A STUDY ON BEARING CAPACITY OF WAVEFORM MICROPILES USING CENTRIFUGE TEST-Paper

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The study evaluated the axial bearing capacity of waveform micropiles, which use enlarged, pitched shear keys along the shaft to improve resistance. Six approximately 1:40-scale pile models were tested in a geotechnical centrifuge in silica sand: a conventional micropile, a jet-grouted pile without shear keys, a waveform pile with multiple keys, and three piles with a single key at different depths.<br /><br />Load–settlement results showed that enlarging the pile body increased resistance, and adding a shear key further improved performance. Compared with the conventional micropile, piles with shear keys achieved at least a 33% increase in estimated capacity. Single-key performance varied with key location; a key near the middle of the shaft provided less improvement than keys at other depths. The multiple-key pile did not consistently outperform the best single-key models.<br /><br />Capacity comparisons depended substantially on the settlement criterion used to define failure. Using a settlement of 25.4 mm, the waveform micropile’s estimated capacity was about 7% higher than that of the jet-grouted pile. Using a settlement equal to 10% of pile diameter, the estimated increase ranged from about 8% to 36%, depending on the diameter assumed for the waveform pile. These differences underscore the need for a more reliable failure criterion for waveform micropiles.<br /><br />Overall, the tests indicate that shear keys can improve micropile bearing capacity, but the benefit depends on key position, pile geometry, surrounding soil conditions, and the method used to estimate ultimate load. The authors recommend further study of failure mechanisms across different key configurations and ground conditions.

Keywords

waveform micropiles

axial bearing capacity

shear keys

geotechnical centrifuge

silica sand

load-settlement behavior

jet-grouted pile

ultimate load

failure criterion

pile model testing