As the core upper and lower layers of the road structure, the subgrade and pavement have essential differences in material properties, load-bearing logic, and construction quality objectives. These differences determine that the selection of roller tonnage and amplitude must follow the core principle of "heavy tonnage + large amplitude for subgrade to achieve deep compaction, and medium/small tonnage + small amplitude for pavement to achieve uniform density". The specific differential requirements and underlying logic are as follows:

I. Subgrade Compaction: Heavy Tonnage + Large Amplitude to Overcome Deep Material Resistance

The subgrade is the foundation of the road load-bearing system. Its core requirement is to achieve the compaction and stability of deep soil/filling materials through layered compaction (with a thickness of 20-30cm per layer). This provides sufficient strength, rigidity, and water stability for the pavement, and needs to overcome the compaction resistance caused by internal friction between filling particles, cohesion, and high porosity.

1. Tonnage Requirements: Focus on Heavy Tonnage, with Consideration for Layer Thickness Adaptation

Subgrade filling materials are mostly natural or modified materials such as silty soil, sandy soil, and gravel soil. They have a wide particle size distribution and are difficult to compact, requiring sufficient compaction force to penetrate to the bottom of the compacted layer (to avoid "dense surface layer and loose deep layer").

• When the layered thickness is 20-25cm, priority should be given to 18-22t vibratory rollers (with a static linear load of ≥350N/cm). These rollers use static pressure generated by their own weight combined with vibration energy to realize particle rearrangement and pore filling.

• When the layered thickness is 25-30cm or the filling material is coarse-grained materials such as gravel soil and block stone soil, 22-26t heavy-duty vibratory rollers (with a static linear load of ≥400N/cm) are required. In some cases, even impact rollers of more than 30t are used for auxiliary compaction to ensure effective interlocking of deep particles and form a stable skeleton structure.

• In special scenarios (such as compaction after soft soil subgrade improvement), a 16-18t medium-tonnage roller can be used for pre-compaction and leveling first, and then a heavy-tonnage roller for enhanced compaction. This avoids filling material displacement and interlayer shear damage caused by direct use of heavy-tonnage rollers.

2. Amplitude Requirements: Focus on Large Amplitude, with Adjustments Based on Filling Material Type

Amplitude directly determines the transmission depth of vibration energy. Subgrade compaction requires large amplitude to transmit vibration energy to the bottom of the compacted layer and overcome the resistance between particles.

• For conventional subgrade filling materials (silty soil, sandy soil): The amplitude is controlled at 1.5-2.5mm, and the vibration frequency is matched at 25-30Hz. The "high-frequency and large-amplitude" combination achieves deep compaction, avoiding insufficient compaction energy due to too small amplitude or surface filling material splashing and structural looseness due to too large amplitude.

• For coarse-grained filling materials (gravel soil, block stone soil): The amplitude can be increased to 2.0-3.0mm. Larger vibration impact force is used to promote particle interlocking, and the frequency should be controlled at 20-25Hz to balance the impact force and compaction uniformity.

• For special filling materials (such as modified soil, fly ash): The amplitude should be 1.2-1.8mm. This avoids damage to the binders (such as lime and cement) in the filling materials caused by large amplitude, ensuring both compaction effect and material stability.

II. Pavement Compaction: Medium/Small Tonnage + Small Amplitude to Balance Compaction and Structural Protection

The pavement directly bears the vehicle load. Its core requirement is to achieve uniform density of surface materials (to ensure compaction degree) while avoiding damage to the pavement structure (such as the aggregate gradation of asphalt mixture and the strength of cement-stabilized base course). It is necessary to control the intensity and transmission depth of compaction force to balance compaction degree and flatness.

1. Tonnage Requirements: Focus on Medium/Small Tonnage, with Adaptation to Pavement Structural Layers

Pavement materials (asphalt mixture, cement-stabilized macadam, concrete surface layer) have strong uniformity, contain binders (asphalt/cement), or are sensitive to structural strength. Excessive tonnage is likely to cause pavement displacement, cracking, and aggregate crushing.

• Asphalt pavement (lower/middle surface layer): 10-14t double-drum vibratory rollers are selected, with a static linear load of ≥250N/cm. The "medium-tonnage + high-frequency vibration" combination achieves mixture compaction, avoiding asphalt mixture displacement and aggregate crushing caused by excessive tonnage. For the upper surface layer: Priority is given to 8-10t light double-drum vibratory rollers or rubber-tired rollers (16-20t). Rubber tires improve compaction degree through "kneading action", and light steel drums avoid damage to the surface flatness and aggregate gradation.

• Cement-stabilized base course: 12-16t double-drum vibratory rollers are selected, with a static linear load of ≥300N/cm. Excessive tonnage is likely to cause base course cracking, while insufficient tonnage fails to meet the design compaction degree. In the later stage of rolling, light rollers (8-10t) are needed for leveling to ensure flatness.

• Concrete pavement: Initial compaction is only carried out after paving, using 6-8t light double-drum vibratory rollers with an amplitude controlled within 0.5mm. Its main function is to level the surface, avoiding surface sanding and cracking of concrete caused by heavy tonnage or large amplitude.

2. Amplitude Requirements: Focus on Small Amplitude, with Precise Control Based on Pavement Type

Pavement materials are sensitive to vibration impact. Small amplitude can avoid damage to binders or pavement structures, while achieving uniform compaction through high-frequency vibration.

• Asphalt pavement: The amplitude is controlled at 0.3-0.8mm, and the vibration frequency is 30-40Hz. The "high-frequency and small-amplitude" combination not only enables the rearrangement of asphalt mixture particles and pore filling but also avoids asphalt film detachment and aggregate crushing caused by large amplitude, ensuring pavement strength and durability. The amplitude of the upper surface layer needs to be further reduced to 0.3-0.5mm to focus on protecting the surface flatness and anti-skid performance.

• Cement-stabilized base course: The amplitude is controlled at 0.8-1.2mm, and the frequency is 28-32Hz. Small amplitude avoids damage to the cement hydration products in the base course, ensuring the base course strength while meeting the compaction degree requirements. In the later stage of rolling, vibration should be turned off, and static rolling should be used for leveling to avoid surface looseness of the base course caused by vibration.

• Special pavements (such as ultra-thin wearing courses, colored asphalt pavements): The amplitude is ≤0.3mm. Light rollers are selected or vibration is turned off for static pressure to maximize the protection of pavement structure and appearance quality.

III. Summary of Core Differences

The core of subgrade compaction is "deep compaction", which requires heavy tonnage to provide sufficient static pressure and large amplitude to transmit deep vibration energy, overcoming the resistance between filling particles. The core of pavement compaction is "surface uniformity + structural protection", which requires medium/small tonnage to control compaction force and small amplitude to reduce vibration impact, avoiding damage to pavement materials and structures. During selection, it is necessary to strictly match heavy tonnage + appropriate amplitude according to "subgrade layered thickness + filling material type", and match medium/small tonnage + small amplitude according to "pavement structural layer + material properties". At the same time, vibration frequency and rolling times should be optimized to ensure that the construction quality meets the design requirements.