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The engineering pile is mechanically excavated to the design elevation to avoid mechanical contact with the pile body
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The soil 200 mm around the pile is manually removed; Due to the close spacing between supporting piles（ A1000@1200 ）And close to the slope, the mechanical excavation shall be carried out to the place 200 mm away from the pile, and the rest shall be manually excavated, and the soil between the piles shall be cleaned
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Construction technology 1 process flow upper concrete breaking → measuring elevation cutting pile protection → opening gap → stripping reinforcement → deepening gap → drilling top breaking → lifting off broken body → chiseling residual → cleaning pile head 2 technical requirements 1
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Before pile head chiseling construction, the surveyor shall accurately set out the design elevation of each pile top and mark it
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2
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During the construction, the construction team shall mark around the pile foundation according to the marks made by the survey team
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At least four places of each pile shall be marked with red paint
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3
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During the pile head chiseling operation, in order to protect the effective pile body, the ring cutting and the next process should be carried out 10 cm above the pile top position, and 10 cm should be reserved for the final manual chiseling, so as to ensure that the height of the pile head extending into the bearing platform and the top elevation are accurate
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4
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After the pile head is disconnected and lifted out of the foundation pit, the construction team shall check whether the top surface of each pile is smooth one by one
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If there is any unevenness on the top surface of the pile, it shall be leveled again with steel chisel
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5
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Before chiseling the pile head, ask the technical personnel whether there is an acoustic pipe in the pile foundation
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For example, when chiseling the pile head, pay attention not to damage the acoustic pipe in the pile
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The acoustic pipe in the pile is arranged at 120 degrees, close to the inner ring of the main reinforcement
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If the acoustic pipe extends into the pile too much or too long, and cannot be lifted up after the pile is broken, cut the acoustic pipe by gas welding, After cutting, immediately plug the upper opening of acoustic testing pipe with cotton cloth to prevent debris from falling into the pipe and blocking the pipe, which will affect the pile foundation detection
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6
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After the pile head with acoustic pipe is disconnected and lifted out of the foundation pit, the construction team shall check whether the acoustic pipe on the top of each pile is exposed to the top of the pile one by one
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If it is not exposed, explain to the technical personnel, and then continue to chisel the pile head until the acoustic pipe is exposed
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If the acoustic pipe protruding from the pile foundation is crushed or deformed in the process of hoisting or pile head chiseling, it should be corrected in time
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7
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When the height of cap and crown beam is less than the anchorage length of reinforcement, the longitudinal reinforcement at the top of pile can rise to the top of cap and crown beam and then bend the straight hook to ensure the anchorage length
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3
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Construction steps 1
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Engineering pile (1) the surveyors measure the elevation of the pile top with a level, determine the position of the pile top required by the design, and set a 100 mm reserved belt on the pile top 100 mm deep into the bearing platform（ 2) Use the cutting machine to cut two lines at the upper and lower cutting lines
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The cutting depth is slightly less than the thickness of the pile foundation reinforcement protective layer
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The thickness of the engineering pile reinforcement protective layer is 60mm
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Do not damage the pile foundation reinforcement（ 3) Manually cut the gap on the upper cutting line, the depth is the thickness of the protective layer of the reinforcement, and the reinforcement shall not be damaged when chiseling（ 4) The air pick peels off the upper steel bar protective layer, peels the steel bar off the concrete, and bends the steel bar slightly to the outside at the same time, which is convenient for subsequent construction（ 5) Drill the top of the pile to break the upper plain concrete, the drill bit is slightly upward, and the position is 100 mm on the pile top line（ 6) After the top of the pile is broken, the pile head shall be lifted out with a crane, and the reserved band concrete shall be chiseled manually to reach the pile head elevation required by the design, and the scum at the pile head shall be removed and washed clean with water（ 7) Manually adjust the pile head reinforcement to the corresponding position according to the drawing requirements（ 8) Pay attention to the protection of the acoustic pipe in the construction process
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After chiseling out the acoustic pipe, temporarily seal it with a wooden plug to prevent the blockage caused by falling debris（ 9) After the pile head is chiseled, small strain test is carried out in different areas, and relevant units are organized to carry out pile foundation acceptance after the test is qualified（ 10) After the pile foundation test is qualified, the foundation pit shall be cleaned, and the local uneven parts shall be manually trimmed and filled
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After the acceptance of the supervision engineer, the cushion concrete shall be poured
