Under-reamed pile foundations are specialized pile types with enlarged bases designed to provide structural stability in weak, expansive soils, particularly beneficial in conditions subject to moisture changes and uplift forces. They are constructed using tools like spiral augers and underreamers, and their design includes critical specifications regarding size, spacing, and load capacity. While they offer advantages like cost savings and reduced excavation needs, they also present challenges in terms of required craftsmanship and supervision.

1. Under Reamed Pile
Construction
05. AKHILA SARA VARGHESE
30. REEBU SAJU STEPHEN

2. • Two types of foundations : • Pile Foundation
 Used where the soil is weak – compressible, water logged and
when the stratum of requires bearing capacity is at greater depth.
 Used to carry vertical compression loads, resist uplift loads, resist
horizontal or inclined loads.
 Failure of pile foundations :
 Lack of adequate boring
 Inadequate driving
 Breaking and buckling of piles
 Collapse of thin shell of the piles
 Tension failure of concrete pile for lack of reinforcement
INTROUCTION TO UNDER REAMED PILE FOUNDATION
Shallow foundation
• Used to handle the
weight distribution for
smaller and lighter
buildings where the
structure is less than 6
ft deep.
• Breadth > Depth
• Types includes :
• Sloped foundation
• Stepped
foundation, etc.
Deep foundation
• Used to transfer the
weight of the
superstructure to a
layer of bedrock down
to a depth of 250+ ft to
ensure structural
stability.
• Breadth < Depth
• Types includes :
• Pile foundation
• Well foundation

3. UNDER REAMED PILE FOUNDATION
 Pile foundation with enlarged bases that are suitable to resist considerable movement
of the ground, filed up ground, soft clay, and loose sand which have advantages to
increase the soil strength, uplift capacity, and decrease the displacement.
 Have expanded base called bulb having shape of a triangle at the base made by one or
the other removing or digging soil.
 Very popular as they provide an effective solution to the swelling and shrinkage due to
seasonal changes in expansive soil regions. The anchorage provided by the under-ream
pile prevents cracks in floors and walls of buildings in expansive soil areas.
 This type of pile specially design for expansion soil - Black cotton soil.
 Under-Reamed Piles are also called bored cast-in-situ concrete piles.
 Manufactured by the Central Building Research Institute (C.B.R.I).
 Such piles are made of R.C.C.

4. DESIGN OF THE UNDER REAMED PILE FOUNDATION
 The bottom end of the pile has a spherical enlarged portion called an under rim or bulb.
 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.
 Under reamed Pile lengths range from 3 m to 8 m.
 The spacing between the two piles is 2 m to 4 m.
 The safe load on the pile is 20 to 40 tons.
 The vertical spacing/distance between two bulbs is 1.25 to 1.50 times the diameter of the bulb.
 More than one bulb is placed if the load on the pile is high.
 Types of underreamed pile foundation :
 Single under reamed pile foundation
 Multiple under reamed pile foundation

5. TOOLS USED FOR CONSTRUCTION
 Spiral auger
• Consists of a sharp twisting blade for boring purposes, to drill a hole in the ground for an under reamed
piles.
• Sharp edge cutter is attached at the end of auger to easily dig ground and used to burrow the dirt at the
lower end of the drill.
• Below the spiral auger, the filling bucket is used for filling the exhumed soil underneath the two cutters.
• Auger handles are also used to increase depth.
• Auger is introduced in the part of the earth to be bored and rotated by hand.
• When spirals get full of soil auger is taken out.
• This process is continued until the required depth is achieved.
 Under Reamer
• Rotatory cutting device used for boring.
• It has cutters that can be extended or shrunk by mechanical methods or by hand and are used to
develop or ream a borehole underneath.
• Underreaming is a method of widening the bottom area of a drilled hole and thus increasing load-
bearing capacity.
 Boring Guide
• To keep the bore opening vertical and in position.
• Each guide is given a round collar and four arms.
• The collar is fixed to the drilling guide on the lower side, and it doesn’t permit the mouth of drill
openings to expand because of frequent insertion and evacuation of the drill and other drilling
equipment.

