1. Process principle
Use a steel bar tester to measure the position of the steel bar, and use a concrete cutting machine to circumferentially cut 2 cutting belts to ensure the elevation of the concrete pile head and the top surface of the pile is smooth. Use a pickaxe to strip off the steel bar, add a drill to break the pile head, and lift the pile head out.
2. Construction technology:
(1) Construction preparation
The strength of the pile should reach 70% of the design strength, and not less than 15mMP, and the age should not be less than 7d, before the foundation pit can be excavated
After the foundation pit is excavated, the foundation pit is manually leveled, the attachments around the pile head are cleaned up with a shovel, and the air compressor is hoisted in place.
(2) Measurement lofting
The surveyor measures the elevation of the pile top of each bored pile (i.e., 10cm deep into the cushion cap) and draws the first thick red line (and cutting line) along the elevation of the pile top, and a thick red line (and cutting line) 10cm above the first red line.
(3) Cutting seams
Cut along the red line with a handheld concrete cutting machine, and the cutting depth is generally about 3~5cm. During the construction, the on-site operator should measure the data table of the reinforcement protective layer according to the confirmed reinforcement position tester, and adjust the cutting depth of the thickness of the reinforcement protective layer. In order to prevent cutting the reinforcement of the pile foundation during the construction process, the cutting depth of the joint is not greater than the thickness of the measured reinforcement protective layer.
(4) Strip off the steel bar
The air pick peels off the protective layer of the steel bar above the cut joint, and after the steel bar is stripped out of the concrete, the steel bar is slightly bent to the outside to facilitate subsequent construction.
(5) Add drilling to top the broken pile head
1~2cm above the top line of the pile, along the perimeter of the pile head, 12-15 holes are evenly arranged for each pile, and the rock drill is used to punch holes, and the drilling depth is 8~10cm. After the drilling is completed, the steel drill is inserted, and the broken pile head is drilled, and the steel drill is horizontal or slightly upward. Each steel drill is equipped with two clamps, which is convenient for the removal of the steel drill after the pile head is broken.
(6) The pile head is hoisted
It is necessary to pay attention to the selection of the position of the hoisting point, find out the position of the center of gravity of the pile head, and after the wire rope is firmly sleeved, command the crane to lift it gently, and determine that the wire rope has been located in the center of gravity position of the pile head, so as to command the hoisting and sliding accident of the pile head. The wire rope of the hanging drill must be soft, high-quality, no dead bend and no broken wire.
(7) Adjust the pile head reinforcement
Two rebar operators adjust the pile head reinforcement to the corresponding position according to the design and specification requirements.
Renderings of the pile top after cleaning.
Renderings of the pile top after cleaning.
3. Quality control
Ensure the elevation of the pile head, extend into the cushion cap about 10cm, and the concrete surface of the pile head is flat.
4. On-site preparation for low-strain non-destructive testing
(1) The pile head slurry or loose, broken concrete chisel away, and expose the fresh and hard concrete surface, the surface of the pile top should be smooth and flat and no water accumulation, in order to ensure that the material, strength, cross-sectional size of the pile top and the pile body are the same;
(2) The diameter of the grinding point should be greater than 10cm, in addition to the center point of the pile, three points should be grinded, each point should be in the same horizontal plane and smooth, the depth should be kept at about 2cm, the grinding point should be far away from the main reinforcement, and its plane layout is shown in Figure 1.
(3) There should be facilities on site that are convenient for inspectors to go down the foundation pit for testing, such as ladders, simple sidewalks in the foundation pit, etc.
Schematic diagram of the grinding point