When a vibratory roller activates its vibration function, the core requirement for the flatness of the working site is "no obvious protrusions, depressions or areas with uneven hardness and softness, and uniform paving of surface loose materials". The purpose is to avoid uneven stress on the vibrating drum, which may cause drum bouncing, inconsistent compaction results, or even damage to the equipment or the compacted layer. The specific requirements and principles are as follows:

Requirements for Surface Paving Flatness

The local height difference of the working surface shall be controlled within 3–5 cm (the specific value can refer to the equipment manual: for large-tonnage rollers, it can be relaxed to 5 cm; for small-tonnage models, it shall be strictly controlled within 3 cm). In addition, loose materials (such as subgrade fillers and asphalt mixtures) shall be evenly paved without local accumulation or missing paving.If there are protrusions, concentrated impact force will be generated when the vibrating drum rolls over them. On the one hand, this will lead to over-compaction and aggregate crushing at the protruding parts; on the other hand, it will cause drum bouncing — the vibrating drum detaches from the ground and then impacts the pavement again, which not only reduces compaction uniformity but also damages the roller's vibration reduction system and bearings.If there are depressions, insufficient stress in the depressed areas will result in inadequate compaction, forming "weak points".

Requirements for the Flatness of the Underlying Compacted Layer

When conducting layered rolling on a compacted layer, the underlying layer must meet the designed compaction degree and have a flat surface without looseness, peeling or wavy undulations. Unevenness of the underlying layer will lead to inconsistent thickness of the upper loose material layer and uneven transmission depth of vibration energy: the thick-material areas will have insufficient compaction, while the thin-material areas are prone to over-compaction.For example, during layered rolling of subgrades, if the surface of the lower layer has wavy undulations, the upper loose layer will form a state of "thicker areas becoming thicker and thinner areas becoming thinner" after paving, and uniform compaction degree cannot be achieved after vibratory compaction.

Supplementary Flatness Requirements for Special Working Conditions

1. Subgrade earthfill/rockfill compactionAfter paving the loose filler, a grader shall be used to level the surface first to ensure consistent loose laying thickness. Local potholes shall be filled with the same type of filler before activating the vibration function. For rockfill subgrades, large rock blocks shall be manually placed flat and stable, and gaps shall be filled with crushed stones to avoid wheel track fluctuations caused by suspended stones during vibration.

2. Asphalt surface course compactionAfter paving, a double-drum roller shall be used for static rolling 1–2 times before the mixture cools down to eliminate paving marks and achieve initial leveling, then the vibration function can be activated for re-compaction. Direct vibratory rolling after paving is strictly prohibited, otherwise, due to the high fluidity of the mixture, shoving and swelling are likely to occur at uneven positions.

Disposal Measures for Substandard Flatness

If the flatness of the working surface fails to meet the requirements, the machine must be stopped for treatment first:

• Local protrusions: Scrape off with a grader or manually remove. The scraped materials shall not be discarded randomly, but should be paved in the depressed areas.

• Local depressions: Fill with the same type of filler with the same moisture content in layers, with each layer thickness ≤ 10 cm. Compact with small-scale tamping equipment before overall paving.

• Areas with uneven hardness and softness (such as "springy soil" with excessively high local moisture content): First carry out drying, replacement filling or lime mixing treatment, and then proceed with paving and rolling after the soil quality becomes uniform.