1, measurement and positioning
Usually, a short steel bar is driven into the center of the pile. If the construction is carried out in soft ground, the pile driver will squeeze the pre-driven short steel bars, so it is generally necessary to re-determine the pile position after the pile driver is in place.
2, pile machine in place
After the selected pile driver is installed and debugged in place, go to the pile location to make the center of the gripper of the pile driver (the center line can be hung) basically align with the sample pile on the ground. After leveling the pile driver, check it again and force the long walk (long boat) to land.
3. Lifting and feeding piles
The length of the static pressure precast pile section is generally less than 12m, and the pile can be hoisted and delivered directly through the working regulator of the pile driver, or it can be equipped with a special regulator to hoist and deliver the pile.
The first pile (bottom pile) should be a pile with a pile tip. When the pile is transported to the vicinity of the pile driver, the single-point hoisting method should be adopted, and the hoisting method of double hoisting weight (sling) and urinal (small beam) can make the pile vertically enter the pile clamp mouth. When sulfur cement method is used to connect piles, the depth of mud anchor hole should be checked, and the inclusions and accumulated water in the hole should be cleaned before lifting.
Step 4 Align and straighten
When the pile is hoisted into the pile gripper, the commander will slowly lower the pile tip to about 10cm from the ground, then lift the pile, fine-tune the pile driver to align the pile tip with the pile position, press the pile into the soil for 0.5~ 1.0m, then stop pressing, and correct the verticality of the pile from two orthogonal edges of the pile. Only when the verticality deviation of the pile is less than 0.5% can the pile be pressed formally.
5. Pile pressing
Pile pressing is to press the pile into the soil by using the telescopic force of the pile pressing cylinder of the main engine. The maximum stroke of the pile driving cylinder of different types of pile drivers is different, which is 1.5~2.0m, so the depth of the pile is about 1.5 ~ 2.0m each time, and then the clamp is loosened-lifted-clamped-pressed again, and so on.
When a pile is pressed to 80~ 100cm above the ground, it can be connected or put into a pile feeder to press the pile to the design elevation.
6. Pile extension
The common joint forms of static pressure precast piles are electric welding and sulfur cement anchorage joint. During electric welding construction, the mortar, rust, oil stain and other impurities at the interface must be removed before welding, the groove surface should have metallic luster, and a positioning plate should be added. If there are air holes in the joint, they should be filled with wedge-shaped iron sheets and welded firmly.
The welding groove shall be welded in 3~4 layers, and the welding slag of each layer shall be removed. When welding, manual symmetrical surfacing should be used to prevent welding defects such as bubbles and slag inclusion. The weld shall be continuous and full. Before applying pressure, the welded joint shall be naturally cooled for 65438 05 minutes. It is forbidden to cool or pressurize with water immediately after welding. The quality of sulfur cement anchorage joint should be strictly controlled during construction.
Extended data
When piling, the foundation soil is strongly disturbed, and the actual shear strength of the soil around the pile is quite different from the static shear strength of the foundation soil. With the sinking of the pile, relative shear displacement will occur between the pile and the soil around the pile. Because of the shear strength of soil and the adhesion between pile and soil, soil will produce friction on the surface around pile.
When the soil around the pile is hard, the shear surface occurs on the contact surface between the pile and the soil; When the soil around the pile is soft, the shear surface generally occurs in the soil near the pile surface. With the pile sinking in cohesive soil, the shear strength of soil around the pile gradually decreases until it is reduced to remoulding strength.
In sandy soil, except loose sand, the shear strength has little change. The pile side friction acting on the pile in each soil layer is not a constant value, but a variable value that decreases significantly with the continuous sinking of the pile. Friction at the bottom of pile plays an important role in pile driving resistance, which can account for 50 ~ 80% of pile driving resistance. It is directly proportional to the strength of soil around the pile and inversely proportional to the pile depth.
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