construction sequence
Construction preparation → leveling the site and mud drain → measuring and setting out → burying liners → drilling construction → mud wall protection → hole cleaning → placing steel skeleton → pouring underwater concrete → breaking pile head and quality inspection.
1, construction preparation
1. 1 technical preparation
1.1.1Before March 2008, be familiar with the construction design drawings and review the original design drawings of K24+073 Chaihe Second Bridge. At the same time, the construction work instructions for bored piles have been issued.
1. 1.2 traverse survey and layout of encrypted traverse points have all been completed, and passed the supervision review and approval. The position of digging pile and protecting pile has been determined according to the construction drawing.
1.2 test preparation: the concrete mixture ratio and raw material test of bored pile have been completed. The test results of reinforcement, aggregate and cement are shown in the test data.
2. Level the site and drain the mud ditch.
After entering the site, clean up the sundries and level the site. Dig mud pits and mud drains according to the construction plan. Before construction, realize "three links and one leveling", that is, water supply, electricity supply, access, three links and one leveling, creating favorable conditions for drilling rig positioning, construction personnel operation and mechanical operation.
3, measuring lofting
Before construction, accurate coordinate calculation should be carried out and submitted to the supervision engineer for review. After approval, survey and lofting shall be carried out to accurately determine the specific construction pile position.
4, liners buried
After the construction lofting results of the middle line of the bridge pile position are approved by the supervision engineer, the specific pile position construction lofting work (using total station lofting) will be carried out. Use "cross intersection method" to control the center position of the pile position, and after adding control piles nearby, excavate the foundation pit and bury the casing; After the liners are buried, mark the crosshair control points with red (white) paint on the upper edge of the liners. The lining is made of rolled steel plates with a thickness of 5 ~ 8 mm, with a diameter of 1.6m and a height of 2 m.. The inner container should be welded firmly, connected tightly and watertight. When the liners are buried on land, the top of the liners should be higher than the construction water level 1.5m and 0.3m above the ground, and the depth of the liners should be 2 ~ 4m. The center line of the embedded pile casing coincides with the center line of the pile, and the plane position deviation is not more than 5cm. During drilling, check and recheck the accuracy of casing position at any time. The liners for onshore or island construction should be pulled out directly after concrete pouring.
5, drilling
According to the geological conditions and the number of pile foundations, considering the tight time, our department is equipped with 5 percussion drills and generator sets 1 set.
Bored pile construction adopts impact drilling machine to form holes, and bulldozer or truck crane is in place. Before the drilling rig is in place, the drilling rig and all kinds of drilling tools should be inspected and maintained, and the specifications of drilling tools must meet the requirements of the designed pile diameter. When the drilling rig is installed in place, the base and the top should be balanced, the foundation of the drilling rig base should be solid and flat, and the drilling support platform should be solid and stable, without displacement or sinking. The top of drilling rig, derrick or mast shall be fixed with cable and wind rope, and shall be inspected frequently during drilling. The plumb line between the rim of the top pulley and the center of the cone head should be aligned with the center of the pile position, and the deviation should be no more than 2cm.
After the above preparations are ready, drilling can be started. After drilling, the original construction records and inspection records should be carefully filled in according to the project. When spudding, the drilling should be done slowly, and the drilling speed can only be increased after the guiding part or the drill bit is completely drilled into the stratum.
The impact method is used to form holes, and the small stroke is used to make the initial holes firm, vertical and round, which can play a guiding role and prevent the holes from collapsing. Only when the drilling depth exceeds the full height of the drill cone can normal impact be carried out. When drilling the rig, Qin Ying loosens the rope to prevent empty hammer. When lifting the cone head, the speed should be uniform, and sudden acceleration is not allowed, so as to avoid hole collapse caused by collision with the hole wall, prevent the cone head from swinging too much, increase reaming and increase the number of concrete pouring. When lifting the impact bit into and out of the orifice, it is forbidden to stand near the orifice to prevent personal accidents caused by the impact of the bit. It is forbidden for the cone head to hit or weigh the casing. When casing displacement is found or suspected, the operation should be stopped, and the surveyor should relocate before drilling.
