The width and diameter of a roller drum directly affect compaction uniformity (i.e., the coefficient of variation of compaction degree at different positions on the same working surface, with an ideal value ≤ 3%) by altering three core dimensions: ground contact pressure distribution, energy transfer path, and operation coverage method. The essence of this influence mechanism lies in the "adaptation of contact characteristics between the drum and materials" — width determines the continuity of lateral coverage and the range of pressure distribution, while diameter determines the uniformity of longitudinal pressure transmission and consistency of compaction depth. The two work synergistically to affect the stress state and reorganization effect of material particles, with specific mechanisms as follows:
The core function of drum width is "lateral coverage and pressure diffusion". It affects the consistency of lateral compaction by changing the pressure distribution density per unit width and the overlap efficiency of adjacent rolling strips. The specific mechanism can be divided into three points:
Drum width directly influences the lateral distribution pattern of ground contact pressure:
Wide drum (2.0–2.3m, suitable for conventional pavement/subgrade operations): Has a large ground contact area, enabling uniform pressure diffusion and a small lateral pressure gradient (pressure difference between edges and center) (≤ 10%). This avoids the phenomenon of "dense center with loose edges" caused by local pressure concentration. For example, when a 2.1m-wide double-drum roller compacts the middle layer of asphalt pavement, the coefficient of variation of lateral compaction degree can be controlled at 2%–3%, far lower than the 5%–8% of narrow drums.
Narrow drum (1.5–1.8m, suitable for narrow spaces): Has a small ground contact area, concentrating pressure at the drum center. Pressure attenuates rapidly at the edges, resulting in a large lateral pressure gradient (≥ 15%). This easily leads to "excessive compaction degree at the center of the rolling strip and insufficient compaction at the edges". Particularly when compacting fine-grained subgrade materials, narrow drums require an increased overlap width (≥ 1/2 of the drum width) to compensate for insufficient lateral uniformity; otherwise, the edge compaction degree may be 3%–5% lower than the design value.
Compaction uniformity relies on effective overlap of adjacent rolling strips, and drum width directly determines the difficulty and efficiency of overlap operations:
Wide drum: The overlap width is usually 1/3 of the drum width (approximately 70–80cm). It covers a large area in a single rolling pass, and the pressure overlap zone between adjacent strips is wide, ensuring smooth longitudinal compaction transition and avoiding "strip-shaped" compaction differences. However, if the width is excessively large (≥ 2.5m), in scenarios requiring small-radius turns (e.g., interchange ramps), the inner rolling strips overlap excessively while the outer strips overlap insufficiently, which instead reduces lateral uniformity.
Narrow drum: To ensure edge compaction effect，the overlap width must reach 1/2 of the drum width (approximately 75–90cm). It covers a small area in a single pass, resulting in low operation efficiency. Frequent turns easily cause fluctuations in the overlap amount of adjacent rolling strips (e.g., overlap amount decreasing from 1/2 to 1/4), leading to "missed compaction" or "over-compaction". Particularly in narrow spaces such as foundation pits and tunnels, lateral uniformity is more significantly affected by operational accuracy.
Different materials have varying adaptability to drum width, which directly affects uniformity:
Fine-grained materials (silty soil, clay): Have poor fluidity and require the uniform pressure of a wide drum to promote lateral reorganization of particles, avoiding local particle accumulation or looseness caused by narrow drums. If a narrow drum is used to compact fine-grained subgrades, "wavy" compaction defects are likely to occur, with a coefficient of variation of compaction degree ≥ 6%.
Coarse-grained materials (crushed stone soil, block stone soil): Have strong fluidity. The concentrated pressure of a narrow drum can promote local interlocking of particles, but the number of rolling passes must be increased (1–2 more passes than with a wide drum) to offset uneven lateral pressure. Otherwise, coarse particles easily form "voids" at the drum edges, reducing the compaction uniformity of deep layers.
Binder-containing materials (asphalt mixtures, cement-stabilized macadam): Are sensitive to pressure uniformity. A wide drum can avoid aggregate crushing or binder detachment caused by excessive local pressure. Especially for the asphalt surface layer, the IRI (International Roughness Index) value of surface flatness achieved by rolling with a wide drum (2.0–2.2m) is 0.3–0.5m/km lower than that with a narrow drum.
The core function of drum diameter is "longitudinal pressure transmission and contact time". It affects the consistency of longitudinal compaction by changing the ground contact length, pressure transmission depth, and contact time with materials. The specific mechanism can be divided into three points:
Drum diameter influences the length and shape of the ground contact footprint, thereby altering longitudinal pressure distribution:
Large-diameter drum (1.5–1.8m, suitable for pavement compaction): Has a long ground contact footprint (approximately 30–40cm), and the pressure distribution is in a "gentle trapezoid" shape. Longitudinal pressure changes continuously without obvious peaks, avoiding local pressure concentration caused by the "point contact" of small-diameter drums. For example, when a 1.6m-diameter drum compacts asphalt pavement, the coefficient of variation of longitudinal compaction degree is ≤ 2%, while that of a 1.2m-diameter drum reaches 4%–5%.
Small-diameter drum (1.2–1.5m, suitable for subgrade compaction): Has a short ground contact footprint (approximately 20–30cm), and the pressure distribution is in a "sharp peak" shape. Longitudinal pressure fluctuates significantly, easily causing material "displacement" in front of the drum. Particularly when compacting high-moisture materials, the concentrated pressure of small-diameter drums tends to cause local "springing" (a phenomenon where the soil rebounds like a spring), damaging longitudinal uniformity.
