| GCL (Geosynthetics clay liner) is a new type of composite waterproofing geosythetics, and it has being widely used in many fields. It appeared in USA in the 80th of last century and was introduced to our country more than ten years ago. In recent years, the use of GCL is increasing in many fields. Some of the advantages of it are: (1) the lower coefficient of permeability; (2) more resistance to the effect of wetting/drying and freeze/thaw cycles; (3) excellent in self-healing; (4) easier to repair during and after installation; (5) more resistance to the unequal settlements. Some foreign researchers have been working on this filed, but it is rare in our country.First of all the principals of waterproof characteristic of GCL are discussed. Then the conclusion is drawn that the permeability of GCL is strongly correlated with the applying circumstance (mainly affected by the applied confining pressure), which must be taken into consideration in practical application. Because ASTM D5887 fixes the overburden effective stress, it is only proper to be used in environmental engineering and it has some limitations for other applications. The authors suggest a new kind of testing method and a new device is designed.The experiment was carried out in a project hosted by China Institute of Water Resources and Hydropower Research. According to observed data, the following conclusions can be drawn: (1) the hydration time of GCL will increase with the effective pressure; (2) the permeability coefficient of GCL will increase with the effective pressure as well; (3) the permeability coefficient of GCL will decrease when the hydraulic gradient increases; (4) when GCL is disturbed, it will take a long time before the permeability coefficient could become stable; (5)A new method to measure the thickness of GCL is also suggested.
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