Common quality defects and prevention measures of bored pile construction

2016-01-23 15:07:28

Bored pile has low construction noise, small vibration, pile length, diameter can be freely transformed according to the design requirements, the pile tip can reliably enter the bearing layer, single pile bearing capacity and other advantages. However, from the beginning of drilling to the end of the pile, due to a variety of factors, easily lead to quality problems or even quality accidents, so quality control has become a difficulty in the construction.
1, steel cage floating
Have heavy steel skeleton onto the design depth, in the concrete process, a skeleton position higher than the original design position, namely "floating cage".
1.1 reason analysis
1) reinforcement cage skeleton and the inner diameter of conduit spacing is small, coarse aggregate size is too large, the main reinforcement lap welding without welding, lifting and sinking in the catheter back process, flange belt reinforcing cage.
2) reinforced during the installation process, skeleton distortion, stirrup deformation, desoldering off or duct tilt, the reinforced wall in close contact with the catheter.
3) sometimes due to equipment failure, pouring concrete stop, between the conduit and reinforced concrete has been condensed, when the reinforcement will be reinforced when the catheter.
4) pouring concrete speed too fast, concrete surface rise to the cage bottom, produce upward "buoyancy", leading to reinforced cage floating up.
1.2 treatment methods
1) just pouring concrete appeared "floating cage", mainly between the catheter and cage with hang phenomenon; should immediately stop pouring concrete, repeatedly up and down the catheter or one-way rotation.
2 in the pouring process, with the catheter pulled out, cage floating, but the concrete surface is not moving, but also because of the catheter and cage with hanging phenomenon, should be repeatedly shaking catheter, repeated to move up and down to cut off the two links.
3 in the pouring process, with the concrete surface rise, cage floating, that should control the amount of concrete pouring and speed.
2, heavy cage
Has sunk into the design of the depth of reinforcement, in the process of pouring concrete, reinforced cage fall, steel skeleton lower than the original design position, commonly known as "sink cage".
2.1 reason analysis
1) between the hanger and the main bar or section steel welding is not strong or ring off.
2) on the vibration of catheter, catheter hanging belt steel, a large force is applied on the steel rings, loose, and once the catheter and the reinforcement cage is separated from the cage into the hole.
2.2 treatment methods
1) such as cage into the concrete depth (less than 2 meters), can not continue to stay, concrete, after excavation, the original pile of artificial or mechanical excavation, cut reinforced pile head with high up, the concrete of pile head to cut hair, and then poured a strength higher than the original label grade of concrete.
2 in the excavation of the foundation pit after digging the pile head floating slurry found sink cage, but I do not know the depth of sinking, this time to re fill the pile or ask the designer approved on the basis of structural reinforcement measures taken.
3, pulling out the space
In the course of pouring concrete, the pipe breaks away from the concrete surface, and the mud enters the conduit, which causes the pile body to become smaller or broken.
3.1 reason analysis
Construction personnel operating mistakes, too fast catheter.
3.2 preventive measures
Strictly control the pipe lifting speed, the height of the concrete surface should be measured before lifting, the length of the concrete embedded in the conduit and the height of the lifting can be calculated.
3.3 treatment methods
1 when the catheter empty, the catheter should be quickly inserted into the concrete, the use of small pumps or small diameter pumping equipment, the catheter water extraction, continue pouring concrete.
2) quickly reset out across the water polo catheter, catheter, catheter should be continued to decline, until the catheter is inserted in a catheter can improve, continue pouring concrete.
4, buried pipe
In the process of pouring concrete, the catheter bought in concrete, did not pull out in time, hardened concrete, forming waste piles.
4.1 reason analysis
1) concrete initial coagulation time is short, or construction equipment, power supply and other reasons for intermittent long time, re pouring concrete when the lower concrete has hardened, catheter pull out.
2) the tube was reinforced on.
3) in the process of concrete hole wall collapse, a large number of mud and sand buried conduit.
4.2 preventive measures
1) concrete initial setting time must ensure normal pouring time of 2 times, summer construction should add retarder, ensure the continuous supply of concrete, pouring ramming.
2) avoid catheter hanging with reinforced cage.
3) to prevent the collapse of hole wall protection measures: depth of soil at least 1m tube. According to the soil characteristics, the correct selection of slurry. Mud concentration should not be too low, no clear water into the hole. In the adjacent just completed the construction of adjacent piles into the hole, the distance shall not be less than 4 times the pile diameter, or the minimum interval of more than 36h.
4.3 treatment methods
1 when the catheter hanging with reinforced cage, if found reinforced cage embedded concrete is not deep, can lift the cage rotation catheter, so that the catheter and reinforced cage from, otherwise had to give up the catheter.
2) catheter embedded in the concrete can not pull out, generally void treatment, with the designer approved after re filling pile.
5, the deviation of pile position deviation is larger
After excavation, the control axis check pile position, pile deviation beyond the allowable scope of the specification.
5.1 reason analysis
1) construction lofting errors or mechanical drilling personnel positioning is not accurate.
2) during the excavation, one-time excavation depth is too large, lateral earth pressure caused by pile dynamic dislocation.
5.2 preventive measures
1) improve the professional level of construction personnel, enhance the incumbent heart, drilling positioning accuracy.
2) should be stratified excavation of earth excavation, every time the depth of excavation is about 4m.
5.3 treatment methods
If the pile position beyond the standard allows a larger range of deviation, should be approved by the designer, take the necessary reinforcement measures; if it is a single pile foundation, generally should be re filling pile.
6, pile head to take water
In the foundation pit cushion concrete pouring finished, pile head parts seepage phenomenon.
6.1 reason analysis
1) concrete pouring is not dense, pile body (especially the pile head position) have cracks or clip mud, concrete gravel size is too large, uneven grading.
2) when pouring concrete, the relative density of mud is too large, there is mud sandwiched between the concrete and the main reinforcement.