Artificial reefs constructed of large geotextile sand containers are becoming a more common method of controlling and managing coastlines around the world. As a relatively new approach, many facets of their behaviour, including their response to wave-induced pressures, have not been fully investigated. While many failure modes have been identified, few have actually been extensively studied and many designs are based on principles derived from rubble-mound breakwaters – structures that, while they serve the same purpose, do not necessarily function in the same manner.
There are three recognised failure modes – horizontal translation, rotation and internal sand migration. This thesis aims to investigate possible mechanisms for failure by internal sand migration and to develop a better understanding of how geocontainers respond in a dynamic wave environment. This was achieved by obtaining pressure data from a prototype geocontainer placed on the Narrowneck Artificial Reef on the Gold Coast.
The major conclusions drawn from these theses are: (1) Attenuation of pressure waves within the bag itself is unhindered by the geotextile membrane and is consistent with current theoretical models for wave-induced pressures in a horizontal seabed. (2) There was an insignificant lag of the transmitted pressure wave. (3) Due to the structure’s response to wave-induced pressures, models which assume that the structure is solid with respect to pressures should be used with caution (4) Liquefaction, combined with horizontal differential pressures, provide a mechanism for internal sand migration. (5) To control this internal sand migration, appropriate bag filling and container shape is essential.