Drum diameter affects the uniformity of deep and shallow layer compaction by changing the transmission path of vibration energy:
Large-diameter drum: Has large mass and strong inertia, enabling vibration energy to be transmitted more deeply and uniformly, avoiding the phenomenon of "dense surface with loose deep layers". When compacting the base course of asphalt pavement (cement-stabilized macadam), the vibration energy of a 1.8m-diameter drum can penetrate to the bottom of the layer (12cm), with a compaction degree difference between deep and shallow layers ≤ 1%. In contrast, the energy of a 1.2m-diameter drum concentrates on the surface layer (5–8cm), resulting in a compaction degree difference ≥ 3%.
Small-diameter drum: Has small mass and rapid vibration energy attenuation, making it suitable for shallow-layer compaction (≤ 10cm). However, when used for medium-deep layer compaction (10–30cm), the amplitude or number of rolling passes must be increased to compensate for insufficient energy; otherwise, the deep-layer compaction degree fails to meet standards, reducing overall uniformity. Especially in layered subgrade compaction, a small-diameter drum requires 1–2 more rolling passes than a large-diameter drum to control the coefficient of variation of compaction degree between deep and shallow layers within 3%.
Drum diameter determines the contact time with materials during rolling, affecting the sufficiency of particle reorganization:
Large-diameter drum: Has a long contact time (approximately 0.15–0.2s per point), providing sufficient time for material particle reorganization. It is particularly suitable for fine-grained materials with strong cohesion or high-viscosity binder-containing materials (e.g., SBS-modified asphalt mixtures), avoiding local voids caused by particles "not having enough time to reorganize".
Small-diameter drum: Has a short contact time (approximately 0.1–0.15s per point), leading to insufficient particle reorganization time. This easily results in uneven pore distribution inside the compacted material. Especially when compacting coarse-grained materials, the short contact time prevents full interlocking of coarse particles, easily forming "false compaction" (a phenomenon where the surface appears compact but the internal structure is loose), which may cause uneven settlement during later operation.
Compaction uniformity is not the result of the independent action of width or diameter; the two must be synergistically adapted. The core logic is "width ensures uniform lateral coverage, and diameter ensures uniform longitudinal depth":
Pavement compaction (pursuing high flatness and uniform compaction): Requires a "wide drum + large diameter" combination (width 2.0–2.3m, diameter 1.5–1.8m) to achieve continuous lateral coverage and uniform longitudinal pressure, adapting to materials with high uniformity requirements such as asphalt mixtures and cement-stabilized macadam.
Subgrade compaction (pursuing deep compaction and lateral continuity): Requires a "medium-width drum + medium diameter" combination (width 1.8–2.0m, diameter 1.3–1.5m) to balance pressure diffusion and energy penetration, adapting to subgrade fill materials such as silty soil and crushed stone soil.
Narrow space compaction (pursuing flexible operation and local uniformity): Requires a "narrow drum + small diameter" combination (width 1.5–1.8m, diameter 1.2–1.3m). However, the overlap width must be increased (≥ 1/2 of the drum width) and the number of rolling passes must be added (1–2 more passes) to compensate for insufficient lateral and longitudinal uniformity.
Wide drum + small diameter: Ensures uniform lateral coverage but causes concentrated longitudinal pressure and insufficient energy penetration, leading to "uniform surface with uneven deep layers". Especially in subgrade compaction, the coefficient of variation of deep-layer compaction degree is ≥ 5%.
Narrow drum + large diameter: Ensures uniform longitudinal depth but results in discontinuous lateral coverage and insufficient edge compaction, leading to "uniform deep layers with uneven surface strips". Especially in pavement compaction, the lateral flatness IRI value is ≥ 2.5m/km.
Expressway asphalt surface layer: Drum width 2.0–2.2m, diameter 1.6–1.8m, ensuring lateral uniformity and surface flatness.
Expressway subgrade (layered thickness 20–30cm): Drum width 1.8–2.0m, diameter 1.4–1.6m, balancing compaction depth and lateral uniformity.
Municipal road base course (cement-stabilized macadam, thickness 10cm): Drum width 1.8–2.0m, diameter 1.5–1.6m, adapting to medium-thickness compaction.
Narrow spaces (tunnels, foundation pits): Drum width 1.5–1.7m, diameter 1.2–1.3m, combined with an overlap width of 1/2 the drum width and 1 additional rolling pass.
Wide-drum rollers: Control the steering angle ≤ 15° to avoid excessive overlap on the inner side; strictly implement an overlap width of 1/3 the drum width, with an error ≤ 5cm.
Large-diameter drum rollers: Maintain a constant travel speed (2.5–3.5km/h) to avoid longitudinal pressure unevenness caused by speed fluctuations.
Narrow-drum/small-diameter rollers: Adopt a rolling sequence of "slow first, then fast; edges first, then center". Add 1 additional compaction pass in edge areas to ensure no compaction blind spots.
The influence of roller drum width and diameter on compaction uniformity essentially lies in the "adaptation of contact characteristics and material response": width ensures lateral uniformity through lateral pressure distribution and coverage efficiency, while diameter ensures longitudinal uniformity through longitudinal pressure transmission and contact time. The core of optimizing both parameters is to "select them synergistically based on the operation scenario (pavement/subgrade/narrow space) and material characteristics (fine-grained/coarse-grained/binder-containing materials)", and then combine them with standardized operational parameters (overlap width, travel speed, rolling sequence). This can control the coefficient of variation of compaction degree within 3%, achieving high-quality uniform compaction. The key is to avoid mismatched combinations such as "wide drum with small diameter" or "narrow drum with large diameter", and dynamically adjust drum parameters or operation methods based on actual compaction results (e.g., detecting insufficient edge compaction).
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