Limitations of the direct shear test (shear strength of soils) Which of the following is a disadvantage of the direct shear test on soils?

Introduction / Context:
The direct shear test is a simple and fast method to estimate shear strength parameters of soils. However, its simplicity comes with several limitations that may affect the interpretation of c and φ, particularly for saturated clays and structured soils.

Given Data / Assumptions:

• Shear box imposes a predetermined horizontal failure plane.
• Drainage and pore pressure conditions are not instrumented at the plane.
• Area changes during relative displacement.

Concept / Approach:

Because the failure plane is forced and instrumentation is limited, controlling drainage and measuring pore pressures are difficult. Stress distribution along the plane is not perfectly uniform due to boundary effects, and the actual area under load reduces as shear displacement progresses.

Step-by-Step Solution:

Verification / Alternative check:

Advanced tests (triaxial, simple shear) overcome many of these issues by controlling drainage and measuring pore pressures, highlighting the comparative limitations of the direct shear test.

Why Other Options Are Wrong:

Each individual statement reflects a real limitation; hence the composite option is correct.

Common Pitfalls:

Assuming measured parameters are fully representative of peak/residual strength for all soils; ignoring scale and boundary effects.

Final Answer:

All of the above