10 Common Quality Problems in Foundation Projects, Nip Them in the Bud!

Common problem one: soil (gray soil) piles are not dense and broken

Phenomenon:

The backfilling of the pile holes is uneven, the ramming is not dense, the density is uneven, and the pile body is loose or even broken.

Measure:

During the filling and tamping process, the tamping quality should be strictly controlled. If the number of tamping blows is not enough, the number of ramming blows should be increased appropriately. If the hole wall collapses, compaction and filling should be stopped, the collapse should be cleared first, then C10 concrete should be poured into the collapse area, and then backfilling and compaction should be continued.

Common problem 2: The pile body shrinks because of the crushing of gravel

Phenomenon:

The local diameter of the pile body of the gravel compaction pile formed is smaller than the design requirement, which generally occurs easily below the water table or in saturated clay soil.

Measure:

(1) The extubation speed is generally controlled at 0.8 to 1.5 meters/minute (the extubation speed is selected according to different regions and geology). Stop extubation every 0.5 to 1.0 meters and vibrate in place for 10 to 30 seconds. Repeat until it comes out of the ground.

(2) Use the reverse insertion method to overcome necking. Partial reverse insertion method: reverse insertion at the site of occurrence, and insert an additional 1 meter downward. All reverse insertion method: Start all reverse insertion from the pile end to the top of the column, that is, start to pull out 1 meter, then insert backward to the bottom, and then insert 0.5 meters backward for every 1 meter pulled out, until it is pulled out of the ground.
(3) Use repeated attacks to overcome necking. Local re-attack method: re-attack at the site of occurrence, with a depth of 1 meter. Full compound shot method: It is the repetition of the second single shot method. Pay attention to the coaxial sinking to the original depth and pour the same stone.

Common problem 3: Insufficient grouting of gravel compaction piles

Phenomenon:

During the construction of gravel compaction piles, the actual amount of gravel poured was less than the design requirement.

Measure:

(1) Use the concrete prefabricated pile tip method to solve the problem of the valve pile tip not being able to open and increase the amount of pouring.

(2) Inject pressure water (generally 0.2~0.4MPa) during filling to lubricate the surface of the stone, reduce friction, and make it easier to flow into the hole.

Common problem 4: Prefabricated pile body fracture

Phenomenon:

During the sinking process of the pile, the pile body suddenly tilted and dislocated. There was no special change in the soil conditions at the pile tip, but the penetration gradually increased or suddenly increased. At the same time, when the pile hammer jumped up, the pile body rebounded.

Measure:

The processing method should be studied together with the designer. According to the engineering geological conditions, the upper load and the structural part where the piles are located, pile replacement methods can be adopted. One or two piles can be added on both sides of the axis.

Common problem 5: The depth of prefabricated piles does not meet the design requirements

Phenomenon:

The final control of construction is based on the final penetration and final elevation of the design. During construction, one standard is generally used as the main standard and the other as a reference. Sometimes the final control requirements of the design are not met.

Measure:

(1) When encountering hard interlayer, pile planting method, water injection method or air blowing method can be used for construction. The tip of the pile must penetrate into undisturbed soil at least 6 times the pile diameter.

(2) If the pile cannot be driven down, you can replace it with a pile hammer with high energy and thicken the buffer cushion.

Common problem 6: Prefabricated pile body tilts

Phenomenon:

The vertical deviation of the prefabricated pile body is too large.

Measure:

(1) Before piling, underground obstacles should be cleared, especially the obstacles under the pile positions. If necessary, each pile position can be explored with a drill. It is not suitable to use piles whose tip is not on the longitudinal axis of the pile or whose pile body is bent beyond the specified limit. The slenderness ratio of a pile is generally controlled within 30.
(2) When driving piles, the stable piles should be vertical and pile pads should be added to the top of the piles. Pile pad failure should be replaced promptly.
(3) The contact surface between the pile cap and the pile and the replacement wood should be smooth, and any unevenness should be dealt with in time.

