Influence of test apparatus on the measurement of transmissivity of geosynthetic drains

The transmissivity of geosynthetic drains differs significantly under different test conditions. Test conditions can vary in terms of confining medium, the length of the specimen, and the direction of flow and properties of the fluid. This paper presents the findings on the determination of transmissivity of two prefabricated vertical drains and a geonet obtained using two different test apparatus. The first apparatus, in accordance with ASTM, comprises two stiff platens which press directly against a 300-mm-long specimen placed horizontally between two foam rubber layers. The second apparatus involves the use of compressed air which acts as the confining medium on a specimen enclosed in an elastic membrane. Flow of de-aired water for this setup is vertically upward. This paper seeks to compare objectively the differences in the performance of these two drainage testing apparatus for planar geosynthetic drainage products. A comparative study of the transmissivity of the prefabricated vertical drains and geonet under different test conditions is also presented.