Undrained bearing capacity of saturated clay under strip footing For the failure mechanism shown (saturated clay, undrained condition), the ultimate bearing capacity of a strip footing is expressed as qc = Nc * Cu. The appropriate value of Nc is:

Introduction / Context:
In saturated clays under short-term loading, shear strength is undrained and independent of confining pressure (φu ≈ 0, Cu = undrained cohesion). Classical bearing capacity solutions specialize to a single factor Nc multiplying Cu for strip footings at the ground surface.

Given Data / Assumptions:

• Soil is fully saturated clay; undrained loading (short term).
• φu = 0; shear strength = Cu.
• Strip footing at ground level; surcharge negligible in the simplified expression.

Concept / Approach:
Terzaghi's general shear solution for φ = 0 gives Nc ≈ 5.7 for strip footings. Many texts also cite Skempton's refined value 5.14 for φ = 0 under certain assumptions, but Terzaghi's widely taught exam value for strip footing at surface is 5.7.

Step-by-Step Solution:
1) Adopt qc = Nc * Cu for φu = 0.2) Use Terzaghi's Nc = 5.7 for strip footing.3) Therefore qc = 5.7 * Cu.4) Choose option 5.7 Cu.

Verification / Alternative check:
Comparing 2π Cu ≈ 6.28 Cu (upper bound) and 4π Cu ≈ 12.57 Cu (too high) helps validate that 5.7 Cu is in the expected range for classical solutions.

Why Other Options Are Wrong:
5.14 Cu is a commonly quoted alternative but not the standard Terzaghi exam value for this strip-footing case; 4π Cu and 2π Cu are not the accepted factors for general shear in undrained clay at the surface.

Common Pitfalls:
Mixing drained and undrained parameters; confusing strip with square/circular footing factors; overlooking depth or surcharge effects.

Final Answer:
5.7 Cu