In the compaction operation of rollers (especially vibratory rollers), amplitude and frequency are core parameters that determine the efficiency of compaction energy transmission and the compaction effect. They work together on construction materials, altering the internal structure of the materials (reducing pores and enhancing compactness) through "dynamic impact". To understand their impact on compaction effect, it is necessary to first clarify the definitions of the two, and then analyze their mechanism of action in combination with material properties.

I. Core Concepts: Definitions of Amplitude and Frequency

The compaction principle of a vibratory roller is as follows: The engine drives the eccentric block inside the vibratory drum to rotate, generating periodic centrifugal force that causes the vibratory drum to vibrate up and down, transferring kinetic energy to the ground material. Amplitude and frequency are precisely the key indicators describing this vibration process, and their physical meanings are completely different:

II. Impact of Amplitude on Compaction Effect: Determines "Compaction Depth and Force"

Amplitude essentially represents the "single impact energy of the vibratory drum on the material" — the larger the amplitude, the stronger the "force" with which the vibratory drum presses downward, the more sufficient the energy transmitted to the interior of the material, and the deeper the compaction depth that can be achieved. Conversely, a smaller amplitude results in weaker impact force, acting only on the surface layer of the material. Its impact needs to be judged based on the material type and layer thickness, with the core rule being: "use large amplitude for thick layers/coarse-grained materials, and small amplitude for thin layers/fine-grained materials".

1. Large Amplitude (1.5-3.0mm): Suitable for Compacting "Deep Layers and Coarse-Grained Materials"

• Applicable Scenarios: Materials with a layer thickness of ≥15cm (such as subgrade fill, graded crushed stone cushion, cement-stabilized soil subbase) and coarse-grained materials (sand-gravel, crushed stone with a particle size of ≥20mm).

• Effect:
  The strong impact energy generated by large amplitude can penetrate the surface layer of the material and reach the deep layer (the compaction influence depth can be 30-50cm). It squeezes and closes the "large pores" (5-10mm in diameter) inside the material, promotes the rearrangement and interlocking of coarse aggregates (e.g., the edges of crushed stones get stuck together), forms a stable skeleton structure, and rapidly improves the material's compactness (e.g., the compactness of the sand-gravel cushion increases from 85% to over 95%) and load-bearing capacity.

• Risk Note: Using large amplitude to compact "thin layers/fine-grained materials" (such as 5cm-thick asphalt surface layer, cement-stabilized fine-grained soil) will cause excessive impact on the materials — the asphalt surface layer may suffer from "pushing and aggregate crushing", and the surface of the stabilized soil may develop "cracks" due to excessive impact, which instead damages the structure.

2. Small Amplitude (0.5-1.2mm): Suitable for Compacting "Surface Layers and Fine-Grained Materials"

• Applicable Scenarios: Materials with a layer thickness of ≤10cm (such as asphalt surface layer, cement-stabilized fine-grained soil, sand-gravel leveling layer) and fine-grained materials (sand soil, asphalt mixture with a particle size of ≤5mm).

• Effect:
  The impact force of small amplitude is weak, acting only on the surface layer of the material (influence depth: 5-15cm). It can avoid structural damage to fine-grained materials, and at the same time, compact the "small pores" (1-3mm in diameter) on the surface layer through "gentle vibration", improving surface flatness (e.g., the flatness error of the asphalt surface layer is reduced from 5mm to within 2mm) without causing asphalt bleeding or fine-grained soil peeling.

• Risk Note: Using small amplitude to compact "thick layers/coarse-grained materials" will result in insufficient energy transmission to the deep layer, leading to a "false compaction" phenomenon where "the surface layer is compact but the deep layer is loose" — the surface roller tracks disappear, but the compactness of the deep layer is only 80%-85% (failing to meet the design value of 95%). Under the action of subsequent vehicle loads, deep settlement will occur, causing pavement cracking.