For concrete cast-in-place piles with a spacing of 5 meters, drilling construction can only be carried out after 24 hours, so as not to interfere with the concrete solidification of adjacent piles. Stop drilling halfway, keep the hole to meet the specified water level requirements and mud specific gravity and viscosity to prevent hole collapse. In case of power failure or mechanical accident, the cone head should be lifted out of the hole or hung into the hole to prevent the hole from collapsing or sediment from burying the cone head. When the drilling depth reaches the weakly weathered rock stratum, notify the supervision engineer for approval in time, and continue drilling to the rock penetration depth after approval. At the same time, check the hole-forming situation with a hole-measuring instrument, and the length of the hole-measuring instrument is 4~6 times of the diameter of the pile foundation. During drilling, rock samples shall be taken with the drilling depth, and drilling records shall be made. After the test is correct, the drilling rig can be moved by crane.
6. Mud for wall protection
In drilling, because the relative density of mud is greater than that of water, the hydrostatic pressure of mud is greater than that of water at the same high water head in casing. Due to hydrostatic pressure, mud can act on the shaft wall to form a protective layer to prevent the shaft wall from collapsing. In addition, mud also plays the role of suspending drilling slag and cooling the drill bit, and mud is used to protect the wall when drilling. Its performance should meet the following requirements: a, the content of clay particles with plasticity index greater than 25 and less than 0.005mm is greater than 50%; B. Relative density 1.20- 1.40, viscosity 22-30Pa.s, sand content ≤4%.
7, hole cleaning
When the drilling depth reaches 2.5 times of the diameter of the embedded weakly weathered rock, the hole cleaning shall be started, and the supervision engineer shall be informed in time after the self-inspection is qualified. The supervision engineer shall test the hole depth, inclination, aperture and mud performance index, and start hoisting the reinforcing cage after it is qualified. After lifting the reinforcing cage, before pouring concrete, the hole depth should be measured again. When the thickness of sediment is greater than 3cm, the hole should be cleaned for the second time, and concrete can be poured only after meeting the following requirements.
① Relative density 1.03- 1. 10, viscosity 17-20Pa.s, and sand content less than 2%;
(2) hole plane position deviation pile group: 100mm single pile: 50mm；;
(3) The diameter of borehole shall not be less than the design pile diameter;
④ The inclination rate of the pile is not more than 65438 0%;
(5) The pile length shall not be less than the design pile length;
During hole cleaning, the water level in the hole should be kept above the groundwater level or the water level outside the hole 1.5 ~ 2.0m to prevent hole collapse. When cleaning the hole, clean the mud attached to the casing wall, and remove the sediment such as drilling slag and mud sand at the bottom of the hole. The quality of hole cleaning has a great influence on the bearing capacity of piles, so when concrete cannot be poured in a short time after hole cleaning, special attention should be paid not to clean holes and temporarily pull out slurry, so as not to reduce the pressure of slurry on the hole wall and cause hole collapse.
Do not use the method of deepening the drilling depth instead of hole cleaning.
If it exceeds the requirements of the above quality standards, the drilling tools should be adjusted for rescue or rework.
8, steel skeleton in place
Fabrication and placement of reinforcing cage
Allowable deviation of steel bar fabrication and hoisting: the spacing between main bars is 20mm；; Stirrup spacing+10 mm; The external diameter of skeleton is10mm; The thickness of skeleton protective layer is10 mm; The elevation of skeleton bottom surface is 50 mm
Before the formal welding of steel bars, the welding performance test under field conditions should be carried out first, and the formal construction can be carried out only after the test is qualified. The main reinforcement of the reinforcing cage adopts flash butt welding, and the extension of the reinforcing cage adopts arc welding. When welding in stormy weather, measures should be taken to prevent wind and rain. After welding, the steel bar joints shall be insulated and cooled in winter, and cooled naturally at other times to avoid rain.
The skeleton is made as a whole, and the crane is used for construction. The welded joint of main reinforcement shall conform to the construction technology of bored pile of bridge. Summary: The first batch of concrete should be poured in a big hopper to ensure that the hole bottom mud residue can be washed clean. The capacity of the hopper shall meet the requirement that the initial buried depth of the conduit shall not be less than 1.0m, and meet the requirement of filling the gap at the bottom of the conduit.
The article comes from the staggered demand of real estate e-net specification.
In order to ensure the protective layer thickness of the reinforcing cage, four "earrings" are welded symmetrically every 2m. During hoisting, in order to ensure that the reinforcing cage is not deformed and avoid the deformation of the reinforcing cage during hoisting, Chinese fir rods are arranged on the reinforcing cage to strengthen the overall rigidity. After the reinforcing cage is inserted into the hole, reliable fixing measures shall be taken and channel steel shall be welded to prevent the reinforcing cage from floating or falling off when pouring concrete.
