The core physical and mechanical properties of subgrade fill, such as particle gradation, cohesion, and porosity, directly determine the "energy form (static pressure/vibrational energy/impact energy)" and "action mode (uniform pressure application/impact interlocking/kneading compaction)" required for compaction. These properties serve as the fundamental basis for roller selection. The core logic of selection is: fill characteristics → compaction challenges → energy requirements → roller type matching. The specific influence mechanisms and implementation plans are as follows:
Different subgrade fills have inherently distinct compaction challenges and required energy forms, which form the core premise of selection:
Fine-grained fill (silty soil, clay): Features moderate cohesion and high porosity. The key compaction challenge is to "break particle cohesion while avoiding surface hardening and deep-layer looseness". It requires "gentle and uniform vibrational energy + static pressure finishing" to prevent structural damage to the soil from excessive energy.
Medium-grained fill (sandy soil, sand-gravel): Has extremely weak cohesion and strong particle fluidity. The main compaction difficulty is to "promote particle interlocking and prevent particle slippage". It needs "high-frequency vibrational energy" to drive rapid particle reorganization, without over-reliance on static pressure.
Coarse-grained fill (crushed stone soil, block stone soil): Exhibits extremely high porosity and strong inter-particle friction. The primary compaction challenge is to "overcome friction and achieve deep-layer skeleton interlocking". It requires "large-amplitude vibrational energy or impact energy" to force coarse particles to undergo plastic deformation and form tight interlocking.
Modified/special fill (lime/cement-modified soil, coal gangue, waste fill): Contains binders or irregular particles. The compaction challenge is to "balance compaction degree and structural protection", requiring targeted matching of energy intensity and action mode.
Main compaction equipment: 16–20t single-drum/double-drum vibratory roller (amplitude: 0.6–1.0mm, frequency: 35–40Hz).
Auxiliary compaction equipment: 18–22t pneumatic tyred roller (static pressure, tire pressure: 0.6–0.8MPa) or 12–16t double-drum static roller.
Prohibited equipment: Impact rollers (excessive impact energy easily damages the cohesive structure, leading to "spring soil"); large-amplitude vibratory rollers (amplitude ≥1.5mm, prone to causing surface looseness).
Low-amplitude vibratory roller: The high-frequency, small-amplitude vibrational energy gently breaks particle cohesion and promotes particle rearrangement. The compaction depth can reach 20–25cm (layered compaction), and the compaction degree is increased to 95%–96%, avoiding surface particle splashing and insufficient deep-layer compaction caused by large amplitudes.
Pneumatic tyred/static roller: The static pressure effect fills tiny pores remaining after vibration, achieving uniform surface compaction, eliminating "surface hardening with deep-layer looseness", and improving subgrade flatness to reduce long-term settlement risks.
Operation process:
Initial compaction: Use a static roller for 1–2 static passes to stabilize the loose laid layer.
Secondary compaction: Use a low-amplitude vibratory roller for 3–4 passes.
Final compaction: Use a pneumatic tyred roller for 1–2 kneading passes or a static roller for 2 static passes to eliminate wheel tracks.
High-moisture silty soil (3% above optimal moisture content): Reduce the number of vibratory passes by 1 and increase the number of pneumatic tyred roller passes by 1–2 to prevent "spring soil" caused by vibration.
Modified fine-grained soil (mixed with lime/cement): Reduce the amplitude of the vibratory roller to 0.5–0.8mm and increase the frequency to 38–40Hz to avoid vibration damaging the binder structure in the modified soil.
Main compaction equipment: 18–22t single-drum vibratory roller (amplitude: 1.0–1.5mm, frequency: 30–35Hz) or 12–16t double-drum vibratory roller.
Auxiliary equipment: Optional 16–18t pneumatic tyred roller (only used for surface flatness correction).
Prohibited equipment: Pure static rollers (no vibrational energy, particles cannot interlock effectively, resulting in a compaction degree of only 85%–90%, far below design requirements); low-frequency large-amplitude vibratory rollers (frequency ≤28Hz, slow particle reorganization speed, low efficiency).
