Underreamed Piles

Q. Consider the following statements regarding under reamed piles:

1. They are used in expansive soils
2. They are of precast reinforced concrete.
3. The ratio of bulb to shaft diameters is usually 2 to 3.
4. Minimum spacing between the piles should not be less than 1.5 times the bulb diameter.

Which of these statements are correct?

1. 1, 2 and 3
2. 1, 3 and 4
3. 2, 3 and 4
4. 1, 2 and 4

Q. In under-reamed pile construction, the ratio of shaft diameter to bulb diameter is

1. 1/1.5
2. 1/2
3. 1/2.5
4. 1/4

Q. Ratio of bearing capacity of double Under Reamed (UR) pile to that of single reamed pile is nearly

1. 2
2. 1.5
3. 1.2
4. 1.7

Q. A single under-reamed pile is to be installed in a hard clay deposit. The undrained strength obtained from a series of vane tests at different depths have shown linear relationship, $C_u=75+5DinkN/m^2$, where 'D' is the depth in metres. The dia of pile shaft and the bulb are 1.5 m & 3 m respectively. The centre of under-ream is located at 10 m from ground surface. The allowable load on the pile to ensure an overall factor of safety 2.5.
$(given\alpha =0.4)$
(Neglect resistance offered by shaft beneath bulb)

1. 3935 kN
2. 1743 kN
3. 6471 kN
4. 5286 kN

Q. A singly-reamed, $8\text{m}$ long, RCC pile (as shown in the below figure) weighing $20\text{kN}$ with $350\text{mm}$ shaft diameter and $750\text{mm}$ under-ream diameter is installed within stiff, saturated silty clay (undrained shear strength is $50\text{kPa}$, adhesion factor is 0.3, and the applicable bearing capacity factor is 9) to counteract the impact of soil swelling on a structure constructed above. Neglecting suction and the contribution of the under-ream to the adhesive shaft capacity, what would be the estimated ultimate tensile capacity (rounded off to the nearest integer value in $\text{kN}$) of the pile?

1. $132\text{kN}$
2. $156\text{kN}$
3. $287\text{kN}$
4. $301\text{kN}$

Q. Consider the following statements:

1. Underreamed piles are designed as bearing piles.
2. In multiple-bulb underreamed piles, the bulbs are spaced at 1.5 to 2.0 times the diameter of the underream, the centre of the first underream being at a minimum depth of 1.75 m.
3. The length of traditional undereamed pile ranges from 3 m to 4 m.

Which of these statements is/are correct?

1. 2 and 3
2. 1 and 2
3. 2 only
4. 1 and 3

Q. Consider the following statements about the under-reamed pile in swelling soils:

1. Its bulb provides anchor against movement due to volume changes of soil.
2. It is a driven pile.
3. Its bulb diameter is 2.5 times its shaft diameter.

Which of these statements are correct?

1. 1, 2 and 3
2. 1 and 2 only
3. 2 and 3 only
4. 1 and 3 only

Q. Consider the following statements:
Problems regarding foundations to be constructed in expansive soils are solved by

1. Resorting to light foundation pressure.
2. Using under-reamed piles for light loads.
3. Making the structure rigid enough so that settlement and uplift would not affect them.
4. Providing a well-designed basement with the foundation below the neutral point.

Which of the above statements are correct?

1. 1 and 2
2. 2 and 4
3. 1 and 4
4. 2 and 3

Q. Directions : The following items consists of two statements; one labelled as 'Assertion (A)' and the other as 'Reason (R)'. You are to examine these two statements carefully and select the answers to these items using the codes given below :

Codes:

Assertion (A) : Bearing capacity of an under-reamed pile is less than that of a straight bored pile of the same diameter.

Reason (R) : Under-reamed piles have enlarged bulbs.

1. both A are R are true and R is the correct explanation of A
2. both A and R true but R is not a correct explanation of A
3. A is true but R is false
4. A is false but R is true

Q. Directions: The following items consists of two statements; one labelled as 'Assertion (A)' and the other as 'Reason (R)'. You are to examine these two statements carefully and select the answers to these items using the codes given below:

Codes :

Assertion (A) : Under-reamed piles are suitable for loose filled up sites and black-cotton soils.

Reason (R) : Black cotton soils have expansive montmorillonite clay minerals.

1. both A and R are true and R is the correct explanation of A
2. both A and R are true but R is not a correct explanation of A
3. A is true but R is false
4. A is false but R is true

Q. Consider the following statements:

1. Underreamed piles are precast piles with one or more underreams in each pile.
2. The ratio of pile shaft size to bulb size in an underreamed pile may be 0.33 to 0.50.
3. In a multibulb underreamed pile, the load-carrying capacity is a function of the area of cross-section of the lowest bulb.

Which of these statements is/are correct?

1. 1 only
2. 1 and 2 only
3. 2 and 3 only
4. 1, 2 and 3