After compacting the subgrade by suitable methods, the tests to ensure that the desired compaction has been achieved is/are:

Asked in SSC JE 10/10/2023 (Morning)

Detailed Explanation

The laboratory Proctor test gives the target: maximum dry density (MDD) and OMC. On site, quality control asks a simple question: has the rolled layer reached the specified percentage of that MDD? To answer it, the engineer measures the field (in-situ) density and the water content of the compacted layer.

\[ \gamma_{d,\text{field}} = \frac{\gamma_{\text{bulk}}}{1 + w} \qquad \text{Relative compaction} = \frac{\gamma_{d,\text{field}}}{\gamma_{d,\max}} \times 100\% \]

Why “moisture content and field density determination test” Is Correct

Field density is found by the core cutter method (for soft, fine-grained soils) or the sand replacement method (for gravelly or hard soils), or with a nuclear density gauge. Water content comes from oven drying or a rapid moisture meter. Typical specifications require 95–98% relative compaction for road subgrades and embankments.

Why the Other Options Are Wrong

• A. direct shear test: A direct shear test measures shear strength parameters in the laboratory; it is not a routine field check of compaction.
• B. compaction test and triaxial shear test: The compaction (Proctor) test sets the target in the lab, and the triaxial test measures strength; neither tells you what density was achieved on site.
• C. consolidation test: Consolidation tests deal with long-term settlement of saturated clays, not with checking a freshly compacted layer.

Key Concepts for Students

• Core cutter: quick, for cohesive soils without stones. Sand replacement: for gravelly soils.
• Tests are repeated at a fixed frequency, for example per layer and per few hundred square metres.
• Water content is checked too, because rolling far from the OMC will not reach the target density.

Practice more: this is question 6 of Compaction of Soil MCQs – Part 1. Try the whole set and check every answer instantly.