Construction of Spiral Welded Pipe

(I) Construction of Precast Spiral Welded Pipe (Suitable for soft soil, silty clay, and sandy soil layers)

Pile Position Verification: Re-verify the pile position coordinates to ensure no deviation; position the drilling rig and adjust the verticality of the drill pipe.

Drilling and Hole Formation: Start the drilling rig, use a helical drill bit to drill clockwise, controlling the drilling speed at 0.8-1.5 m/min, adjusting according to the soil layer (slower for hard soil layers, faster for soft soil layers); monitor the verticality of the drill pipe during drilling and correct it promptly.

Hole Cleaning and Soil Removal: After drilling to the design pile length, idle the drill for 30-60 seconds to remove loose soil at the bottom of the hole (loose soil thickness ≤ 100 mm); remove the soil mechanically to avoid accumulation around the hole opening.

Pile Body Lifting: Use a crane (16-50t) to lift the precast helical pipe pile, using a two-point lifting method (lifting points at 1/3 of the pile length from the pile end) to prevent bending of the pile body; the verticality deviation of the pile body ≤ 1‰.

Pile Driving and Positioning: Slowly lower the pile body into the hole, align it with the center of the hole, and drive the pile to the design elevation using self-weight + hammering (or static pressure), controlling the pile driving speed at 0.5-1.0 m/min to avoid impact load damage to the pile body.

Pile Section Splicing (if needed): Use flange connection or welding. For flange connection, tighten the bolts symmetrically (torque ≥ 300 N·m); for welding, the weld height ≥ 8 mm, with no slag inclusion or pores; the verticality deviation after splicing ≤ 2‰.

Hole Sealing: The top of the pile should be 500 mm higher than the design elevation (for subsequent pile cutting), and the hole opening should be sealed with concrete or clay to prevent debris from entering.

(II) Construction of Drilled and Grouted Helical Pipe Piles (Suitable for water-rich soil layers, sand layers, and hard interbedded layers)

Pile Position Layout and Drilling Rig Positioning: Same as precast helical pipe piles, install a grouting pipe (internal or external) on the drill pipe.

Drilling and Hole Formation: Drill with a helical drill bit, while simultaneously injecting clean water or mud (for wall protection) through the grouting pipe, controlling the drilling speed... 0.5-1.2 m/min; impact drill bits can be used for auxiliary crushing when penetrating hard interlayers.

First-stage grouting: After drilling to the designed pile length, start the grouting pump and inject cement grout (water-cement ratio 0.5-0.6), with a grouting pressure of 1.5-3.0 MPa. The grouting volume should be controlled at 1.2-1.5 times the pile body volume. During grouting, slowly lift the drill rod (lifting speed 0.3-0.5 m/min) to ensure full grouting at the bottom of the hole.

Reinforcement cage installation (if required): After grouting is completed, immediately lower the reinforcement cage (main reinforcement cover thickness ≥ 50 mm). The verticality deviation of the reinforcement cage should be ≤ 1‰, and the top should be fixed to prevent sinking.

Second-stage grouting (optional): Before the initial setting of the first-stage grouting cement grout (usually 4-8 hours), perform second-stage grouting with a grouting pressure of 2.0-4.0 MPa to supplement the pile side friction and improve the single pile bearing capacity.

Concrete pouring (if designed as reinforced concrete piles): After the second-stage grouting is completed, pour concrete (slump 180-220 mm) using the tremie pipe method to prevent segregation. The pile top elevation should be 500 mm higher than the design elevation.

III. Key Quality Control Points

Pile position deviation: Single pile position deviation ≤ 50 mm, group pile position deviation ≤ 100 mm

Pile body verticality: ≤ 1‰ (prefabricated piles), ≤ 1.5‰ (drilled and grouted piles)

Pile length and elevation: Pile length deviation ± 500 mm, pile top elevation deviation ± 50 mm

Grouting quality: Cement grout strength ≥ design requirements (usually ≥ 30 MPa), grouting volume deviation ≤ ± 10%

Pile body integrity: Tested using the low-strain method (sampling rate ≥ 10%), no defects such as broken piles or necking.

Single pile bearing capacity: Tested using static load test (sampling rate ≥ 1% and ≥ 3 piles), bearing capacity meets design requirements.