A soil compaction test shows 92% of maximum density. The specification requires 95% compaction. What volume of additional compactive effort is needed if the test area is 1,000 square feet at 8 inches thick?
Correct Answer
D) Scarify, add material if needed, and recompact to achieve 95%
When compaction is below specification (92% vs required 95%), the area must be scarified, additional material added if necessary, and recompacted to achieve the specified density. Simply recompacting without scarifying rarely achieves proper results.
Why This Is the Correct Answer
Option C is correct because when soil compaction falls below specification requirements, proper remediation requires scarifying (loosening) the existing compacted material to break up any hard spots or layers that prevented proper compaction. Additional material may be needed to achieve the required density, and then the entire area must be recompacted using proper techniques. This systematic approach addresses the root cause of inadequate compaction rather than just applying more effort to already-compacted material.
Why the Other Options Are Wrong
Option A: Add 3% more material and recompact
Simply recompacting the entire area without scarifying will likely not achieve the required 95% compaction because the soil has already been worked and may have formed a crust or hard layer that prevents proper densification. The existing compacted surface needs to be broken up first.
Option B: Recompact the entire area
92% compaction does not meet the 95% specification requirement. In construction, compaction specifications are critical for structural integrity, drainage, and long-term performance. Accepting substandard compaction can lead to settlement, structural failure, and liability issues.
Option C: The compaction is acceptable as-is
Adding 3% more material without scarifying the existing base ignores the fundamental problem that the underlying soil was not properly compacted. The percentage difference (3%) doesn't directly translate to a volume of material needed, and this approach doesn't address the compaction methodology issues.
Memory Technique
Think 'SSR' - Scarify, Supplement, Recompact. Like a car that won't start, you can't just keep turning the key (recompacting) - you need to diagnose and fix the problem first (scarify and add material).
Reference Hint
Florida Building Code Chapter 18 - Soils and Foundations, or ACI 318 for soil preparation requirements
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