Location

Arlington, Virginia

Session Start Date

8-11-2008

Session End Date

8-16-2008

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

Appears In

International Conference on Case Histories in Geotechnical Engineering

Meeting Name

Sixth Conference

Publisher

Missouri University of Science and Technology

Publication Date

8-11-2008

Document Version

Final Version

Rights

© 2008 Missouri University of Science and Technology, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

Share

 
COinS
 
Aug 11th, 12:00 AM Aug 16th, 12:00 AM

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.