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The Triaxial Test is one of the most important laboratory tests used to determine the shear strength parameters of soil under controlled conditions. Principle A cylindrical soil sample is subjected to: • All-round pressure (σ₃) → confining pressure • Axial load (σ₁) → vertical stress Failure occurs when shear stress reaches maximum. Types of Triaxial Tests 1. UU Test (Unconsolidated Undrained) • No drainage allowed • Quick test • Used for short-term analysis 2. CU Test (Consolidated Undrained) • Drainage allowed during consolidation only • Measures pore pressure 3. CD Test (Consolidated Drained) • Full drainage allowed • Used for long-term stability Applications • Foundation design • Slope stability analysis • Earth dam design • Retaining wall design • Bearing capacity calculation Important Points (Exam Tips) • Most accurate shear strength test • Suitable for all soil types • Controls drainage and pressure conditions • Gives both c and φ values