Common problem 7: There is a lot of empty soil at the bottom of the hole for cast-in-place piles in dry operation

Phenomenon:

After the hole is formed, there is too much empty soil at the bottom of the hole, exceeding the standard limit of no more than 100 mm.

Measure:

(1) Make two or more drilling passes in the hole. That is, the drill is thrown to the design elevation once, rotated in place for a moment, and then stopped rotating to pull out the drill pipe quietly.

(2) Use a spoon drill to clean the empty soil at the bottom of the hole.
(3) If the virtual soil is sand or gravel, the hole bottom slurry can be used to mix it first, and then concrete can be poured.
(4) Use the hole bottom pressure grouting method, pressure concrete grouting method and hole bottom tamping method to solve the problem.

Common problem 8: Poor concrete quality of cast-in-hole piles in dry operation

Phenomenon:

The concrete of the pile body has honeycombs and cavities, the pile body contains soil, and the segmentation gradation is uneven.

Measure:

(1) If the bearing capacity of a single pile is not large and the defects are not serious, the method of enlarging the cap beam can be used.

(2) If the defect is serious, the treatment method should be studied together with the designer. Generally, the method of filling piles on both sides of the axis can be adopted.

Common problem 9: Broken piles caused by wet work

Phenomenon:

After the pile is formed, there is no concrete in the middle of the pile body, but soil.

Measure:

(1) When the duct is blocked and the concrete has not yet initially set, two methods can be used: Method 1 is to use a drilling rig to lift equipment, lift a rail or other heavy object and impact it in the duct to break away the blocked concrete; Method 2 is to Quickly pull out the catheter, flush it with high-pressure water, and re-inject the water septum. During pouring, when the water-proof ball rushes out of the conduit, the conduit should continue to be lowered until the conduit can no longer be inserted, and then the conduit should be slightly raised to continue pouring concrete.

(2) When the concrete is interrupted above the groundwater level, if the diameter of the pile body is more than 1 meter and the mud wall protection is better, the water in the hole can be pumped out, protected by a steel cage, the original concrete surface is chiseled and the steel bars are cleaned, and then Continue pouring concrete.

(3) When the concrete is interrupted below the groundwater level, a drill bit smaller than the original pile diameter can be used to drill holes at the original pile position. When it reaches an appropriate depth below the broken pile site, clean the hole again and add a steel cage at the broken pile site. , its lower part is buried in the new drilled hole, and concrete pouring continues.

(4) When the conduit joint flange hangs on the steel cage, if the steel cage is not buried deep in the concrete, you can lift the steel cage and rotate the conduit to separate the conduit from the steel cage. Otherwise, you have to abandon the conduit.

Common Problem 10: Hole-forming Grouting Piles in Casing Walls Shrinkage

Phenomenon:

The local diameter of the pile body is smaller than the design requirements, which generally occurs below the groundwater level, in the upper aquifer or in saturated clay soil.

Measure:

(1) When necking occurs in silty soil, repeated blowing can be used.

(2) When necking occurs in other soils, it is best to use prefabricated pile heads and at the same time use casings with bell mouths at the bottom for construction, and use the reverse insertion method at the necking part.

(3) Place a section of reinforced concrete precast piles at the constriction.

The concrete of the blasted cast-in-place pile refuses to fall. After the explosive explodes to form an enlarged head, the concrete does not fall, which is called “stuck neck”.

(1) Insert a steel pipe or plastic pipe into the concrete for exhaust, or use strong vibration of a vibrator to make the concrete fall.

(2) When the concrete has initially set, you can drill a new pile hole nearby, penetrate it into the cavity, put the same amount of chemical bags, pour concrete into the cavity at the bottom of the rejection pile and the new pile hole, and energize it to detonate. New Explosive Expansion Pile.

The blasted cast-in-place pile is necked and the local diameter of the pile body is smaller than the design requirement.

(1) If the necking is slight, you can use an earth-moving tool to dig out the soil at the necking area, and then pour concrete immediately.

(2) If the necking is severe, a hole-forming machine should be used to re-hole it. In addition to using the casing method, an appropriate amount of explosives can also be used for blasting at the necking part.

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