Reason for Saturation Investigation

For saturating sand in centrifuge model tests, several saturation techniques are available. One of the most widely employed method is the vacuum method. One commonly arising issue with this method is the time it takes for saturation. The rate of saturation is highly variable and a solution to this problem was in need to be found.

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Picture of Bubble in Trough

Surface Tension Issues

Surface tension also causes problems in the tubing of the saturation procedure. It was noted during empirically controlled saturation's that air bubbles would become stuck in the top portion of the tubing in the connector tube interface between the saturation trough and the tubes leading to the base of the model. One solution to this problem is to replace the tubing with ones with a bigger diameter and less wall (shear) friction. Another remediation for this issue is to use Dish Soap in the saturation solution.

Air Interface Issues

Another problem found in the saturation process is the entrapment of air in the Monterrey sand by its interface with the finer Nevada sand. This reduces the surface area that the water may flow through the Monterrey sand into the Nevada sand. Sample Ventilation proved effective in empirical saturation tests.

Air is Trapped in the Coarse Monterrey Sand

Aquarium Grade Monterrey Sand and Its Effectiveness

Through empirical investigations, it is apparent that Aquarium Grade Monterrey sand impeded the saturation process more than it helped it. It was noted that more air was trapped in the Aquarium Grade Monterrey sand because it has much larger pores and smaller capillary tension than that of the #0-30 (finer than aquarium grade) Monterrey Sand. As stated above, those air pockets inhibit the saturation process. The Aquarium Grade Monterrey sand's original use was to prevent the finer Monterrey sand from entering the saturation tubes through the geotextile filter. The geotextile prevents the finer Monterrey sand from entering and clogging the saturation tube, thus there is no need for the Aquarium Grade Monterrey sand to act as a filter.

Recommendations

Increase Saturation tube diameter size.

Insert ventilation tubes in the top portion of the interface between different soil.

Discontinue use of the Aquarium Grade Monterrey Sand, instead using the finer #0-30 Monterrey sand to surround the geotextile filter.

Use Dish Soap as a solute in the solvent that is saturating the sample.

Back to Saturation Procedure

Tests and Results by David Dickey, 2009