DEW CONSTRUCTION used its new AB1 telescopic piling leader rig with a 60t resonance-free vibratory hammer to drive sheet piles for an underground car park in the centre of Manchester.
The resonance-free vibratory hammer means pile driving is quieter and causes less vibration, making it particularly suitable for contracts in built-up areas.
Standard vibratory hammers operate at about 50Hz.At the beginning and end of the cycle, the speed of the rotating weights passes through the resonant frequency of the surrounding soil.
The ground resonates, transmitting vibrations to any nearby structures.
In a resonance-free vibrator, the rotating weights are balanced to prevent vibration until the operational speed of the machine is reached - ie above the resonant frequency of the ground.
On the Manchester contract, the AB1 rig installed heavy section sheet piles to 4m depth before a Dew Pilemaster drove them a further 7m.
Monitoring of surrounding buildings and structures was carried out throughout the £144,000 contract to ensure no damage occurred.