Soil Mechanics: Terzaghi 1D Consolidation, Mohr-Coulomb Shear Failure & Foundation Design
Geotechnical engineering essentials, pore water pressure dynamics, slope stability, and shallow/deep foundation bearing capacity.
In-Depth Interview Questions & Model Solutions
Q1Explain Terzaghi’s Principle of Effective Stress and how excess pore water pressure dissipates during Consolidation.
Terzaghi stated that total stress (σ) in a saturated soil is the sum of Effective Stress (σ') and Pore Water Pressure (u): `σ = σ' + u` => `σ' = σ - u`. All soil deformation, volume change, and shear strength are strictly governed by effective stress, not total stress. When external compressive load is applied to a saturated clay layer with low permeability, the incompressible pore water initially carries 100% of the additional stress (excess pore pressure Δu = Δσ). Over time, water drains out slowly through soil voids, transferring stress to the mineral soil skeleton until Δu becomes 0 and primary consolidation settlement completes.
- Effective stress σ' controls shear resistance and compressibility.
- Consolidation time factor Tv = (Cv * t) / d².
- Over-Consolidated Clay (OCR > 1) exhibits peak shear strength with dilatancy.
Technical Panel Interview Strategy Tips
- Memorize Terzaghi’s General Bearing Capacity formula: `qult = c*Nc + γ*Df*Nq + 0.5*γ*B*Nγ` for continuous strip footings.