What are the key points of quality control in the construction of precast concrete static pressure piles?
Pile foundation is a foundation that can adapt to various geological conditions and load requirements of various types of buildings (structures). It has engineering characteristics such as large bearing capacity, good stability, small deformation, and fast convergence.
There are many types of precast concrete piles. Various materials and different production methods can be used to produce different pile types. This article briefly describes the quality control issues in the construction of precast concrete static pressure square piles.
1. Construction of static pressure piles
1. Requirements for construction of static pressure piles
1) Compared with hammering, static pressure piles are noiseless , no vibration, no pollution, safety and other advantages. However, pile pressing and pile driving in saturated soft clay areas may produce excess pore water pressure. During the piling period, the construction unit shall entrust a qualified monitoring unit to conduct dynamic tracking and monitoring of existing buildings and pipelines.
2) Drainage work at the construction site must be done well to ensure that there is no accumulation of water on the site during the pile driving process, and that construction water and electricity have been connected to the specified places on the construction site.
3) Check piling machinery and equipment, lifting equipment, pressure gauges, etc.
4) The installation of the pile driver must be carried out in accordance with the equipment instructions and relevant prescribed procedures.
5) Start the mast support cylinder to slightly tilt the mast 15 degrees to facilitate the insertion of prefabricated piles.
6) When the pile tip is inserted into the pile position, slightly start the pile driver cylinder. When the pile is 50 cm deep into the soil, correct the verticality of the pile and the level of the platform again, and then start the pile driver cylinder again. , slowly press down the piles, and the construction speed is generally controlled within 2 meters/minute.
7) When the pile pressing 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 pile driving construction, special personnel should be assigned or automatic recording equipment should be turned on to keep records of pile driving construction.
9) Before piling 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 pressing equipment, pile sinking construction technology and technical measures meet the actual requirements.
2. Construction process flow of static pressure piles
Construction sequence and process flow of static pressure piles: Measuring and laying out→Pile driver in place→Lifting prefabricated piles→Stabilizing piles→Piling pressure→ Pick up the pile → Deliver the pile → Inspect and accept → Transfer the pile driver.
3. Preparations for static pressure pile construction
1) Before construction, the site must meet the requirements of "three connections and one level" so that the construction pile driver equipment can smoothly enter the construction site.
2) Be familiar with construction drawings, participate in design drawing review, and do a good job in construction laying out work. Prepare various preparations such as pile location numbers and pile driving route procedures.
3) Do a good job on-site to clear underground space obstacles, such as basic air-raid shelters, underground pipelines, etc. of old buildings.
4) The safe distance between the side piles and surrounding buildings should be more than 4 meters, and the area 5 meters outside the axis of the side piles in the pile pressing area should be compacted with a road roller.
5) In order to control the construction of static pressure piles, necessary measuring instruments must be prepared.
4. Acceptance, lifting, moving and stacking of static pressure piles
1) Most of the prefabricated static pressure piles are produced and supplied by professional factories. After entering the site, please contact the supervision unit *Accept the static pressure piles in accordance with the "Prefabricated Reinforced Concrete Square Piles (04G361)" and the design drawings and the "Construction Quality Acceptance Code for Building Foundation Engineering" (GB50202-2002), and the manufacturer is required to provide the prefabricated square pile certificate, Test reports and other relevant quality assurance information.
2) Prefabricated piles should reach 70% of the design strength before they can be lifted, and the strength must reach 100% before they can be transported. When lifting and carrying piles, they must be balanced and must not be damaged. Horizontal lifting can use two-point lifting, the lifting point is 0.207L from the pile end (L is the pile length); one-point lifting, the lifting point is 0.29L from the pile end (L is the prefabricated pile length, at 10 meters3) Prefabricated reinforced concrete square pile The appearance quality should comply with the following regulations:
The surface is smooth and dense, the depth of the fallen corners shall not exceed 10 mm, and the defective area of ??local honeycombs and fallen corners shall not exceed 0.5% of the total pile surface area, and shall not be excessively concentrated; The depth of concrete shrinkage cracks shall not be greater than 20 mm, the width shall not be greater than 0.15 mm, and the length of transverse cracks shall not exceed 1/2 of the side length; there shall be no honeycombs, pitted surfaces, cracks or dropped corners at the top and tip of the pile.
4) Stacking of prefabricated static pressure piles
The stacking site of prefabricated static pressure piles must be flat and solid, and uneven settlement must not occur. The number of stacking layers shall not exceed 4, and piles of different specifications should be stacked in different places. Stacking must be elevated, level and firm at two points. The pad point is 0.21L, and the pad points are required to be aligned.
2. Quality control of static pressure piles
1. When sinking static pressure piles, the pressure of the pile should be based on the geological conditions of the site. The average resistance value and the standard penetration test N value are used to evaluate the possibility of pile sinking and select the pile pressing machinery and equipment.
2. According to factors such as geological conditions, the vertical ultimate bearing capacity of a single pile and the density of piles, the pile driver should be configured with a fixed total weight. The weight of the press (excluding static pressure piles) The weight of the machine's large and small shoes should not be less than 1.2 times the ultimate bearing capacity of a single pile.
3. The oil pressure gauge must be appraised by a qualified legal testing unit and have an appraisal certificate.
4. The control of static pressure pile sinking should be based on the principle of combining the design elevation, pile pressing force and steady pressure sinking amount, and should be comprehensively determined based on geological conditions and design requirements.
5. When the pile end enters hard, hard plastic cohesive soil, medium-density or above silt soil, and sandy soil layer, the pile pressing force of the static pressure pile is the main control indicator, and the pile end elevation is determined after obtaining the design After the unit agrees, it can be used as an auxiliary control indicator.
6. When the end of the static pressure pile enters the bearing layer and reaches the comprehensively determined pile pressure requirements, but does not reach the design elevation, it is advisable to maintain steady pressure for 1 to 2 minutes, and the steady pressure sinking amount can be Determined based on regional experience.
7. During the construction of static pressure piles, the verticality of the piles must not be adjusted or corrected arbitrarily to avoid causing large secondary bending moments on the pile bodies. During the process of static pressure piles passing through the hard soil layer or entering the bearing layer, pile driving construction shall not be stopped except for mechanical failures.
8. During the pile pressing process, the pressure, pile verticality, pile connection interval, pile connection quality and pressing depth should be checked.
9. After the pile pressing construction is completed, the single pile vertical bearing capacity test and small strain test of the pile body should be carried out to check the quality of the pile body.
10. Quality control of pile driving
1) Before pile driving, surrounding and underground obstacles should be cleared and the site leveled. The foundation bearing capacity of the site within the movement range of the pile driver should meet the pile machine operation and rack verticality requirements.
2) The sequence of pile sinking is generally from deep first to shallow, proceeding symmetrically from the middle to both sides, or from the middle to all sides.
3) The verticality deviation when the pile is inserted into the soil and positioned shall not exceed 0.5%.
4) After the pile feeding is completed, it should be backfilled with gravel or yellow sand in time.
11. During the pile pressing process, it cannot be stopped at will. If it is necessary for operation, the stop time should be short. The stop time in the middle shall not exceed 2 hours, and it is strictly prohibited to stop the pressure in the middle and cause difficulties in pile sinking.
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