Soil Mechanics & Foundations (Civil)

Soil properties:

• Specific gravity (G): typically 2.6-2.8.
• Void ratio (e): voids/solids volume.
• Porosity (n): voids/total volume.
• Moisture content (w): water/solids weight.
• Bulk density (γ): total weight/total volume.

Atterberg limits:

• Liquid limit (LL): boundary between liquid and plastic states.
• Plastic limit (PL): between plastic and semi-solid.
• Shrinkage limit (SL): between semi-solid and solid.
• Plasticity index (PI): PI = LL − PL.

Classification of Soils (IS):

• Coarse: gravel, sand (G, S).
• Fine: silt, clay (M, C).
• Organic: O.

Permeability: Darcy's law q = k·i·A.

Compaction:

• Standard Proctor test.
• Modified Proctor test (higher energy).
• Optimum Moisture Content (OMC).

Consolidation:

• Time-dependent settlement under load.
• Coefficient of consolidation Cv.

Shear Strength:

• Mohr-Coulomb: τ = c + σ·tan φ.
• c = cohesion; φ = angle of internal friction.

Bearing Capacity:

• Terzaghi's formula: q_ult = cNc + γDfNq + 0.5γBNγ.
• Allowable bearing capacity: ultimate / factor of safety (FoS = 3).

Foundation types:

• Shallow: isolated, combined, mat/raft.
• Deep: piles (driven, bored), wells, caissons.

RRB JE focus: Atterberg limits, basic compaction, simple footing selection.