[Construction engineering] 6 common quality problems and prevention measures of bored pile construction

2) In the process of pouring concrete, the cage will float up as the tremie is pulled out, but the concrete surface will not move, which is also due to the phenomenon of hanging belt between the tremie and the cage.

3) During the excavation of foundation pit, the excavation machinery collides with the pile body, causing cracks at the pile head.

2) During the installation of the reinforcement, the skeleton is twisted, the stirrup is deformed, the desoldering falls off, or the conduit is inclined, making the reinforcement and the outer wall of the conduit close contact.

Before lifting, measure the height of the concrete surface, calculate the length of the tremie embedded in the concrete and the height that can be lifted this time.

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2) When the tremie is vibrated up and down, the tremie is hung with reinforcement, which exerts a great external force on the reinforcement, and the lifting ring is loose.

6.1 Cause analysis 1) The concrete pouring is not dense, there are cracks or mud inclusions in the pile body (especially at the pile head), the stone particle size in the concrete is too large, and the grading is uneven.

1.1 Cause analysis 1) The inner diameter of the reinforcement cage skeleton is small from the conduit, the coarse aggregate particle size is too large, the main reinforcement overlap welding head is not welded flat, and the flange plate is hung with the reinforcement cage during the lifting and sinking back of the conduit.

The deviation of pile position exceeds the allowable range of the specification.

After the excavation of the foundation pit, manually or mechanically excavate the soil on the original pile position, chisel out the pile head reinforcement and connect it up.

2) The conduit is hung by the rebar.

3.1 Cause analysis The constructors made mistakes in operation and pulled up and out the conduit too quickly.

4.1 Cause analysis 1) The initial setting time of concrete is short or the intermittent time is long due to construction machinery, power supply and other reasons.

However, from the beginning of drilling to the end of pile formation, quality problems and even quality accidents are easily caused due to various factors, so quality control becomes a difficult point in construction.

The mud concentration should not be too low, and it is forbidden to put clean water into the hole.

Part 5 After the excavation of foundation pit with large deviation of pile position, check the pile position according to the axis.

Part 6 The water from the pile head is poured in the foundation pit cushion concrete, and the water seepage occurs at the pile head.

2) When excavating the foundation pit, the one-time excavation depth is too large, and the soil side pressure causes the pile dislocation.

3) During concrete pouring, the hole wall collapsed and a large amount of mud and sand buried the conduit.

2) When the laitance at the pile head is chiseled off after the excavation of the foundation pit, the sinking cage is found, but the sinking depth is unknown.

2) The excavated earth shall be excavated in layers, and the depth of each excavation shall be controlled at about 4m.

The hole construction shall be carried out next to the adjacent piles that have just been poured, and the distance shall not be less than 4 times the pile diameter, or the minimum interval shall be more than 36h.

2) Avoid hanging reinforcement cage on conduit.

3.2 Preventive measures Strictly control the lifting speed of the tremie.

According to the characteristics of the soil on the site, the slurry for wall protection shall be selected correctly.

4.3 Treatment method 1) When the conduit is hung with reinforcement cage, if it is found that the reinforcement cage is not deeply embedded in the concrete, the reinforcement cage can be lifted to rotate the conduit to separate the conduit from the reinforcement cage, otherwise the conduit has to be abandoned.

2.1 Cause analysis 1) The welding between the suspender and the main reinforcement or between the segmented reinforcement is not firm or the lifting ring falls off.

3.3 Treatment method 1) When the tremie is empty, the tremie shall be inserted into the concrete quickly, and the water in the tremie shall be pumped out by using a small water pump or small-caliber pumping equipment to continue pouring concrete.

3) Sometimes due to machine failure, the concrete pouring stops, and the concrete between the conduit and the reinforcement has been solidified Knot, take the reinforcement out when lifting the conduit.

3) Measures to prevent hole wall collapse: the original soil depth of pile casing shall be at least 1m.

The pile head concrete must be roughened, and then pour concrete with a strength grade higher than the original mark.

2) Quickly raise the tremie, reset the water trap to flush out the tremie, and then continue to lower the tremie until the tremie can not be inserted, and then slightly lift the tremie to continue pouring concrete.

In the process of pouring concrete, the pipe of Part 4 is buried in the concrete, and it is not pulled out in time.

2) The tremie is buried in the concrete and cannot be pulled out.

5.1 Cause analysis 1) There is deviation in setting out by construction personnel or inaccurate positioning of mechanical drilling.

5.2 Preventive measures 1) Improve the professional level of the construction personnel, strengthen the current heart, and ensure accurate drilling positioning.

The reinforcement cage of Part 1 floats upward and has been sunk to the design depth.

5.3 Treatment method If the pile position exceeds the allowable deviation range of the specification, it shall be approved by the designer and necessary reinforcement measures shall be taken; In case of single pile foundation, the pile shall be supplemented again.

2.2 Treatment method 1) If the depth of the cage sinking into the concrete is not deep (less than 2 meters), it can not be treated temporarily and continue pouring concrete.

4) The concrete pouring speed is too fast, and the concrete surface rises to the bottom of the reinforcement cage, resulting in upward “buoyancy”, causing the reinforcement cage to float up.

At this time, the pile must be supplemented again or the designer shall be asked to check and approve the reinforcement measures on the foundation structure.

4.2 Preventive measures 1) The initial setting time of concrete must be 2 times of the normal pouring time, and the retarder should be added during the construction in summer to ensure the continuous supply and pouring of concrete.

The bored pile has the advantages of low construction noise, small vibration, free change of pile length and diameter according to the design requirements, reliable access of pile tip to the bearing layer, and large bearing capacity of single pile.

1.2 Treatment method 1) “floating cage” occurs at the beginning of concrete pouring, mainly due to the phenomenon of hanging belt between the conduit and the cage; The concrete pouring shall be stopped immediately, and the tremie shall be repeatedly shaken up and down or rotated in one direction.

It is generally discarded, and the pile shall be repaired after being approved by the designer.

3) In the process of concrete pouring, as the concrete surface rises, the cage floats, that is, the concrete pouring volume and speed shall be controlled.

2) When pouring concrete, the relative density of the slurry is too high, there is mud between the concrete and the main reinforcement, and groundwater emerges along the mud.

Part 2 sinking cage has been sunk to the design depth of the reinforcement.

After the concrete is hardened, the waste pile will be formed.

When the concrete is poured again, the lower concrete has hardened and the tremie cannot be pulled out.

Once the tremie is separated from the reinforcement cage, the cage will sink into the hole.

During concrete pouring, the position of the reinforcement cage is higher than the original design position, Commonly known as “floating cage “.

Part 3: During the concrete pouring process, the tremie breaks away from the concrete surface and mud water enters into the tremie, causing the pile body to become smaller or broken.

The tremie should be shaken repeatedly to move up and down repeatedly to cut off the connection between the two.

During the concrete pouring process, the reinforcement cage fell and the reinforcement skeleton was lower than the original design position, commonly known as “sinking cage”.


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