DRILLING & DEEP FOUNDATION
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DRILLED SHAFTS
Drilled shafts (also called caissons) are constructed in diameters ranging from 18 inches to 12 feet or more. They provide deep foundations for buildings, bridges and retaining walls as well as stabilizing landslides. Drilled shafts are proven to be a cost-effective, excellent performing, deep foundation system that is utilized worldwide.
Drilled shafts are typically used to support bridges and large structures where large loads and lateral resistance are major factors. The large diameter reinforced concrete member is also capable of providing substantial resistance to lateral and overturning forces. Drilled shafts are commonly used in depths of up to 200 feet in the U.S., but they can extend to depths of 300 feet or more. Reinforced steel cages are placed in the excavated shaft. Then concrete is placed by using a full-length tremie pipe to fill the shaft.
DRILLED DISPLACEMENT PILES (DDP)
Drilled displacement piles (DDP) refers to a specialized technology for creating bored piles. The bored pile is constructed using a process in which a specially designed tool advances into the ground using both rotation and downward thrust (“crowd force”) to displace the in-situ soil radially outward into the surrounding formation. Then, concrete is injected and steel reinforcement (if required) is inserted to fill the newly-created hole and provide structural stiffness.
DDP has been used as structural foundation elements (for example, support column loading) and ground improvement (such as column-supported embankments) in both commercial and public work type projects. The maximum achievable diameter and depth are directly related to the capability of the drill rig used to construct the DDP.
AUGER CAST PILES (CFA)
Auger cast piles are concrete piles drilled with a continuous flight auger to the specified depth, then a high strength cement grout is pumped through the auger shaft as the auger is slowly withdrawn Reinforcing can be installed after the auger has been withdrawn, while the concrete or grout is still fluid to aid in lateral and tension design forces as required. Auger Cast Piles are high in friction and end bearing at a minimum cost.