On the possibility of simulating pile set-up in sand by means of centrifuge model testing

On the possibility of simulating pile set-up in sand by means of centrifuge model testing

De Lange, D.A.

Van Tol, A.F. (mentor)
Bakker, K.J. (mentor)
Dijkstra, J. (mentor)
Everts, H.J. (mentor)
Stoevelaar, R. (mentor)

Civil Engineering and Geosciences

Geoscience & Engineering

Geo-engineering

2013-04-23

An increase over time in bearing capacity of displacement piles is often found in the field. This phenomenon is called pile set-up. The increase is predominantly caused by an increase in shaft resistance and is observed even until 1000 days after installation. In the Dutch situation, a proposed tightening of the design standard for pile foundations makes the need to understand this phenomenon relevant. It is thought that pile set-up and group effects can contribute to the bearing capacity of piles and it would be worthwhile to incorporate them into the design standards. Although there are some ideas on the mechanisms that play a role there is no quantitative model to describe this mechanism. From literature the bearing capacity seems to increase linearly with the logarithm of time, however, the results depict a large scatter. It is assumed that a lot of factors influence pile set-up. This thesis depicts the results of a study on the possibility of simulating pile set-up in sand by means of centrifuge model testing. Conditions of this type of physical models can be controlled and makes them very useful for parameter studies. This study presents relevant literature about pile set-up. The presumed mechanisms behind the phenomenon and influencing factors are discussed. Because set-up is only observed for displacement piles, installation effects are also investigated. It is believed that the governing mechanism behind pile set-up is to some extent rearrangement of sand grains. Some literature indicates that long-term set-up is already present minutes and hours after installation. This allows investigating the set-up mechanisms under controlled conditions in a centrifuge. A pilot test is performed with the geotechnical centrifuge of Deltares. Two test series are run to investigate the set-up of a single pile and a group pile until 1000 minutes after installation. Two instrumented piles are tested several times during the run. Special attention is given to the installation and the surface roughness of the piles. Two different installation methods are applied: monotonically jacking and pseudo-driving. From the test results, it cannot be concluded if it is possible to simulate pile set-up in sand, observed in the field, by means of centrifuge model testing. Increases in shaft friction are observed for the jacked pile, as well as the cyclically installed pile. However, it is unlikely that these changes are only due to the factor of time. It is believed that the imposed pile displacements (test boundary conditions) disturb the results to a great extent. Clear influences of the installation of neighbouring piles are observed. It is recommended to perform following tests force-controlled. Perhaps longer lasting tests are needed. It is advisable to vary with soil homogeneity, soil uniformity and pile diameter in further model investigations. All of these parameters can influence the degree of set-up. Future research should also focus on field studies.

pile set-up
centrifuge model test
geotechnical engineering
group effect
bearing capacity
time dependent

http://resolver.tudelft.nl/uuid:f837675a-5b88-478b-abb9-038f2e4416b3

2013-07-09

Student theses

master thesis

(c) 2013 De Lange, D.A.