Soil Mechanics – SSC JE Exam Oriented Overview
1️⃣ Soil Formation & Classification
🔹 Origin of Soils
- Residual soil – formed at same place
- Transported soil – by water, wind, ice, gravity
🔹 Soil Types (IS Classification)
- Coarse-grained: Gravel (G), Sand (S)
- Fine-grained: Silt (M), Clay (C)
- Organic: O, Peat (Pt)
🔹 Index Properties
- Water content:
- Specific gravity:
2️⃣ Atterberg Limits
| Property | Meaning |
| Liquid Limit (LL) | Soil changes from plastic → liquid |
| Plastic Limit (PL) | Semi-solid → plastic |
| Shrinkage Limit (SL) | Volume stops shrinking |
Important
- Plasticity Index
- Liquidity Index
3️⃣ Soil Structure & Phase Diagram
🔹 3-Phase System
- Solids + Water + Air
🔹 Key Relations
🔹 Unit Weights
- Dry:
- Saturated:
- Submerged:
4️⃣ Permeability & Seepage
🔹 Darcy’s Law
🔹 Types
- Constant head test – sands
- Falling head test – clays
🔹 Seepage Force
5️⃣ Effective Stress Concept
Where:
- = total stress
- = pore water pressure
🔹 Quick Rule
- Strength + settlement depend on effective stress, not total stress.
6️⃣ Compaction of Soil
🔹 Purpose
- Increase density
- Reduce settlement
- Increase strength
🔹 Proctor Tests
- Standard Proctor
- Modified Proctor
🔹 Key Terms
- OMC – Optimum Moisture Content
- MDD – Maximum Dry Density
🔹 Zero Air Void Line
7️⃣ Consolidation of Soil
🔹 One-dimensional compression of saturated clay.
🔹 Terzaghi’s Theory
🔹 Settlement
Where
- = compression index
- = clay thickness
8️⃣ Shear Strength of Soil
🔹 Mohr–Coulomb Equation
🔹 Tests
| Test | Drainage |
| Direct Shear | Drained |
| Triaxial UU | Undrained |
| Triaxial CU | Consolidated |
| Triaxial CD | Drained |
9️⃣ Earth Pressure Theory
🔹 Rankine Theory
| Condition | Formula |
| Active | |
| Passive |
🔹 Pressure
🔟 Bearing Capacity of Soil
🔹 Terzaghi’s Equation
🔹 Safe Bearing Capacity
1️⃣1️⃣ Slope Stability
🔹 Factor of Safety
🔹 Methods
- Swedish slip circle
- Bishop’s method
- Taylor stability number
1️⃣2️⃣ Soil Exploration
🔹 Field Tests
- SPT – most common
- CPT – continuous profile
- Plate Load Test
🔹 Lab Tests
- Grain size analysis
- Atterberg limits
- Shear strength tests
- Consolidation test
🎯 SSC JE Exam Tips
✔ Most Important Chapters
- Atterberg limits
- Effective stress
- Compaction
- Consolidation
- Shear strength
- Bearing capacity
- Earth pressure
✔ Frequently Asked
- Formula-based numericals
- Conceptual questions on:
- Effective stress
- Compaction vs consolidation
- Drained vs undrained tests