Punched pile process:

Operating conditions:

1. Engineering geological data are complete, the pile foundation design drawings have been reviewed, and the special construction scheme for the pile foundation has been approved.

2. Obstacles in the air, on the ground, and underground within the pile foundation area have been removed; the site has been leveled and compacted; pile foundation construction machinery can operate normally within the site; and drainage measures for rainy season construction have been implemented.

3. According to the actual site conditions, vibration isolation measures have been taken for buildings (structures) near the piling site.

4. The pile foundation axis and benchmark control piles have been set up, reviewed, and confirmed with handover procedures completed.

5. Pile positions have been rechecked and confirmed, marked with wooden stakes, short steel bars, or white lime lines.

6. The access routes for piling equipment and the construction sequence for the pile foundation have been selected and determined.

7. The appearance quality of pipe piles has been inspected and found qualified; the required piles have been stacked near the piling machine according to the layout plan; unqualified pipe piles have been marked and arranged for removal from the site.

8. Pile foundation construction equipment has been installed; the completeness of pile foundation construction machinery and lifting tools has been checked; and water and power supply lines have been laid.

9. Before construction of pipe piles, rotary drilled piles, etc., trial piles shall be conducted according to design requirements. The number of trial piles shall meet design requirements, generally not less than 2. Manual excavated piles generally do not require trial excavation, but when geological conditions are complex or design explicitly requires, trial excavation may be conducted, and large-scale excavation shall proceed after inspection and confirmation by the survey and design units.‍

Key quality control points for each process:

1. During hole formation, a circular 6–8mm steel plate casing shall first be installed at the hole opening. The inner diameter of the casing (ring) shall be 200mm larger than the drill bit diameter, and the depth is generally 1.2–1.5m. The punching machine shall be positioned. Before starting punching, rubble and clay slurry shall be added promptly to protect the wall, compacting the hole wall. The slurry density and stroke shall comply with relevant specifications. During hole creation, residual slag in the hole shall be discharged outside.

2. The materials for slurry preparation and the slurry quality shall be self-inspected and meet requirements. During punching, the slurry density shall be measured and controlled at all times. Slag shall be discharged once every 1–2m of punching until the design depth is reached. During slag discharge, slurry must be replenished promptly to prevent hole collapse due to slurry loss.

3. During drilling, the verticality of the hole shall be rechecked every 1–2m. If deviation is found, drilling shall be stopped immediately and measures taken to correct it.

4. After hole formation, the hole depth shall be measured. After rechecking and confirmation, hole cleaning shall begin. Clear water replacement shall control the slurry density between 1.15 and 1.25.

5. After hole cleaning, the reinforcement cage shall be immediately placed and fixed on the steel casing at the hole opening to prevent the cage from floating up or sinking during concrete pouring. After the reinforcement cage is installed and checked, concrete shall be poured immediately to avoid slurry sedimentation and hole collapse.

6. For underwater concrete pouring, the tremie method is generally used for underwater placement.

6.1. The selection and connection of tremie pipes shall comply with regulations, and the flange shall be prevented from catching the reinforcement cage and affecting its positioning. Before splicing, the tremie pipe shall be subjected to a sealing pressure test. The test water pressure shall be 0.6–1.0MPa, or shall comply with equipment specifications, and shall be qualified if there is no water leakage or air escape.

6.2. Each tremie pipe connection shall be 1–7m, extending to 1m above the hole depth. The embedded pipe depth shall meet the requirement of 2–4m; it is strictly prohibited for the embedded depth to be less than 2m or greater than 6m.

6.3. Underwater concrete construction must be continuous. The pouring time for each pile shall be controlled according to the initial setting time of concrete, generally not exceeding 3 hours. During pouring, a dedicated person shall be responsible for measuring the rising height of the concrete top and monitoring the embedded depth of the tremie pipe at all times. During the first concrete pour, the lower end of the tremie pipe should be controlled at 300–500mm above the hole bottom, and after the first pour is completed, the embedded depth of the tremie pipe should be more than 0.8m.

6.4. During underwater concrete pouring, supervisors and project department engineers shall track and inspect, and promptly urge rectification of existing problems.‍

Quality standards and acceptance methods

1. Wall-protecting slurry preparation: The materials used for slurry and the quality shall be self-inspected according to regulations; when necessary, a testing unit shall be commissioned to test relevant indicators.

2. Reinforcement cage fabrication: Check the quality assurance documents of steel materials, and accept the diameter, length, specification, quantity, and fabrication quality of steel bars according to design and specification requirements.

3. The concrete strength of the pile foundation shall meet design requirements and construction specification provisions. The hole depth and sediment thickness shall meet design requirements, measured by the sinker method. When the sediment thickness exceeds design requirements, slag shall be cleaned.

4. The pile top elevation after pouring, the position of inserted bars, and the treatment of laitance must comply with design requirements and construction specification provisions.

5. Allowable deviations and inspection methods shall comply with design and specification requirements. Pile foundation quality testing shall be commissioned to a third party according to relevant standards.‍

Final hole acceptance and quality testing of pile foundation:

1. Pile foundation quality testing and acceptance

1.1. Integrity testing of cast-in-place pile body: Before testing, the pile head to be tested shall be chipped to remove laitance, floating slag, or loose concrete, and the pile head shall be leveled.

