Consolidation history — the over-consolidation ratio (OCR) is the maximum past effective vertical stress divided by the current effective vertical stress. For an overconsolidated clay, OCR is:

Introduction / Context:
OCR indicates whether a clay deposit has experienced higher effective stresses in the past than it carries today. This controls compressibility, stiffness, and shear strength. Overconsolidated clays typically show lower compressibility and higher shear strength than normally consolidated clays at the same current stress.

Given Data / Assumptions:

• OCR = sigma'max_past / sigma'current.
• Overconsolidated clay has been unloaded (e.g., erosion, groundwater rise).

Concept / Approach:

If sigma'max_past exceeds sigma'current, the ratio exceeds unity. OCR = 1 indicates normally consolidated conditions; OCR < 1 is not meaningful in standard definition for intact soils.

Step-by-Step Solution:

Verification / Alternative check:

Laboratory oedometer e–log(sigma') curve with Casagrande method identifies preconsolidation pressure; OCR computed thereby exceeds 1 for overconsolidated clays.

Why Other Options Are Wrong:

OCR = 1 is normal consolidation; OCR < 1 contradicts the definition.

Common Pitfalls:

Confusing preconsolidation pressure with OCR; using total instead of effective stresses.

Final Answer:

more than 1