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Normal and reverse circulation drillCauses of ash-filling duct blockage in underwater concrete pouring
Our project department was constructing the first pile foundation (0 ～ 2 #) of Jinshan Reservoir Bridge, and the pipe was blocked when the underwater concrete pouring rose to 5m (designed pile length 20m); during the construction of Dawan Middle Bridge (1 ～ 3 #) ) When the pile foundation, the pipe plugging occurred when the underwater concrete pouring rose to 14m (designed pile length 30m); (2 ~ 3 #) When the pile foundation, the underwater concrete pouring rose to 12m (designed pile length 31m) A blockage occurred. Based on the comprehensive analysis of similar phenomena that occurred during the construction of bored cast-in-situ piles in other places through the above-mentioned three pile foundations when the pipe is blocked in the concrete pouring (referred to as "stuck pipe"), the main reasons are:
Leakage (water seepage) in the flange of the conduit. The concrete in the duct is separated by a water layer. At this time, the concrete in the duct cannot flow, and the duct is blocked.
The concrete in the duct is isolated by air pockets. It also appears that the concrete in the duct cannot flow and the duct is blocked (this is the case for the 1 ~ 3 # pile foundation of Dawanzhong Bridge).
duct cracks. The pipe wall is too thin. It is pulled too much during construction, which causes cracks in the pipe wall. There are other reasons for cracks in the pipe wall. After the crack appears, the water pressure in the hole is relatively large. The water will inevitably dilute and segregate the concrete in the pipe, which will cause the concrete to lose its fluidity and increase the frictional force of the concrete against the duct wall, which will cause the problem of blockage.
The grading of raw materials such as sand and stone used for concrete construction is unqualified, the size of crushed gravel is too large, or the water-cement ratio is incorrect, and the concrete segregates, which causes the stone and sand to deposit at the bottom of the pipe or block directly (Jinshan Reservoir) This happened to the bridge foundation of the bridge 0 ～ 2 #), the cement slurry floated; there was a failure of the electronic metering equipment of the mixer during the construction, the amount of water added was too large, and the concrete slump increased, which deviated greatly from the actual requirements. Make the precipitation and separation speed up.
The concrete pouring process is interrupted due to power failure or other reasons, the interruption time is too long, or the time of adjusting the pouring process is too long, so that the poured underwater concrete is solidified, and the conduit is blocked.
Too many welded joints in the next section of the duct cause the internal diameter of the weld on the inner wall of the duct to be too small and the particle size of the gravel to be too large, and the duct is blocked here directly (this occurs in the 2 ~ 3 # pile foundation of Dawanzhongqiao), These reasons will make the underwater concrete pouring construction impossible.
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