Effects of soil improvement on the axial load capacity of drilled displacement piles – a CPT based case history analysis
Effects of soil improvement on the axial load capacity of drilled displacement piles – a CPT based case history analysis
Pile installation is known to affect the surrounding soil, its mechanical properties, and consequently its performance under any type of loading. Data from 11 construction sites, where Cone Penetration Tests (CPT) were performed before (CPTPRE) and after (CPTPOST) pile construction, was used to analyze the change in soil resistance surrounding the Drilled Displacement Piles (DDP). Six of the 11 project sites included static axial load tests, allowing for a comparison between axial pile load predictions using CPTPRE data, load test results during field testing, and analytical capacities obtained through CPTPOST data. This paper will first present a comparison of post-installation soil improvement observed at all 11 sites. The improvement ratio was defined as the CPT tip resistance post-installation (qc.post) divided by the pre-installation resistance (qc.pre). Hereafter, the axial load capacity is analytically estimated using soil resistance parameters before and after the pile construction. Results do not differ considerably when using CPT parameters for stratified soil profiles but showed notable analytical improvement (by a factor of 1.4) for cohesionless soils. However, when comparing analytical estimates using CPT-post data to in-situ failure loads observed from axial load tests, the use of post-installation CPT-based soil parameters for design was deemed premature. While field improvement is evident, its benefit is not correctly reflected in the predicted pile performance, primarily attributed to the uncertainty of capacity predictions for these specialty type of foundations. For cohesive sites, the analytical pile capacity estimated with the CPTPOST and the axial load test data did not show a consistent trend.
G. Figueroa Palacios; Anne Lemnitzer
18th European Conference on Soil Mechanics and Geotechnical Engineering (ECSMGE2024)
D - Current and new construction methods
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