A geotextile tube is a type of geocontainer typically filled with sandy slurries and fine-grained dredged sediments. Its performance in strength, dewatering, fine-particle retention, and stacked stability has been studied extensively. However, very little is understood about the shape-deformation behavior of geotextile tubes. In this paper, slurry-settlement, constant head permeability, and seepage-force tests were conducted to determine the geocontainers' geotechnical design parameters. The characteristics of the dredged fill material determined from the slurry-settlement, constant head permeability, and seepage-force tests are presented. Large-scale tests on model geotextile tubes were also conducted. A large-scale apparatus for geotextile tube-filling test simulation is introduced. The apparatus consists of a slurry mixing station, a pumping and delivery station, a geotextile tube-filling station, and a data station. The results of the model tests conducted on a transparent geobag (undrained condition) and a geotextile tube (drained condition) are presented in this paper.