III. Impact of Frequency on Compaction Effect: Determines "Compaction Efficiency and Material Adaptability"

Frequency essentially represents the "number of impacts per unit time" — the higher the frequency, the faster the "continuous impact frequency" of the vibratory drum on the material. The material particles are subjected to multiple vibrations in a short period, making it easier to overcome the friction between particles and quickly reach a "stable and compact state". Conversely, a lower frequency leads to longer intervals between impacts, and material particles tend to "rebound", resulting in low compaction efficiency. Its impact needs to be judged based on the "mobility" of material particles, with the core rule being: "use high frequency for fine-grained materials/cohesive soils, and medium-low frequency for coarse-grained materials/soils with high moisture content".

1. High Frequency (35-50Hz): Suitable for "Fine-Grained Materials and Cohesive Materials"

• Applicable Scenarios: Asphalt mixture (especially modified asphalt), cement-stabilized fine-grained soil, cohesive soil (with moderate moisture content).

• Effect:
  The "cohesion/friction force" between fine-grained particles (such as mineral powder in asphalt, clay particles) is strong, making it difficult for the particles to move. High-frequency vibration can break the force between particles through "fast and continuous small impacts", allowing the particles to quickly fill pores in a short period (3-5 rolling passes) and preventing the material from rebounding due to "long vibration intervals". For example, using high-frequency rolling (40Hz) on the asphalt surface layer can ensure the compaction degree (≥96%), reduce residual roller tracks, and improve surface smoothness. If low frequency (25Hz) is used, 2-3 additional rolling passes are required to meet the standard, and obvious surface roller tracks are likely to occur.

• Risk Note: High-frequency vibration generates "high noise" (up to 100-110 decibels), so it is necessary to pay attention to the protection of construction personnel. In addition, high frequency causes significant wear on the roller's vibration system, so regular maintenance of the eccentric block bearing is required.

2. Medium-Low Frequency (25-35Hz): Suitable for "Coarse-Grained Materials and High-Moisture-Content Materials"

• Applicable Scenarios: Graded crushed stone, subgrade fill (with high moisture content), sand-gravel cushion.

• Effect:
  The "interlocking force" between coarse-grained particles (such as crushed stone, pebbles) is the main resistance, and the particles can move without high-frequency impact. The "slightly longer impact interval" of medium-low frequency vibration provides sufficient time for the rearrangement of coarse aggregates (e.g., large particles sink, small particles fill gaps), avoiding "disordered aggregate jumping" caused by high frequency (which would otherwise prevent interlocking).
  For subgrade soil with high moisture content (moisture content exceeding the optimal moisture content by 2%-3%), low-frequency vibration can discharge excess moisture in the soil through "slow impact" (moisture penetrates upward to the surface with vibration). If high frequency is used, moisture cannot be discharged in time, forming a "water film" inside the soil, which causes the material to exhibit the "springing phenomenon" (the surface rebounds after rolling, failing to achieve compaction).

• Risk Note: Using low frequency to compact fine-grained materials will result in insufficient impact times, making it impossible for material particles to move fully. To meet the compaction standard, 5-6 additional rolling passes are required, which significantly reduces construction efficiency (e.g., originally 200 meters can be compacted in one day, but only 120 meters can be compacted under low frequency).

IV. "Synergistic Effect" of Amplitude and Frequency: Not "The Larger the Better", But "Optimal Matching"

In actual construction, amplitude and frequency are not adjusted independently; instead, they need to be "synergistically matched" according to material properties to achieve the best compaction effect. Incorrect matching will lead to "insufficient compaction" or "over-compaction damage". Common optimized matching schemes are as follows:

V. Summary: Core Impact Logic of Amplitude and Frequency

• Amplitude determines the "depth and force of compaction: It addresses the issue of "whether the deep layer can be compacted" and should be selected based on the layer thickness and material particle size (thick layer/coarse particles → large amplitude, thin layer/fine particles → small amplitude).

• Frequency determines the "efficiency of compaction and material adaptability: It addresses the issue of "whether compaction can be achieved quickly" and should be selected based on the cohesiveness/mobility of material particles (fine particles/cohesive materials → high frequency, coarse particles/high-moisture-content materials → medium-low frequency).

Ultimately, high-quality compaction effect does not mean "the larger the amplitude and the higher the frequency, the better". Instead, it requires finding the "optimal amplitude-frequency combination" that matches the material properties and construction requirements through "trial compaction tests", so as to achieve the goal of "meeting compaction standards, ensuring surface flatness, and avoiding structural damage".