High-frequency medium-amplitude vibratory roller: Vibrational energy quickly drives particle resonance, breaks the accumulated state, and promotes particle interlocking to form a stable skeleton structure. Compared with static rolling, compaction efficiency is increased by 30%–50%, the compaction depth can reach 25–30cm (layered compaction), and the compaction degree reaches 96%–97%.
No static roller assistance needed: Sandy soil has weak cohesion, and particles are already fully interlocked after vibration. Static pressure cannot further improve compactness but instead increases operation time. Only when extremely high surface flatness is required (e.g., the upper subgrade layer connecting to the pavement base), a pneumatic tyred roller is used for 1 kneading pass for correction.
Operation process:
Initial compaction: Use a vibratory roller for 1 static pass to stabilize the loose laid layer.
Secondary compaction: Use the vibratory roller for 3–4 high-frequency medium-amplitude passes.
Final compaction: If needed, use a pneumatic tyred roller for 1 static pass to eliminate wheel tracks.
Sandy soil with high silt content (20%–30% silt particles): Reduce the amplitude to 0.8–1.2mm and increase the frequency to 35–38Hz to avoid uneven compaction caused by silt particle agglomeration.
Sand-filled subgrade (pure sand fill): Select a 22–26t large-tonnage vibratory roller (amplitude: 1.2–1.5mm). Utilize greater static pressure combined with vibrational energy to improve deep-layer compactness and prevent long-term liquefaction.
Main compaction equipment: 22–26t single-drum vibratory roller (amplitude: 1.8–2.5mm, frequency: 25–30Hz).
Enhanced compaction equipment: 25–30t triangular impact roller (impact energy: 20–30kJ, impact frequency: 12–15 times per minute).
Prohibited equipment: Small vibratory rollers (tonnage ≤16t, insufficient energy to penetrate deep-layer crushed stones); pure static rollers (only capable of compacting the surface layer, with insufficient deep-layer particle interlocking, resulting in an 8%–10% deficit in compaction degree).
Large-amplitude vibratory roller: The strong impact energy provided by the large amplitude overcomes the friction between crushed stone particles, forcing particles to displace, rotate, and interlock. The compaction depth can reach 30–40cm (layered compaction), reducing the porosity from 35%–40% to 20%–25%.
Impact roller: The instantaneous impact energy is similar to "heavy hammer compaction", which enhances the interlocking effect of deep-layer crushed stones. It is particularly suitable for rock-filled embankments or subgrade base reinforcement of crushed stone soil, improving foundation bearing capacity by 20%–30% and reducing long-term settlement (≤5cm).
Operation process:
Initial compaction: Use a vibratory roller for 1–2 static passes to prevent crushed stone displacement.
Secondary compaction: Use the vibratory roller for 4–5 large-amplitude passes + 2–3 passes with an impact roller.
Final compaction: Use the vibratory roller for 2 static passes to correct flatness.
Crushed stone soil with high block stone content (block stone diameter ≥50cm): Increase the impact energy of the impact roller to 25–30kJ and the amplitude of the vibratory roller to 2.2–2.5mm to extend the particle interlocking time.
Compaction of crushed stone soil in narrow spaces (e.g., tunnel portals, foundation pit backfilling): Select an 8–12t small large-amplitude vibratory roller (amplitude: 1.5–2.0mm, turning radius ≤2.5m), combined with a 1–3t walk-behind micro vibratory roller for corner compaction, replacing the impact roller (which is too large to enter the site).
Recommended equipment: 16–18t double-drum vibratory roller (amplitude: 0.8–1.0mm, frequency: 32–35Hz) + 18t pneumatic tyred roller.
Selection basis: Vibrational energy must be gentle to avoid damaging the hydrated product structure of the binder. The kneading effect of the pneumatic tyred roller improves surface compactness, with a target compaction degree of ≥97%.
Recommended equipment: 20–22t single-drum vibratory roller (amplitude: 1.5–1.8mm, frequency: 28–30Hz).
Selection basis: Medium amplitude balances particle crushing and interlocking effects, avoiding excessive angular particle crushing caused by large amplitudes, with a target compaction degree of ≥96%.
