Dynamic formulae are best suited to coarse grained soils for which the shear strength is independent of rate of loading.

In dynamic formulae, the energy loss due to vibrations, heat and damage to dolly or packaging are not taken into account.

The Engineers News formula as proposed by Wellington and Hiley’s formula given by the original expression of Hiley are the commonly used dynamic formula.

The greater objection to any of the pile driving formulae is the uncertainty about the relationship between the dynamic and static resistance to soil.

The ultimate load carrying capacity, or ultimate bearing resistance or ultimate bearing capacity Q up is defined as the maximum load which can be carried by a pile and at which the pile continues to sink without further increase of load.

For clays, the dynamic formulae are valueless because the skin friction developed in clay during driving is very much less than which occurs after a period of time.

The allowable load Qa is the safe load which the pile can carry safely and is determined on the basis of: i) overall stability of the pile-foundation ii) the permissible settlement iii) ultimate bearing resistance divided by factor of safety.

The load carrying capacity of a pile can be determined by the following methods: i) Penetration tests ii) Dynamic formulae iii) Static formulae iv) Plate load test.

When a pile hammer hits the pile, the total driving energy is equal to the weight of hammer the height of drop or stroke.

A disadvantage of a dynamic formula is that it gives no indication about the reduced bearing future settlement or temporary changes in soil structure.