Load Testing for Acceptance of Shafts with Questionable Integrity

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The paper presents two bridge projects in which Thermal Integrity Profiling (TIP) identified possible anomalies near the bases of drilled shafts. Pile Integrity Testing (PIT) generally confirmed the indications, but neither method could reliably establish shaft capacity below the detected anomalies. Rather than relying on coring—which was unlikely to characterize defects spanning the full shaft section—the project teams used High-Strain Dynamic Testing (HSDT) to assess the shafts’ axial resistance as installed.<br /><br />In the first case, HSDT showed that a shaft at the rock-bearing forward abutment mobilized 372 kips, exceeding the 254-kip required load, so the shafts were accepted. At the rear abutment, a shaft in dense sand mobilized only 181 kips and moved substantially; additional driven piles were therefore installed to provide the needed capacity. The targeted remediation helped avoid schedule delays.<br /><br />In the second case, TIP and PIT indicated anomalies extending roughly 10 to 20 feet above the shaft bases. HSDT showed that both tested shafts mobilized resistance exceeding their required factored loads, so they were accepted. Their design had not relied on much of the resistance demonstrated by testing.<br /><br />The authors conclude that HSDT can help determine whether shafts with questionable integrity have adequate axial capacity and can guide the extent of remediation. It should be considered alongside installation records and other test results, not used as a stand-alone measure of acceptance. Evaluation must also account for lateral and uplift loads, anomaly location, concrete quality, and long-term durability. HSDT requires specialized equipment and its limitations should be understood before it is specified or accepted.

Keywords

Thermal Integrity Profiling

Pile Integrity Testing

High-Strain Dynamic Testing

drilled shafts

bridge foundations

axial resistance

shaft anomalies

remediation

load capacity

structural integrity