Comparative bearing capacity — which ground has the least allowable capacity? Among the following ground types, which generally exhibits the lowest safe/allowable bearing capacity for shallow foundations under typical conditions?

Introduction / Context:
Allowable bearing capacity varies widely with ground type. Understanding the relative order helps in early design choices and in selecting foundation systems without detailed testing at the concept stage.

Given Data / Assumptions:

• Typical undisturbed conditions and standard safety factors.
• Shallow foundation regime (not deep foundations).
• No special improvements or reinforcements.

Concept / Approach:

Hard rocks provide very high capacities; coarse dense sands also have high capacities due to high friction and low compressibility. Soft rock can support moderate loads but below those of sound hard rock. Moist clay (especially soft to medium) often has the lowest allowable capacity because of low undrained shear strength and high compressibility, particularly under saturated conditions that reduce effective stress.

Step-by-Step Solution:

Verification / Alternative check:

Indicative values: hard rock (hundreds of t/m²), dense coarse sand (50–100+ t/m²), soft rock/laminated strata (tens to low hundreds), moist clay (often below ~10–20 t/m² depending on consistency).

Why Other Options Are Wrong:

• Hard rock and coarse sandy soil typically have much higher capacities.
• Soft or laminated rock still exceeds that of soft/moist clays in most cases.

Common Pitfalls:

• Confusing “moist clay” with stiff overconsolidated clays; consistency controls capacity.

Final Answer:

Moist clay.