type piles. These piles are typically used for sites with similar subsurface soil conditions in the San Francisco Bay Area, and are generally considered to be the most cost-effective deep foundation system. However, because of issues with schedule, noise and potential vibrations, we recognized that other deep foundation systems might be favored. Pile Contractor Selection The project team developed a set of criteria to select the piling contractor. These included: • qualifications and experience • ability to play an active role in pile and pile cap design • ability to address issues with noise and vibrations during pile installation • ability to minimize and handle potential spoils caused by foundation installation • ability to meet the aggressive construction schedule (over 3,000 piles in 32 working days) Four pile installation operations circled to be tested. In the first phase, three compression piles, 40, 48 and 56 ft (12.2, 14.3 and 17.1 m) long and one 40 ft (12.2 m) long tension pile were installed at each test site. All of the test piles consisted of 16 in (0.4 m) diameter APGD piles installed using Bauer BG drill rigs to advance the displacement tooling down to the desired tip elevation. The tooling was then 4,500 psi (31,026 kN/m ), and was injected from the tip of the displacement auger. Grout quantity was measured and recorded in real-time using magnetic flow meters to ensure the full theoretical volume of grout was placed for each 2 ft (0.61 m) increment of pile length. Two local concrete batch plants provided the grout and pumped it to the drill rigs. Grout workability and strength were observed by a third-party testing agency. Following the grout, steel reinforcing was placed, including 28 ft (8.5 m) long and 10 in (0.25 m) diameter spiral reinforcing cages and a full-length center bar. During the installation, T&R personnel observed and recorded slowly retracted as fluid grout, with a 28 day unconfined strength of 2 pertinent data, including grouting techniques, spoil accumulation and adequacy of the data collection system. During drilling and grouting, an automated data acquisition system was used. Such data consisted of the ground surface elevation cutoff and tip elevations, torque resistance with depth, grout pressure and grout flow rate. Data were available via wireless tablet computers, which allowed the T&R engineer to evaluate issues regarding installation techniques and consistencies in real time. Berkel subsequently submitted output records to confirm field observations for each pile. The piles were tested 30 days after installation, and the static axial compression and tension tests were performed in general accordance with ASTM D1143 (Procedure A) and ASTM D3689, respectively. The team evaluated the results of the pile load tests, using three ultimate geotechnical failure criteria methods. These included the Davisson Offset Limit Load, the Brinch-Hansen 90% Criterion (Brinch-Hansen 1963) and the Slope and Tangent method (Butler and Hoy 1977). The pile load test results from Phase I indicated that Test Site A performed much better (stronger) than Test Site B. Test Site A, underlain by clay with interbedded sand and gravel layers, also showed significant pile set-up, and the Following bid evaluation, Berkel & Company Contractors, Inc. (Berkel) was selected as the piling contractor and proposed to design and install Auger Pressure Grouted Displacement (APGD) piles for the project, a pile type that fulfilled the criteria. APGD piles are a specialty pile type offered by Berkel that is installed with an auger that displaces penetrated soil laterally as the auger is advanced. Berkel undertook an extensive testing program to demonstrate that its system could support the design loads of 180 kips (800 kN) in axial compression and 150 kips (667 kN) in axial tension per pile. Berkel had to achieve twice these loads as ultimate capacity for its piles to meet building codes. Berkel and T&R selected two test areas. Site A was underlain by clay with interbedded layers of discontinuous sand and gravels. Test Site B was selected as a clayey profile with little to no granular layers. Each included three compression piles and one tension pile (91 kN/m ). Conversely, the pile load testing within Test Site B, (52.7 kN/m ) during Phase I testing. Our assumption was that the soils in Test Site B showed slower post-installation strength gain (i.e., soil set-up) because of the slower dissipation of excess pore pressures generated during pile installation. This slower dissipation in pore pressures was likely due to the lack of sandy layers in Test Area B; resulting in much longer drainage/dissipation paths. Berkel and T&R concluded that Test Site B needed further resulted in an average ultimate skin friction value of 1.1 ksf 2 evaluation and a second phase of pile installation and testing was conducted. The second phase consisted of testing six new piles in Test Site B (some of which were 64 ft [19.5m] long), retesting of three piles in Test Site B after a longer set up period, and retesting of one pile in Test Site A. The results from the retest at Site A indicated DEEP FOUNDATIONS • MAY/JUN 2014 • 23 piles showed an average ultimate skin friction value of about 1.9 ksf 2
