Significance of Gradient Ratio Test for Determining Clogging Potential of Geotextiles

Abstract

This paper presents a comprehensive evaluation and synthesis of the literature on clogging resistance of geotextile. The soils used ranged from sand through silt to fine-grained clay. Fifteen types of geotextile including both woven and nonwoven materials were used. The latter included heat bonded and needle punched versions. The gradient ratio (GR) test was utilized to evaluate clogging characteristics in all the filtration and drainage-related research. The research has been summarized into three areas of focus. The more pronounced the granular nature of a particular soil (sandy soils) the more definitive the GR test results, and the more clearly defined the contrast between clogging and unhindered filtration. For clayey soils, however, it is difficult to identify clogging using the GR test. It is apparent that the design guide of whether to adopt the FHWA-suggested limit of 3 for GR values should be reconsidered. In a case study of vertical drain applications for example, the stable GR values tend to hover around 5. For silty soils, the need for resistance to clogging narrows the range of suitable materials to the point where it is difficult to find an appropriate type of geotextile. Hence, it is suggested that placing a layer of sandy soil between the geotextile'and the weathered mudstone (the selected silty soil) leads to much better system flow rates and better performance in the GR test. All findings indicate that soil type is an important consideration when using the GR test to evaluate the clogging potential of geotextiles.