Gradient Ratio Tests on Nonwoven Geotextiles Filtering Clay Under Normal Stresses

Clogging of the soil-geotextile filters in the blind drainage system has become a key issue for the anti-floating safety of underground structures. Since fine-grained soils are more commonly encountered in underground engineering projects such as blind drains, it is necessary to investigate the filtration performance of soil-geotextile filters in clayey soil. For simulating the actual working condition of the soil-geotextile filters subjected to normal stresses in the field, a gradient ratio permeameter device that could apply vertical loads to the soil-geotextile filters was developed in this study. The filtration performance of nonwoven geotextile filtering clay was studied by gradient ratio (GR) tests under different normal stresses. Two types of nonwoven geotextiles with different filtration opening sizes were utilized. Test results showed that the normal stresses and the filtration opening size were two important factors affecting the clogging and permeability of the geotextile filter. The soil-geotextile combinations composed of two geotextiles had the same filtration response to the normal stress. The GR values of the nonwoven geotextile filtering clay increased with the increase in normal stress and the decrease in filtration opening size. The hydraulic conductivity of the entire clay-nonwoven geotextile system decreased with the increase in normal stress. Furthermore, the GR values were tested at no larger than 3, indicating that no unacceptable clogging occurred per the anti-clogging criterion.