A small-scale physical modelling system was developed and employed to investigate the effects of tube sampling. Amorphous silica and an oil blend of matching refractive index were mixed to form a transparent soil. Black glass beads were embedded within the soil body on the vertical central plane. After consolidation in a Perspex box, a glass model sampler was pushed into the transparent soil. Movements within the soil body were recorded using digital photography; these images were later analysed by Particle Image Velocimetry. The centreline strain path (CSP) of the sample during tube penetration was calculated and compared to existing analytical and numerical models’ strain predictions, and some degree of correlation was observed. However, it is shown that the CSP is not constant throughout the sample, but varies with depth below the base of the borehole. It was also noticed that after tube penetration, significant residual extensive strains remain for soil on the centreline of the specimen. Different tube geometries were tested and a correlation was found between strain magnitudes and the Area Ratio, Inside Clearance Ratio and the Outer Cutting Edge Taper Angle. It was also found that samples taken in normally consolidated soils were more heavily disturbed than those in lightly overconsolidated soils. After removal from the soil model, samples were stored for six months and volumetric strains within them, set up by a redistribution of pore fluid pressures, were found to be small, typically less than 1%. Soil at the edge of the sampler wall reduced in volume, while the centre swelled. Specimens were thereafter extruded from the sampling tube and the strain path created by this step was quantified. It was found that extrusion compresses the soil while still inside the tube, with soil closest to the extruder more significantly affected. All of these parts of the sampling process contribute to the overall sample disturbance and can therefore have an effect on the sample’s measured properties.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:632915 |
| Date | January 2014 |
| Creators | Hover, Eyre D. |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/65103/ |
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