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Abstract

This research concerns the development of a technique to create sedimented anisotropic clay soil bed suitable for modelling construction events using a geotechnical centrifuge. Geotechnical centrifuge testing has been used to investigate complex geotechnical events; however, natural soil is fundamentally different to a ‘typical’ homogenous clay soil bed. Natural soil contains structure (Mitchel, 1976) which, in part, governs soil behaviour (Leroueil & Vaughan, 1990). Changing key soil parameters, such as strength, and creating anisotropy where soil properties such as permeability vary in the vertical and horizontal directions. Modelling the soil permeability is also essential for modelling long-term soil behaviour (Wongsaroj et al., 2007). Currently no method for creating a sedimented soil bed suitable for centrifuge modelling exists. At the element testing scale sedimenting a dilute soil slurry has been effectively used to recreate a sedimented structure comparable to a naturally occurring sedimented sample (Stallebrass et al., 2007). This research sought to develop a framework to create centrifuge soil beds which include permeability anisotropy and to conduct a small series of centrifuge tunnel tests to assess the influence of different soil beds on the resultant soil behaviour.

A series of 15 centrifuge sedimentation tests (60 sedimentation columns) were completed at 100g to develop a framework where the resultant soil structure and permeability of different sample preparations could be determined. The key findings of the results were as follows:
1. It was possible to sediment a sample on the centrifuge such that it contains a sedimented structure and permeability anisotropy.

2. Anisotropy was dependent on the initial water content and the constituent parts of the slurry.

3. The water content required to develop a sedimented structure can be significantly reduced using a dispersion agent.

Following the development of a framework and the selection of a suitable sample preparation technique the procure was transferred into a centrifuge soil container to create a sedimented soil bed. The soil bed consisted of four sedimented clay layers with a permeability anisotropy of approximately four. A tunnel construction event was then modelled on the centrifuge using both a reconstitutes soil beds and a sedimented soil bed at 100g. The key findings of the results were as follows:

I. The sedimentation procedure was applied to create a soil bed in a centrifuge strongbox.

II. Following tunnel construction, the sedimented soil bed had a higher undrained shear strength yet experienced a larger volume loss than an equivalent homogenous sample.

III. The homogenous soil bed experienced the largest change in pore pressure above the tunnel shoulder whereas in the sedimented soil bed the largest change occurred above the crown coinciding with a more permeable layer.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > T Technology (General) T Technology > TA Engineering (General). Civil engineering (General)
Departments:	School of Science & Technology > Engineering School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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