Load Testing and Interpretation of Instrumented Augered Cast-in-Place Piles-Article

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The technical note discusses challenges in testing and interpreting instrumented augered cast-in-place (ACIP) piles, which are not fully covered by the general ASTM static compression test standard. Accurate interpretation is important both to assess pile capacity and to distinguish shaft resistance from toe resistance.<br /><br />The author recommends applying load in equal increments with consistent hold times and recording the load at the end of each interval. Readings should be taken directly from the pile. Repeated efforts to maintain a constant top load are unnecessary and can disrupt measurements. Unload-reload cycles should also be avoided because they create nonuniform internal forces and reverse shaft friction in parts of the pile, complicating interpretation of strain-gage and telltale data. Unloading behavior should not generally be used to estimate pile settlement.<br /><br />Strain-gage measurements reflect not only the applied test load but also installation effects, grout curing stresses, and residual load within the pile-soil system. Residual load can significantly affect the inferred axial-load distribution, particularly when testing occurs well after installation. Longer delays may therefore require a correction for residual-load development.<br /><br />The note also emphasizes that ACIP pile stiffness varies with strain. Using a constant modulus derived from grout strength tests may distort the inferred load distribution, often overstating resistance in the upper pile and understating it lower down. Site-specific, strain-dependent modulus values are preferred.<br /><br />Overall, reliable results depend on careful instrumentation, consistent testing procedures, and interpretation that accounts for residual loads and nonlinear pile stiffness.

Keywords

augered cast-in-place piles

ACIP piles

static compression test

pile capacity

shaft resistance

toe resistance

strain gage measurements

residual load

pile stiffness

load distribution