Multi-Source Geotechnical Characterization and Axial Bearing Capacity of Cast-in-Place Bored Piles in Alluvial Soils
Year: 2026
Type: preprint
Abstract: Axial design of bored piles requires combining measurements that sample different soil volumes, strain regimes, and failure processes. This paper compares SPT resistance, CPTU soundings, cross-hole seismic profiles, laboratory strength data, and static compression tests of eight 800 mm diameter bored piles (18.2–22.2 m long) at the Dhi-Qar Combined Cycle Power Plant, southern Iraq. SPT, Vs, and borehole descriptions all identify a common stiffness transition at 13–16 m, with median SPT N rising from 12 to 56 and mean Vs from 217 to 517 m/s. However, the apparent SPT-Vs correlation (pooled r = 0.835) is largely a depth artifact: both variables are strongly depth-dependent, and depth-adjusted descriptive correlations fall to r = 0.45 after linear depth adjustment and r = 0.39 after within-profile demeaning. Because the observations are nested within four profiles, these correlations are descriptive rather than independent inferential tests. Penetration-implied undrained strength is 2.40–4.21 times laboratory strength; known biases explain only about half of this gap. Small-strain stiffness ratios (6,100-6,800) confirm that seismic stiffness cannot substitute for strength parameters. Proof tests at twice service load produced head movements of 2.50–7.53 mm (0.31–0.94% of D), of which 13–70% is elastic pile shortening rather than ground deformation. The eight-pile dataset is too small for reliable resistance-factor calibration. The study's contribution is methodological: multiple sources can agree on stratigraphy while disagreeing on design parameters, and reconciliation requires explicit treatment of spatial support, strain regime, and transformation uncertainty.
Source: Research Square
Language: English
Subfield: Civil and Structural Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7225374547