Monday, December 31, 2012

Augered Piles - Characteristics.

The augered pile is usually constructed by screwing a rotary auger into the ground. The material is either augered out in a similar manner to that of a carpenter’s bit and the open hole filled with concrete or alternatively an auger with a hole down its centre is used and a cement grout injected under pressure down the hole during withdrawal of the auger. Early problems experienced with voids left by rapid withdrawal of the auger before properly filling the pile shaft have now been overcome by the use of computer controlled rigs which monitor concrete pressure and give a continuous readout for quality control purposes. Augers can be used to drill large-diameter holes in a wide range of soils, the range having been extended by the use of  bentonite slurry to assist the support of the sides of the hole in soft silts and clays. In addition, the large-diameter auger can be used with under-reaming tools to enlarge the end bearing base of the pile (see Fig. 9.37).

Probably one of the most successful auger methods is the use of the hollow tube auger in soft silt, etc., where
water and squeezing of soft silts in the surrounding ground can cause necking problems for many other systems, i.e. squeezing in of the pile shaft due to side pressure. The use of the hollow auger and injected sand cement grout can produce good-quality piles in these soft and difficult conditions at competitive prices, particularly where large numbers of piles are involved. For small numbers of piles the on-site cost of the rig and grouting plant can prove to be prohibitively expensive.

Fig. 9.37 Under-reamed augered pile.

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