Augered Cast-In-Place (ACIP) piles are the most common form of foundation support for large buildings. Although the installation of ACIP piles is a common practice, it is a complicated operation that requires experience, attention to detail, and a good quality control program to be done correctly.
The installation process consists of using a hollow stem auger (typically 12 to 30 inches in diameter) suspended from a crane to drill down to the pile bearing depth (typically 20 to 120 feet below the ground surface). Grout is then pumped down the hollow center section of the auger while the auger is slowly withdrawn forming a column of grout slurry. A steel reinforcing cage is then lifted by the crane and lowered into the column of grout slurry before it begins to harden. ACIP piles should be installed by an experienced contractor under the supervision of a knowledgeable geotechnical engineer. The greatest concern during ACIP pile installation is the danger of defects such as voids or soil inclusions in the pile shaft occurring during the auger withdrawal and grouting process.
Defects can compromise a pile’s ability to carry its load and result in foundation failure, excessive settlement, or even collapse of the building. To prevent these defects, a “head” of grout must be maintained above the tip of the auger. This is commonly achieved by beginning the pumping of grout prior to beginning the withdrawal of the auger and then strictly controlling the rate of auger withdrawal.The geotechnical engineer should be retained to monitor the installation of all piles. The engineer will ensure a qualified engineering technician is on site during all pile installation and that he maintains accurate records of the drilling time, depth of the drill, grout volume in the hole, that a proper grout head is maintained so that there are no voids, inclusions, or other problems in the pile shafts. Additionally the technician will perform grout strength tests to ensure the mix strength achieves the design strength.
The Florida Building Code requires on piles that the total load exceeds 35 tons that at least one ACIP pile on every project be “load tested” to confirm that the piles can safely support the design load.
The testing and monitoring of the installation of an ACIP pile foundation system is typically paid for by the General Contractor; however owners and developers will sometimes retain these services.
Upon completion of the pile installation and load testing the geotechnical engineer will issue signed and sealed engineering reports documenting the pile installation procedures, the length, diameter, and grout volume of each pile, and the load test procedure, data, and evaluation.
How GFA International can help?
GFA International can provide all these services and many more tests and inspections required by codes and specifications.
Check out our web site at www.teamgfa.com for further information or contact us at
561-347-0070 (South Florida), 239-489-2443 (Southwest Florida),
772-489-9989 (Treasure Coast), or 407-447-9865(Central Florida).
We would be happy to assist on your project.