There is no fixed standard for the number of compaction passes of a roller. The core principle is to comprehensively determine it based on three major factors: material type, compaction degree requirement, and equipment tonnage. Ultimately, on-site tests are required to verify and ensure that the designed compaction density index is met.

1. Core Influencing Factors: Determining the Basic Range of Passes

The basic range of compaction passes varies significantly under different conditions, and the following key conditions must first be clarified.

• Material type:

• Coarse-grained materials such as graded crushed stone and rock-filled subgrade require 8-12 passes.

• Fine-grained materials like asphalt mixture and cement-stabilized soil usually only need 4-8 passes.

• Compaction degree requirement:

• The compaction degree requirement for expressway subgrades is ≥96%, which requires more passes than that for Class II highways (≥93%), with a possible difference of 2-3 passes.

• Equipment tonnage:

• Heavy-duty rollers above 10 tons have high compaction efficiency. For the same material, they require 2-4 fewer passes than light-duty rollers of 3-5 tons.

2. On-Site Tests: Determining the Final Accurate Number of Passes

The theoretical range needs to be adjusted based on on-site reality, and common test methods can accurately lock in the number of passes.

• Test compaction method:Select a representative road section and follow the process of "2 initial compaction passes → 3-5 re-compaction passes → 2 final compaction passes". Measure the compaction density every 2 passes until the density stabilizes and no longer increases. The total number of passes at this point is the optimal value.

• Process parameter comparison method:Refer to mature data from similar projects (e.g., same material + same roller), first conduct test compaction according to the reference number of passes, then make fine adjustments through testing to reduce the workload of the test.

3. Dynamic Adjustment: Optimizing Based on On-Site Feedback

During actual operation, flexible adjustments should be made according to the material status and test results to avoid over-compaction or insufficient compaction.

• If the test shows that the compaction density fails to meet the standard:Increase 1-2 re-compaction passes, and prioritize using a roller of the same tonnage to avoid material displacement caused by switching to a larger-tonnage roller.

• If material peeling or cracking occurs (e.g., on asphalt pavement):Reduce 1-2 passes or decrease the compaction speed to prevent over-compaction from damaging the material structure.