Problems and Countermeasures in Rotary Excavation Construction of Deep Piles and Large Piles

Problems and Countermeasures in Deep Pile Construction

1. The construction efficiency is low. The main reasons are that the time taken to lift the drilling tool is too long and the efficiency of the drill pipe in transmitting the drilling pressure is low.
   Countermeasures:

(1) Increase the length of the drill bit to increase the amount of ballast drilled per drill;

(2) The drill bit has a ventilation hole to increase the drilling speed;

(3) If it is not possible to enter the rock, try to use a friction rod to save the time of unlocking.

2. The failure rate of the drill pipe has increased sharply. After the drill pipe is lengthened, the slenderness ratio of the drill pipe is particularly unreasonable. During construction, it must withstand greater torque and pressure, especially the machine lock rod must be unlocked frequently, so the drill pipe must be unlocked frequently. Rod failure rates can rise dramatically.
   Countermeasures:

(1) The working site should be as flat and solid as possible to reduce the swing of the drilling rig;

(2) Frequently correct the leveling system to make the drill pipe work vertically;

(3) It is strictly prohibited to jack up the drilling rig when drilling under pressure;

(4) Add a centralizer to the drill pipe.

3. The pile hole is deflected, mainly due to the uneven softness and hardness of the formation, the overall rigidity reduces after the drill pipe is lengthened, and the accumulated gap increases after the drill tool becomes longer and the drill bit swing increases.

Countermeasures:

(1) Increase the height of the drilling tool;

(2) Add a centering ring to the drill pipe;

(3) Add a counterweight device to the upper part of the drill bit and use pressure at the bottom of the hole to make the drilling tool have a self-suspension effect when drilling.

4. Accidents occur frequently in the hole, mainly due to unstable hole wall collapse and buried drill.

Countermeasures:

(1) Due to the prolonged construction time of deep piles, if the wall protection effect is not good, the hole wall will become unstable, and high-quality mud should be prepared;

(2) The drill bit is equipped with a ventilation hole to reduce the impact and suction on the hole wall when lifting the drill.

Problems and Countermeasures in Large Pile Construction

1. Construction efficiency will drop sharply Countermeasures:

(1) Select a reasonable drill bit (according to the formation conditions);

(2) Formulate a reasonable drilling plan. If the drilling rig has sufficient capacity and the formation is soft, it is best to drill the hole from the bottom to the bottom. If the footage efficiency is significantly reduced, graded drilling must be used, but two principles must be followed. One is steering. Drill until the bottom of the hole and then use a larger-diameter drill bit to enlarge the hole. Second, the diameter of the first drill should be selected reasonably. Generally, the drilled area should not be less than half of the total area.

2. Pile holes are easy to tilt because the drill bit straightness is greatly different from the diameter of the drill pipe, the drill bit height is small, and the stratum is uneven.

Countermeasures:

(1) Drill pipe plus centralizer;

(2) When the lifting height and lifting capacity of the drilling rig are sufficient, increase the drill bit height as much as possible;

(3) Graded drilling can also prevent inclination. When drilling small diameters, the hole inclination is well controlled, and then when enlarging the hole, the drill bit will drill according to the original pilot hole trajectory.

(4) If you encounter a particularly inclined formation, try to use a long-length coring barrel to transition

3. There are many accidents in the hole (drill pipe is broken, the drill bit is dropped, and it is difficult to pour the drill bit into the soil). Reasons: Due to the large diameter of the drill bit, its heavy weight, and the large load on the drill pipe, the drill pipe will break, and the pin of the drill pipe will be broken, causing the drill bit and the drill bottom plate to fall off. The dead weight plus the heavy weight of a bucket full of ballast makes it difficult to open the drill bucket.

Countermeasures:

(1) Strictly follow the correct usage method of drill pipe;

(2) It is best to use double pins for the drill pipe and drill bit and use a wire rope to secure the drill bit to the tray above the square head of the drill pipe. Even if the pin and the square head are broken, the drill bit will not fall into the hole;

(3) Put the drill bit on the ground and then open the door, or lift the drill bit off the ground and reverse it at high speed, so that the soil inlet between the two bottom plates opens and the ballast soil automatically leaks out.

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