Continuous Flight Auger (CFA) piles were introduced fifty years ago in North America and they are constructed with soil removal and also lateral soil compression that increases pile capacity. The drilling method allows excavation in a wide variety of soils, dry or water-bearing, sandy or cohesive. CFA piles can be used for load transfer beneath structural elements and also for tangent and secant retaining walls and range in diameter between 40 to 120 centimeters, and can have depths up to 25 meters.
The equipment generally consists of a flanged or tubular type leader and of a crawler unit on which the leader is mounted. Drilling is performed with hollow stem augers. The cutting tools has teeth/bits which break up the ground which is then transferred upward on the flights (Archimedes screw). A special plug is used to prevent the soil from entering the augers when the auger string is rotated down. The sides of the hole are supported at all times by the soil-filled auger, eliminating the need for casing or slurry. When the required depth is reached, highly workable concrete is pumped through the string stem by means of a concrete pump and the auger is lifted in a controlled manner. The concrete gradually fills the borehole to the top, and then the reinforcement cage is inserted into the fresh concrete by means of a vibrator.
This cast in-situ process is suitable to soft ground where deep casings or use of drilling support fluids might otherwise be needed. Should problems occur during pile construction, it is relatively simple to re-drill and install the pile at the same location, thereby eliminating the need to redesign the pile group or the pile caps. Concrete mix requirements have to be carefully designed to maintain workability yet avoid segregation and bleeding during placement. It is important to select an experienced company for your CFA piling application as the effect of the construction technique on different ground conditions has to be fully evaluated. Please contact us for more details.
GT GROUND ENGINEERING & CONSTRUCTION SERVICES has constructed thousands of CFA piles of various diameters and depths. Our vast experience enables us to apply this method even to the most difficult soil conditions. Projects involved residential and office buildings, warehouses, port developments, etc. Recent examples include the foundations for office towers 4 and 5 at AFI Park, foundation piles for Hypermarket Auchan, for the support of 8 metallic silos at Constanta Port and many others.