Introduction of rotary excavation pile construction technology?

Through the application of rotary drilling rig in the construction of bored pile of bridge foundation in Wuhan North Marshalling Station, this paper introduces the construction technology, construction characteristics and common problems of rotary drilling rig. CBI Zhong Da Consulting Company introduced the following information about rotary excavation pile construction technology:

(A) lofting positioning

Before the project starts, according to the arrangement of axis and pile positions, a survey control network is established at the site, and then the center points of each pile position are laid out according to the control network.

(2) The rotary excavator is in place

The drilling rig must be stable, upright, horizontal and positioned, and the error between the center of the drill bit and the center of the pile position shall not be greater than 10 mm. ..

(3) Buried liner

The diameter of the liners should be 200mm larger than the diameter of the pile hole, and the length should meet the requirement that the bottom of the liners should enter the clay layer at least 0.5m. The top of the liners should be 0.3m higher than the ground, the inclination of the liners should be controlled within 65438 0%, the deviation of the liners should not exceed 30mm, and the liners should be backfilled with clay and compacted in layers.

(4) forming holes with a rotary excavator.

Combined with previous construction experience, we use modern tool rotary drilling rig to drill holes: after casing embedding and positioning, SR-250 rotary drilling rig is used to drill holes. The drilling rig has the advantages of large torque, high rotating speed and high hole-forming efficiency, and is suitable for drilling in moderately weathered layers. After the drilling rig is in place, it should be re-measured and positioned, and mud should be used to protect the wall during the hole-forming process. Mud is naturally made by using the stirring effect of drill bit on soil when drilling, and the specific gravity of mud can be adjusted according to actual needs. In the process of construction, the specific gravity of mud is generally controlled between 1.2 ~ 1.3, and mud forms mud skin on the surface of the hole wall during circulation, which together with its own weight protects the hole wall and prevents the hole wall from collapsing. Through hole-forming construction, the effect of slurry wall protection is good, which can fully meet the construction needs. The specific gravity of mud can be adjusted by digging out the slag bucket and adding clean water into the hole. According to the actual construction needs, the specific gravity of mud is generally controlled above 1.3, which is beneficial to drilling and hole wall stability.

(5) hole cleaning (hole cleaning is only needed when the head is enlarged)

After the drilling rig reaches the designed hole depth, lower the drill bit to the bottom of the hole and rotate slowly, with the focus on removing the residual mud after expanding the expanding head.

(6) Fabrication and placement of reinforcing cage

1. The reinforcing cage shall be fabricated in segments at the site, and all main reinforcement and reinforcing ribs shall be welded. Spiral reinforcement and main reinforcement shall be reinforced by spot welding. In addition to meeting the design requirements, the reinforcing cage shall also comply with the provisions in Table 2. The fabricated reinforcing cage shall be accepted section by section, and listed for storage after it is qualified. 2. The length (greater than 16m) of the reinforcing cage placed in the hole of the reinforcing cage shall be welded at the orifice, with one side welded 10d, the weld height ≥0.3d, and the weld width ≥ 0.7d. Two reinforcing cages shall be kept straight, and the joints with the same cross section shall not exceed 50% of the reinforcement, and the spacing shall be staggered, not less than 35d. After the steel bar is welded in good condition, it should be lowered into the hole slowly, and it is forbidden to smash the cage.

(7) downcomer

1. The conduit is a threaded conduit with an inner diameter of φ 250 ~ φ 280, a bottom pipe length of 4m and a middle section length of 2.5m generally. Before using the catheter, it must be visually inspected and docked. (1) Appearance inspection: check whether the conduit is deformed, sunken, bent, damaged or cracked. , and check whether the inner wall is smooth. For the new conduit, check whether its inner wall is smooth and whether there is welding slag. For the old conduit, check whether there is concrete adhesion and consolidation on its inner wall. (2) Docking inspection: The thread of the conduit joint should be kept in good condition. Straight and concentric after connection. It can only be put into use after passing the above inspection, and unqualified catheters are strictly prohibited. The length of the conduit should be equipped according to the depth of the hole to meet the needs of hole cleaning and underwater concrete pouring, that is, it can go down to the bottom of the hole when cleaning the hole; When pouring underwater, the bottom of the conduit is about 0.5m away from the bottom of the hole, and the concrete should be poured smoothly from the conduit to the bottom of the hole. 2. The conduit shall be firmly placed at the orifice joint, and a sealing ring shall be provided. When hoisting, the position should be centered, the axis should be straight, and the lowering should be stable, so as to avoid hanging the reinforcing cage and scraping the hole wall.

(8) Concrete pouring

1. Mixing and transportation of concrete truck; The slump of concrete shall be controlled at18 ~ 22 cm; Concrete is directly poured into the hopper from the opening by a mixer truck. 2. Underwater concrete pouring: Before pouring, calculate the initial concrete pouring amount of pile holes with different diameters and depths. Ensure the initial pouring quantity during construction. When pouring, the buried depth of the conduit should be controlled at 2 ~ 6m. Before dismantling the conduit, the concrete surface in the hole shall be measured by special personnel and recorded. When the pouring concrete is close to the elevation of the pile top, the last pouring amount should be controlled to ensure that the elevation of the pile top meets the design requirements. 3. Making test blocks: During the process of filling piles, randomly select 1 ~ 2 plates of concrete as test blocks, and make a set of test blocks for each pile. 12h later, the manufactured test block will be removed and put into still water for maintenance. The evaluation of test block adopts mathematical statistics method.

(9) Pull out the gasket

After concrete pouring, pull out the liners, clean up the pouring equipment and tools, and pile them up neatly.

(10) Backfill the pile hole

After the concrete pouring of the pile hole is completed, the upper part that has not been poured with concrete shall be backfilled with soil and slag dug out from the pile casing, ditch, pool and trough in the site. After backfilling, the orifice should be closed with concrete again to form a complete hard floor. Pore-forming content: 1. Before drilling, the drilling tool parameters should be calibrated, including bit height, diameter, main rod length, rod length, orifice and platform elevation and hole bottom elevation. 2. During drilling, the following parameters should be recorded: mud specific gravity, viscosity, penetration rate, rotation speed and footage speed, and the abnormal drilling situation of each layer should be described. 3. Record the final hole depth in time, adjust the mud specific gravity and time record, record the measured hole depth and record the lifting time.

The above is the introduction of rotary excavation pile construction technology provided by Zhong Da Consulting for architects. For more knowledge of architectural terminology, please pay attention to the architectural knowledge column of Zhong Da Consulting.

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