Proceedings - DFI Specialty Seminar, "Augered Cast-In-Place Piles Seminar- 1998, Houston, TX", (DFI)
Pile Installation Recorder Tests for ACIP/CFA Piles
Garland Likins, George Piscsalko & Chris Cole
The Texas DOT, now considering using Augered Cast-in-Place (ACIP) Piles (also known as Continuous Flight Auger or CFA piles) in their foundations, awarded a research project to Professor Mike O’Neill at the University of Houston (UH) to study the advantages and potential difficulties with ACIP/CFA piles. ACIP/CFA piles were installed on three sites for UH; they had extra instrumentation and additional measurements by UH staff during installation, which are beyond the scope of this paper. Independent visual logging of the pile was done by an experienced inspection firm. The main advantages of ACIP/CFA piles are their speed of installation and their economy. Potential savings are substantial. Disadvantages include an unknown structural condition of the shaft. Inspection is critical, but many simultaneous observations make accurate inspection difficult. Because of resulting uncertainty, many engineers have avoided ACIP/CFA piles in the past. Pile Dynamics Inc. (PDI) developed the Pile Installation Recorder™ (PIR) to monitor ACIP/CFA piles installation. A schematic of the system is shown in Figure 1. The PIR is normally permanently installed so that every pile installed is inspected. These PIR measurements automatically document the augering and grouting processes and result in a graphic display of the grout volume pumped versus auger depth profile. The actual grout installed compared with the theoretical volume of the shaft is called the grout ratio. Ideally, the auger withdrawal rate should be just less than the displayed maximum withdrawal rate which results in the minimum objective grout ratio and optimal economy. If the operator observes a low grout ratio at any depth, the operator can simply redrill and regrout the hole while the grout is still fluid. PIR results are printed for a permanent record. Such inspection provides engineers with assurance that grout volume versus length was adequate, thus alleviating concerns about structural integrity, and allowing the engineer to specify ACIP/CFA piles with confidence. Using a preliminary version PIR, PDI conducted tests on nine augercast piles for UH as part of the UH research project on augercast piles. The PIR included a magnetic flow meter to precisely measure the delivered grout volume, a pressure transducer to measure line pressure, and a depth sensor on the leads to measure auger depth. Several findings clearly demonstrate the potential value of such automated documentation.
|article #276; publication #28 (ACIP-1998)|