Bearing Capacity Design of Strength Composite Piles Considering Dominant Failure Modes and Calibrated Adjustment Coefficients

Significant discrepancies persist between the predicted and measured bearing capacities of Strength Composite (SC) piles in engineering practice, largely due to incomplete consideration of dominant failure modes and the absence of scientifically calibrated adjustment coefficients. Existing design specifications treat side and tip resistance inconsistently and often neglect failures induced by insufficient pile material strength, which compromises accuracy and reliability. To address these limitations, this study systematically analyzed static load test data from 159 SC piles across 44 projects. Statistical evaluation revealed clear dependencies between soil type, pile–soil interface performance, and failure mechanisms, from which stratified adjustment coefficients of side resistance and the unified adjustment coefficient of tip resistance were derived. On this basis, a new calculation method for pile capacity was developed that, for the first time, explicitly integrates material strength limitations and interface failure mechanisms into design. Validation against 112 additional test piles confirmed that over 50% of predicted-to-measured ratios approximated 1.0, and 82.1% fell within ±20%. The study proposes a calculation method for SC pile bearing capacity that is broadly applicable, simple in form, and explicitly accounts for dominant failure modes, thereby providing both theoretical rigor and engineering practicality.