Proposed UCS-Based Correlation for Rock-Socket Design of Bored Piles in Abu Dhabi, UAE-Paper

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The study proposes a UCS-based method for preliminary design of bored piles socketed into Abu Dhabi’s weak rocks, where existing design practice may underestimate shaft resistance and lead to unnecessarily long sockets.

The authors analyzed eight instrumented bi-directional static load tests on 750- and 900-mm piles at two Abu Dhabi Island sites. The ground comprised interbedded mudstone and crystalline gypsum. Design UCS values were derived from 995 test results using a cautious statistical estimate. Test loads ranged from 200% to 600% of design loads, but no pile reached geotechnical failure.

Measured unit shaft friction was compared with published UCS correlations. Based on the test data, the authors propose a preliminary correlation of <strong>unit shaft friction = 0.38 × UCS^0.5</strong> (with UCS and friction expressed in MPa). They also identify the Rosenberg and Journeaux correlation as a useful upper bound and Horvath’s correlation as a lower bound. The tests indicate that friction mobilization depends on displacement and distance from the loading cell, with the greatest mobilization generally occurring within about 6 m of the cell, mainly in gypsum.

The proposed correlation may support more economical preliminary socket design in Abu Dhabi and similar geological settings. However, because none of the tests confirmed full ultimate shaft resistance, the authors recommend validating preliminary designs with confirmatory pile load testing.

Keywords

UCS-based design

bored piles

shaft resistance

Abu Dhabi weak rocks

bi-directional static load tests

socketed piles

unit shaft friction

gypsum

mudstone

pile load testing