What to Do if an Accident Occurs? Recommended Emergency Plan for Bored Pile Quality Accidents

When problems occur during bored pile construction, the on-site technical personnel on duty must immediately adopt the correct handling method and report to the chief engineer and manager of the operation team immediately. The chief engineer and manager of the operation team will report to the chief engineer of the work area and the on-duty leader according to the severity of the problem, and strive to solve the problem in the shortest time to prevent Class II piles and broken piles.

1. Collapse is easy to occur in quicksand and silt formations. After the collapse occurs during the drilling process, increase the mud density (controlled between 1.2 and 1.4) to improve its hole wall structure. When the collapse is serious, backfill the collapsed position with large pieces of clay and drill again.

2. Shrinkage is easy to occur in soft plastic and hard plastic clay layers. When the hole is bent or shrunken during drilling, the drill bit can be lifted to the deviated hole for repeated sweeping until the hole is straight. If a serious bend occurs, use a mixture of small pieces of stone and clay blocks, backfill to the deviated hole, and drill to correct the deviation after the filler settles.

3. Drill burial and drill stuck. Drill burial usually occurs with hole collapse. Deal with drill burial firs,t and then hole collapse. After the accident, ensure that there is enough mud in the hole to maintain the pressure in the hole and stabilize the hole wall to prevent collapse and expansion. Use a high-power mud pump to pump out the sediment at the drill bit to eliminate resistance, and then slowly lift the drill. It is strictly forbidden to force it, otherwise, it may cause more serious accidents, such as drill rod twisting.

4. Drill bit drop usually occurs in circulating drilling rigs and impact drilling rigs. After the drill bit drops, maintain the water head height in the hole, increase the mud density (1.15~1.3), make an L-shaped salvage hook, fix it at the lower end of the drill rod, extend the drill rod into the bottom of the hole, rotate to hook the drill bit and lift it.

5. Casing sinking. When the bottom of the casing has not completely penetrated the silt layer or is located in the quicksand layer, the casing is prone to sinking. When the casing sinks, if the drilling is not too long ago, backfill the hole, lengthen the casing, and rebury it. If the hole is close to being completed, increase the mud specific gravity (1.15-1.3) to maintain the mud head height in the hole, use sleepers to lay symmetrically on the outside of the casing, and use channel steel and other load-bearing poles to support the casing on the pile of sleepers. Try not to clean the hole after the hole is completed. The steel cage ring is loaded with a pile of sleepers to shorten the grouting time.

6. The steel cage falls off. If the welding of the cage suspension bar is not firm or the load-bearing shoulder pole at the hole is unstable, the cage is easy to fall off. After the cage falls off, maintain the water head in the hole and increase the mud-specific gravity (1.15-1.4). If the concrete has not been poured, use a double L-shaped hook to tie it to the bottom of the drill pipe for salvage. If part of the concrete has been poured, try to reduce the buried depth of the conduit. The original steel cage can be abandoned in the hole. A new steel cage can be placed within 2 hours for continuous pouring.

7. The conduit for pouring concrete is located below the bottom of the steel cage, and the depth of the concrete buried pipe is large. At this time, the top force of the concrete has the greatest impact on the steel cage, and it is easy to float.
After the steel cage floats, stop pouring concrete immediately, check the accurate position of the bottom of the steel cage and the bottom of the conduit with a measuring rope, remove the conduit, reduce the buried depth of concrete, and after the bottom of the conduit rises above the bottom of the steel cage, reduce the concrete discharge speed of the tank truck and resume pouring.

8. Bottom sealing failure. The common reason for bottom sealing failure is that the length of the conduit entering the hole is wrong, resulting in an error in the calculation of the distance between the bottom of the conduit and the bottom of the hole. After the bottom sealing fails, a high-power mud pump is immediately connected to the conduit to suck out the concrete before the concrete at the bottom of the hole is finally set. After the hole depth is measured and qualified, the bottom is sealed again.

9. Pipe blocking. Pipe blocking is common in hole pouring. There are many reasons for pipe blocking, such as too small concrete slump, too large buried depth of the conduit, large foreign objects blocked in the conduit, concrete waiting time exceeding 1 hour, and continuous pouring not forming. At the same time, threaded steel with a diameter of 12 to 14 can be used to connect a long steel bar, and the conduit can be inserted manually and poked back and forth. Generally, the pipe-blocking problem will be solved.

10. Cage hanging. When the conduit and the steel cage are not straight and centered, and the inclination of the hole position is too large, the cage is easy to hang when the conduit is pulled out during concrete pouring. When the cage is hung, the steel cage can be seen to be lifted up at the same time. At this time, the conduit cannot be pulled out hard, and the conduit can be slightly lowered. The conduit can be rotated manually, and the conduit can be lifted experimentally after changing the direction and position of the conduit. Generally, the cage hanging problem can be solved.

11. Concrete cannot be poured near the top of the pile. When the concrete is poured near the top of the pile, if the top of the pile is close to the ground, the height difference is not enough, or the interval between concrete tankers is too long, it is easy to cause the concrete to not be poured. At this time, the method of discharging materials from the tanker chute to the small hopper should be abandoned. A large hopper with a sealed bottom should be used. After the calculated amount of concrete is loaded, the hopper is slowly raised by a crane to increase the height difference of the pouring and appropriately reduce the buried depth of the conduit to complete the pouring.

12. Broken piles. When a broken pile occurs, find out the position of the broken pile. If it is within 10 meters from the ground surface and the surrounding terrain has excavation conditions, it can be excavated to the position of the broken pile, the floating slurry can be removed, and a rough wooden mold with a diameter of about 10 cm larger than the pile diameter can be used as a template to connect the pile to the designed pile top. If a deep broken pile occurs, clay can only be backfilled at the original pile position. After the hole position is stable, the impact drill is adjusted to the site to crush the broken pile in situ, and the crushed steel bars are sucked out with a large magnet, and re-poured.

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