Triaxial Shear Test – Reasons for Its Suitability for Shear Strength Evaluation Why is the triaxial shear test widely regarded as the most suitable laboratory test for determining shear strength parameters of soils?

Introduction / Context:
Laboratory shear tests aim to derive soil strength parameters under controlled drainage and stress paths. The triaxial apparatus offers flexibility and measurement capability far beyond simpler tests like direct shear, making it the standard choice in research and advanced design.

Given Data / Assumptions:

• Cylindrical specimen with confining pressure and axial load control.
• Instrumentation available for pore pressure and volume change (as needed).
• Standard test variants: UU, CU with pore pressure, and CD.

Concept / Approach:

The triaxial test controls the stress state (σ1, σ3) and permits different drainage conditions to mimic field situations. With pore pressure and volume-change measurements, effective stress paths and constitutive behavior can be analyzed. The stress distribution is well defined, and Mohr–Coulomb parameters can be obtained with confidence.

Step-by-Step Solution:

Verification / Alternative check:

Comparisons with direct shear show that unknown failure plane and non-uniform stresses limit parameter interpretation there, while triaxial circumvents these issues.

Why Other Options Are Wrong:

Each listed feature is a true advantage; thus only 'All of the above' captures the full justification.

Common Pitfalls:

Confusing undrained strength (UU) with effective stress parameters (require CU/CD with measurements); neglecting specimen preparation quality.

Final Answer:

All of the above