The formed steel skeleton must be placed on a flat and dry site. During storage, the contact place between each stiffener and the ground should be padded with wooden blocks with the same height, and the segments of each group of skeletons should be arranged neatly, so as to be loaded and transported out in an orderly manner when in use. Signs should be hung on each skeleton, indicating pier number, hole number, section number, captain, operator, elevation of pile casing, elevation of pile bottom, length of pile, length of steel bar from the top of pile casing and length of concrete top from the top of pile casing.
9, underwater concrete pouring
Before pouring underwater concrete, re-examine the hole depth, mud deposition thickness and reinforcement cage deviation. After passing the inspection, start pouring underwater concrete, test the pressure of the conduit in advance, and try to assemble the conduit outside the hole. One end of the conduit is connected with the steel plate with rubber pad and the casing by bolts, and the other end is connected with the air pipe joint. Inject 70% water first, then input the air pressure of 4.0kPa, and roll the catheter several times. After fifteen minutes, no leakage is considered as qualified. The inner diameter of the conduit is 30cm, and it is connected with a flange. The bottom section is 4m, and the rest sections are 1.5m and 2m. Conical sheath is set at the joint to prevent the reinforcing cage from hanging when lifting the conduit. The length of the conduit is 0.3~0.4m from the bottom of the hole.
Calculation process of the first batch of concrete pouring
v≥π* D2/4 *(h 1+H2)+(π* D2 * h 1)/4
Where: v-the quantity required for pouring the first batch of concrete (m3);
D- pile hole diameter (m);
H 1- The distance from the bottom of pile hole to the bottom of conduit is generally 0.4m；;
H2—— initial buried depth of conduit (m);
D- the inner diameter of the catheter (m);
H1-the height (m) required for the concrete column in the conduit to balance the pressure outside the conduit (or mud) when the concrete in the pile hole reaches the buried depth H2, that is, h1= HW * yw/YC;
Hw- depth of water or mud in borehole (m);
Yw- severity of water or mud in borehole (kn/m3);
Yc- strength of concrete mixture (24KN/m3).
The first batch of concrete should be poured in a big hopper to ensure that the bottom mud residue in the hole can be washed clean. The capacity of the hopper shall meet the requirement that the initial buried depth of the conduit shall not be less than 1.0m, and meet the requirement of filling the gap at the bottom of the conduit. After pouring concrete, it shall be carried out continuously, and the concrete mixture shall be slowly poured into the conduit to prevent high-pressure air bags from being generated in the conduit. In the process of pouring, the height of the top layer of concrete is often detected and recorded, and the conduit is lifted and removed in time. The buried depth of the conduit is generally controlled at 2.0 ~ 4.0m.. The maximum buried depth is generally not more than 6m, and the minimum buried depth shall not be less than 2m. When lifting the catheter, lift it slowly at a constant speed, and don't use too much force. The conduit is always in the center of the hole, so that the conduit is not stuck, the reinforcing cage is not hung, and there is no water leakage. Avoid pulling the catheter out of the concrete surface with excessive force, and put an end to pile breaking accidents. In order to prevent the reinforcing cage from floating, when the concrete surface is close to the bottom of the reinforcing cage about 1 m, the pouring speed should be slowed down. When the concrete surface rises to about 4 meters from the bottom of the reinforcing cage, the bottom of the conduit can be raised more than 2 meters above the bottom of the reinforcing cage by lifting the conduit, and the normal pouring speed can be restored. In the later stage of underwater concrete pouring, the upper opening of the conduit should be 4 to 6 meters higher than the water surface at the top of the pile or in the pile casing, and it is not allowed to lift the conduit to make the concrete fall.
During the whole pouring process, the builder, quality inspector and operator stick to their posts, carefully organize the construction, solve problems in time when they are found, fill in the original records of underwater concrete pouring pile construction, take samples of test blocks and notify the supervision engineer at the same time.
In order to ensure the quality of the pile top, the height of the pile top of the cast-in-place pile is 0.8m higher than the design elevation, and the excess part should be chiseled before the pile connection. After the pile head is chiseled, there shall be no defects such as looseness, mud inclusion, deviation and insufficient protective layer to facilitate the connection of columns.
When pouring underwater concrete, concrete tanker must be used to transport concrete. It is not allowed to use handcart, tractor and other simple means of transportation to pour underwater concrete. Before pouring underwater concrete, carefully check the integrity of the sealing ring of the conduit. In general, replace the sealing ring every 100 linear meter.
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