Causes of Pile Breakage in Pipe-Sinking Piles

Cracks in broken pipe-sinking piles are typically horizontal or slightly inclined and usually traverse the entire cross-section, often occurring 1 to 3 meters below the ground at the junction of soft and hard soil layers.

Main Causes of Pile Breakage:

Small Pile Spacing: The horizontal thrust and uplift force generated by soil squeezing during the driving of adjacent piles.

Differential Horizontal Force Transmission: Soft and hard soil layers transmit horizontal forces differently, causing shear stress on the pile.

Early Final Setting of Concrete: The concrete in the pile has not set fully and has low strength, making it unable to withstand external forces.

Preventive Measures for Pile Breakage:

Pile Layout: Adhere to the principle of fewer piles with wider spacing. The center distance between piles should not be less than 3.5 times the pile diameter.

Minimize Vibrations and External Forces: Avoid vibrations and external disturbances when the concrete strength is low. Therefore, determine the piling sequence and pile driver route reasonably.

Use Skip Piling or Time Control Method: Reduce the impact on adjacent piles. The time control method involves completing the piles within the influence range before the initial setting of the concrete in adjacent piles.

Inspection and Treatment of Pile Breakage:

Shallow Layers (2-3m): Use a heavy hammer to strike the side of the pile head while stepping on it. If the pile is broken, it will feel like it is vibrating loosely.

Deeper Breakage: Use dynamic testing or excavation methods for inspection. Once pile breakage is detected, the broken section should be pulled out, the hole cleaned, and the area slightly enlarged or connected with iron hoops before re-casting the concrete to repair the pile body.

What is the Reverse Insertion Method for Vibratory Cast-in-Place Piles?

The reverse insertion method involves vibrating while pulling the pipe out during the extraction process. For each pull of 0.5-1.0 meters, reinsert the pipe 0.3-0.5 meters. Repeat this while maintaining vibration until the pile pipe is fully extracted.

Within 1.5 meters of the pile tip, reverse insertion should be performed multiple times to expand the local cross-section of the pile.

When passing through a silt interlayer, slow down the pipe extraction speed and reduce the extraction height and re-insertion depth. The reverse insertion method should not be used in highly fluid silt.

Precautions for Soil Compaction Pile Foundation Construction:

Supervision: Appoint a dedicated supervisor to monitor the quality of hole forming and backfilling compaction, and keep detailed construction records.

Remove Loose Soil: Before laying the compaction pile hole top ash (or soil) cushion, excavate the reserved loose soil above the pile hole top elevation according to design requirements and compact it with water.

Moisture Treatment: For soil layers within the compaction pile treatment range, especially within the compression layer depth below the foundation, if the soil moisture content is below 11%-12%, moisten the treated soil layers.

Contents of Low Strain Testing Report for Reinforced Concrete Piles:

Velocity Signal Curve

Pile Wave Speed Value

Description of Pile Integrity: Including the location of defects and the category of pile integrity.

Time Domain Signal Segment: Corresponding pile length scale, index, or linear amplification range and factor; or frequency range of the amplitude-frequency signal curve analysis, frequency difference between adjacent resonance peaks corresponding to the pile bottom or pile body defects.