Pile pressing incident
Pile pressing incidents: Piles tilted too far as prescribed (greater than 1%), unfinished piles due to sand foreign objects, abnormally hard clay seams, broken piles... must be handled by pulling them up and re-pressing them or additional pressing them. Add new piles (specified by design). Due to the heterogeneous geological structure of the ground, the following problems may occur during pile pressing construction:
• When pressing to a certain depth that has not yet reached the design depth but the pressure has been reached, then you must reduce the speed and gradually increase the pressure but not greater than Pep max. If the pile still does not go down, stop pressing and report to the design party to check and resolve the pile pressing problem.
• If the cause of the pile pressing problem is that the medium-grained sand layer is pressed too tightly, stop pressing the pile for a while, wait for the compaction of the soil layer to gradually decrease, and then press again.
• If you encounter an obstacle, drill, guide, and force the pile to create a hole.
When pressing concrete piles, there are also a few reasons why pile pressing incidents can affect adjacent apartments, so in this case we must drill before pressing concrete piles for the following reasons:
1. – The adjacent house's foundation is weak, due to long-term construction.
2. - The effect of drilling reduces soil extrusion that can cause settlement, cracking, and bulging of the house's foundation.
Many people think that the cost of drilling can be very expensive, but on the contrary it is relatively cheap, about 30-50,000/m2 depending on the number of md when drilling.
• When pressing to the design depth, the pile head pressure still does not reach the calculated requirement. This case often occurs because the pile head has not yet reached the middle-grained sand layer, or encountered lenses or soft soil. We stop pressing the pile and notify the designer to check, determine the cause and find solutions. If the geology has quite thick layers of sand (fine grain, coarse grain, medium grain), the normal pile pressing method will not be feasible:
The pile cannot penetrate because when pressed, false rejection will appear (with sand, the false rejection is smaller than the designed rejection), the sand particles under the tip of the pile and around the pile will compact, increasing the force. close around the pile, increasing the resistance to the tip (increasing the bearing capacity of the ground), the soil bearing capacity should increase proportionally to the pressure force, the more pressure you increase, the more difficult it is to press when the sand layer is too thick.
(Therefore, when pressing piles through sand, it is necessary to have time to think for the sand layers to return to their normal state before pressing again. This is only feasible when pressing through sand layers that are not too thick) (TCXD 205:1998_Tieu pile foundation design standards).
Therefore, to avoid the above phenomenon, it is necessary to reduce the appearance of false rejection by vibrating pressing, drilling before pressing, and pressing with water. This method will temporarily break the soil structure while pressing and driving the pile down. Among them, the guided drilling method is currently widely used because of its feasibility (it is not convenient to compare the methods with each other).
Principle of the guide drilling method (shown in the name of the method): Before pressing, at the design center of the pile, we pre-drill a hole with a diameter equal to (1/8 - 1/10) the edge of the pile, The depth of the hole depends on the underlying geological layer, so that it can be constructed, the hole wall is kept with bentonite solution.
After that, we proceed to press the pile. The solution in this case is to add piles after inspection and clearly determine that the soil layer below is weak soil layer, then press until the design pressure is reached.
• When the pressure has just reached the design value and the pile cannot go down anymore, while the pressure on the pile continues to increase beyond the maximum pressure (Pep)max, before stopping the pressure, a valve must be used to maintain the force. maintain (Pep)max for 5 minutes. In case the press does not have a holding valve, press the press three to five times with (Pep)max pressure.
(According to Structure Wiki)
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