| Dynamic measurements are being performed during restriking of steel pile piles along the Bayshore Viaduct in San Francisco, California. These piles were installed as part of a seismic retrofit program. Measurements are being taken by Caltrans staff using the PDA (pile driving analyzer) system. The data were later used in CAPWAP analyses to estimate the axial capacity of the piles at this point in time (i.e., by restriking at various times, the “set-up” of the piles can be monitored). |
This portable computer data acquisition systems acquires time histories from strain gauges and accelerometers attached to a pile during driving or restriking. The hand is holding a strain gauge and accelerometer that will be attached to the pile. The computer will record these instruments and convert the measurements to driving stresses and velocities.
Close up view of the Junta (60,000 foot-pound rating) hammer positioned on a pile. Note that “restriking” means that the pile was already installed to its intended depth some time ago, and that the hammer has been brought back for the sole purpose of “restriking” the pile to obtain these measurements. An accelerometer/strain gauge pair have been bolted to each side of the pile near the ground surface.
Close up view of the accelerometer and strain gauge bolted to the pile on one side. An identical pair of instruments is bolted on the opposite side.
The Junta hammer is now ready for restriking the pile. Only a few hammer blows will be performed while the PDA measurements are obtained. CAPWAP and/or other analyses of the PDA measurements from restriking at various times after installation will enable an estimate of how the pile’s axial capacity changes with time (i.e., set-up).