What are the specifications for bored piles? The following Zhongda Consulting brings specific and relevant content about bored pile specifications for reference.
1. Construction preparation
Materials
⑴ Cement: No. 425 or 525 ordinary Portland cement should be used, with factory certificate and testing qualified.
⑵Sand: medium sand or coarse sand, with a mud content of no more than 3.
⑶Gravel: particle size 10~40mm, with a mud content of no more than 2.
>⑷Reinforcement bars: The varieties and specifications should comply with the design regulations, and can be used only after passing the factory certificate and passing the test according to the regulations (if it is imported steel, it must have an import commodity inspection certificate and chemical composition analysis report)
Operating conditions
⑴ Site survey work should be carried out before construction. If there are overhead wires, underground cables, water supply and drainage pipes and other facilities that hinder construction or affect safe operation, they should be cleared and moved first. Construction can only be started after the location or proper handling. ⑵ Site leveling work should be done before construction, and effective measures must be taken to deal with loose sites that are not conducive to the operation of construction machinery. Effective drainage measures must be taken at the site.
⑶ Engineering geological data in the construction area, construction drawings confirmed by joint review, construction organization design or plan, various raw materials and their sampling test reports, concrete mix ratio design reports and related information should be available. ⑷The performance of construction machinery must meet the design requirements of the completed pile.
2. Process flow
Measurement and laying out → Buried casing → Drilling rig in place, mud production → Impact (or punching machine, rotary, submersible drill) hole forming → Slag extraction →Grouting →Inspect the hole →Clean the hole →Check the sediment →Place the steel cage →Down pipe →Pour underwater concrete.
3. Operation process
1. After the site is leveled, set out the pile positions. After positioning, drive a line at the center of each pile position
φ16 ×800mm steel bars are used to mark the pile positions and are fixed with concrete. After the pile position is laid out, the axis pile position will be reviewed together with relevant personnel, and a review record visa will be issued. Construction can only begin after the axis pile position is verified to be correct.
2. The casing should be set according to the following regulations
⑴The casing is generally made of 4~8mm thick steel plate with a height of 1.5~2m. Casing of bored piles The inner diameter should be 100mm larger than the diameter of the drill bit; the inner diameter of the casing of the punching pile should be 200mm larger than the diameter of the drill bit. 1~2 grout overflow openings should be opened on the top of the casing and 0.15~0.30m above the ground.
⑵The casing has important functions such as positioning, protecting the orifice and maintaining the water level difference. The position of the casing should be based on the designed pile position and buried in the center of the vertical and horizontal drawing lines. The pit where the casing is buried should not be too large. After the pit is dug, the bottom of the pit is leveled, and then the casing is placed. After checking that the position is correct and the barrel is upright, the surrounding area is backfilled with clay and compacted layer by layer. Observe as you fill to prevent the casing from being damaged during filling. Position offset. After the casing is buried, the correction should be reviewed. The center of the casing should coincide with the center of the pile position, and the deviation should not be greater than 50mm.
⑶ The burial depth of the casing: not less than 1m in cohesive soil; in sandy soil It should not be less than 1.5m, and the mud level in the hole should be kept at least 1m above the groundwater level.
3. The production and performance requirements of mud used for wall protection and ballast removal should comply with the following regulations:
⑴⑸ When forming holes in clayey soil, clean water should be injected to remove the original mud. Soil pulp protection wall. The specific gravity of circulating mud should be controlled at 1.1~1.3.
⑵ When forming holes in sandy soil and thick sand layers, mud should be prepared (punching piles can put mud balls into the holes to create slurry) , the specific gravity of the mud should be controlled at 1.2~1.3.
⑶ When holes are formed in the sand and gravel layer or the soil layer that is prone to collapse, the specific gravity of the mud should be increased to 1.3~1.5. (4) Mud control indicators: The viscosity is 18~22S; the sand content is not more than 8; the colloid rate is not more than 90. The specific gravity, viscosity, sand content and colloid rate of the mud should be measured frequently during construction.
4. The pool surface elevation of the mud tank sedimentation tank should be 0.5~1m lower than the casing to facilitate smooth mud return. The location of the mud tank and sedimentation tank must be reasonably arranged and must not hinder the movement of the crane and drilling rig.
The capacity of the mud tank is the slag discharge volume of each hole, and the capacity of the sedimentation tank should be 1.5 to 2 times of the slag discharge volume of each hole.
5. Special personnel should be assigned to remove the sediment in the mud trench to ensure that it is not blocked. Sediments in sedimentation tanks and mud pools should be removed frequently, and excess mud should be discharged from the foundation pit in a timely manner.
Drilling tools and drill bits can be selected according to the following regulations:
⑴ In general clay soil, silt, silty soil and sandy soil, cage drill bits should be used. ⑵ In sandy pebble layers and strongly weathered layers, cage drill bits with welded carbide tips can be used. ⑶ When encountering isolated stones or old foundations, a barrel drill bit with a carbide knife can be used.
