Tutorial no-3

Pile Foundation
1. 200mm diameter, 8m long piles are used as foundation for a column in a uniform deposit
of clay (qu = 100 kN/m²). The spacing between the piles is 500mm. There are 9 no piles in
the total arranged in a square pattern. Calculate the ultimate pile load carrying capacity of
the pile group. Take α = 0.90
2. A piles group consists of 9 piles, diameter of 30 cm, are arranged in square pattern and 10
m length driven in clay. If cohesion at ground surface is 100 kN/m²and at the base is 150
kN/m². Find the load carrying capacity of group pile. Take α = 0.6, spacing = 0.75 m C/C
and FOS = 3.

3. A group of nine piles, 8 m long, is used as the foundation for a column. The piles are 30
cm diameters with center spacing of 90cm. The subsoil consists of clay with unconfined
compression strength of 180kN/m². Estimate the safe load with 3.0 factor of safety. Take
α = 0.6.
4. A pile group consists of 9 frictional piles of 30 cm diameter and 10 m length driven in
clay (Cu = 100 kN/m², γ = 20 kN/m³. The spacing of the piles is 75 cm/cc and arrange in
the square pattern. Find the safe load for the pile group taking α = 0.60 and factor of
safety = 3.0.
5. A group of 9 piles with 3 piles in a row were driven into soft clay extending from group
level to a great depth. The diameter and the length of the piles were 30 cm and 10m
respectively. The unconfined compressive strength of the clay is 70 kPa. If the piles were
placed 90 cm center-to-center, compute the allowable load on the pile groups on the basis
of shear failure criteria for a factor of safety of 3.
6. A concrete pile, 30 cm diameter, is driven into a medium dense sand (Φ’= 35o, K = 1,
tanδ = 0.70,γ = 21 kN/m3) for a depth of 8m. Estimate the safe load taking the factor of
safety of 2.5. Assume Nq = 60. Assume Dc/ B = 12 for Φ’= 35o.
7. A bored pile in a clay soil failed at an ultimate load of 400 kN. The pile with 40 cm
diameter is 10 m long. Determine the capacity of group of 9 piles, spaced 1 m center to
center both ways. Take α = 0.5.
8. A symmetrical 16 piles group in soft clay with unconfined compressive strength of 40
kN/m2 is to be used as foundation for a column. The piles are 300 mm in diameter and 10
m long and spaced at 900 mm centers. Determine the maximum load the group can carry
with the piles failing. (a) individually and (b) as a block.

9. A 40×40 cm reinforced concrete pile 20 m long is driven through loose material and then
into dense gravel to a final set of 3 mm/ blow, using a 30 kN single acting hammer with a
stroke of 1.5 m. Determine the ultimate driving resistance of the pile if it is fitted with a
helmet, plastic dolly and 50 mm packing on the top of the pile. The weight of the helmet
and dolly is 4 kN. The other details are: Weight of pile = 74 kN, Weight of hammer = 30
kN, pile hammer efficiency ηh = 0.80, the coefficient of restitution Cr = 0.40. Use (a)
Hiley’s formula and (b) Engineering News Formula. The sum of elastic compression of
pile cap, pile material and of soil is 19.6 mm.
10. A reinforced concrete pile weighing 30 kN (inclusive of helmet and dolly) is driven by a
hammer weighing 40 kN and having effective fall of 80 cm. The average settlement per
blow is 1.4 cm. The total temporary elastic compression is 1.8 cm. Assuming the
 coefficient of restitution as 0.25 and factor of safety of 2, determine the bearing capacity
and allowable load for the pile.
11. Piles 200 mm diameter, 10 m long are used as foundation for a column in a uniform
deposit of medium clay (unconfined compressive strength = 100 kN/m² and adhesion
factor = 0.6). There are nine piles in a square pattern of 3×3. For a group efficiency = 1.0,
find the spacing between the piles (neglect bearing).
12. Determine the approximate safe load that a single friction pile driven in a clay may carry.
Use dia. of pile as 30 cm, length of pile as 12 m. Unconfined compressive strength of
clay, qu = 90 kPa. Take F.O.S. as 3..
13. A R.C.C. pile weighing 30 kN is driven by drop hammer weighing 40 kN and having
effective fall of 0.8m. The average set per blow is 1.4 cm. The total elastic compression is
1.8 cm. Assume coefficient of restitution as 0.25 and F.O.S. as 2. Determine allowable
load.
14. A group of concrete pile is square in plan and consist of 4 piles in each row & column.
Each pile are 10 m long and 50 cm in diameter. They are spaced at 1.5 m c/c in clay
deposit. The unconfined compressive strength of clay is 60 kPa. At the tip of the pile, the
undrained shear strength c =40kPa. The unit weight of soil is 18.5 kN/m3 and unit weight
for concrete is 22.5 kN/m3. Estimate total Ultimate load for pile group.
15. In a 16 pile group, the dia. of pile is 450 mm and spacing is 1.5 m., c = 50 kPa.
Determine weather the failure would occur with the pile acting individually or as a
whole. The length of pile is 10 m and bearing at the tip is negligible. Take adhesion
factor(or movilization factor) as 0.7.
16. A pile foundation is to support a load of 4000 kN. Diameter of pile is 0.5m and length is
12m. The qu = 120 kPa.. Take, adhesion factor,  = 0.6. Design a pile group. Take F.O.S.
of 3. Check block failure also.
17. A group pile foundation consist of 9 pile placed in square pattern. The piles are 300 mm.
in diameter and 10 m long placed at 750 mm c/c. take qu = 80 kPa, γ = 14 kN/m3,  =
0.8, F.O.S. = 3. Calculate the safe load carrying capacity of pile group.
18. Design a pile to carry a load of 200 kN. The soil below G.L. is of sandy having  = 30o ,
γ = 17.5 kN/m3. The length of pile has been restricted to 10m. take F.O.S. = 2.5
19. Find out load carrying capacity of a pile having diameter 50 cm. The length of pile is 10
m. The water table is at G.L. There is a layer of sand for a depth of 4 m below G.L.
having γsat =20 kN/m3 And  = 32o . The remaining portion of soil is a clay having c =
30 kPa,  = 0o. Take movilization factor as 0.8 for cohesive soil.

20. A concrete pile of square section 35 cm*35 cm is driven into layered sandy strata up to a
depth of 13 m. The average SPT value (N), unit weight of soil and other particulars are
given in the figure, determine the allowable load Qu by static method. Assume factor of
safety = 3.

̅̅̅̅̅̅
(Hint: For bored pile, 𝑄𝑢 = 1.33𝑁𝑐𝑜𝑟 𝐴𝑏 + 0.67𝑁 𝑐𝑜𝑟 𝐴𝑠 )
 Layer 1
Ncor = 12

9m

Layer 2
4m Ncor= 40

By:
P.B.A.- Prakash Bahadur Adhikari
Lecturer (SOE PU)
Previously Lecturer at WRC, IOE, TU
(Teaching Experience: 15 years +)

H.J.T.- Him Jyoti Thapa