There are clear advantages in the establishment of reliable, direct cone penetration test (CPT) based methods for assessment of the axial capacity of driven piles. These advantages motivated the formation of a joint industry project (JIP) under the management of the Norwegian Geotechnical Institute (NGI), which initially led to the creation of a unified database of high-quality pile load tests in sand and clay. The unified database has the consensus approval of representatives of the profession and personnel in multiple companies from the offshore energy sector. This paper presents a component of the research from the second phase of the JIP, which had the objective of developing a new CPT-based method for driven piles in clay to unify several CPT-based methods that are in use today. First, a rational basis for the CPT-based formulation is described, using trends from instrumented pile tests; the description facilitates an understanding of the approach and illustrates its empirical nature and limitations. The unified database was used to calibrate the formulation and it led to good predictions for an independent database of pile load tests and for measured distributions of shaft friction.

@en

This paper outlines the development of a new ‘Unified’ CPT-based method for estimating the axial capacity of driven piles in sand. The method adapts key features of the four CPT-based methods currently in the API and ISO guidelines. The new method was calibrated with the Unified database of pile load tests developed as part of an earlier joint industry research project (Lehane et al. 2017). Key factors known to influence pile capacity are incorporated in the new Unified method formulation, including (i) the degree of soil displacement (plugging) during installation, (ii) the influence of relative pile tip depth, (iii) sand-pile interface friction angle, (iv) changes in radial stress during loading and (v) the influence of loading direction. It is shown that the new method provides more reliable predictions of the capacities of the pile load tests in the Unified database than any of the existing axial pile capacity design methods in the API and ISO guidelines.@en