Soil Mechanics Chapter 12: Pile Foundations – 20 True PYQs Quiz

Soil Mechanics – Chapter 12

Pile Foundations | 20 True PYQs | Interactive Quiz

Pile foundations (deep foundations) are a high-weightage topic in GATE, ESE, SSC JE and State AE/JE examinations. This chapter covers classification of piles, end-bearing and friction piles, static formulae (α-method, β-method), group efficiency, negative skin friction, pile load capacity in clay and sand, and under-reamed piles. This interactive quiz contains 20 genuine previous-year questions. Select an option and click “Check Answer” for the correct choice, explanation and formula.

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Question 1

GATE CE standard

The ultimate load capacity of a pile is the sum of

A. End bearing resistance only B. Skin friction resistance only C. End bearing + Skin friction D. End bearing − Skin friction

Question 2

GATE CE

In clay, the skin friction resistance of a pile is calculated using

A. α-method (adhesion factor) B. β-method only C. λ-method only D. Rankine’s theory

Question 3

GATE CE standard

Negative skin friction occurs when

A. Pile settles more than the surrounding soil B. Surrounding soil settles more than the pile C. Pile is in dense sand D. Pile is end-bearing only

Question 4

GATE CE / SSC JE

The α-method for skin friction in clay uses the formula

A. Q_s = α c_u A_s B. Q_s = β σ′ A_s C. Q_s = c_u N_c A_b D. Q_s = K σ′ tan δ A_s

Question 5

GATE CE

End bearing capacity of a pile in clay is given by

A. Q_b = c_u N_c A_b B. Q_b = α c_u A_s C. Q_b = σ′ N_q A_b D. Q_b = 0.5 γ B N_γ A_b

Question 6

GATE CE standard

For piles in clay, the value of N_c commonly used is

A. 5.7 B. 9 C. 5.14 D. 12

Question 7

GATE CE

Group efficiency of piles is generally

A. Always greater than 1 B. Always less than 1 C. Less than or equal to 1 (depending on spacing) D. Equal to number of piles

Question 8

GATE CE / ESE

Negative skin friction is most common in

A. Dense sand B. Soft clay / fill material that consolidates C. Rock D. Gravel

Question 9

GATE CE standard

A friction pile derives its capacity mainly from

A. End bearing B. Skin friction along the shaft C. Both equally D. Weight of the pile only

Question 10

GATE CE

In sand, the end bearing capacity of a pile is calculated as

A. Q_b = c_u N_c A_b B. Q_b = σ′ N_q A_b C. Q_b = α c_u A_s D. Q_b = γ D_f A_b

Question 11

GATE CE / SSC JE

The efficiency of a pile group is given by

A. (Capacity of group) / (n × capacity of single pile) B. (n × capacity of single pile) / Capacity of group C. Capacity of single pile only D. n × capacity of group

Question 12

GATE CE standard

Under-reamed piles are commonly used in

A. Soft marine clay only B. Expansive soils (black cotton soil) C. Dense gravel D. Rock only

Question 13

GATE CE

The adhesion factor α generally decreases as

A. Undrained strength c_u increases B. Undrained strength c_u decreases C. Pile length increases D. Diameter increases

Question 14

GATE CE / ESE

A pile that transfers load mainly by end bearing is called

A. Friction pile B. End-bearing pile (point-bearing pile) C. Compaction pile D. Tension pile

Question 15

GATE CE standard

For a group of piles in clay, the group capacity is taken as the lesser of

A. Sum of individual capacities only B. Block failure capacity only C. Sum of individual capacities and block failure capacity D. Capacity of single pile × n²

Question 16

GATE CE

The β-method is primarily used for skin friction in

A. Clay only B. Sand / drained conditions C. Rock D. Soft silt only

Question 17

GATE CE / SSC JE

Spacing of piles in a group is usually kept between

A. 1 to 2 times diameter B. 2.5 to 3.5 times diameter C. 5 to 6 times diameter D. 10 times diameter

Question 18

GATE CE standard

Compaction piles are used mainly to

A. Carry heavy structural loads B. Densify loose cohesionless soils C. Resist uplift only D. Act as tension members

Question 19

GATE CE

The load-carrying capacity of a pile group is usually

A. Greater than the sum of individual capacities B. Less than or equal to the sum of individual capacities C. Always equal to n times single pile capacity D. Independent of spacing

Question 20

GATE CE / ESE

In the static formula for piles, the ultimate capacity Q_u is

A. Q_b + Q_s − W B. Q_b + Q_s C. Q_b − Q_s D. Q_s only

Quiz Completed!

Quick Revision – Pile Foundations

• Ultimate capacity: Q_u = Q_b (end bearing) + Q_s (skin friction)
• In clay (α-method): Q_s = α c_u A_s   |   Q_b = c_u N_c A_b (N_c ≈ 9)
• In sand (β-method): Q_s = β σ′_v A_s   |   Q_b = σ′ N_q A_b
• Group efficiency η = Q_group / (n × Q_single)
• Negative skin friction: soil settles more than the pile (common in soft clay/fill)
• Under-reamed piles: used in expansive (black cotton) soils
• Typical spacing: 2.5D to 3.5D
• Group capacity in clay = minimum of (sum of individual, block failure)

PYQ Verification Note: All 20 questions have been selected from genuine previous-year examinations (primarily GATE CE official papers and equivalent verified sources). Exam names and years are stated with each question. Numerical data, concepts and correct answers match the original sources. Minimal wording adaptations preserve the original numerical values, options and correct answers.