FOUNDATION ENGINEERING – DEEP FOUNDATIONS
PILE FOUNDATIONS (DESIGN + PYQs)
(SSC JE | RRB JE | OSSC JE | State AE/JE – VERY HIGH WEIGHTAGE)
👉 3–5 questions every exam
👉 Direct capacity numericals + concept traps
👉 One of the MOST predictable scoring chapters
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🔹 1. ONE-PAGE PRECISE ONE-LINER NOTES (EXAM FOCUSED)
🔸 Deep Foundation
- A foundation where:
- Transfers load to deep, strong strata
🔸 Pile Foundation
- Slender column made of concrete / steel / timber
- Transfers load by:
- End bearing
- Skin friction
- Or both
🔸 When Piles Are Used (VERY IMPORTANT)
✔ Weak soil near surface
✔ Heavy structural loads
✔ High water table
✔ Uplift / lateral loads
✔ Scour conditions (bridges)
🔹 2. CLASSIFICATION OF PILES (FAVOURITE)
🔸 Based on Load Transfer
| Type | Load Transfer |
| End bearing pile | Through tip |
| Friction pile | Through shaft |
| Combined pile | Both |
🔸 Based on Function
| Pile | Purpose |
| Bearing pile | Vertical load |
| Batter pile | Inclined, lateral load |
| Tension pile | Uplift resistance |
| Compaction pile | Densify soil |
| Sheet pile | Earth/water retention |
🔸 Based on Material
| Material | Example |
| Concrete | RCC, PSC |
| Steel | H-pile |
| Timber | Temporary works |
🔹 3. LOAD CARRYING CAPACITY OF SINGLE PILE (MOST IMPORTANT)
🔸 Ultimate Load Capacity
Where:
- = End bearing resistance
- = Skin friction resistance
🔸 End Bearing Resistance
🔸 Skin Friction Resistance
🔹 4. STATIC FORMULA (CLAY & SAND)
🔸 Pile in Clay (φ = 0°)
End bearing
Skin friction
🔸 Pile in Sand
🔹 5. SAFE LOAD ON PILE
Typical FOS = 2.5 to 3
🔹 6. PILE GROUP & EFFICIENCY (IMPORTANT)
🔸 Group Efficiency (η)
- η < 1 → overlapping stress zones
- η ≈ 1 → piles act independently
🔸 Block Failure in Clay
- Pile group behaves like one large pile
- Capacity = shear + end bearing of block
🔹 7. PILE LOAD TEST (DIRECT QUESTIONS)
🔸 Types
1️⃣ Initial load test
2️⃣ Routine load test
🔸 Purpose
✔ Determine safe load
✔ Check settlement behavior
🔹 8. IMPORTANT NUMERICAL EXAMPLES (SSC JE LEVEL)
🔢 Example 1 (Pile in Clay – End Bearing)
Given:
Diameter = 0.4 m
cu = 50 kN/m²
🔢 Example 2 (Skin Friction)
Length = 10 m
Assume α = 0.7
🔢 Example 3 (Ultimate & Safe Load)
For FOS = 2.5:
🔢 Example 4 (Conceptual)
Pile in soft clay → Friction pile dominant
🔢 Example 5 (Group Efficiency)
If η = 0.8 and single pile capacity = 200 kN, n = 4:
🔹 9. PYQ-LEVEL MCQs (SSC JE | RRB JE)
🟢 THEORY MCQs (1–15)
Q1. Pile foundation is preferred when:
- SBC is high
B. SBC is low near surface ✅
C. Loads are small
D. Soil is rock
Q2. Load transfer in friction pile occurs mainly through:
- Tip
B. Shaft friction ✅
C. Base pressure
D. Bending
Q3. Value of Nc for pile end bearing in clay is:
- 5.7
B. 7
C. 9 ✅
D. 30
Q4. Batter piles are used to resist:
- Vertical loads
B. Lateral loads ✅
C. Uplift
D. Settlement
Q5. Sheet piles are used mainly for:
- Load transfer
B. Settlement control
C. Retaining earth & water ✅
D. Bearing capacity
🟡 NUMERICAL / CONCEPT MCQs (16–30)
Q16. A pile of diameter 0.5 m in clay with cu = 40 kN/m².
Ultimate end bearing capacity is:
A. 47
B. 70
C. 141
D. 70 kN
Correct:
Q17. Factor of safety generally used for pile design is:
- 1.5
B. 2
C. 2.5–3 ✅
D. 5
Q18. In pile group in clay, failure generally occurs by:
- Individual pile failure
B. Block failure ✅
C. Punching
D. Sliding
Q19. Which pile resists uplift forces?
- Bearing pile
B. Batter pile
C. Tension pile ✅
D. Sheet pile
Q20. Efficiency of pile group is usually:
- Greater than 1
B. Equal to 2
C. Less than or equal to 1 ✅
D. Zero
(Remaining PYQs include: α-method traps, sand vs clay formulas, pile load test concepts, spacing effects)
🔥 EXAM TRICKS & SHORTCUTS (VERY IMPORTANT)
✔ Qu = Qp + Qs
✔ Clay → Nc = 9
✔ Pile FOS = 2.5–3
✔ Soft clay → friction dominates
✔ Pile group efficiency ≤ 1
✔ Batter pile → lateral load
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