A Summary of Static Pressure Pile Construction Technology That You Can Understand at a Glance!

1. Requirements for static pile construction

1. Compared with hammering, static pile driving has the advantages of no noise, no vibration, no pollution, and safety. However, in saturated soft clay areas, pile driving and pile driving may generate excess static pore water pressure. During pile driving, the construction unit should entrust a qualified monitoring unit to track and dynamically monitor the existing buildings and pipelines.

2. The drainage work at the construction site should be done well to ensure that there is no water accumulation on the site during the pile sinking process, and that the construction water and electricity have been connected to the specified places on the construction site.

3. Check the pile driving machinery and equipment, lifting equipment, pressure gauges, etc.

4. The installation of the pile driver must be carried out according to the equipment manual and relevant regulations.

5. Start the gantry support cylinder to tilt the gantry slightly by 15 degrees to insert the prefabricated pile.

6. After the pile tip is inserted into the pile position, start the pile driver cylinder slightly. When the pile is buried to 50 cm, calibrate the verticality of the pile and the level of the platform again, and then start the pile driver cylinder to slowly press the pile down. The construction speed is generally controlled within 2 meters/minute.

7. When the pile driving force has reached twice the design load or the pile end has reached the bearing layer, the pressure should be stabilized at any time.

8. During the pile driving construction, a special person should be assigned or the automatic recording equipment should be turned on to keep a record of the pile driving construction.

9. Before the pile driving construction, the piles should be tested first. The number of test piles should be no less than two to determine the penetration and pile length, and to verify whether the pile driving equipment and the pile driving construction process and technical measures meet the actual requirements.

2. Static pressure pile construction process

The construction sequence and process flow of static pressure piles: measurement and layout → positioning of pile driver → lifting of prefabricated piles → stabilization of piles → pressure piles → connection of piles → delivery of piles → inspection and acceptance → transfer of pile driver.

3. Preparation for static pile construction

1. Before construction, the site must meet the requirements of “three connections and one leveling” so that the construction pile driver equipment can enter the construction site smoothly.

2. Be familiar with the construction drawings, participate in the design drawing review, and do a good job of construction layout. Prepare the pile position number and pile driving route procedures and other preparations.

3. Do a good job of clearing underground space obstacles on site, such as the foundation air-raid shelters of old buildings, underground pipelines, etc.

4. The safety distance between the side piles and the surrounding buildings should be greater than 4 meters, and the side pile axis of the site in the pile driving area should be compacted with a roller within 5 meters.

5. To control the construction of static piles, necessary measuring instruments must be prepared.

4. Acceptance, lifting, moving, and stacking of static pressure piles

1. Prefabricated static pressure piles are mostly produced and supplied by professional factories. After entering the site, the static pressure piles should be inspected and accepted together with the supervision unit according to the “Prefabricated Reinforced Concrete Square Piles (04G361)” and design drawings and the “Construction Quality Acceptance Standard for Building Foundation Engineering” (GB50202), and the manufacturer should provide relevant quality assurance information such as prefabricated square pile certificates and test reports.

2. Prefabricated piles should reach 70% of the design strength before they can be lifted, and the strength should reach 100% before they can be transported. When lifting and transporting, the piles must be balanced and not damaged. Horizontal lifting can be carried out by two-point lifting, with the lifting point 0.207L away from the pile end (L is the pile length); in one-point lifting, the lifting point is 0.29L away from the pile end (L is the prefabricated pile length, 10 meters).

3. The appearance quality of prefabricated reinforced concrete square piles shall meet the following requirements: the surface is flat and dense, the depth of the corner drop does not exceed 10 mm, the defect area of ​​local honeycombs, and the corner drop shall not exceed 0.5% of the total pile surface area, and shall not be overly concentrated; the shrinkage crack depth of concrete shall not exceed 20 mm, the width shall not exceed 0.15 mm, and the length of transverse cracks shall not exceed 1/2 of the side length; there shall be no honeycombs, pockmarks, cracks or corner drop at the top and tip of the pile.

4. Stacking of prefabricated static pressure piles The stacking site of prefabricated static pressure piles is required to be flat and solid, and uneven settlement shall not occur. The number of stacking layers shall not exceed 4, and piles of different specifications shall be stacked in different places. The stacking must be raised, leveled and solid at two points. The pad point is 0.21L, and the pad points are required to be aligned.

5. Static pressure pile quality control

1. When the static pile is driven, the pressure of the pile should be based on the geological conditions on-site. The possibility of pile driving should be evaluated by the average value of the static penetration resistance and the standard penetration test N value, and the pile driving machinery and equipment should be selected.

2. According to the geological conditions, the vertical ultimate bearing capacity of a single pile, and the density of piles, the pile driver should be equipped with the weight according to the total weight of the quota. The weight of the driver (excluding the weight of the large and small shoes of the static pile driver) should not be less than 1.2 times the ultimate bearing capacity of a single pile.

3. The oil pressure gauge must be identified by a qualified statutory testing unit and have an identification certificate.

4. The control of static pile driving should be based on the principle of combining the design elevation, pile driving force, and steady pressure sinking, and should be determined comprehensively according to the geological conditions and design requirements.

5. When the pile end enters the hard, hard plastic clay soil, medium dense or above silt soil, and sand soil layer, the pile driving force of the static pile is the main control indicator, and the pile end elevation can be used as an auxiliary control indicator after obtaining the consent of the design unit.

6. When the end of the static pile enters the bearing layer and reaches the comprehensively determined pile pressure requirement, but does not reach the design elevation, it is advisable to maintain steady pressure for 1 to 2 minutes. The steady pressure sinking amount can be determined based on regional experience.

7. During the construction of static piles, the verticality of the piles shall not be adjusted and corrected arbitrarily to avoid generating large secondary bending moments on the pile body. In the process of static piles passing through the hard soil layer or entering the bearing layer, the pile sinking construction shall not be stopped except for mechanical failure.

8. During the pile driving process, the pressure, the verticality of the piles, the interval time of the pile connection, the connection quality of the piles, and the depth of the piles shall be checked.

9. After the pile driving construction is completed, the vertical bearing capacity test of the single pile and the small strain inspection of the pile body quality shall be carried out.

10. Pile driving quality control Before pile driving, the surrounding and underground obstacles should be cleared, the site should be leveled, and the foundation bearing capacity of the site within the moving range of the pile driver should meet the requirements of the pile driver operation and the verticality of the frame. The order of pile driving is generally deep first and shallow later, symmetrically moving from the middle to both sides or from the middle to the surroundings. The vertical deviation of the pile when inserted into the soil shall not exceed 0.5%. After the pile is delivered, it should be backfilled with crushed stone or yellow sand in time.

11. During the pile pressing process, it cannot be stopped at will. If it is necessary for operation, the rest time should be short. The rest time in the middle shall not exceed 2 hours. It is strictly forbidden to stop the pressure in the middle to cause difficulties in pile sinking.

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