Pile Design Philosophies for Coralline and Weak Carbonate Rocks-PPT Presentation

PPT Presentation

Pdf Summary

The paper examines pile design in coralline deposits—carbonate-rich sands and weak limestone or calcarenite—and explains why conventional methods developed for siliceous sands can produce unsafe capacity estimates.<br /><br />Coralline sediments are often porous, weakly cemented, crushable and highly variable. They may contract during shearing, lose friction angle as confining pressure rises, and contain karstic cavities, solution channels, pinnacles and irregular rock profiles. During pile installation, particle crushing, cementation-related arching and inadequate lateral stress can weaken pile–soil interaction and reduce shaft resistance. For driven piles, full end resistance may also require displacements greater than typical service limits.<br /><br />The authors recommend assessing coralline materials separately from ordinary sands and applying cautious, evidence-based design parameters. For bored piles, they discuss estimating frictional properties from relative density while allowing for carbonate effects; evaluating stiffness using in-situ measurements or rock-mass correlations; and assigning conservative shaft and base resistance. Suspected cavities should be mapped and treated as providing no side shear. Where voids could undermine end bearing, increasing pile length is preferred to relying on base resistance or base grouting.<br /><br />The paper also highlights uncertainty in limiting shaft friction: published pile-test results show substantial variation, and assumptions based on conventional practice may be unconservative. Cyclic loading can further degrade shaft capacity through pore-pressure increases, grain rearrangement and bond damage, though the extent of this effect remains uncertain.<br /><br />The authors conclude that dedicated geotechnical investigation and instrumented pile load testing are essential. Design based on siliceous-sand principles alone is inadequate; particular caution is needed when relying on end bearing in carbonate rock because undetected cavities can compromise foundation performance.

Keywords

pile design

coralline deposits

carbonate sands

calcarenite

pile capacity

shaft resistance

end bearing

geotechnical investigation

karstic cavities

pile load testing