Prestressed Pipe Pile Foundation Construction Procedures and Quality Control Points

Prestressed pipe pile construction process

The construction process of prestressed pipe piles is: measuring and setting out positioning → pile driver positioning → pile driver counterweight → feeding piles in front of the pile driver → installing pile tips → crane to lift piles and align pile positions → adjust the verticality of piles and pile frames → Apply pressure → recheck verticality, continue to apply pressure → connect piles → measure penetration → shift pile driver → pile foundation static load test → pile foundation acceptance.

Working conditions

(1) The engineering geological data are complete, the pile foundation design drawings have been reviewed together, and the special construction plan for the pile foundation has been approved.

(2) High-altitude, ground, and underground obstacles within the scope of the pile foundation have been eliminated, the site has been leveled and compacted, the pile foundation construction machinery can operate normally on the site, and drainage measures have been implemented during rainy periods.

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

(4) The pile foundation axis and horizontal base point control piles have been set up, and the handover procedures have been confirmed after review.

(5) The pile position has been checked and corrected and marked with wooden piles, short steel bars, or white ash sprinkling lines.

(6) The entry and exit routes of piling equipment and the sequence of pile foundation construction have been selected and determined.

(7) Check that the appearance quality of the pipe piles is qualified, and stack the piles near the pile driver according to the floor plan. Unqualified pipe piles have been marked and arranged to leave the site.

(8) The pile foundation construction equipment has been installed. Check whether the pile foundation construction machinery and equipment and lifting tools are intact, and lay water and electricity pipelines.

(9) Before construction of pipe piles, rotary piles, etc., test piles should be carried out according to the design requirements. The number of test piles should meet the design requirements, generally not less than 2. Generally, test digging of manually dug piles is not performed. However, when the geological conditions are complex and the design has clear requirements, piles can be test dug and large-area excavation can be carried out after inspection and confirmation by the survey and design unit.

Quality control of each process of prestressed pipe piles

Test pile

(1) The pile driving records that should be provided to the designer include the following items: number of hammer blows per meter, number of hammer blows per 30cm in the last 2~3m, total number of hammer blows, height of falling weight, pile verticality, pile deviation, welding Time, pile segment composition, welding operation, etc., to determine the pile driver, pile hammer and pile hammer performance, liner and its parameters for construction, check geological data, and cooperate with the design work.

(2) Select according to various types of piles and their location, pile length, inclination, bearing layer conditions, and terrain and geomorphological conditions. The quantity shall be subject to confirmation by the designer and the project department. The pile sinking process report shall be approved by the project department and Large-scale construction can only be carried out after supervision approval.

Pile foundation construction

hanging pile

When using two-point lifting, the pipe pile should be sent to the lifting position of the pile driver within 3m, and the pipe pile should be prevented from being damaged or broken during lifting. Precast concrete piles can only be lifted when the concrete strength reaches 100%.

pile sinking

1. Static pressure pile

(1) When sinking piles, the verticality of the pile body should be controlled to comply with regulations, and the center line of the pile hammer, pile cap, and pile body should be in a straight line to avoid deflection and damage to the pile head during pile sinking.

(2) When the pile is 50cm into the soil, the verticality of the pile and the horizontality of the platform should be corrected. When the pile sinks about 3m into the ground, the verticality of the pile body should be measured again to ensure that the vertical deviation of the pile in both directions should not exceed 0.5%.

(3) According to the design and specifications, the verticality of the pile body should be controlled within 1%L (L is the pile length), and the verticality of the pile sinking in the first section of the pile should be controlled within 0.5%L.

(4) Pile sinking construction can only be carried out when the concrete strength of precast concrete piles reaches 100% of the designed strength value.

2. Hammer pile

(1) The pile tip should be made according to the design requirements, and the welding and installation should be carried out on-site after inspection and acceptance by the supervisor. In order to prevent the pile head from being damaged during hammering, before piling, a pile cap should be placed on the top of the pile head, and hardwood should be placed on it to reduce vibration. wooden mat.

(2) According to the sequence of pile foundation construction, the construction should be carried out backward. When the pile group foundation or the pile center distance is less than 3.5 times the pile diameter, the jumping method should be used for construction.

(3) If water or mud enters the pile pipe during the pipe sinking process or may happen, concrete about 1.5m high should be poured into the pipe before sinking the pipe.

(4) When driving piles, the verticality of the pile guide rods and piles should be checked and corrected, and the hammer, pile cap, and pile should be kept on the same axis. The penetration depth of the pile should meet the design and specification requirements. When the pile top sinks to 60~80cm above the ground, stop hammering and connect the pile. When there is a certain gap between the pile top elevation and the ground and the pile connection is not used, a pile feeder can be used to drive the pile to the design elevation.

(5) The last three arrays of hammering construction must be strictly controlled, and the penetration of each array should meet the design requirements.

