Effective oscillation, no damaging vibrations.

The forecourt of the church was undergoing a complete redesign. Initially, a vibrating plate had been used for compaction, but its vibrations had caused cracks in the elaborately painted barrel vault of the church interior. The operation was stopped to prevent further cracking of the vault’s ceiling, and investigations were carried out to determine the detrimental effect that different types of compaction equipment – required for the construction work in front of the church – would have on the centuries-old building.

To do that, sensors were installed at the foundations and in the vault. The vibrations inside the church were then measured during trials performed with oscillating and vibrating rollers, and with manual vibrating equipment. A single-drum compactor type 3307 VIO from Hamm was also used as part of the trials, working with high-frequency oscillation. The vibratory roller and manual vibrating equipment produced considerable vibrations of similar intensity both in the foundations and in the vault ceiling.

The measured results clearly indicated that oscillation was the only compaction technology suitable for this operation. Oscillation produces less damaging vibrations in the subgrade, while the compaction performance in oscillating mode is much higher than with static rollers. The principal feature of oscillation is that horizontal shear forces are applied to the material to be compacted, as opposed to the vertical forces applied by vibratory compaction systems. In view of that, the soil in the church forecourt was compacted by a single-drum compactor 3307 VIO from Hamm working in oscillating mode.

Because oscillation is a gentle, yet highly effective compaction method, it has today become a standard compaction method in old town centres or in the vicinity of sensitive buildings.