⑷In hard rock, a roller cone drill bit can be used.
⑸Punch piles generally use cross-shaped impact drill bits. Impact drill bits are divided into punching drill bits, rock punching drill bits, repair drill bits and reaming drill bits. Compared with the designed pile diameter, the drill bit diameter is 50~80mm smaller for punching drill bits and rock drilling bits; 10~20mm larger for repairing drill bits; 60~100mm larger for reaming drill bits. Impact drill bits must be set up to salvage ring.
7. When drilling with a drilling rig, the corresponding drilling speed should be determined based on the soil layer type, hole size, drilling speed and slurry supply amount. The drilling speed should comply with the following regulations:
⑴In silt and silty soil layers, the drilling speed should be strictly controlled according to the mud supply situation, and generally should not exceed 1m/min; in loose sand layers, the drilling speed should not exceed 3m/h.
⑵ The drilling speed in hard soil or rock formations shall be subject to the fact that the drilling rig does not jump.
8. The following regulations should be followed when forming holes by impact:
⑴ When opening the hole, the hammer should be struck closely with a low hammer. If the topsoil is soft soil such as silt or loose fine sand, clay blocks can be added with small pieces of stone to repeatedly impact the hole wall to ensure the stability of the casing.
⑵ The supply of mud must be ensured to stabilize the slurry in the hole.
⑶ When drilling in various soil and rock formations, the construction points in the following table can be carried out. Key points for construction of bored (punched) cast-in-place piles
Backfill in weak soil layers or collapsed holes, drill with small strokes and impact repeatedly, add clay blocks and small stones, mud specific gravity
1.3~1.5 . Create a solid hole wall
⑷The YKC repetitive punching pile driver is characterized by a relatively fixed stroke and high impact frequency. The construction points in Table 3-1 should also be referred to during construction. If the impact energy needs to be increased, You can also adjust the stroke or change impact drill bits of different shapes and weights.
⑸When starting to drill bedrock, use low hammering or intermittent impact to avoid deflection. If it is found that the drill hole is deflected, the rubble should be backfilled immediately to the upper 0.3~0.5M of the deflected hole, and the hole should be drilled again.
⑹ When encountering arc stones, you can appropriately throw and fill the fragments with similar hardness, and impact with a heavy hammer, or alternately impact with heavy and low strokes. Crush the large arc stone and squeeze it into the hole wall.
⑺The length of the loose rope must be accurately controlled to avoid empty hammering. Generally, it is not advisable to use a high stroke to avoid disturbing the hole wall and causing hole collapse, hole expansion or drill stuck accidents.
⑻ The wear of the wire rope, the tightness of the buckle, and the flexibility of the steering device should be checked frequently to avoid falling off the drill.
⑼ The wear of the impact drill bit should be checked frequently. If the wear is excessive and the cutting angle does not meet the requirements, it should be replaced and repaired in time to improve drilling efficiency and prevent accidents such as drill pinching and stuck drill.
9. If inclined holes, bent holes, neckings, collapsed holes, slurry emerging around the casing, or ground subsidence are found during bored pile drilling, drilling should be stopped and the following measures should be taken. Construction can only continue after effective measures are taken. ⑴ When the borehole is tilted, the hole can be repeatedly scanned and corrected. If the correction is ineffective, the hole should be backfilled with clay or weathered rock to 0.5m above the offset hole, and then drill again;
⑵ Drilling If a hole collapses, stop drilling immediately, backfill with clay, and wait until the hole wall is stable before drilling again; (3) If slurry appears around the casing, straw mixed with yellow mud can be used to plug the hole, and a layer of mud and sand bags can be applied.
10. If one of the following situations occurs during punch pile construction, drilling should be stopped immediately.
⑴ When oblique holes, curved holes or shrinkage holes occur, drill should be stopped and the clay block should be thrown to 0.5~1m above the start of the eccentric hole. Drill again. Do not use a punching drill bit to repair the hole to prevent Drill stuck;
⑵ If a hole collapses during drilling, drilling should be stopped immediately, backfilled with clay blocks sandwiched with rocks, increase the proportion of mud, and repeatedly impact wall building and drilling;
⑶ When slurry emerges around the casing, causing the hole mouth to collapse and the ground subsides, drill should be stopped immediately to prevent the drilling rig from tipping, and clay (mixed with straw) should be backfilled around the casing in a timely manner; it should be compacted, and a layer of mud should be applied if necessary. , sand bag before continuing drilling.
11. If the drill is stuck or dropped, the following methods should be used to deal with it:
⑴ When the drill is stuck, the rope should be tightened and loosened alternately, and the drill bit should be slowly lifted. Lift and pull hard. If necessary, you can use fishing hooks, jacks and other laying tools to help lift;
⑵ When the drill falls out, fish it out immediately. Use the fishing hook to hook the preset fishing ring of the drill bit and lift the drill bit. Come up.