Recommended equipment: 25–30t pentagonal impact roller (impact energy: 20–25kJ) + 20t pneumatic tyred roller.
Selection basis: Impact energy compresses the waste volume (reducing landfill capacity occupation by 20%–30%), and static pressure from the pneumatic tyred roller seals the surface layer to prevent landfill gas leakage. The bearing capacity of the compacted waste mass should be ≥100kPa.
| Fill Type | Core Compaction Energy | Recommended Roller Combination | Key Parameter Control | Compaction Challenge Resolution |
|---|
| Fine-grained (silty soil/clay) | Low-amplitude vibrational energy + static pressure energy | 16–20t low-amplitude vibratory roller + pneumatic tyred/static roller | Amplitude: 0.6–1.0mm, Frequency: 35–40Hz | Gentle vibration breaks cohesion; static pressure finishing prevents looseness |
| Medium-grained (sandy soil/sand-gravel) | High-frequency medium-amplitude vibrational energy | 18–22t high-frequency medium-amplitude vibratory roller | Amplitude: 1.0–1.5mm, Frequency: 30–35Hz | High-frequency vibration promotes interlocking; prevents particle slippage |
| Coarse-grained (crushed stone soil/block stone soil) | Large-amplitude vibrational energy + impact energy | 22–26t large-amplitude vibratory roller + impact roller | Amplitude: 1.8–2.5mm, Impact energy: 20–30kJ | High energy impact overcomes friction; enhances skeleton interlocking |
| Modified soil (lime/cement-modified) | Medium-amplitude medium-frequency vibrational energy + static pressure energy | 16–18t medium-amplitude vibratory roller + pneumatic tyred roller | Amplitude: 0.8–1.0mm, Frequency: 32–35Hz | Gentle vibration preserves structure; kneading compaction improves strength |
Hazards: Using a large-amplitude vibratory roller for silty soil easily causes surface looseness and "spring soil"; using a small-amplitude vibratory roller for crushed stone soil fails to meet the design compaction degree.
Avoidance: Lock in vibration parameters (amplitude, frequency) based on fill particle gradation, then match the roller tonnage, rather than uniformly selecting based solely on "subgrade".
Hazards: The kneading effect of pneumatic tyres is ineffective for sandy soil; instead, it causes particle slippage and substandard compaction degree.
Avoidance: Use a high-frequency medium-amplitude vibratory roller as the core equipment for sandy soil subgrades. Pneumatic tyred rollers are only used for surface flatness correction and do not participate in main compaction.
Hazards: For large-diameter crushed stones or deep-layer compaction (≥30cm), vibrational energy is insufficient, leading to inadequate deep-layer particle interlocking and potential long-term settlement.
Avoidance: Rock-filled embankments and crushed stone soil subgrade base reinforcement must be combined with impact rollers. For conventional crushed stone soil subgrades, impact rollers can be used selectively based on compaction depth (≥30cm).
Hazards: Large-amplitude vibration damages the hydrated product structure of the binder, resulting in a strength loss of ≥10% for the modified soil.
Avoidance: Select a medium-amplitude (0.8–1.0mm) vibratory roller for modified soil subgrades, combined with static pressure from a pneumatic tyred roller to balance compaction degree and structural protection.
The influence of subgrade fill type on roller selection essentially lies in the "precise matching of fill characteristics and compaction energy":
Fine-grained fill requires "gentle and uniform energy", suitable for the combination of low-amplitude vibration + static pressure.
Medium-grained fill needs "energy for efficient reorganization", suitable for high-frequency medium-amplitude vibration.
Coarse-grained fill demands "highly penetrative energy", suitable for the combination of large-amplitude vibration + impact.
Modified/special fill requires "customized energy" to balance compaction degree and structural protection.
During selection, it is necessary to first identify the fill type through particle gradation tests, then lock in the form of compaction energy, and finally match the corresponding roller type and parameters. Meanwhile, misunderstandings such as "energy mismatch" and "equipment misuse" should be avoided to ensure the subgrade meets compaction standards (≥95%) and maintains reliable stability.
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