First, the construction preparation
(1) Investigate the site capacity and surrounding environment characteristics in detail, comprehensively consider the influence of these factors on survey control, and optimize the layout of survey lines and control networks.
(2) Ensure that the site is flat and convenient for mechanical construction.
(3) Carefully review the general plan, formulate detailed measurement scheme, be responsible for the positioning of the pile center and the layout of the axis and elevation of the pile top, and ensure that the coordinates and elevation of the pile foundation are accurate and meet the design requirements.
(4) Check the coordinate control points and leveling points provided by the urban planning department, and establish a survey control network.
(5) Send the instruments and equipment used in the construction survey of this project to the Metrology and Testing Institute of the local technical supervision bureau for verification to ensure that all instruments and equipment are in normal condition.
Second, the construction process of rotary bored pile: site excavation leveling → pile location lofting → drilling rig positioning → rotary drilling → hole inspection → hole cleaning → fabrication and installation of reinforcing cage → installation of conduit → pouring underwater concrete. Main construction methods and control points 1. Site leveling: The construction site of this project has been leveled to the level of the design site.
2. Pile location setting-out: After the site is leveled, accurately determine the position of the pile hole by coordinate method with total station, and bury the protection pile (the protection pile is buried by cross method and marked). On-site technicians track and set out the whole process, and recheck the setting-out results.
3. Rig in place: The rig platform must be compacted. Drive the drilling rig to the hole to be constructed, adjust the mast angle, align the center of the drilling rig with the drilling center, and adjust the verticality parameters of the drilling rig to make the drill pipe vertical.
4. Drilling: When drilling, the drill bucket should be grounded first, and the original position of the drill bit should be recorded through the reset button on the display. When the drill bucket is squeezed and pressurized, it will be lifted off the ground. After emptying the drill bucket, the machine will automatically return to the drilling operation position by operating the automatic return alignment button on the display screen, or manually return to the drilling operation position by operating the rotary operating handle to continue drilling. The drilling residue generated in the process should be moved to an appropriate place for disposal in time to meet the requirements of environmental protection.
In the process of construction, the verticality of the hole is repeatedly checked by the three-way vertical control system of the drilling rig itself to ensure the quality of the hole. Control the drilling speed according to the geological conditions when drilling: when drilling from hard stratum to soft stratum, the drilling speed can be appropriately increased; When the soft stratum becomes hard stratum, slow down and advance slowly; In the formation prone to shrinkage, the number of hole sweeping should be appropriately increased to prevent shrinkage; Fast drilling is used in hard plastic layer to improve drilling efficiency; In the sand layer, slow rotation speed and slow drilling are adopted to appropriately increase the specific gravity and viscosity of mud; If there is a pebble bed in the actual construction process, the following measures should be taken: for the pebble bed with small particle size, use a bucket bit to drill slowly, for the pebble bed with large particle size, use a conical spiral bit to drill, then replace the bucket bit to remove slag, and so on until it passes through the pebble bed; For shallow cobble layer, the method of manual direct excavation can be adopted, and then drilling with rotary drilling rig. Records of geological conditions shall be recorded according to relevant tables of corresponding geology; Fill in the drilling record form in time when the rotary drilling rig is drilling, which mainly includes: work items, drilling depth, drilling speed and hole bottom elevation; The drilling record form shall be filled in by a special person, and the handover record shall be kept when the shift is changed. According to the change of drilling speed of rotary drilling rig and the situation of soil borrowing, carefully record the geological situation. After the drilling reaches the design depth, the geological conditions must be verified. If it meets the design requirements, the hole depth, aperture and pass shall be checked immediately. Detection of hole depth and sediment thickness: after hole formation, measure the hole depth L2 with measuring rope according to the hole depth L 1 in the display interface of rotary drilling rig and compare them. If L2 is less than L 1, replace the bottom cleaning bit, carry out bottom cleaning and re-measure the hole depth.
5. Hole cleaning detection: hole cleaning method is used to clean the hole, and the water level in the hole should be maintained during hole cleaning.
6. Installation of reinforcing cage: The reinforcing cage is made of rigid frame in the field reinforcing workshop. Mark the position of the main reinforcement on the reinforcing hoop at equal intervals. Firstly, 6 ~ 8 main bars are welded on the reinforcing hoop one by one in turn to form a steel skeleton, and then other main bars are welded evenly on the steel skeleton to form an integral skeleton. Finally, according to the spacing of the design drawings, spot weld stirrups on the steel skeleton. According to the up and down position of the reinforcing cage, the joint position of the main reinforcement shall be arranged, and the number of joints of the same section for flash butt welding of the main reinforcement shall not exceed 25% of the number of the main reinforcement.
