Stability of Upper Geotextile Tube in a Stacked Formation Under Wave Loading

The geotextile tubes find wide range of applications in coastal protection structures in the form of submerged breakwaters, artificial reefs and the core of sea walls and groins. These tubes are generally arranged in a stacked manner to achieve the required height as per the design requirements of the coastal protection structure. The upper geotextile tube in the stacked section is subjected to the maximum wave load in submerged breakwaters or reefs. Various parameters affect its stability, such as the wave load, percentage of fill in the tubes, which determines the weight and the shape, frictional interaction between the upper and lower tubes, the slope of the sea bed, gap between the supporting tubes, etc. In this study, laboratory model pullout tests are carried out on geotextile bags to understand the influence of each of these parameters on the stability under lateral loads. The test configuration has considered two bags at the lower level, with a single bag placed centrally above the two in the upper level. Woven and nonwoven geotextile bags are used in the study under submerged and moist conditions. The results show that the stability of the upper tube is higher in the case of nonwoven geotextile tubes compared to the tubes made of woven fabric. The resistance to lateral load is directly proportional to the friction between the surfaces, the gap between the lower tubes and the percentage of fill. The combined influence of these parameters is discussed in this paper. Based on the results of the investigation, empirical relations are developed to estimate the lateral loads.