1.2. The concrete quality of the pile body and the sediment at the pile bottom shall be tested by core drilling, and core samples shall be retained. The concrete quality shall be judged based on the core samples, and records shall be kept. Core samples shall be taken for compressive strength tests.

1.3. When the length of cast-in-place piles is ≤15 meters, the low-strain dynamic testing method may be used, and the sonic transmission method shall be used for 10% of the piles.

1.4. When the pile length is greater than 15 meters, the ultrasonic transmission method shall be used for testing. Detect defects and their positions in the pile body, and determine the integrity category of the pile body.

1.5. The number of embedded sonic logging pipes shall meet the following requirements: pile diameter D≤800mm, 2 pipes; 800＜D≤2000mm, not less than 3 pipes; D＞2000mm, not less than 4 pipes. Sonic logging pipes shall be installed at uniform spacing.

1.6. After the construction of prestressed pipe piles is completed, static load tests and pile integrity testing shall be conducted.

2. Pile foundation acceptance procedure provisions

2.1. After all pile foundations are completed and the curing age meets the 28-day requirement, pile foundation testing shall be conducted according to regulations and a test report shall be submitted.

2.2. Pile foundation acceptance shall be organized by the supervision unit, with participation of relevant personnel from construction, supervision, survey and design, and the project department. After acceptance, an acceptance report signed and confirmed by each unit shall be formed. Before the pile foundation is accepted, the next process shall not proceed.‍

Finished product protection measures

1. The axis piles and horizontal benchmark piles of the pile foundation shall have protective measures or conspicuous marks to avoid displacement caused by collision and vibration.

2. Foundation pit excavation shall be carried out according to the excavation sequence and protection measures determined in the construction scheme to prevent pile inclination or displacement. Rechecking shall be conducted promptly after construction.

3. Completed piles shall be guarded by dedicated personnel or enclosed with fences and signs to prevent vehicles from running over or passing nearby, which may cause pile breakage or position deviation.

4. Pile head reinforcement shall have protective measures to prevent bending or breaking by vehicle rolling.

5. For formed reinforcement cages of cast-in-place piles, twisting, loosening, or deformation is not allowed. When lifting the reinforcement cage into the hole, prevent collision with the hole wall. The tremie pipe shall be placed vertically to avoid concrete impacting the hole wall at an angle, causing the hole wall to collapse and form inclusions.

5.1. When chipping the pile head concrete of cast-in-place piles that exceeds the design elevation, it shall be done from top to bottom, not by horizontal chipping, to avoid damage or loosening of the pile due to horizontal impact force.

5.2. During winter construction, when the concrete strength of the pile head has not reached 40% of the design strength, appropriate insulation measures shall be taken to prevent freezing.

5.3. After newly poured concrete for cast-in-place piles, adjacent pile holes should not be constructed immediately. Interval construction should be adopted to prevent pile foundation deformation or fracture caused by vibration or lateral soil extrusion.

5.4. After placing the reinforcement cage in the formed hole, concrete shall be poured within 4 hours. During pouring, measures shall be taken to prevent the reinforcement cage from floating up and to prevent slurry contamination.

5.5. For manual excavated piles, a retaining platform shall be provided around the upper opening of the pile hole to prevent water ingress and soil falling.

5.6. Reinforcement cages tied on site shall be prevented from slurry contamination. When pouring concrete, the top of the reinforcement cage shall be firmly fixed to limit floating.

5.7. After the pile foundation concrete pouring is completed, the pile head shall be covered with plastic sheeting, etc., to prevent concrete shrinkage and drying cracks.‍

Common quality problems

1. During hole formation and at final hole for punched piles, the liquid level is too low (the liquid level in the hole should be 1.5–2.0m above the groundwater level), leading to hole wall collapse and hole shrinkage.

2. The specific gravity of the slurry for punched piles is low, and quicksand occurs on the hole wall.

3. The reinforcement cage lacks stiffening hoops, resulting in deformation, twisting, and slurry contamination. Reserved reinforcement at the pile head deforms or breaks; main reinforcement joints of the cage are not staggered; welded joint quality is poor. The reinforcement cage damages the hole wall during installation, and floating or deviation occurs during concrete pouring.

4. During concrete pouring for cast-in-place piles, soil or other debris falls in, causing necking, voids, soil inclusions, pile breakage, or insufficient strength; the pile head concrete exceeds the cushion cap elevation.

5. During rotary drilling, loose soil is not cleaned promptly or collapse occurs due to groundwater.

6. The sediment thickness at the pile bottom does not meet regulations and is not cleaned promptly.

7. Pile position control measures are inadequate, and pile position deviation occurs during construction.

8. Slurry wall protection or support is not carried out as required, resulting in hole collapse.

9. During excavation of manual excavated piles, rechecking is not performed; verticality and excavation dimension deviations exceed specification requirements; upper and lower sections of the wall protection are not connected.

10. During construction of manual excavated piles, groundwater is encountered but dewatering is not performed, causing soil disturbance or hole wall collapse.

11. For manual excavated piles, the reinforcement cage is tied inside the pile hole, making on-site quality acceptance difficult and posing safety risks.‍