7. Selection and lowering of conduit: use special flange for connection, and use 300mm inner diameter conduit for conduit. The conduit shall be firm, the inner wall shall be smooth and straight, and there shall be no local unevenness. For the old conduit, whether the wall thickness of the conduit meets the use requirements should be judged by weighing before pressure test. Before using the catheter, besides carefully checking its specification, quality and splicing structure, splicing and pressure test should also be carried out. The length of pressure test conduit should meet the needs of the longest cast-in-place pile, and the conduits should be numbered and segmented from bottom to top, and the assembly order of conduits should be strictly maintained. Each group of catheters shall not be mixed. The axis difference of the assembled conduit shall not exceed 0.5% of the drilling depth, and shall not exceed 10cm. The pressure test pressure is 1.5 times the hydrostatic pressure at the bottom of the hole. It can only be used after inspection.
The length of the conduit should be determined according to the depth of the hole and the height of the working platform. Non-standard joint conduit should be used from the bottom of funnel to the upper opening of drilling hole. The conduit should be lowered vertically and slowly to avoid collision with the reinforcing cage. When descending, record the number of descending parts. After running to the bottom of the well, compare the theoretical length with the actual length to see if they are consistent. Lower the catheter completely to the bottom of the hole. After checking it, gently lift the catheter, and control the bottom opening to be 0.25~0.4m away from the bottom of the hole, and locate it in the drilling center.
8. Pouring concrete: The concrete adopts commercial concrete with the strength required by the design, and is transported to the pouring point by truck. Underwater pouring concrete should maintain good workability, slump should be controlled between 180 ~ 220 mm, after the concrete is transported to the site by tanker, it will be discharged into the hopper set at the top of the conduit for pouring after the slump is qualified. The quantity of the first batch of concrete to be poured should be calculated to make it have a certain impact energy, and the mud in the conduit should be discharged by combining the waterproof glue ball at the bottom of the funnel, and the depth of the lower opening of the conduit buried in the concrete should be not less than1m. When the amount of concrete in the hopper reaches the first pouring amount, pull out the cock at the bottom of the hopper and start pouring. During pouring, observe the falling of concrete in the hopper and the fluctuation of water level in the hole, and measure the height of concrete surface in the hole at any time, so as to lift or dismantle the conduit in time and ensure the buried depth of the conduit is 2m ~ 6m. Use a drilling rig to cooperate with the removal of the conduit. After the concrete is transported to the pouring site, if there is segregation, serious bleeding or the slump does not meet the requirements, it should be stirred for the second time, and water should not be added at will during the second stirring. If it still does not meet the requirements after the second time, it should be resolutely returned. Keep in touch with the commercial mixing station during the whole pouring process to ensure the continuity of on-site concrete pouring. The elevation of the concrete pouring pile top should be 0.5m higher than the design pile top to ensure the concrete quality of the design pile top. Slowly pull out the liner after dumping.
Three, rotary drilling bored pile construction safety
1. When the drilling rig is moving, the road and the surrounding environment should be carefully surveyed first, and reinforcement measures should be formulated when necessary to prevent accidents such as overturning of the drilling rig.
2, the construction site safety electricity must meet the following requirements:
(1) The installation and removal of all power supplies and circuits on the construction site must be managed by certified electricians, and electrical appliances must be strictly grounded and connected to zero, and leakage protectors should be used.
(2) Multi-machine operation power must be switched off, and it is forbidden to use more than one brake.
(3) The wires and cables on the construction site must be overhead in accordance with the regulations, and it is forbidden to mop the floor and pull them randomly.
(4) After the installation of electrical appliances, the power supply must be turned on after acceptance.
3. After the rig is in place, conduct a comprehensive inspection of the rig and supporting facilities. The drilling rig should be installed firmly.
4, when drilling, closely monitor the excavation situation, observe whether there is any abnormal situation in the hole, whether there is any inclination of the drill frame, whether there is any looseness in the connection part, whether there are any signs of hole collapse, etc. , if there is any abnormality, handle it in time.
5. When the rig stops drilling, lift the drill bit out of the hole, put it on the drill frame, and don't stay in the hole.
6, drilling rig construction, the driver should concentrate, obey the command, and shall not leave his post at will.
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