >2MPa for 3 minutes @ 80% volume

4. Quality Assurance

  • Material certification and testing

  • Valve fabrication inspection

  • Pipe positioning verification

  • Pressure/flow monitoring

  • Complete documentation

  • Load testing after 20 days

Common Defect Prevention Measures

1. Hole Deviation

Causes: Unstable rig setup, bent drill pipe, uneven ground
Solutions:

  • Proper site leveling

  • Regular tool inspection

  • Guide stabilizers

  • Correction methods: Reaming or clay backfill

2. Hole Collapse

Prevention:

  • Skip drilling pattern

  • Optimized mud properties

  • Casing depth adjustment

  • Continuous operation (<3hr standby)

3. Diameter Variation

Control methods:

  • Tool maintenance

  • Parameter adjustment

  • Reaming operations

  • Mud pressure management

4. Pipe Blockage

Avoidance:

  • Proper tremie seals

  • Slump control

  • Equipment maintenance

  • Gradation compliance

5. Rebar Cage Floatation

Countermeasures:

  • Secure positioning

  • Placement rate control

  • Embedment monitoring

  • Emergency stop procedure

6. Defective Piles

Prevention:

  • Thorough hole cleaning

  • Continuous placement

  • Mix design compliance

  • Proper lifting technique

7. Cage Settlement

Remedies:

  • Shallow settlement: Extension

  • Deep settlement: Supplemental piles

Pile Testing Protocol

  • Test method: Static load testing

  • Test quantity: ≥1% of total piles

  • Timing: After 20-day curing (post-grouting)

  • Criteria: Per JGJ94-2008 specifications

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