Results of an Instrumented Static Loading Test and Its Application to Design Compilation of an International Survey-Article

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The paper analyzes an instrumented static load test on a 25 m-long, 400 mm precast concrete pile in clay and silt, then examines how engineers interpreted the results and applied them to foundation design. An international survey received 52 submissions from 20 countries.

A central finding is that the test-pile strain records were affected by <strong>residual force</strong>—force already present before the test, arising from soil movement and pile installation. This force can distort calculated shaft and toe resistance and make the pile appear to perform differently than it would without residual loading. Only 12 submissions recognized and estimated its presence. The author shows that adjusting for residual force changes the estimated long-term settlement of a single-pile foundation from about 40 mm to about 25 mm.

The site’s planned fill and groundwater lowering were expected to cause approximately 200 mm of ground-surface settlement. This subsidence could produce downdrag on the piles, but the author emphasizes that settlement, rather than the drag force itself, is the principal design concern. Small pile groups may settle more than single piles because their loads also compress soil below the pile toes.

Settlement estimates varied substantially among participants. Most calculated pile-foundation settlements of 10–50 mm, while 11 submissions reported 60–200 mm. Only 20 estimates of ground settlement were close to the textbook value of 200 mm.

The paper concludes that pile-test interpretation and design depend heavily on assumptions, methods, and engineering judgment. Designers should account for residual force, distinguish pile movement during a test from long-term foundation settlement, and coordinate allowable total and differential settlement criteria with structural engineers. The study also highlights the value of better test planning, including appropriate pile-toe placement and reliable measurements.

Keywords

static load test

precast concrete pile

residual force

pile settlement

shaft resistance

toe resistance

downdrag

ground settlement

foundation design

instrumented pile test