Use of Reinforced Concrete Drilled Shafts for Landslide Control in Pakistan

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The paper documents the design, installation, and performance assessment of six 54-inch open-ended steel piles supporting the Wiriagar Deep A platform in Berau Bay, Indonesia. The piles were driven about 72.5 m through dense sands, gravels, and stiff to hard clays, near 14 well conductors.<br /><br />Thick gravel layers created uncertainty in predicting pile capacity and drivability because standard methods may not reliably represent gravel density or pile resistance. Geological analysis suggested the deposits were formed in braided-river environments and that large cobbles or boulders were unlikely. Design studies also considered possible impacts from nearby conductors and future drilling. To manage these risks, the conductors were set at least 7 m below the pile tips, the pile tips were strengthened, and a drilling spread was available if driving encountered excessive resistance.<br /><br />All piles and conductors were instrumented during installation. Monitoring supported efficient control of the driving programme and reduced the need for contingency measures. Driving resistance in gravel was generally lower than predicted by accepted methods, particularly during continuous driving; resistance also decreased with penetration, possibly because driving loosened the soil or reduced shaft friction. Most piles behaved as expected as unplugged piles during driving, although partial plugging occurred in one pile.<br /><br />Restrike tests showed capacity increased with time after installation. A 30-day restrike produced a CAPWAP-estimated soil resistance of 48 MN, close to the 47 MN design ultimate axial capacity. The results supported the suitability of the pile design and demonstrate how instrumentation, geological interpretation, and targeted mitigations can manage the uncertainties of driving large piles in gravel.

Keywords

steel piles

pile driving

gravel layers

axial capacity

CAPWAP

instrumentation

geotechnical design

Berau Bay

Wiriagar Deep A platform

restrike tests