Hebron Main Shaft Slipforming Completed In Under 4 Weeks
Hebron Offshore Gravity Based Structure
Newfoundland, Canada. The main shaft of the platform was finished on December 22, 2015 and completed in under four weeks. The shaft is 153 ft / 47 m tall and has a base diameter of 115 ft / 35 m. To slipform the variable cross-section, a 200 ton truss system was required to guide the forms as they climbed upwards. The slipform system and construction supervision were supplied by a specialist subcontractor. Slipforming operations continued around the clock to complete this very demanding project in record time and also under severe winter conditions.
The surface finish and concrete color came out exceptionally uniformly, as can be seen in the picture above. Hydraulic jacks were used to raise the form system every few minutes, by a few millimeters at a time. The jacks were attached to special climbing rods which were embedded in the concrete wall. Vertical lasers guided the slipform system as it moved upwards to construct the shaft. The custom-designed truss system that guided the forms transversely was also used as a work platform and storage area for rebar and post-tensioning materials. About 3000 tons of post-tensioning was installed in total in the concrete substructure.
Lower platforms suspended from the truss system were used for concrete finishing work. A third platform below the finishing platform provided a work area for survey activities as part of the geometry control operations. The platforms and flooring had to be re-worked repeatedly as the concrete walls moved within the footprint of the truss system. This made for great logistical challenges as the steady supply of materials to the work point had to be maintained at all times.
Slipform Truss System Being Removed After Completing the Variable Geometry Shaft
