How to make top of rebar cage of CIP pile exposed

Question

A long time ago I saw that when cast in place piles were poured, the rebar cage was lowered all the way to the hole and the concrete was cast. After the concrete hardened, the soil around the top of the piles was removed (which was not as easy as removing a whole area at once since the work needs to be done around installed piles).

After exposing the top of cast piles, workers demolished the concrete from the top parts with jackhammers, exposing the rebar, which was to be embedded in the pile cap that would come on top for a strong connection between the pile and pile cap.

Why they did not excavate the ground first, and position the rebar cage so that its top part was exposed in air, so they did not later have to do the delicate excavation around the pile heads, plus they did not have to remove the concrete at top of piles? Or is it that it can be done that way too? What are the advantages of each method?

Answer 1

I suspect what you have seen was wrong.

The correct way is:

1-Excavate/ drill the pile holes with the caps excavation or the top grade beam excavation if the pile is part of a soldier-pile network at the same time.

2- Have the soils engineer check the excavation for depth and penetration into competent soil.

3 -Install the formwork for the cap or the grade-beam and lower the pile rebar cage. Pour the concrete with the pump hose lowered into the hole near the top of the concrete to prevent the separation of aggregate with adequate vibration. The top of the pile rebars should stand clear out of the pile concrete with the 90-degree bend or another type of hook as specified by the engineer. the top surface of the pile concrete should be a rough finish with no air entrapments and cured properly. This step of the work is usually done under continuous inspection by a deputy inspector.

4- Install the pile cap or grade beam rebars into the formwork and pour that stage.

The majority of building departments require the signature of the engineer on every one of these stages on cardboard kept at the job site for the project records.

Answer 2

Yas, of course, jack hammering reinforced concrete creates hard to see cracks in the concrete comproming its strength and making it vulnerable to water penetration and rebar oxidation. it is used only for demolition.

Answer 3

The method you saw was to shorten the duration of the excavated area exposed to the environment, especially in a rainy area that poses the risk of flood.

Two procedures are used for the construction of the pile foundation:

1. Excavate the entire site, dill pile holes, inspect the holes, place concrete, and lower the rebar cage. This procedure does not require breaking the concrete, but if the concrete is not placed immediately after drilling the hole, there is a risk of the hole will collapse if the pile casing is not used. Sometimes the pile casing is not desirable as it prevents visual inspection of the pile hole.

2. Drill pile holes from the ground, inspect the holes, place concrete, lower the rebar cage, and excavate the site after the concrete has cured and developed the desirable strength. This method leaves the rebar cage to be exposed by chipping out the concrete. As the chipping usually takes place while the concrete strength is relatively low, so it has less impact on the integrity of the pile.

The second procedure is usually used/preferred for the installation of the pile with large size/diameter like cassion, or bearing pile with bottom bell, that the hole will collapse if inundated. The risk is eliminated by excavation after pile installation.