HC Pipe Pile Static Pressure Construction and Testing Procedure

Project Overview

This project utilizes PHC (Prestressed High-strength Concrete) Type B pipe piles with the static pressure method, including both tension-resistant piles and non-tension-resistant piles. The piles have a diameter of φ500 with a wall thickness of 125mm, a concrete strength grade of C80, and an anti-seepage grade ≥P10. The concrete protective layer thickness for reinforcement is ≥40mm.

The pile end bearing layer is a strongly weathered layer, with pile lengths ranging from 21-35m from the pile cap bottom. The pile end must penetrate the bearing layer by ≥1 meter. The characteristic value of single pile vertical compressive bearing capacity is 1800kN, while tension-resistant piles have a characteristic tensile bearing capacity of 300kN.

Purpose and Location Selection of Test Piles

Purpose of Test Piling

1. Verify the applicability of pile pressing equipment and determine construction parameters, including pressing speed, pressure, and pile length control for the PHC pipe pile static pressure method.

2. Conduct pile quality inspection to understand pile integrity, length, and bearing capacity.

3. Determine the final pressure for stopping pile sinking during construction.

4. Establish mechanical combinations, personnel allocation, and quality control measures for formal construction.

Test Pile Location Selection

1. Quantity: Approximately 1% of total project piles will be selected for testing, none of which will be used as engineering piles.

2. Timing: Preliminary test piling scheduled for February 5-8, 2018. Static load testing will follow after the required soil settlement periods (7 days for sandy soil, 15 days for clay, 25 days for saturated soft clay).

3. Location:

   • First phase: Three test piles at specified coordinates (X=1912.136; Y=56615.262; X=1890.389; Y=56615.789; X=1898.838; Y=56629.468)

   • Second phase: Additional test piles randomly selected by the owner/designer based on geological reports, spaced at ≥3 times the pile diameter from engineering piles

   • Recommended additional test points in areas with representative 17 m-thick silt layers (ZK43, ZK44)

Material Preparation and Equipment

Materials

1. PHC Pipe Piles:

   • First phase test piles: Three piles with lengths of 31.5m, 37.1m, and 38.5m

   • Diameter: φ500, wall thickness: 125mm

   • Concrete strength: C80, anti-seepage ≥P10

   • Protective layer thickness: ≥40mm

   • All piles are Type B

2. Other Materials: Welding rods, hydraulic oil, etc.

Equipment

1. Pile Formation Equipment:

   • Hydraulic static pile driver model HJYZ600

   • Flat-bottom cross-type pile tip

   • Appropriate length pile sender

2. Auxiliary Equipment:

   • CO₂ protected welding for pile connection

   • Special pile cutter for pile cutting

   • Electronic total station, level, tape measure, vernier caliper

Construction Process Principles

The construction adopts the hydraulic static pressure method. After site leveling and positioning, the pile driver clamps and vertically adjusts the pile before applying pressure. The machine uses its weight and counterweight to gradually press the pile into the ground. Pile sections are connected by welding, and pile tops are sent to the design elevation using a sender.

Construction Methods

Pre-construction Preparation

1. Technical Briefing: Review geological data and design documents, conduct technical exchanges

2. Survey Work: Set out axes and pile positions with ≤2cm deviation

3. Site Leveling: Clear surface, fill depressions, ensure bearing capacity ≥1.2 times machine grounding pressure

4. Pile Inspection: Check factory certificates, concrete strength, and appearance

5. Pile Storage: Store on level ground with proper supports, ≤3 layers, prevent rolling/slipping

6. Equipment Check: Install and debug the pile driver, configure proper counterweights

Pile Exploration

Use a same-diameter steel pipe to explore surface soil conditions. May be omitted if soil conditions are good.

Pile Insertion

1. Select pile lengths and sequence

2. Use the machine’s crane to position piles

3. Carefully align the first pile section – crucial for verticality

4. Monitor verticality with two theodolites at 90° angles

Pile Pressing

1. Apply gradual pressure, starting lightly

2. Maintain a 1m/min sinking speed

3. Keep the pressure rod and pile aligned

4. Record pressure and depth data per meter

5. Complete each pile continuously if possible

Pile Connection and Welding

1. Clean connecting surfaces thoroughly

2. Align new section precisely (≤2mm offset)

3. Weld symmetrically with 4-6 temporary points first

4. Use a small current to minimize heat impact on the concrete

5. Allow 5 minutes to cool after welding

6. Maintain verticality during the process

Final Pressure Control

1. Design requires a final pressure of 4200kN

2. Apply pressure 3 times with 3-5s stabilization each

3. If the design length is reached, maintain pressure for 5- 8s

4. Adjust counterweights if needed

5. Notify the designer if requirements can’t be met

Pile Sending

Use an 11m steel sender to press the pile to the final elevation. Align carefully and maintain verticality during sending.

Verticality Control

Critical quality control point:

1. Initial adjustment at 50-80cm depth

2. Monitor with two theodolites 20m from the pile

3. Maintain ≤0.5% deviation

4. Make gradual corrections if needed

5. Observe penetration changes for obstacles

Quality Inspection

1. Verticality deviation ≤1%

2. Pile top elevation tolerance ±50mm

3. Visual inspection of pile quality

4. Single pile load test after 25 days – must meet design requirements

Quality Control Measures

Key Controls

1. Relate termination pressure to ultimate bearing capacity via coefficient k (σk=k*σs)

2. Continuous operation with clean connection surfaces

3. Strict verticality control (initial adjustment at 50cm depth)

4. Pause and investigate if:

   • Pressure changes abruptly

   • Depth differs significantly from design

   • Cracks or breaks appear

   • Pile tilts suddenly

   • Ground heaves or adjacent piles float

   • Can’t reach design pressure

Testing Methods

1. Process: Graded loading → Settlement observation → Termination → Unloading → Analysis

2. Operation:

   • Slow maintenance load method

   • Counterweight reaction system

   • Large-range displacement sensors

   • Load increments = 1/10 estimated ultimate capacity (first = 1/5)

3. Termination: When reaching 2× design bearing capacity with stable settlement

4. Data Analysis: Compile load-settlement curves and evaluate if the bearing capacity meets the design

This comprehensive procedure ensures proper installation and verification of PHC pipe piles using the static pressure method, meeting all quality and safety requirements for foundation construction.