6. Boring Guide
Spiral Auger
Under Ream

7. STEPS OF CONSTRUCTION
 The first step is to set guide assembly.
 A spiral auger is used to drill a hole in the ground for opening of bore of an under reamed piles.
 Cutter is attached at the end of auger to easily dig ground. Below the spiral auger, the filling bucket is
hung to remove soil dug.
 Auger handles are also used to increase depth.
 Unique cutters are utilized for making the bulb. The dia. of the bulb can be expanded by applying more
significant pressure on the handle of the auger.
 The drill is set up on a tripod after the burrowing is finished. As arriving at adequate profundity, the
drill is pulled out.
 Excavation is carried out from the auger only after passing the handle of the auger through a special
design made on the head of a tricycle placed on the ground so that the digging of the pile hole is done
in the vertical direction only.
 After digging the pile hole and the bulb to the required depth, the auger is taken out and the case of
reinforcement is inserted in the hole. Then Concreting is done.
 On the off chance that more than one pile, the bar is developed, which associates the piles and makes
them act like a solitary unit.
 All the piles are connected to each other by forming a beam at the head of the pile.
 The wall is constructed over the beams.

8. APPLICATIONS OF THE UNDER REAMED PILE FOUNDATION
 Under reamed pile is used as a foundation in black cotton soil.
 Black cotton soil expands when it comes in contact with water and contract when water is removed, so that cracks are
formed in this structure.
 Under reamed piles are used in low bearing capacity soil.
 Under reamed piles are used in sandy soil when water table is high.
 Under reamed piles are used where lifting forces appear at the base of foundation.
• Used to avoid the undesirable effect of seasonal moisture changes in expansive soils such as black cotton soils.
• Used to reach hard strata.
• Used to obtain adequate capacity for downward, upward, lateral loads and moments.
• Used to take the foundations below the scour level.
• Used in factory buildings and machine foundations.
• Used where the vibration and noise caused during construction of piles, are to be avoided.

9. INCREASING LOAD BEARING CAPACITY
 The load carrying capacity of the under-read pile can be increased in the following ways.
 By increasing the number of bulbs.
 By increasing the diameter of the bulb.
 By increasing the length of pile.
 By proper designing and placing of reinforcements.

10. DESIGN CONSIDERATIONS OF UNDER REMED PILE FOUNDATION
 CONCRETE
 shall have a slump of 10-15 cm for concreting in water-free unlined bore holes.
 should have a slump of 15-20 cm For concreting by tremie, for better workability.
 M-15 or M-20 concrete with respective minimum cement content of 350 or 400 kg/m3 may be used.
 The minimum length of under-ream piles, in deep deposits of expansive soils, should be 3.5 m below the ground level.
 The diameter of the under-ream is kept as 2.5 times the stem diameter.
 The maximum vertical spacing between under-reams is 1.5 times the diameter of the under-ream for piles up to 0.3-m
diameter.
 For large-diameter piles, the spacing may be reduced to 1.25 times the stem diameter.
 The topmost bulb should be at a minimum depth of two times the bulb diameter.
 For expansive soils, this depth should not be less than 1.75 m below the ground level.
 The number of bulbs provided should be normally not more than 2.
 The minimum center-to-center spacing of under-ream piles in a group is 1.5 times the diameter of the under- ream but
usually kept at two times the under-ream diameter.

11. ADVANTAGES OF UNDER REAMED PILE FOUNDATION
 15 to 20% cheaper than strip footing because less amount of concrete is required to fill the excavated area.
 No heavy digging is required, so operations can be carried out even in the rainy season.
 There is no need for back filling in such piles.
 Shoring is not required.
 Dewatering is not required.
 Diminishes the vertical settlement and furthermore differential settlement.
 It is utilized when soil expands because of the dampness variety or sweeping nature of the dirt.
 Arrangement of under-reams or bulbs has the upside of expanding the bearing and inspire limits.
 When the quantity of bulbs is expanded from one to two, the pile conveying limit is expanded.
 The arrangement of bulbs is of unique benefit in under-reamed piles to oppose uplift, and they can be utilized as
anchors.
 Due to the reduced pile shaft diameter, only less concrete needed to replace the excavated material.

12. DISADVANTAGES OF UNDER REAMED PILE FOUNDATION
• Require great workmanship.
• Skills required for placing of such type of piles.
• Maintaining verticality in ground is difficult. Because some time such pile are driven by hand-operated
machine and it is very difficult.
• Require strict and regular supervision with great quality control.
• The depth of under-reamed piles is restricted and depending on the climatic situation, the under-reamed
piles are not proved ideal for waterlogged soil since they seize over by friction.
• More energy-consuming and time-consuming process.
• Requires expensive equipment as well as tools for detecting the performance of under reamed pile
foundation