The primary objective of dynamic monitoring with the PDA is to collect supporting data for the development of a wave equation based field acceptance criteria for use by Office of Structure Construction field personnel during the installation of production piles. This acceptance criteria is used in lieu of the pile driving formula contained in Section 49-1.08 of the Standard Specifications. The primary advantage of the wave equation based field acceptance criteria is its site-specific and hammer-specific applicability and treatment of time dependent capacity relationships.
In the wave equation based field acceptance criteria, pile capacity is determined as a function of blow count, hammer stroke, and time. Use of these relationships consists of two components corresponding to two graphs:
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A Capacity Relationship Plot relating blow count and hammer stroke to pile capacity for a specific hammer is developed. PDA data collected during pile installation is analyzed using the Case Pile Wave Analysis Program (CAPWAP) to estimate static axial capacity. If static axial load test data is available, it is also used to refine the capacity estimates. Axial capacities are then correlated to hammer stroke and measured energy using the Wave Equation Analysis Program (GRLWEAP). The output of these analyses is used to generate a plot, as shown in the sample, which may be used to estimate pile capacity based upon a visual observation of hammer stroke and blow count.
An Anticipated Set-Up Plot relating percent of ultimate capacity as a function of time is developed as shown in this sample. The elapse of time from initial driving allows for the dissipation of any excess pore water which may have been generated during the advancement of the pipe pile. The time rate of pore water pressure dissipation is directly related to the time rate of pile frictional capacity increase. This plot is developed from multiple dynamic monitoring events over an extended period of time and static load test data.
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