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The setting out and leveling shall be carried out according to the design elevation, and red paint shall be used to mark on the reinforcement and pile top to ensure the level of cushion
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2
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Because the supporting pile is close to the slope, it is not convenient to construct on one side of the slope, and the spacing between piles is small, so it can only be constructed from one side
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During the construction, the slope stability should be paid attention to at all times
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In case of danger, the construction should be stopped immediately
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Reinforcement measures should be taken for the slope, and the construction can be continued only after the safety is confirmed（ 1) The surveyors measured the pile top elevation (18.4m) with a level, determined the pile top position required by the design, and set a 100 mm cutting band on the 100 mm depth of the pile top into the crown beam（ Fig
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6) (2) cut two lines at the upper and lower cutting marks on the soilless side with the cutter
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The cutting depth is slightly less than the thickness of the protective layer of the reinforcement of the pile foundation
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The protective layer of the reinforcement of the supporting pile is 50 mm
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Do not damage the reinforcement of the pile foundation（ 3) Manually cut and chisel the gap on the steel bar, the depth is the thickness of the protective layer of the steel bar, and the steel bar shall not be damaged during chiseling（ 4) The air pick peels off the upper steel bar protective layer, peels the steel bar off the concrete, and bends the steel bar slightly to the outside at the same time, which is convenient for subsequent construction（ 5) Drill the top of the pile to break the upper plain concrete, the drill bit is slightly upward, and the position is 100 mm on the pile top line
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Use the air pick to knock off the concrete from the soilless side of the pile body one by one
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At the beginning, the steel drill can be driven to assist the construction
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When the construction is fast to the side of the slope, slow down the speed
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Pay attention not to damage the main reinforcement
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Use the air pick to peel off the concrete until the main reinforcement is completely separated（ 6) The concrete fragments are transported out to reach the pile head elevation required by the design, the scum at the pile head is removed, and the water is washed clean（ 7) Manually adjust the pile head reinforcement to the corresponding position according to the drawing requirements（ 8) Pay attention to the protection of the acoustic pipe in the construction process
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After chiseling out the acoustic pipe, temporarily seal it with a wooden plug to prevent the blockage caused by falling debris（ 9) Clean up the foundation pit, and repair and fill the local uneven parts manually
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After the acceptance of the supervision engineer, the cushion concrete shall be poured
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The setting out and leveling shall be carried out according to the design elevation, and red paint shall be used to mark on the reinforcement and pile top to ensure the level of cushion
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3
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Abandoned pile (1) the surveyors shall measure the pile top elevation (the pile top elevation is the bottom elevation of cushion) with a level and mark it（ 2) Strip the reinforcement from the pile top elevation with air pick（ 3) Cut the steel bar from the pile top elevation by gas welding（ 4) Use pneumatic drill to drill holes around the pile body at the pile top elevation and drive steel drill rod（ 5) Use excavator to break the top of the pile (because the tensile strength of the concrete is very low, the tensile stress is increased after driving the steel drill, which makes the pile easy to short crack) (6) transport the broken pile out, clean the pile head, and chisel the pile head flat
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Common pile head defects pile head defects are common and important quality problems of reinforced concrete bored piles
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Generally, when the foundation trench is excavated and the pile head is broken to the design pile top elevation, if the pile body (visible part) below the design elevation has the following conditions, it is the pile head defect: 1
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The anchorage length of the main reinforcement does not meet the design requirements; 2
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The strength of mud and concrete is not enough; 3
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The protective layer is not enough and the reinforcement is missing
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The pile head defect must be treated, otherwise it can not be connected with the upper structure
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The corresponding measures should be taken according to the nature of the defect
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2 defect treatment measures 1
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The anchoring length of the main reinforcement does not meet the design requirements: the main reinforcement is broken, the main reinforcement is too short to expose the pile head measures: double sided lap welding process: cleaning the pile head → chiseling the pile → slag removal → welding construction sequence: clean the pile head, chisel the concrete at the part of the pile head with chisel, so that the original main reinforcement is exposed for not less than 5 days, The chiseled concrete ground shall be left in a straight plane or slightly inclined to the center of the pile, not inclined to the outside of the pile
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The steel bars to be welded shall be cleaned with steel wire, and the steel bars shall be welded with double-sided lap welding, and the welding length shall not be less than 5D.
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