Self-boring pressuremeter permeability measurements in Bothkennar clay

Ratnam, S.; Soga, K; Mair, RJ; Whittle, R. W.

doi:10.1680/geot.2002.52.1.55

Cited by 5 publications

(3 citation statements)

References 6 publications

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“…Such soils might possess bonding that would provide sufficient strength at low effective stresses to inhibit cavity degradation. In experiments complementing those described in this paper, no evidence of cavity degradation was found in specimens of a natural stiff clay (Hird & Srisakthivel, 2004), and, for a natural soft clay, Ratnam et al (2002) reported evidence of sustained cavity integrity in field tests at Bothkennar. Nevertheless, the present research casts some doubt over whether cavities in field tests on soft or firm clays maintain their integrity.…”

Section: Discussionsupporting

confidence: 70%

“…1. The self-boring mechanism employed was very similar to that of the Cambridge self-boring pressuremeter used by Ratnam et al (2000Ratnam et al ( , 2002. A 35 mm diameter tube, with an internally tapered lower end, served as a casing and was pushed into the soil by a motorised driving system.…”

Section: Self-boring Devicementioning

confidence: 99%

“…On the other hand, plausible measurements appear to have been made using unsupported cavities in soft clays, as well as in stiff ones (e.g. Ratnam et al, 2000Ratnam et al, , 2002.…”

Section: Introductionmentioning

confidence: 99%

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Laboratory investigation of permeability measurement in clay using outflow from unsupported cavities

Hird¹,

Srisakthivel²

2005

Géotechnique

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Specimens of reconstituted clay were contained under vertical pressure in a 250 mm diameter cylindrical test cell fitted with a peripheral drain. Using a self-boring device, a 35 mm diameter cavity was formed in the centre of each specimen, and outflow permeability tests were performed to simulate possible in situ test procedures. Either the cavity extended over the whole specimen height and radial flow conditions prevailed, or the cavity was shorter and a steel lining was progressively withdrawn to induce both vertical and radial flow. Generally, the cavities were observed to degrade and partially fill with softened material, yet the measured permeabilities were higher than expected on the basis of other information. Pore water pressure measurements suggested that hydraulic fracturing was taking place around the cavities, even though applied pressure heads were very small. Fractured material is then thought to have fallen into the cavities. In specimens containing silt layers, the cavities did not degrade so much, and more satisfactory permeability measurements proved possible. The results suggest that the assumption of a stable cavity, necessarily made when interpreting some in situ tests, may not be justified.

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Section: Discussionsupporting

confidence: 70%

Section: Self-boring Devicementioning

confidence: 99%