(6) Hammer stop principle: When the pile end is located in a general soil layer, the design elevation of the pile end is the main control condition and the penetration is the reference basis. When the pile end is located in other soil layers, the opposite is true.

(7) If there are serious deviations, tilts, broken piles, etc., the design unit should be notified in time for processing.
pick up stakes

(1) Reinforced concrete prestressed pipe piles should be connected by welding. The welding rods used for pile connection should meet the design requirements. Generally, E43 series welding rods are used. Construction can only continue after the welds at the pile connection are accepted and accepted (flaw detection is carried out if necessary).

(2) Pile connection is generally carried out about 1m from the ground. The centerline deviation of the upper and lower piles should be less than 10mm, and the node bending height should not be greater than 1% of the pile length.
Pile sank and driving stopped

(1) The stopping standard for pile sinking shall be based on the determined hammer-stopping standard. After the pile sinking is completed, the pile feeding hole shall be filled and covered in time.

(2) When encountering one of the following situations during the pile sinking process, promptly notify the on-site supervision and project department engineers, contact the geological survey and design units, and determine the treatment plan after research by all parties: 1) The penetration changes drastically, or the final penetration The strength is too large or too small relative to the design value or test pile data; 2) The pile body suddenly tilts, shifts or has severe rebound when struck; 3) The top of the pile is seriously cracked or the pile body has cracks; 4) The pile frame shakes violently;5) Other abnormal situations.

(3) Under normal circumstances, pile-pressing construction should be carried out continuously, and the pause time for the same pile should not exceed 30 minutes.
Broken pile occurs

For broken piles, the treatment plan should be determined on-site together with the design and other units.
Piling sequence

(1) It should be carried out following the approved pile foundation construction plan.

(2) When the building area is large and the number of piles is large, the foundation piles can be divided into several sections, and pile pressing can be carried out separately within each section.

(3) When constructing multiple pile platforms, the requirements of the pile foundation construction plan should be met. It is strictly prohibited to press piles from both sides to the middle.
Pipe pile concrete core filling

(1) Before construction, the pipe piles should be cleared, and the height of the core-filled concrete should meet the specific design requirements of each location.

(2) Pile cutting: The allowable deviation of the pile top elevation is ±50mm. For piles with a diameter L≥800mm, the height of the pile top entering the cap should not be less than 100mm; for piles with a diameter of 250≤L<800, the height of the pile top entering the cap should not be less than 100mm. If the pile head is less than 50mm, an electric pile saw should be used to cut the pile head, and manual chiseling is strictly prohibited.

(3) Pile connection: When the top of the pile is more than 2 times the pile diameter below the design elevation, the short piles cut off on-site can be used to connect the pile; when the bottom pile head is 0.5~1.0m away from the ground, hammering should be suspended. Extension of pipe piles; when connecting piles, the soil and rust of the joints should be cleaned first until the metallic luster is exposed, and then the special pile clamp should be fastened, and the pile to be connected should be lifted into the clamp. The butt deviation should not be greater than 2mm. After welding, clean the weld The quality of the weld must be inspected and accepted by the supervision unit before construction can continue.

Quality Standards and Acceptance Methods

(1) The quality of prestressed pipe piles must comply with the design and relevant requirements. Before construction, the supervision unit shall organize an appearance and data inspection of the pipe piles entering the site. Unqualified piles shall be marked and removed from the site promptly.

(2) During the construction of pipe piles, the axis, verticality, pressure, penetration, pile connection interval time, appearance quality of pile connection welds, etc. should be checked. If necessary, flaw detection of pile connection welds should be carried out per local regulations.

(3) The joint treatment of pile joints, pile head reinforcing bars and other joints should comply with the design requirements and construction specifications.

(4) During the waterproofing construction of the base plate, the waterproofing method at the pile head should comply with the design and relevant specifications.

(5) The test method and a number of tests for the bearing capacity of reinforced concrete precast piles should meet the requirements of the design and relevant standards. The static load test method is generally used for testing.

Finished product protection measures

(1) The prefabricated pipe piles that have entered the site are stacked neatly, and the stacking height should not exceed 4 layers. Square wooden support pads should be used on each layer, with the upper and lower support points on the same vertical line, and care should be taken to prevent collisions with construction machinery.

(2) The pile heads after construction should be prevented from collision and rolling by vehicles and damage to the pile heads.

(3) Pile caps should be installed during pile driving to prevent pile head damage.

Common quality problems

(1) Unqualified piles are not marked and are not withdrawn from the site and are used in pile foundation construction.

(2) If the concrete strength of the finished pipe pile does not reach 100% of the design strength, pile foundation construction must be carried out.

(3) Obstacles around the pile position and underground were not cleared before pile foundation construction. The straightness of the pile body did not meet the requirements. The upper and lower piles were not on the same axis. Fracture or lateral displacement occurred during pile pressing.

(4) The welding quality of the welds during pile connection did not meet the requirements, and construction continued without natural cooling after welding was completed.