How Under Reamed Piles are Constructed ?
What is under reamed pile ?
Under Reamed pile is a special type of pile manufactured by the Central Building Research Institute (CBRI). The Pile Is made of R.C.C. Near the bottom end of the pile is a spherical enlarged part called the under rim or bulb.
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| Under reamed pile |
The diameter of the pile is 20 cm to 50 cm and the diameter of the bulb is 2 to 3 times the diameter of the pile. The length of the pile varies from 3m to 8m, the spacing between the two piles is 2m to 4m. The safe load on the pile is between 20 and 40 tonnes. Vertical spacing between two bulbs is 1.25 to 1.5 times of diameter of the bulb. If the load on the pile is high then more than one bulbs are provided.
Construction of under reamed piles.
The construction of under reamed Pile is done by manually. C.B.R.I developed tool for carried out Construction of under reamed.
The tool are simple and lightweight.
Following tools are used.
1)Spiral Auger
2)Under – reamer
3)Boring guide
1)Spiral Auger
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| Spiral auger |
The under reamed pile uses a spiral auger to hole in the ground, with special cutter blade is use to dig the soil at the lower end of the auger. And a bucket is hang to fill the excavated soil beneath the two cutters.
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| Spiral auger and under reamer |
2)Under reamer
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| Under reamer |
Special types of cutters are used to prepare the bulbs, the diameter of which can be increased by applying pressure on the handle of the auger so that the bulbs are Constructed.
3)Boring Guides
Boring guides are provided to dig vertical. They are provided at ground level. Three leg tripod are used as a boring guided. Auger handle is pass trough this guide and then augering is done.
Placing of cage and pouring concrete
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| Reinforcement |
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| Concreting |
After digging the pile hole and the bulb to the required depth, the auger is taken out and the reinforcement cage are place into the hole and hole is poured by concrete. All the piles are joined together by forming a cap at the head of the pile and structure is constructed over a cap.
How to increase load bearing capacity of under reamed pile ?
1)By increasing numbers of bulbs.
2)By increasing Diameter of bulbs.
3)By increasing Lengh of pile.
4)By proper design of pile.
Advantages of under reamed pile
1.Under reamed pile is 15 to 20% cheaper than Strip Tooting.
2) Material is is less needed for such piles.
3) No need of heavy dig. Therefore, the operation can also be done in the rainy season.
4)No need for shoring
5)No dewatering is required.
Application of under reamed pile
1)Black cotton soil
This type of soil is expand when it come in contact with water and contract when water is removed, so that the cracks are formed in structure. Under Reamed Pile is used as a foundation in black cotton soil.
2)Less soil bearing capacity.
3)High water table in ground.
4)High uplift forces in soil.
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