AXIAL CAPACITIES OF DRILLED DISPLACEMENT PILES PREDICTED BY SPT AND CPT BASED METHODS-PPT Presentation

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The study evaluates direct methods based on cone penetration test (CPT) and standard penetration test (SPT) data for predicting the axial load capacity of drilled displacement piles (DDPs). Researchers compiled data from about 45–46 construction projects and more than 100 tested piles, including load tests, pile dimensions, and geotechnical information. Sites were grouped as sand-like, clay-like, or mixed soils.<br /><br />Because measured failure loads depend on how failure is defined, the researchers compared 11 load-test interpretation methods. Van der Veen, Butler and Hoy, and L1–L2 methods most closely matched the in-situ failure loads in the dataset.<br /><br />The study then compared interpreted failure loads with estimates from established CPT- and SPT-based analytical methods. Results varied by soil type. Among CPT methods, Brettmann and NeSmith performed best for sandy soils, while Bustamante and Gianeselli gave the closest estimates for clayey and mixed soils. For SPT methods, O’Neill and Reese showed the best agreement for sandy and mixed soils.<br /><br />The findings highlight that method performance depends on soil conditions and that ground improvement can materially affect pile-capacity estimates. Overall, the database provides evidence for selecting more suitable load-test interpretation and in-situ-test-based prediction methods for DDP design, while underscoring the need to account for soil type and site conditions.

Keywords

drilled displacement piles

axial load capacity

cone penetration test

standard penetration test

load test interpretation

failure load

pile design

soil type

CPT methods

SPT methods