General presentation of under-reamed piles. Mainly for diploma engineers, it is really helpful as its objective, dimensions, usage, etc are shown with proper images. It will really helpful for the basic knowledge of under-reamed piles.

1. UNDER REAMED PILES
PREPARED BY :- RAVAL DIVY DINESHKUMAR

2. INTRODUCTION
 Under reamed piles are made by C.B.R.I.( Central Building Research Institute).
 They are made of R.C.C.
 In the bottom portion of the pile, enlarged portion is given which is called ‘under reamed’
or ‘bulb’.
 If pile has one bulb, it is called single reamed, if the pile has two bulbs then it is called
double reamed, and if there are more than two bulbs, it is called multiple under reamed
piles.
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3. SINGLE AND DOUBLE UNDER REAMED PILES
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4. FEATURES
 Dia. Of the pile = 20 to 50cm
 Dia. Of the bulb = 2 to 3 times of dia. of pile
 Length of the pile = 3 to 8m
 Spacing between two piles = 2 to 4m
 Spacing between two bulbs = 1.25 to 1.5 times of bulb dia.
 Load carrying capacity = 20 to 40 ton
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5. APPLICATIONS
1. Black cotton soil expands as it comes in contact with water and it gets contracted as it is
dried out. Because of this reason, there may be a chance of cracks in the structure. To avoid
such damage, under reamed pile are used in black cotton soil.
2. When the soil doesn’t have much load carrying capacity, under reamed piles are used to
increase the capacity.
3. It is used when the water level in sandy soil is high.
4. When there are lifting forces acting, it should be used.
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6. INCREASING LOAD CARRYING
CAPACITY
1. By putting more bulbs
2. By increasing the dia. of bulb
3. By increasing the length of pile
4. By providing proper reinforcement
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7. Construction of under reamed pile
 Under reamed piles are mostly constructed by manual work.
 The machine for the construction of pile is made by C.B.R.I. Rurki.
 The machine is easy to use and it is light weighted.
 It consists of three tools :
1. Spiral Auger
2. Under – reamer
3. Boring guide
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8.  Spiral auger is used to make a hole in the land for the under reamed pile.
 The auger contains special cutter at the bottom to dig the land.
 The soil that is dug is taken out by the bucket.
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9. SPIRAL AUGER INSERTED THROUGH TRIPOD IN VERTICAL DIRECTION
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10. BUCKET PROVIDED TO TAKE OUT THE SOIL
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11. REINFORCEMENT
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12. CONTRUCTED UNDER REAMED PILE
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13.  Special cutter is used for making the bulb. By putting enough pressure, we can increase the
dia. of bulb.
 The auger is kept through the tripod and after than the digging is done. So the digging is
done in the vertical direction.
 After digging the desired depth, the auger is pulled out. The reinforcement is then inserted
in the hole. Concreting is done. If more than one pile, beam is constructed which connect
the piles and make them act like a single unit. The wall is than constructed on the beam.
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14. PILE CAP CONNECTING ALL THE PILES
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15. ADVANTAGES
1. It is 15 to 20% cheaper than the strip footing.
2. Less material required.
3. Digging is normal so the work is carried out for anytime of the year.
4. No back filling is required.
5. Shoring is not required.
6. Dewatering is not necessary.
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16. Reference
 ADVENCED CONSTRUCTION TECHNOLOGY, DR. R.P.RETHALIYA..
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17. THANK YOU
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