The commonly used apparatus for performing shear box test is ____

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Option A: Shear-box apparatus

Explanation & Concepts:
The Direct Shear Test, commonly known as the Shear Box Test, is a laboratory test used to determine the shear strength parameters of soil. In this test, a soil specimen is placed in a square metal box that is split horizontally into two halves, and a shearing force is applied to the upper half while a normal force is applied to the top.

Working Principle: The sample is subjected to a constant normal load ($\sigma_n$). A horizontal force is applied to one half of the box, causing the soil to shear along a predetermined horizontal plane. As the shear force increases, the resistance is measured until failure occurs. This test is primarily suited for granular soils due to its inability to control drainage or pore pressure conditions.

Key Formulas: $	au = c + \sigma_n 	an(\phi)$ — Coulomb's Law where $c$ is cohesion, $\sigma_n$ is normal stress, and $\phi$ is the angle of internal friction.

Key Points: The failure plane is forced to occur along the horizontal plane between the two halves of the box.; It is a stress-controlled test usually performed at a constant rate of strain.; Best suited for cohesionless soils (sands and gravels) where drainage is rapid.; The test does not allow for the measurement of pore water pressure.

Advantages: Simple and easy to perform for granular soils.; Useful for determining the residual shear strength of soil.

Disadvantages: The failure plane is predefined and not necessarily the weakest plane.; Non-uniform stress distribution within the specimen.; Cannot control drainage or measure pore pressure.

Applications: Determining the shear parameters for stability analysis of slopes.; Foundation design in granular soil deposits.

Additional Info: Option B (Bishop's apparatus) is used to measure pore water pressure in Triaxial tests.. Option C (Triaxial test) is a more advanced test that allows for controlled drainage conditions and better stress-state representation.

Answer: A is correct — The shear-box apparatus is the standard equipment used for the direct shear test to determine the shear strength of cohesionless soils.

Exam Tip: Always remember that in a Direct Shear Test, the drainage condition is uncontrolled, which is why it is unsuitable for low-permeability cohesive soils where pore water pressure build-up significantly impacts strength.

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Option B: Bishop’s pore pressure apparatus

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Option C: Triaxial shear test apparatus

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Option D: None of the mentioned

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