Rotary Piling

Rotary piling is often used in places such as factories and town centres where it is often difficult to have concrete ready to be poured. The advantage of rotary piling is that there can be a gap between the drilling of the holes and the concrete.

Rotary piling is where the piling rig is equipped with a telescopic arm or bar known as a Kelly bar which slides vertically and holds a short length of auger or a digging bucket on the end of it. When the auger or bucket is rotated it excavates the ground. The bar is then retracted, the rig slewed, and the excavated material ejected by spinning the Kelly and tool rapidly.

Depending on the rig piles over 40m deep and up to 2.5m diameter are possible. A reinforcement cage is then placed in the hole and the pile concreted using tremie techniques. This is a very simple method of piling and has a big advantage over CFA, in that the size and depth range is greater and a number of piles can be drilled in advance of concreting. A further advantage of rotary or open hole piling is that with special tools the base of the hole can be reamed out to create a bell shape to increase the bearing area of the pile.

However the disadvantage against CFA is that in the drilling operation the sides of the rotary hole are not supported and in loose conditions could collapse. A steel liner (known as temporary casing) is normally used to maintain the integrity of the hole at the top of the bore, or to the depth of the loose soil but while a liner can be used to support the sides of the hole but it is expensive in terms of time and cost if most of the hole is lined.

This rotary piling technique works well in stiff clay and good ground. At Tritech Pilng and Foundations Ltd. we have constructed numerous rotary jobs in London clays and Glacial clays and recently successfully completed a major rotary pile contract for the mineshaft capping at Manchester's Sports City

Find out more about our Rotary Piling Projects

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