Centrifuge modelling of discrete pile rows to stabilise slopes

Yoon, Boung Shik (2008) Centrifuge modelling of discrete pile rows to stabilise slopes. PhD thesis, University of Nottingham.

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Abstract

Discrete pile rows are widely used for improving the stability of potentially unstable slopes, where columns of reinforced concrete are constructed in the ground to reinforce it and inhibit instability. The method becomes more cost effective with wider pile spacings, but simultaneously there is also increasing risk that the soil will flow through the gap between adjacent piles, rather than arching across it. The impact of pile spacing along the row, which is likely to have a significant effect on stability, is not clearly understood from a current design perspective. In this study the effects of pile spacing on passive interaction with the slope are investigated using a series of geotechnical centrifuge model tests which are interpreted with a proposed theoretical framework.

A total of 23 geotechnical centrifuge model tests were successfully carried out (Chapters 3 and 4):

• A plane strain model slope was subjected to up to 50 g centrifugal acceleration, with the upper layer of the slope tending to fail on an underlying predefined surface. The model piles were instrumented to measure bending moment, and hence the shear force and pressure on the piles resulting from interaction with the unstable layer were deduced using a curve-fitting technique. Cameras ‘on-board’ the centrifuge model allowed in-flight photogrammetry to be used to determine soil or pile displacement.

• Pile spacing (s/d) was varied, which determined limiting pile-soil interaction for the row, and variation of other geometrical parameters (l/h) for the slope controlled the total load on the pile row.

• A number of mechanisms of behaviour for the reinforced slope were identified ranging from a successfully stabilised slope to shallow and deeper slips passing through the pile row, as well as slips which occurred upslope of the pile row and thus did not interact with it.

A theoretical framework was developed and used to interpret the results (Chapter 5):

• The centrifuge model test results have been successfully interpreted using the proposed analytical approach.

• The centrifuge test results confirm previous numerical modelling results, and hence a simple theory which can be used for calculation of the maximum stabilising force available from interaction of the pile row with the slope.

The work presented here also confirmed that another previous theoretical model, although quite widely used, is somewhat flawed. Comparison with a field study where stabilisation has been successful (to date) indicated consistency with the experimental results and associated interpretation.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Ellis, E.A.
Yu, H-S.
Keywords: Soil stabilization, Piling, Pile spacing,
Subjects: T Technology > TA Engineering (General). Civil engineering (General) > TA 703 Engineering geology. Rock and soil mechanics
Faculties/Schools: UK Campuses > Faculty of Engineering > Department of Civil Engineering
Item ID: 28510
Depositing User: Blore, Mrs Kathryn
Date Deposited: 09 Mar 2015 13:25
Last Modified: 13 Sep 2016 23:26
URI: http://eprints.nottingham.ac.uk/id/eprint/28510

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