Location
Arlington, Virginia
Date
14 Aug 2008, 7:00 pm - 8:30 pm
Abstract
This paper presents details of the installation and axial compressive cyclic load tests performed on the UCD 76mm diameter highly instrumented steel pile at a soft clay test site in Belfast. Lateral stress measurements and pore pressures are obtained through pressure transducers mounted diametrically opposite each other in the pile wall at three levels. The pore pressures during installation are seen to drop off as pile-slip occurs for a given jacking stroke before rising to higher ultimate values, resulting in a brittle load response. Following an equalisation period two cyclic load tests were performed, where the loads were applied from zero up to a prespecified maximum and cycled about these values for a number of cycles, N, before ramping up the load and repeating the process. Cyclic loads at 33% and 66% of the installation resistance generate negligible displacements with the pore pressure and total stresses remaining relatively stable. High level loads at 150% of the installation resistance cause rapid displacement accumulation to occur. The pore pressure behaviour for a given cycle is comparable to that observed during installation as temporary reductions in pore pressure when cyclic loads are applied results in a dynamic capacity resisting cyclic loading which is greater than the static capacity. However positive pore pressure generation results in decreased effective stresses as the pile displaces under the higher loads. A comparison with normalised uncycled fully equalised radial effective stresses indicates degradation in excess of 50%, resulting from the high level cyclic displacements.
Department(s)
Civil, Architectural and Environmental Engineering
Meeting Name
6th Conference of the International Conference on Case Histories in Geotechnical Engineering
Publisher
Missouri University of Science and Technology
Document Version
Final Version
Rights
© 2008 Missouri University of Science and Technology, All rights reserved.
Creative Commons Licensing
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.
Document Type
Article - Conference proceedings
File Type
text
Language
English
Recommended Citation
Doherty, Paul and Gavin, Kenneth, "Degradation of Axial Shaft Capacity of Piles in Soft Clay Due to Cyclic Loading" (2008). International Conference on Case Histories in Geotechnical Engineering. 4.
https://scholarsmine.mst.edu/icchge/6icchge/session09/4
Degradation of Axial Shaft Capacity of Piles in Soft Clay Due to Cyclic Loading
Arlington, Virginia
This paper presents details of the installation and axial compressive cyclic load tests performed on the UCD 76mm diameter highly instrumented steel pile at a soft clay test site in Belfast. Lateral stress measurements and pore pressures are obtained through pressure transducers mounted diametrically opposite each other in the pile wall at three levels. The pore pressures during installation are seen to drop off as pile-slip occurs for a given jacking stroke before rising to higher ultimate values, resulting in a brittle load response. Following an equalisation period two cyclic load tests were performed, where the loads were applied from zero up to a prespecified maximum and cycled about these values for a number of cycles, N, before ramping up the load and repeating the process. Cyclic loads at 33% and 66% of the installation resistance generate negligible displacements with the pore pressure and total stresses remaining relatively stable. High level loads at 150% of the installation resistance cause rapid displacement accumulation to occur. The pore pressure behaviour for a given cycle is comparable to that observed during installation as temporary reductions in pore pressure when cyclic loads are applied results in a dynamic capacity resisting cyclic loading which is greater than the static capacity. However positive pore pressure generation results in decreased effective stresses as the pile displaces under the higher loads. A comparison with normalised uncycled fully equalised radial effective stresses indicates degradation in excess of 50%, resulting from the high level cyclic displacements.
