Paper presented at Stress Wave Conference 2022. Authors: Ricardo Sánchez Manjón, Luis Alberto Vázquez Mardones, Jon Ruiz Zabaleta, Carlos Fernández Tadeo and Rafael Gil Lablanca.
Two test piles have been installed for the foundations of the future expansion of a shopping center in Spain. The piles were prefabricated of reinforced concrete, installed by driving with a hydraulic hammer. A load testing campaign has been carried out by various methods and on various dates, which has permitted to validate the design of the projected foundation system. Prior to the installation of the piles, a geotechnical survey campaign was carried out, which has provided the necessary parameters for the initial design. The piles were driven into an artificial embankment of variable thickness formed by local clayey and sandy soils, reaching the tertiary substrate of the area, formed by clays with interspersed sandy levels. Dynamic load tests have been carried out on the piles throughout the driving process, at the end of the driving and after several weeks. Static load tests have been carried out several months after the last dynamic tests, delayed due to the interruption of work due to the coronavirus pandemic. The piles were instrumented with embedded strain gauges to be able to measure deformation under load at different depths.
The article analyzes the results of the load tests carried out on the two preliminary piles. On the one hand, the ultimate resistance obtained with the two test methods, static and dynamic, is compared, observing that they reach quite similar values. On the other hand, the evolution of the ultimate resistance is analyzed over the weeks after driving, without any significant increases being observed. However, changes are observed in the resistance distribution between the top and shaft of the pile. At the end of the driving, the resistance at the pile toe mobilized in the dynamic load tests was of the order of 80% of the total resistance, and in the following tests the resistance at the toe decreased to approximately 50% of the total resistance mobilized. The results of the tests carried out do not support a theory that some consultants apply, who combine the toe resistance in the load test at the end of the driving with the shaft resistance obtained in the test carried out a few weeks later, so that the maximum values are added, and the result is better than the total resistance obtained from any individual test.
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