Pile cap construction is the follow-up project of pile foundation construction, and its quality is also an important part of foundation quality and will directly affect the quality of the project.

▍1. Process

1. Foundation pit excavation and foundation pit excavation, drainage, bricklaying (block), ground formwork, cement mortar plastering, tamping the pile body Other cap cushions

2. Check, classify, and place steel bars for binding, steel bar binding, and pre-embedding (plugging) cement mortar pads

3. Concrete pouring Mixed concrete pouring, vibrating and curing

▍ 2. Foundation pit excavation

1. Foundation pit excavation: Excavate one by one according to the released foundation pit excavation line. Excavation should be carried out in layers, and the height of each layer should not be too large. The excavated earth shall not be piled near the foundation pit.

2. Dewatering and drainage: When the groundwater level is high and precipitation is needed, internal and external precipitation measures should be adopted according to the actual situation. After the excavation of the foundation pit is completed, blind trenches and water collection wells should be made at the bottom of the pit. If there are precipitation facilities around, they should still operate normally.

3. Brick (block) floor molds: Bricks and masonry should be watered and moistened in advance. The moisture content of ordinary clay bricks is 10 to 15. First, pop up the axis and edge of the brick mold according to the position of the brick wall, and arrange the bricks to determine the width of the mortar joints. Consider the laying positions of quarter-head bricks, half-bricks, etc., and be sure to stagger the vertical joints of each skin brick. If four types of soil are encountered, in-situ soil molding can be used for construction.

4. Cement mortar plastering

(1) The volume ratio of cement mortar should be 1:3; in order to control the amount of water added, a mixer should be used to stir evenly and the color should be consistent.

(2) Spread the cement mortar evenly, then smooth it with a wooden trowel, and smooth it with an iron trowel before final setting.

5. After the foundation formwork of the cap cushion other than the pile body is laid and plastered, the cap cushion other than the pile body should be poured as soon as possible. Elevation lines should be popped up on the outer ground mold according to the base elevation, such as when using the original soil mold.

Bamboo skewers about 10 hoe lengths should be staggered on the outer soil wall, and 2-75px should be exposed. The surface of the bamboo skewers is level with the base elevation, and the distance between the bamboo skewers is about 3m. . After clearing away the silt and debris on the bottom of the cushion, concrete is continuously poured in blocks from low to high according to the depth of the platform. Construction joints should not be left in the same block.

▍3. Steel bar tying

1. Steel bar checking, classification, and placement: Check the specifications, models, shapes, etc. of the formed steel bars according to the design drawings and steel bar processing orders, and then classify them The tags are stacked and transported to the lashing site by vertical transportation equipment and manpower.

2. Steel bar binding: Determine the binding sequence. Under normal circumstances, start with the shortest and then the longest, and advance from one end to the other. During operation, it is necessary to draw lines according to the requirements of the drawing, lay the main bars, thread the stirrups, and then tie them into shape.

The position of the stressed steel bar lap joints should be correct, the lap length must comply with the specifications, and the joints should be staggered from each other. Normally, the upper steel bars should be in the middle of the span, and the lower steel bars should be at the supports as much as possible. Each Within an overlapping length range, the area of ??the overlapping steel bars should not exceed 1/4 of the total area of ??the steel bars within the length range. All joints of stress-bearing steel bars and stirrups are fully tied and no skipping is allowed.

3. Reserved and embedded: The location of the reserved holes should be correct. The steel bars extending from the pile tops to the cap beams and the column and wall insertion bars on the cap beams must be tied or welded firmly with cross buckles in accordance with the drawings and specifications. Their elevation, location, anchoring length and other dimensions should be accurate and must not be omitted. , backfill or shift.

4. Tie cement mortar pads: The strength of the pads must meet the usage requirements. Pads should be added under the bottom steel bars. The protective layer should not be less than 50nyr-. The spacing is lm. The pads on the sides should be in line with the requirements. The steel bars must be tied securely and must not be left out.

▍4. Concrete pouring

1. Mix concrete: Before mixing, calculate the amount of cement, sand, gravel and admixtures for each plate according to the test ratio. The backend must be strictly weighed, and the weight ratio must be strictly followed during operation. The feeding sequence is generally: gravel, cement, sand, and water. Admixtures should be added together with water.

2. Watering: The pile head, the bottom of the groove and the mold should be watered and moistened. The concrete for the cap should be poured in one go.

When pouring, the concrete should be poured directly into the mold in sequence. If the initial setting time is exceeded, it should be treated as a construction joint. If a tower crane is used to transport unloaded materials into the mold, the height of the discharging port of the bucket from the operating surface should be 30 to 1000px, and the materials should not be dumped in one place. Effective measures should be taken when pouring large-volume caps to prevent cracks caused by the accumulation of temperature stress.

3. Vibration: Concrete vibration should be carried out by oblique vibration method according to the pouring sequence. The inclination angle between the vibrator rod and the horizontal plane should be maintained at about 30 degrees, and the rod head should be facing the forward direction. The spacing between the insertion points of the vibrator rods should be 500mm to prevent leakage and over-vibration. The vibration time shall be based on the appearance of grouting on the concrete surface and the overflow of bubbles. The vibrated concrete should be smoothed with a wooden trowel at any time according to the elevation control line.

4. Curing: After the concrete is poured, it should be covered with water and cured within 12 hours under normal temperature conditions. The frequency of watering is appropriate to keep the concrete moist. The curing time should be no less than 7 days. If it is mixed with admixtures, it should be cured for 14 days. .