Reasons for the interrupted pile construction of bored cast-in-situ piles and preventive measures

First, the reasons for the formation of broken piles

During the construction of bored cast-in-situ piles, due to the effects of work errors, poor equipment and hydrogeological conditions, the phenomenon of pile breakage is extremely prone to cause major engineering accidents. Therefore, to find out the cause of the mistake, preventing micro-duration is a major issue that the construction personnel must solve.

In general, there are four common forms of broken piles:

1. The concrete pile and the bedrock are filled with non-solidified concrete software. The reason is that because the bottom of the duct is too far from the bottom of the hole, the concrete is diluted by the washing liquid, which increases the water-cement ratio and causes the concrete to not set.

2, concrete inconsistency appears in the middle of the pile body. The reason is that due to the influence of groundwater activities or poor sealing of the duct, the immersion of the washing liquid will increase the concrete water-cement ratio.

3. The rock slag is deposited in layers in the pile body to separate the concrete pile from top to bottom. The reason is that when the concrete is poured, the pipe is lifted and lifted too much, exposing the concrete surface, or slag inclusion due to power outages, waiting for materials and other reasons.

4. Hollow appears in the pile body. The reason is that the "back to top" method is not used for pouring, but the concrete is poured by pouring directly from the orifice, resulting in segregation, which results in instability and solidity after solidification, and the porosity and porosity of individual holes.

2. Prevention of broken piles

For the prevention of broken piles, the author believes that it should be done completely, and it can be done well. The author puts forward the following opinions for my colleagues' reference.

1. After the pile hole is formed, the hole must be carefully cleaned. Generally, flushing liquid is used for punching. The punching time should be determined according to the sediment in the hole. Concrete should be poured in time after punching to avoid sediment at the bottom of the hole.

2. Carefully measure the hole diameter before pouring the concrete, and accurately calculate the concrete requirements for the whole hole and the first pouring hole section. Special attention should be paid to the pore size expansion in the bedrock to avoid insufficient initial perfusion.

3. The amount of concrete pouring for the first time should meet the requirement of burying the lower end of the duct above 0.8m.

4. For the first pouring, the initial part or the first or second bucket feeding should use cement mortar, and try to fill it into the hole at one time.

 The lower limit of the diameter of the perfusion catheter should be controlled above 200mm. The lower end of the catheter should be as smooth as possible. An "O" -shaped sealing ring should be placed at the connection to prevent the washing liquid from infiltrating. The catheter should be cleaned before use to remove dirt and residue. The lower end of the catheter should be 0.5 meters from the bottom of the hole. Rubber plugs should be placed in the cement water plugs in the conduit to enhance the water-proof effect.

5. The concrete mix ratio should be reasonable, and its slump should be strictly controlled (generally controlled at 16 ~ 20cm). When changing the cement label, variety and manufacturer, the mix ratio test must be done first, and the quality should be controlled according to the mix ratio. In areas where groundwater activity is large, casing or cement must be used for water stopping treatment in advance, and the concrete can be poured only after the water stopping is successful.

6. Use the "back-to-top" method of perfusion from the perfusion catheter for perfusion. A sufficient amount of concrete should be prepared for pouring, and water and power outages should be avoided during the pouring process. The wire of the cement water plug should be selected according to the amount of the first pouring, to prevent breakage. According to the rising height of the concrete inside and outside the duct, reasonably grasp the disassembly length of the duct. Under normal circumstances, the lower end of the duct should be kept buried for 2-3 meters, and it should not be lifted too much.

Summary

During the process of pouring concrete, the depth of concrete inside and outside the duct shall be measured regularly, and a curve shall be drawn to monitor the occurrence of broken piles. Under normal circumstances, the distance between the concrete interface inside and outside the duct starts to increase, then gradually decreases, and finally overlaps. If the distance between the concrete filling curve inside and outside the pipe is widened, and the concrete curve outside the pipe is flattened, but the concrete curve inside the pipe is steep, it is a sign of broken piles. The cause should be identified and dealt with as soon as possible.