Shaft Resistance of Piles Driven in Clay: Field Study of an Instrumented Full Scale Pile

This paper presents the results of measurements of total stress against the shaft and base of a mandrel-driven cast-in-situ steel "Multiton" pile 57 m long, 508/457 mm in diameter, installed in NC clay. The pile was instrumented with 8 dilatometer cells (4 pairs at 6 m depth intervals) along the shaft and one dilatometer cell at the pile tip center. The cell measurements (total stresses) were made during installation, subsequent consolidation and test loading to failure. During installation, driving was interrupted at various depths in order to make measurements immediately after stopping driving and, at three different depths, during consolidation of the surrounding soil. The "initial" σh measurements and the subsequent decay curves have been compared to the p0 measurements and the subsequent decay curves against a "standard" dilatometer blade, in order to explore the possibility of using DMT-p0 to get indications of σh against the pile at installation stage and subsequently. The total stress measured by the cell installed at pile tip has been compared to CPT-qc. Two loading tests to failure were performed on the same pile at two different depths. The first loading test was performed with the pile tip in clay at 50 m depth, with the mandrel inside the steel shell, without concrete. The second one was performed with the pile tip in sand at 57 m depth on the pile filled with concrete and instrumented with long base extensometers.