Every system has both advantages and disadvantages. In relation to driving energy vibratory pile hammer in pile foundation construction shows its superiority over other conventional pile driver. Dear reader in the very before post we have published different types of pile drivers namely drop hammer, single-acting steam hammer, double-acting steam hammer, diesel hammer including vibratory hammer.
We have all known that when impacts of blows are exerted over pile top, the energy is not transferred to pile directly; this must has a system of medium. For various reason these mediums are used; we are not discussing these in this post. Hopefully in the next post we will discuss about this facts. Dear reader we will leave no stone unturned about pile foundation, any types of foundation operation and problems.
So we were on energy transferring medium; the most common are driving head and cushion blocks. Sometimes both of these are used in combination. These mediums absorb some energy which is considered loss of energy in pile driving.
- Energy dissipation by cushion block
- Energy dissipation by driving head or both (a)and (b)
- Energy dissipation to cope with inertia of pile
- Same from skin resistance
In the last two cases, the inertia and skin resistance that are overcome in one blow are developed again between blows of wide interval. In case of vibratory pile driver, the energy render by the oscillator in closely spaced interval, restricting the development of these energy absorbing mechanism.
Let have little idea about vibratory hammer. In this hammer, the vibration energy is derived by the rotation (rotation about own axis) of eccentric mass. This rotation is done in pair. Two eccentric mass rotated in opposite directions such that only vertical components remain active to force pile to move downward. The horizontal forces are counterbalanced by the opposite motion of mass, driven by electric motor.
With this advantage, some disadvantage cannot be avoided in case of vibratory hammer. This hammer does not supply any information about pile capacity. In case of conventional pile driver/hammer, we can estimate pile capacity by either static energy of drop hammer or static energy and pressure or energy supplied by steam or diesel engine considering energy loss as discussed above (i.e. efficiency of pile hammer). With this disadvantage, vibratory hammer has become popular through whole world.