DESIGN OF ROCK SUPPORT SYSTEM FOR SUB-SEA DOCK EXCAVATION

J.BERGH-CHRISTENSEN ¹ and T.K.SANDAKER ²

¹ Nor consult AS, Norway
(jbc@norconsult.no )

² Norconsult AS, Norway
(tks@norconsult.no )

Aker Kv rner has commissioned the construction of a new dock at their naval yard in Egersund on the south-western coast of Norway to the contractor AF Spesialprosjekt.

The new dock will have a length of 100 m, a width of 40 m and an excavated depth of 7 m below mean sea level, with vertical rock walls. The docksides are designed to support very heavy loads (up to 1000 kN/m) from cranes used for assembly of drilling platforms that will be constructed within the dock.

The bedrock at the site is anorthosite, an igneous rock with a high content of feldspar. The rock is jointed, and a geological survey of the area revealed that for all the three sides of the dock, joints with strike parallel to the excavation line and with a dip of 45 70 towards the excavation must be expected, with inherent risk of instability and failure of the dock walls during excavation.

The contractor AF Spesialprosjekt commissioned Norconsult AS to undertake the overall design of the dock, including design of a rock reinforcement system that would ensure the integrity of the dock walls both during excavation and under full load conditions during subsequent operation.

A major restriction was that the reinforcement system had to be installed prior to start of the excavation work and had to be...