The geotextile tubes find applications in coastal protection structures such as submerged breakwaters, artificial reefs and the core of sea walls and groins. They are made from polymeric materials, are permeable and retain the soil fill. 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, and the gap between the supporting tubes, etc. 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 and a single bag placed centrally above the two lower bags 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. Based on the results of the investigation, empirical relations are developed to estimate the lateral loads.
Numerical model studies were carried out using the FEM package, ABAQUS, to simulate the failure of the upper geotextile tube in a stacked formation under wave loading. The wave loading is applied using the AQUA module. The dimensions and shapes of geotextile tubes used in the numerical analyses were obtained from the results of GeoCops software. The results of the Geocops software matched with the dimensions of the two full-scale geotextile tubes filled on the land as part of the study. The two-dimensional numerical model set up for the scenario is validated using the physical model tests carried out at the Deltares laboratory and reported in the literature. The validated model predicts the wave height at failure for geotextile tubes of various dimensions and filling percentages.
The results of the numerical analyses and laboratory tests will be discussed in this seminar. The study helps in understanding the failure mode under wave loading and the development of robust designs for improving the stability of these structures.