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The conventional retention and filtration guideline of geotextile mainly focus on the nonwoven geotextile and granular soil. Based on conventional retention criteria, the fine grain soil is not possible to be retained by the woven geotextile. It implies that excessive piping of fines through the opening of geotextile will take place. Thus, for the fine grain soil to be effectively retained by the woven geotextile, flocculation process, to form a large floc size, with the aid of chemical accelerant or flocculent is critical. This is an essential key to determine the success of the dewatering application of geotextile tube infilling with fine grain soil slurry. This paper presents a conceptual filtration mechanism and modified retention criteria for flocculated-clay to be filteredby woven geotextile and remain throughout the service life. To account for the final size of resulting floc formed from the fine-grain particles, an equivalent diameter “D90,eq” of the resulting floc is introduced. This floc size with “D90,eq” will be able to bridge across the opening of woven geotextile, O90, and form a stablefilter cake that subsequently intercept the migration of fines. The equivalent diameter “D90,eq” of the flocculated-clay particle can be estimated based on the settling velocity from a column settling test. The woven geotextile designed based on this “D90,eq” is found to be able to effectively retain the flocculated-clay in a simulation test called Modified Geotube Dewatering Test (M-GDT) with expulsion of clear supernatant after short period of fines-piping.