Geotextile tubes hydraulically or mechanically filled with dredged materials have been successfully applied to hydraulic and coastal engineering in recent years (e.g. shore protection structures, sea dikes, groins, jetties, detached breakwaters). This method is becoming popular and has been widely applied in the developed countries of the world. It is economical as well as useful, and enables us to store and isolate contaminated materials obtained from harbour dredging. In this study, a numerical analysis was performed to investigate the behaviour of geotextile tubes in terms of various properties of the material, shape condition and pumping pressure. The computer program GeoCoPS was employed for this analysis. Also, field tests were conducted in order to identify the construction workability of Saemangeum inner dike when the geotextile tube method is applied. In the field tests, geotextile tubes of 62m in length and 4.0m in diameter were used. The field tests found that geotextile tubes, when filled, did not have the same diameter as the unfilled theoretical one, but might reach approximately 55% of the theoretical diameter. At that time, the effective height of a geotextile tube was about 2.2m. The behaviour during and after construction was measured to confirm the construction method and workability, which ended in successful identification. Copyright (c) 2016 John Wiley & Sons, Ltd.