State of Practice for quality assurance in drilled foundations-Paper

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The paper reviews current quality-control and load-testing practices for large-diameter bored piles, whose construction under slurry makes direct inspection difficult and whose increasing loads demand more reliable verification.<br /><br />Traditional methods have limitations. Low-strain impact testing may miss defects near the pile top or toe, particularly in long, slender piles. Cross-hole sonic logging (CSL) examines only the concrete between access tubes, omitting cover outside the reinforcement cage, and tube debonding can produce misleading indications. Older excavation-profiling methods also provide limited information about pile shape and verticality.<br /><br />The paper describes three complementary technologies. The SHAPE ultrasonic device rapidly measures excavation radius with depth, enabling assessment of bore geometry and verticality before concreting. Thermal Integrity Profiling (TIP) uses heat generated during concrete hydration to evaluate pile integrity, estimate concrete cover and effective radius, and identify reinforcement-cage eccentricity. Bi-directional static load testing (BDSLT) applies load through jacks embedded in the pile, avoiding large external reaction systems and allowing assessment of shaft and toe resistance at high loads.<br /><br />Field examples from German projects demonstrate these methods in practice. SHAPE measurements verified toe expansions on some piles and identified an undersized, misplaced expansion on another; TIP independently supported that finding. TIP also indicated an intact pile with greater-than-planned concrete volume. BDSLT tests on three piles were completed successfully and provided resistance–settlement data for design. Dynamic load tests on 16 piles demonstrated capacities up to 35 MN, while CSL was used as an additional integrity check.<br /><br />The authors conclude that combining modern geometry, thermal-integrity, and load-testing methods provides a more complete and efficient assessment of whether bored piles meet design requirements. These tools are particularly valuable for large, highly loaded foundations, where conventional inspection and top-down load testing may be inadequate, costly, or impractical.

Keywords

bored piles

quality control

load testing

thermal integrity profiling

bi-directional static load testing

cross-hole sonic logging

ultrasonic excavation measurement

pile integrity

foundation verification

large-diameter piles