Drilled Shafts

Drilled shafts Overview

Drilled shafts and piling covers multiple pile types used in deep foundation construction, all of which require a hole to be bored before setting the pile. Also known as caissons, drilled piles can be formed in a wide variety of ground conditions, ranging from dense, dry strata to softer, water-logged strata. These piles can be used in many types of construction projects, and are especially effective for structures like tall buildings, bridges, and tanks. Drilled piles can withstand compression, tension, or lateral loads.

80 ft. deep drilled shaft

Installing Drilled Shafts

The drilled shaft is formed by using an auger to remove soil. To create a high-capacity pile with sufficient strength, the borehole must extend deep enough into the ground to reach a strong strata layer like a hardpan or rock layer. Depths for drilled piles can reach up to a depth of 50 yards. The diameter and depth of a pile are carefully chosen based on ground conditions and the drilled pile’s usage. Casings or drilling fluid is used to keep the borehole open for softer strata. Steel reinforcement cages are lowered into the hole and concrete is poured into the hole, forming the pile.

 Benefits of drilled shafts

Sound Transit 1 - Drilled Shafts

Drilled piles are excellent in case where the site requires low noise and vibrations, and can withstand heavier loads than prefabricated piles. In addition, the least amount of soil is displaced, eliminating the need for large-scale excavation, soil removal, and subsequent soil backfill. Wider diameter piles can be formed using this technique, which can remove the need for caps over pile groups.

While adaptable to most ground conditions, drilled piles must be constructed carefully, as the environment largely defined how the pile should be constructed. In a soft soil, an incorrectly-formed pile can bulge in places, greatly reducing load capacity. Drilled piles are not recommended for contaminated sites, as the contaminants can corrode the pile over time.