Pile Driving

Piles are generally driven through means of a pile driver, basic elements of that are a hammer and a frame. The frame or trestle is commonly of steel and has a pair of vertical guides, called as leaders inside that the hammer is held. Mobile units are also available and are convenient while a large number of piles are to be driven.

The hammer could be an easy drop hammer or more capable steam, air, diesel or hydraulic hammers. It the fall of hammer is because of gravity alone, it is called as single acting. If pressure is applied through steam etc., it is called as double acting.

Drop hammers weigh from 1000 to 5000 kg and fall by a distance of about 1 meter. As a rough rule, the weight of a drop or single acting hammer could be the similar as the weight of the pile. For heavy piles, this would not be probable but for proper driving the hammer shall weigh not less than a third of the weight of the pile. A cast steel helmet is placed over the top of the concrete pile along with a resilient dolly on top to avoid the pile head from shattering under the impact of the hammer blow.

The resistance to pile driving is expressed within terms of number of blows per inch of penetration. Resistance of 6 to 8 blows per inch is particular for concrete piles.

If piles have to be driven by dense layers, jetting around the pile is resorted to within order to loosen the soil and ease penetration. If piling is planned to be completed through jetting, it is preferable to insert an M.S. pipe of 50 to 75 mm in diameter at the centre of the pile although casting.

In saturated plastic clays, displacement of soil on account of driving of pile might cause heaving of adjacent area or within such cases piles could be placed in holes made by augering.