D. Open Stone Asphalt Mattresses

Open Stone Asphalt (OSA) is a robust material consisting of aggregate bound together with asphaltic mastic.

Above water OSA is placed in-situ whilst underwater per-fabricated mattresses are used. The OSA is placed on a geotextile and a reinforcing steel mesh, onto which the lifting hooks are secured.

Mattress thickness is designed to suit the hydraulic design loads.