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Donohue, Shane
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Donohue, Shane
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Donohue, Shane
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Now showing 1 - 3 of 3
- PublicationAssessment of Skempton's pore water pressure parameters B and A using a high-capacity tensiometer(ICE Publishing, 2019-10-14)
; ; ; ; Saturation of soils is a prerequisite in many laboratory tests involving consolidation, permeability and stress-strain behaviour. The saturation process is usually time consuming, particularly in clay-rich soils, and this can incur substantial cost and potential delays in reporting findings. The saturation of samples is assessed using the well-established Skempton's pore water pressure parameter B. In a situation where the soil is fully saturated the B-value is approximately one. It is often the case that fine soil samples extracted from the ground, particularly those from below the water table, remain saturated. However, current testing protocols require evidence to verify a complete saturation prior to subsequent laboratory investigations. This paper reports experimental results exploring the hypothesis that, if the sample is ‘perceived’ to be saturated, then further saturation procedures may not be necessary to obtain reliable geotechnical parameters. Laboratory investigations were conducted on three different clays (Kaolin Clay, Belfast Clay and Oxford Clay) in a testing chamber instrumented with a high capacity tensiometer. The confining pressures were applied in a ramped fashion under undrained conditions. The response of the tensiometer confirmed that the samples were saturated from the very beginning of the loading process, as implied by the B-value being close to one. Further supplementary investigations were carried out to assess the Skempton's pore water pressure parameter A and the stress-strain behaviour of the soils. The combined finding provides further evidence to suggest that the saturation process as suggested in standards may not be necessary for fine grained soils to establish reliable geotechnical design parameters.300Scopus© Citations 4 - PublicationEngineering characterisation of Norwegian glaciomarine silt(Elsevier, 2010-02-09)
; ; ; Guidance is provided for geotechnical engineers designing civil engineering works in silty soils based on a detailed characterisation of a glaciomarine silt from Os in western Norway. It was found that these soils are susceptible to disturbance by good quality fixed piston tube sampling and care needs to be taken when using laboratory derived design parameters, particularly for consolidation and shear strength properties. A technique for assessing sample disturbance using shear wave velocity and suction measurements proved promising. Conventional techniques for determining soil strength from triaxial tests in silt are inappropriate due to the dilational nature of the material and more reliable and logical strength estimates can be made from a limiting strain criterion. Field vane data should be used with caution as measured strength, particularly remoulded values, may be high and it seems more reliable parameters can be derived from CPTU tests. One dimensional consolidation and creep of these silts can be modelled successfully by the well-known Janbu formulation. The behaviour of the Os silts does not fit easily into classical soil mechanics and published frameworks for soft soils. It seems the material is of “transitional” type and this work adds to the database of such soils which includes other natural silts and gap graded soils. For future work it is recommended that larger sample tubes (say 75 mm) with a very sharp cutting edge should be used in parallel with in situ CPTU testing.1726Scopus© Citations 20 - PublicationSample disturbances due to removal of confining pressure in laminated clay(ICE Publishing, 2020-08-20)
; ; ; ; Sample disturbances in laminated soils may be caused by several factors including water movement between the clay and sand layers upon removal of overburden pressures. The research reported in this article examines the impact of this water movement on various geotechnical parameters. Samples of kaolin with laminations were formed and subjected to isotropic consolidation and subsequently sheared under undrained conditions. Further tests were carried out in which the samples were isotropically unloaded after consolidation and isotropically reloaded under undrained conditions and this was then followed by undrained shearing. Tests were also carried out to examine the impact of unloading/reloading on the yield stress and small strain stiffness (Gmax). The results have shown that the isotropic unloading/reloading process under undrained conditions leads to reduction in undrained shear strength, small strain stiffness (Gmax) and yield stresses. Comparative tests carried out on unlaminated samples showed that the unloading/reloading process has a marginal impact on the above mentioned geotechnical properties.329Scopus© Citations 1