Whether to do advanced drilling before the construction of percussion hole forming piles

No, you don't. Percussion drilling, punching and grabbing drilling and rotary drilling into holes can all be used mud wall protection construction method. The main processes are leveling the site, preparing the mud, burying the casing, laying the working platform, installing the drilling rig and positioning, drilling into the hole, cleaning the hole and checking the quality of the hole, and lowering the reinforcement cage.

Pouring underwater concrete, pulling out the casing, checking the quality.

In order to prevent the pile position is not accurate, it is very important to set the center position and correctly install the drilling machine, for the drilling machine with the drilling tower, first use the power of the drilling rig to cooperate with the nearby ground cage, and the drill pipe is moved roughly positioned, with a jack.

Jack up the frame and position it accurately, so that the lifting pulley, drill bit, or fixed drill pipe is jammed.

It is on a perpendicular line with the center of the casing to ensure the verticality of the drilling rig.

The main purpose of advanced drilling is to find out whether the bearing layer (carbonate, such as limestone or dolomite) at the end of the pile has karst or soil cave adverse geological effects.

The purpose of advanced drilling is to find out whether there are unfavorable geological conditions such as weak strata, fracture layers, karst caves, etc., within 3 times the pile diameter below the pile end or within 5 meters (the specific exploration depth is combined with the design requirements). It doesn't matter which construction process you use to form the hole. If you don't, in case there is a weak stratum or cave at the bottom of the pile, then you will have to gamble on fate.

No, impact hole forming is a relatively mature process.

1. When encountering a partial hammer, it proves that the rock below is very hard, and the height difference of the rock surface in the hole is relatively large, which is biased to one side;

2. When encountering a stuck hammer, it proves that the formation has a very soft silt layer (shallow), and there will be shrinkage holes, covering the hammer body, or sucking the impact hammer; If it is deep, it proves that a hard rock layer with cracks has been encountered;

3. When encountering a karst cave, the hammer will shake, and the take-off and landing will not be smooth;

4. When encountering the quicksand layer, the basic footage of the hammer is very slow or not at all;

5. When encountering silt clay, the footage is normal;

6. When encountering a gravel layer, although the footage is a little slow, it can still be normal.

Experienced operators will have the means to deal with these geological formations.

Advanced drilling is to test some points of doubt in geological formations (such as lava areas) before drilling, so as to prepare equipment, materials, technology, and changes in advance (this is detailed in the "Technical Specifications for Highway Bridge and Culvert Construction").

According to the design code for building foundations, there should be no weak interlayer within the range of three times the pile diameter below the pile end of the rock-socketed pile. In order to find out the geology within three times the pile diameter below the pile end, it is necessary to use advanced drilling.

Mainly for the foundation pile in the karst area, the drilling method is used to check the bedrock at the bottom of the pile before the pile is formed, which is basically a pile with one hole and a large pile with multiple holes. Generally, after the pile design drawing comes out, the pile is dug in place, and the concrete is poured out. Generally, the strata can be selected for investigation, and it is best to survey each pile in karst areas.

Applicable scheme for advanced drilling.

1. Conventional hole forming scheme.

When the karst cave has filling, is plastic or soft plastic sub-clay, and the cave does not leak, then no matter how big the cave is or how many caves are in the vertical direction, the existence of the cave can be ignored, and the construction is carried out according to normal geological conditions. The percussion drilling is used to form a hole, and the soil quality in the cave is no different from the soil outside the karst cave, and it can be constructed according to the non-karst cave.

2. Flake stone backfilling.

Adopt the normal hole forming method construction, when drilling through the karst cave leakage, repeatedly put in loess and flake, use the drill bit impact to squeeze the loess and flake into the karst cave and karst fissures, and can also be mixed with cement, caustic soda and sawdust, in order to increase the self-stability capacity of the hole wall.

3. Plain concrete backfill.

The normal hole-forming method is adopted, and when drilling through the karst cave and leaking slurry or encountering the inclined face, low-grade concrete is filled, and percussion drilling is used to form a hole after a certain interval of time.

4. Grouting reinforcement.

It is to fill and reinforce the karst cave through which the pile passes by comparing the geological column map. The grouting sequence is mastered by the site. And the filling effect should be tested by coring in the pile foundation range, and the pile foundation construction can be carried out only after the karst cave is completely filled and the strength is reached.

5. The steel casing is followed up and reinforced.

The steel casing jumping method is adopted: one side is punched, the other side is connected to the steel casing, and it is pressed or vibrated and sunk into the drilled hole. When the steel casing is followed up by percussion drilling, the reaming performance of the percussion drill should be fully utilized in the construction, so that the steel casing can sink smoothly.

The diameter of the drill bit is greater than the outer diameter of the rigid casing 3 5cm, and the drill bit is changed to meet the drill bit diameter of the hole forming requirements after the casing is in place.

Refers to the pile hole formed in the foundation soil by means of mechanical drilling, steel pipe squeezing or manual excavation at the engineering site, and the pile made of steel cage and concrete is placed in it, according to the different hole forming methods, the cast-in-place pile can be divided into several categories such as immersed pipe cast-in-place pile, bored cast-in-place pile and excavated cast-in-place pile.

Bored piles are a way to strengthen the pile foundation by piling to increase the bearing capacity of the foundation; At the same time, it can also be used for slope maintenance to resist the lateral pressure of the earthwork and prevent the displacement of the earthwork.