Bore Pile Stabilization Issues in Offshore Marine Works-Paper

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The paper examines stability challenges in offshore bored piles constructed with a partial steel casing and third-generation polymer drilling fluids. Drawing on more than 500 piles, typically over 2 m in diameter and 50 m deep, it defines acceptable stability as concrete overbreak of 2–15%. Results outside this range may indicate excessive soil collapse or, in the case of underbreak, a potentially serious foundation defect.<br /><br />The authors group the main risks into soil stabilization, project design, work methodology, and operational factors. Polymer fluids support excavation mainly by maintaining positive hydrostatic pressure. Fluid levels can fall as drilling tools are removed, while tides can raise surrounding water levels; either may allow water into the shaft and trigger instability. A watertight seal between casing and suitable ground is also essential, particularly in porous or non-cohesive soils.<br /><br />Design and operating practices can reduce these risks. The casing should extend at least 1.5 m above the highest expected water level, with slurry levels monitored and replenished. Water trapped inside the casing before drilling—potentially saline—must be replaced or conditioned with properly mixed polymer slurry before excavation advances. On barges, careful planning is needed to balance stored fluid and equipment, secure the platform against horizontal movement, and ensure reliable slurry supplies. Vertical barge motion may also cause the drilling tool to disturb shaft walls.<br /><br />The paper concludes that a logical, carefully planned work sequence and close control of fluid pressure, casing installation, barge stability, and material supply can address recurring problems without changing approved construction methods and help keep pile overbreak within the target range.

Keywords

offshore bored piles

stability challenges

partial steel casing

polymer drilling fluids

overbreak

underbreak

soil stabilization

hydrostatic pressure

casing installation

barge stability