The potential clogging and filter performance of selected geotextiles with different soil types under unidirectional flow conditions in sub-soil drainage applications

Abstract

Non-woven and woven geotextiles have long been used as a cost effective solution in different applications such as separation, reinforcement, protection, filtration and drainage. One of the most common use of geotextiles is as filters in sub-soil drainage systems. The main function of a filter is to retain particles of the base soil whilst maintaining a good flow of water through the system. There’s still a lot of uncertainties concerning the long term performance of geotextile filters in filtration and drainage applications. However, there’s a lot of ongoing research to better understand the performance of these products. The purpose of this study is to determine the range of problematic soils in the particle size distribution graph and soil-geotextile compatibility of the different soils with selected geotextiles. In order to achieve the ultimate objective of the study, analysis of the permeability, gradient ratio, coefficient of uniformity and clogging potential of the soil-geotextile systems was achieved through the filtration compatibility test (Long Term Gradient Ratio test) of five different geotextiles against 3 soil types. The soil-geotextile systems were subjected to a maximum waterhead of 1420 mm for a maximum of 1008 hours or until the system has reached equilibrium. The results have shown that soils with high clay/silt fractions tend cause blocking, blinding, and clogging which can close most of the geotextile filter pores. Larger sand/gravel sized particles tend to form a filter bridge that hold back finer soil particles. Sandy gravel with bidim A2 and sandy gravel with bidim A4 were the overall best performers with overall gradient ratios of less than 1 which represents a more open filter. The gradient ratios of the other soil-geotextile combinations were higher than 1 which represents clogging and reduction in permeability. However, no geotextile was completely clogged by the soils.