Alternative Title

Paper No. 1.25

Location

St. Louis, Missouri

Session Start Date

3-8-1998

Session End Date

3-15-1998

Abstract

Long-term set-up of piles in non-cohesive soil can roughly be divided into two time-dependent causes: stress relaxation leading to an increase in horizontal stress on the shaft, and soil aging leading to an increase in stiffness and dilatancy of the soil. The present paper describes a field test in which driven concrete piles, instrumented with earth pressure cells on the shaft, were tested dynamically for static pile capacity determination at different times. The objective was to measure tl1c increase in horizontal stress due to stress relaxation and compare it with the set-up evaluated from the dynamic tests. The results show that only a fifth of the long term set-up was due to stress relaxation. Il was concluded that the remaining set-up was due to soil aging and the ruling mechanism was most probably increasing dilatancy with time at the pile-soil interface. The paper provides a discussion of this mechanism in light of the presented results.

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conference on Case Histories in Geotechnical Engineering

Meeting Name

Fourth Conference

Publisher

University of Missouri--Rolla

Publication Date

3-8-1998

Document Version

Final Version

Rights

© 1998 University of Missouri--Rolla, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

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Mar 8th, 12:00 AM Mar 15th, 12:00 AM

Long-term Increase in Shaft Capacity of Driven Piles in Sand

St. Louis, Missouri

Long-term set-up of piles in non-cohesive soil can roughly be divided into two time-dependent causes: stress relaxation leading to an increase in horizontal stress on the shaft, and soil aging leading to an increase in stiffness and dilatancy of the soil. The present paper describes a field test in which driven concrete piles, instrumented with earth pressure cells on the shaft, were tested dynamically for static pile capacity determination at different times. The objective was to measure tl1c increase in horizontal stress due to stress relaxation and compare it with the set-up evaluated from the dynamic tests. The results show that only a fifth of the long term set-up was due to stress relaxation. Il was concluded that the remaining set-up was due to soil aging and the ruling mechanism was most probably increasing dilatancy with time at the pile-soil interface. The paper provides a discussion of this mechanism in light of the presented results.