I. Material Characteristics (Internal Factors)
1. Soil Moisture Content
Moisture content is one of the most sensitive factors affecting compaction. At the optimum moisture content, the lubrication between soil particles is optimal, making it easy to compact and reaching peak dry density. Excessive dryness leads to high frictional resistance, while excessive moisture results in high pore water pressure, both detrimental to compaction.
2. Soil Type and Gradation
Sandy Soil: Coarse particles, good permeability, easy to compact, but excessive compaction must be prevented to avoid particle breakage.
Clayey Soil: Fine particles, strong cohesion, difficult to compact, requiring controlled moisture content and an appropriate increase in the number of compaction passes.
Well-graded mixtures (such as crushed stone + sand + clay) are more likely to achieve high density.
3. Filler Particle Size and Uniformity
Excessively large particle size or uneven gradation can easily create "gap" phenomena, leading to insufficient local compaction. Generally, the maximum particle size should not exceed 2/3 of the compacted layer thickness.
II. Mechanical and Operating Parameters (External Factors)
1. Roller Type and Tonnage
Different models are suitable for different working conditions:
Light Rollers (<10 tons): Suitable for surface asphalt or narrow areas.
Medium-Heavy Rollers (10–30 tons): Used for subgrade and base course compaction.
Impact Rollers (30kJ and above): Can achieve deep compaction of over 2 meters, suitable for high embankment sections.
2. Vibration Frequency and Amplitude
High Frequency (>50Hz): Suitable for thin asphalt layers, improving surface smoothness.
High Amplitude (>0.8mm): Strong penetration, suitable for thick paving layers or cohesive soil compaction.
3. Compaction Speed
The optimal operating speed for impact rollers is 10–15 km/h. Too slow a speed affects energy transfer, while too fast a speed results in uneven compaction.
III. Construction Process Control
1. Number of Compaction Passes
Insufficient passes will result in substandard compaction, while excessive passes may lead to "springy soil" or fragmented particles. Generally:
Conventional subgrade: 8–12 passes
Rock fill or soft soil: 15–20 passes, the specific number needs to be determined through compaction testing.
2. Compacted Thickness
The compacted thickness of a single layer should generally not exceed 30cm. Excessive thickness will make it difficult to effectively compact the lower layer, affecting the overall quality.
3. Compaction Method and Overlap Width
Use the "staggered wheel compaction method," with adjacent wheel tracks overlapping by 1/3–1/2 of the wheel width to ensure no missed compaction and no overlap, improving uniformity.
4. Subgrade or Lower Layer Strength
A weak lower layer will make it difficult to compact the upper layer, easily leading to the "springy" phenomenon. The soft subgrade must be treated before proceeding with the upper construction.
