Broken pile refers to the bored pile in the process of pouring concrete, mud or gravel into the cement concrete, the pouring concrete is separated and formed up and down two sections, resulting in concrete deterioration or cross-sectional area damage, so that the pile can not meet the force requirements. Broken pile is a very serious quality accident. Prevent the occurrence of accidents or take timely remedial measures in case of accidents. The following describes several reasons for broken piles.
1. The pouring time is long, the surface concrete loses its fluidity and forms a hard cover, while the concrete that continues to pour breaks the hard layer and rises, covering and wrapping the surface mixed with mud and gravel, which is the main factor causing the pile-breaking accident.
The conduit disassembly process takes too long, the working capacity of lifting equipment is small, the inner wall of the conduit is not smooth enough, the slump is too large, the gravel or pebble particle size is too large, the sand is too coarse or too fine, the fineness of grading is not good, the mixing is uneven, the concrete produces segregation phenomenon, increases the concrete falling resistance in the conduit, and makes the concrete not go down in the conduit, resulting in pipe sticking accident. The initial setting of the first batch of poured concrete reduces the fluidity, while the continued pouring of concrete breaks through the top layer and rises, with mud and muck in the concrete, forming broken piles.
2. Broken pile caused by insufficient section strength of pile body
In the design, the destructive effect of frost heave force on the pile is ignored, especially for the reinforced long concrete pile with thicker soil layer and deeper soil, only the overall freeze-pulling of the pile body is considered and the strength relationship between the tangential frost heave force and the pile section is ignored. The tangential frost heave force is greater than the strength of the pile section, and the pile is broken by freezing. Inaccurate sounding or calculation errors during pouring will lift the conduit too high, so that the bottom of the conduit will be separated from the concrete layer. In the construction, the cement dosage is insufficient and the concrete ratio is improper, which can not meet the concrete design strength. Reinforcement of reinforced concrete pile without mechanical experiment, poor quality, steel welding specification can not reach the design strength.
3. Broken pile caused by hole collapse
Because of the tension and continuity of the pouring construction, the height of the water head is ignored, and the water level in the hole decreases due to the leakage at the bottom of the casing, which reduces the water level difference in the hole and cannot maintain the original hydrostatic pressure. In the process of drilling, if it is found that the water (mud) level in the well casing suddenly rises and overflows the casing, then drops suddenly and bubbles appear, the amount of slag is significantly increased without the footage, and the load of the drilling rig is significantly increased, it should be suspected to be the phenomenon of hole collapse, which can be detected by depth sounder probe or depth hammer, and depth hammer is generally used on the site. If in the concrete pouring, the original stay in the hole of the depth of the depth of the hammer can not be pulled up or put into the depth of the hammer, the measured hole depth and the original hole depth difference is large, can be proved to be a collapse hole.
4. Broken pile caused by the inlet of the conduit or the bottom of the conduit
The water tightness, pressure bearing and tensile properties of the conduit are not good, and the water separation facilities are poor, resulting in water seepage of the conduit, and the first batch of concrete reserves are insufficient, causing water to enter the bottom of the conduit.
5. Pile breakage caused by failure to carefully handle the redundant pile head when connecting piles
At the end of concrete pouring, the concrete construction during pile connection was not considered, and the pile head was not handled well or cleaned well during pile connection, resulting in the concrete on the pile top failing to reach the design strength.
The key to broken pile accident is prevention. Before perfusion, each operation link and post shall be carefully inspected and effective preventive measures shall be formulated. Strictly abide by the operation rules during pouring to ensure the continuous, compact and orderly pouring operation; Repeatedly and carefully detect the concrete surface, and calculate the height of the concrete surface by theoretical method. After comparison, the lower concrete surface is taken as the standard for dismantling the catheter; The catheter shall be lifted at a uniform speed, smoothly and slowly. Control the pouring time within an appropriate range. Ensure the normal operation of the equipment and have spare equipment; notify the power distribution department before perfusion to ensure the supply of electricity during perfusion; pay attention to the weather forecast and arrange the perfusion time reasonably.