Pile foundation for the bridge pier is very complicated construction. In this post we will see the different stage of pile construction.
You know the purpose of foundation is to transfer the load into the soil. Foundations do that work for us. But when the soil below the building does not posses good strength the normal footing fails. Then we generally use pile foundation.
Piles goes below and find the strong layer of soil. It also uses the skin friction also to improve the bearing capacity. It also gives the confining effect to the soil . Hence the strength of soil increases.
Pile is in demand as the deep footing for various structures. For the bridge, we generally cast the bridge pier above the pile foundation. It supports the load by skin friction and the end bearing resistance. Different types of piles are categorized based on the material, loading type, and resistance type. In this post, we are going to discuss cast-in-situ concrete construction. There are the following stages of concrete pile construction,
Marking
Inserting the casing
Drilling of bore
Clearing the bottom
Inserting the reinforcement cage
Concreting
Chipping off
Leveling
Reinforcement for pile-cap
Centering
Pire reinforcement
concreting of pile-cap
Also read: design of pile, quality test of concrete, index properties of soil, seepage
First of all, we try to align the bore machine over the center mark. After the alignment, we generally check level by spirit level. This process maintains the hole straight.
After marking the point, we first insert the casing. This casing supports the bore wall. Now, after this process, we can start the drilling of the bore.
We use rotary drill for drilling the bore, generally of 1.2 m dia in the case of the bridge pier. In this process, we keep flowing the bentonite solution. This solution keeps the wall stuck in a place and prevents it from falling. Before drilling, we generally perform the density test for bentonite, which should come around 1.
After drilling process we perform the cleaning of bore hole. This process make concrete more effective.
We have to insert the reinforcement cage vertically into the bore hole. This is a very critical operation. As the weight of the reinforcement cage is higher and we have to maintain the proper spacing between reinforcement and the wall of the borehole.
Concreting is done through the tremie pipe method. Tremie pipe is shown in fig. Concreting is done from the bottom of the hole. As concrete is heavier than the water in concrete, it settles down. As concreting proceeds, impure water starts rising and finally comes out from the top of the bore hole. The minimum grade of concrete is M25, and the slump is about 110 to 140 mm.
After concreting, we allow it to cure for 28 days. After the sufficient curing period, the concrete pile is ready up to ground level. Now we excavate up to the cutoff level. We generally chip off all the concrete above this level. We call this process chipping of concrete. All concrete above the cut-off level has been chipped; only reinforcement remains there.
After chipping of concrete up to the cutoff level we generally level the surface. After leveling of surface we generally provide plain cement concrete. Above this, we cast the PCC concrete.
As mentioned in the above point, reinforcement for pile-cap is being laid on the PCC. All top, bottom, side reinforcement according to the drawing is provided.
After the reinforcement of pile-cap we generally find out the center of pile-cap and make the reinforcement of pier of the bridge.
After this process, we cast the pile-cap. After concreting we allow it to cure properly. Then start casting the pier of the bridge.
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