The resonant pile driving method used by Dieseko with its PVE RD 260 pile driver is gaining acceptance around the world as a new method to drive piles free of ground-borne vibrations. A high-speed oscillating piston resonates the pile, essentially turning the pile into a spring, to excite the toe of the pile with high accelerations and low amplitude. High acceleration with low amplitude generates high penetration rates but the high-frequency stress waves are quickly dissipated in the soil. Typically, ground-borne vibrations are measured at below 1mm/sec within 1 to 5m of the pile. Dieseko Group says the resonant method can drive a pile next to a glass of wine, without causing a ripple in the wine, something that it has demonstrated on numerous piling sites.
How does it work?
The resonant method uses hydraulic piston-cylinder geometry to generate high-magnitude, high-frequency oscillating force. This is a very different mechanism to the eccentric mass technology used in conventional and variable moment vibrators. The unique valve geometry achieves the high-frequency flow switching necessary to oscillate the hydraulic piston at up to 180Hz (10,800vpm). The valve is controlled electronically to achieve maximum accuracy of the desired frequency.
The volume of hydraulic oil delivered through the valve to the piston (flow rate) determines the amplitude while the hydraulic pressure determines the peak force.
The main advantage of the resonant piston-cylinder method is that it allows the vibration frequency to be tuned to the natural frequency of the pile, which excites the pile like a spring. Exciting the pile like an axial spring allows the storage (build up) and release of vast amounts of energy. In this way, the pile is brought to a high acceleration state that penetrates through the soil.
The challenge is to continuously tune the vibration frequency to the natural frequency of the pile as it is being driven into the ground. A computer algorithm has been developed for the resonant driver which automatically performs this tuning function. Through tuning to the resonant frequency of the pile the maximum driving efficiency and maximum force at the pile tip is achieved.
Resonating-drilling
In the Netherlands, a new application has been tested where a rotary head is added to the resonator. With a soil-displacing drilling technique in combination with the PVE RD 260, anchor piles and so-called RESOpiles (patent pending) can be installed controlled and vibration-free to a great depth. With only a 55t rig and a very small torque, and without water-cement jetting (grouting), RESOpiles of ø0.355/Æ420 x 20.0m were installed quickly. A promising and sustainable new application for sensitive areas where heavy equipment is not allowed.
Several case histories in the Netherlands and Australia have demonstrated the features and benefits of resonant pile installation. For example, an oil storage facility in the Port of Rotterdam to install pipe and sheet pile within an active pumping gallery. While in Den Haag and Driebergen the RD 260 was used to drive anchor piles adjacent to railroads and in Breskens where RESOpiles installed near a water treatment basin. The resonator has proved itself as a new, vibration-free installation technique.
