Abstract

Geotextile screens are increasingly being used as a wrapping on a base pipe for the screening of fine aquifer materials. This is due to the ease with which they may be installed and specified. They are a relatively recent development and the hydraulic efficiency associated with their use as abstraction screens has not yet been quantified.

In this study, the efficiency has been tested using a physical well model and a variety of commercially available textiles. The purpose of the programme was to compare the hydraulic efficiency of various geotextile fabrics screening differing aquifer materials. In addition the requirements of the open area of the casing of the screens were also examined. The results of the tests indicate that geotextiles must be matched to aquifer material on the basis of hydraulic efficiency. It is clear that the presence of aquifer particles reduces the permeability of any screen and this is also true in the case of geotextile-wrapped screens. The extent of this reduction varies between geotextiles and appears to be a function of their structure. On the basis of the test results, recommendations may be made for geotextile selection. Geotextile screens appear to be particularly suited to the screening of fine unconsolidated aquifers if the correct fabric is selected. Losses incurred from the screening of other coarser aquifers also appear to be negligible. Too conservative a filter criterion may result in unnecessary well losses. The open area of casing used as part of geotextile screens installed in fine sands may be as low as 300025; without incurring significant losses.

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