12. The method of slurry circulation or ballast pumping tube can be used to remove ballast from pile holes. If a ballast drum is used to remove ballast, after drilling to a depth of 4~5m, the ballast should be pumped every 0.5~1m and the mud should be replenished in time.
13. When drilling large holes, the holes can be graded. The diameter of the first-level drill bit should be 0.6~0.8m times the diameter of the second-level drill bit.
14. After punching into the rock, take a rock sample every 200mm of drilling and keep it properly for final hole verification. After the bored pile is drilled into the rock, rock samples should be taken every 100mm.
15. The cleaning of bored piles should be carried out in accordance with the following regulations.
⑴ For boreholes made of raw soil, after drilling to the designed level, the drill bit can be idle without drilling, and the slurry can be replaced cyclically. The specific gravity of the mud should be controlled at around 1.1;
⑵ For sandy soil layers and sand-cobbled layers with poor soil quality, the specific gravity of the mud at the bottom of the hole after cleaning should be about
1.15~1.25m;
(3) The bottom of the hole after cleaning The thickness of the ballast should not be greater than 50mm for end-bearing piles, or not greater than the design specified value; the friction pile should not be greater than 200mm. The thickness of the ballast must be re-measured before pouring underwater concrete. If the ballast exceeds the regulations, the hole must be re-cleaned to comply with the regulations. Only then can underwater concrete be poured.
The hole cleaning of punched piles should be carried out in accordance with the following regulations.
⑴ If the soil quality of the hole wall is good and the hole is not easy to collapse, an air suction machine can be used to clean the hole.
⑵ If the soil quality of the hole wall is poor, mud circulation or ballast pumping can be used to clear the hole. After hole cleaning, the specific gravity of the mud should be controlled at about 1.15~1.25m, the viscosity ≤28s, and the sand content ≤10;
(3) During the hole cleaning process, sufficient mud must be supplied in time and the slurry level in the hole must be maintained stability; (4) The allowable thickness of hole bottom ballast after hole cleaning shall comply with the relevant provisions of Article 15 of this Chapter.
17. The production of steel cages for drilled (punched) piles should comply with the following regulations:
⑴ The clear spacing of steel bars must be more than 3 times greater than the particle size of the concrete coarse aggregate;
⑵ Reinforcement hoops should be outside the main bars. The main bars generally do not have hooks, and the steel bar heads must not be bent inward, so as not to hinder the work of the conduit;
⑶ The lap and welding of the main bars should be staggered, 35 The number of joints within a section that is twice the diameter of the steel bar shall not exceed half of the total number of steel bars;
⑷The outer diameter of the steel cage should be 140mm smaller than the design diameter of the drilled (punched) hole;
⑸Reinforcement bars The inner diameter of the cage should be more than 100mm larger than the outer diameter of the conduit joint;
⑹ The net protective layer of the main bars of the steel cage should not be less than 70mm, and the allowable deviation is ±20mm; ⑺ The production of steel cages should also comply with relevant specifications. .
18. When lifting the reinforced cage of drilled (punched) piles, appropriate measures should be taken to prevent torsion and bending. When installing the steel cage, you should align the hole position, hang it straight and steady, and sink slowly to avoid collision with the hole wall. After the steel cage is sunk to the designed position, it should be fixed immediately to prevent movement. If the steel cage does not reach the bottom of the hole, in order to prevent it from floating when pouring concrete, 3 to 4 main bars extending to the bottom of the hole can usually be installed as anchors, or the steel cage and the hole casing can be temporarily welded.
19. The length of the steel cage made of drilled (punched) piles in sections is preferably 5~8m. The two sections of steel cages can be connected by single-sided lap welding, lashing and Spot welding, but the joints shall be set up in accordance with the relevant provisions of Article 17 of this Chapter.
20. After the installation of the drilled (punched) pile steel cage is completed, the concealed engineering acceptance of the pile should be carried out together with the construction, design unit and quality supervision department. After passing the inspection, underwater concrete should be poured in time, and the interval should be It should not exceed 4 hours. Before pouring, the sediment thickness should be re-measured in accordance with Article 15 of this chapter.
21. Underwater concrete mixture shall comply with the relevant provisions of Article 1 of Section 2 of this chapter on operating techniques.
22. The structure and use of the conduit shall comply with the relevant provisions of Article 2 of Section 2 of this chapter, Operating Techniques.
23. When pouring underwater concrete, the relevant provisions of Article 3 of Section 2 Operating Techniques of this Chapter shall be followed.
IV. Quality Standards
Guaranteed Projects
⑴ The raw materials and concrete strength used for cast-in-place piles must comply with the design requirements and construction specifications. ⑵The depth of the hole must meet the design requirements. For piles mainly based on friction, the thickness of ballast shall not be greater than 200mm; for piles mainly based on end bearing, the thickness of ballast shall not be greater than 50mm.
⑶The actual amount of concrete poured must not be less than the calculated volume.
⑷The pile top elevation and laitance treatment after pouring must comply with the design requirements and construction specifications. Allowable deviation table.
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