✍ Scribed by C.F. Moon
No coin nor oath required. For personal study only.
There appears to be a certain body of evidence in support of the approach to the quickclay failure mechanism postulated by . Experimental work performed in the past shows that aqueous mixtures of very fine quartz particles of the order of 2pm diameter exhibit unusual rheological properties (e.g. .
Simple tests carried out by myself show that such a material having a water content of about 35% exhibits a phenomenon termed shear-rate blockage which is probably best described as a type of "super-dilatancy". The shear strength of this material is totally dependent upon the rate of shear to which it is subjected. In the undisturbed state, the material has a reasonable stability, however, a gentle deformation (especially gentle vibration) causes it to take up a fluid consistency which flows quite easily. A rapid deformation on the other hand, causes the strength to drastically increase and in fact the material behaves as a brittle solid under these conditions. It appears that the fluid--solid transition is abrupt and occurs at a well-defined threshold level of shear rate. This effect is shown purely diagrammatically in Fig. . If the shearing is stopped the material immediately reverts to its initial condition.
It is of interest to note that Pryce-Jones (1948) observed a similar effect with a starch--water mixture.
This liquefaction of an otherwise solid material at a low shear rate compares favourably with the observations of quickclay phenomena cited by Cabrera and SmaUey. If this then is correct, it seems that many workers (e.g. Ackermann, 1948) have focussed their attention on the wrong rheologicat property, i.e., thixotropy which can be regarded as the antithesis of dilatancy. However, it should be borne in mind that as certain authorities have observed, the addition of a small amount of true clay material to a dilatant soil may induce thixotropic properties . So here, the matter becomes somewhat: enigmatic.
An interesting fact arises concerning the shape of the quartz particles which the authors suggest are plate-shaped. in experiments with fine quartz powder (1--15~m diameter) also suggest this:
"Concentrated suspensions of this fine quartz powder in water or aqueous solutions show, when stirred, streaks of a silky lustre, a sign that the particles
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