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Sheet piling with vibratory hammers
The most suitable application method for sheet pile walls, is determined by a number of issues:
- type and quality of soil (cohesion) on site
- height, depth and weight of the sheet piles
- presence of obstacles in the soil
- onshore or offshore
In general, vibro technology is the most effective, efficient method and therefore best practice to drive steel sheet piles. A vibratory hammer is suitable for driving at limited depth in coarse-grained soils, including gravels and sands. After placing a pile driving frame, the sheet piles are driven by a crane, arig or excavator mounted vibratory hammer.
The vibratory hammer is positioned on top of the sheet pile with clamps. It produces a sine-wave vertical pressure and the energy of the hammer will quickly drive the pile into the soil. The critical frequency is overruled by the stress waves in the sheet pile and the weight of the hammer acts as static loading. Thanks to the strongly reduced critical frequency, there is no risk of deformed sheet piles or missing interlocks.Pressing machines
The technique of pressing (or extracting) a sheet pile wall too, goes without causing any vibrations or disorder for the environment. Pressing is often used for jobs in urban surroundings, close to ancient constructions or at sites that are subject to stringent regulations as to noise and vibrations.
On average, the compression stress of pressing machines varies from 600 to 1500 kN and is supplied by a hydraulic cylinder. Depending what system, single of fourfold sheet piles (not punched) are applied. If soil conditions are heavy, a small amount of water is injected under high pressure (fluidisation).
The pile driving technique is powered by pneumatic or diesel pile drivers of which the dynamic weight is driven by hydraulics. By pulsating load on top of the sheet pile, the critical frequency is being passed and the sheet pile is driven into the soil. This technique is mainly used for the driving of piles and solid caissons, especially in cohesive soils and fine-grained soils including silts and clays. What pile driver to use, is depending on the soil conditon, working depth and strength of the sheet pile wall. For plastic and composed sheet pile walls, there are special pile drivers on the market with less impact pressure in order not to damage the elements. Pile driving can also be done by a conventional drop hammer, with or without steel framework.