Deflection testing timing?

• A. Immediately after backfill
• B. 7 days after backfill
• C. 15 days after backfill
• D. 30 days after final backfill

Answer: (D)

Deflection testing should be timed after the surrounding soil has stabilized and the bedding and backfill have settled under actual service conditions. If you test too early—immediately after backfill or just a week or two later—the readings can be skewed by ongoing compaction, moisture changes, and transient support conditions as the trench settles. Waiting longer allows the soil to consolidate and reach a representative load on the pipe, so the deflection you measure reflects what will happen in normal use rather than temporary conditions.

Thirty days after the final backfill is typically when settlement has largely completed and the test results are more reliable for assessing whether the installation will stay within allowable deflection limits during its life. This timing minimizes the risk of false indications caused by ongoing backfill settlement and provides a stable, repeatable reading that matches expected service conditions.