NICET - Highway Construction Inspection Practice Exam

When backfilling culverts and storm drains, what is the maximum lift measurement recommended?

1. 3 inches

2. 6 inches

3. 12 inches

4. 18 inches

The correct answer is: 6 inches

The recommended maximum lift measurement for backfilling culverts and storm drains is 6 inches. This limit is important for several reasons: 1. **Compaction Efficiency**: Using a lift height of 6 inches allows for more effective compaction of the backfill material. When each lift is kept to this height, there is less risk of leaving voids or un-compacted areas that could compromise the integrity of the structure being backfilled. 2. **Material Type Consideration**: Different materials behave differently when compacted. A 6-inch lift helps ensure that granular materials, such as sand and gravel, achieve optimal density, while cohesive materials can be adequately compacted without being too difficult to work with. 3. **Control of Settlement**: Smaller lifts help control settlement issues by allowing for more thorough compaction and making it easier to monitor the operation. If lifts are too high, areas can settle unevenly, leading to possible future structural issues, water pooling, or other drainage problems. 4. **Operational Ease**: Working with smaller lifts generally allows operators to have better control over the compaction process, ensuring consistent results and reducing the likelihood of failures related to improper backfill practices. This approach is established in industry standards and best practices