| Dam safety
Constructing the chute raise Preparation of the rock foundation area was
undertaken. Some sections were too fractured and needed to be removed or treated with rock bolts. The next stage was the installation of 95 passive vertical rock anchors spaced at a nominal spacing of 1.5m along the wall raise footprint, as well as the installation of 15 sub-horizontal anchors. The passive vertical rock anchors were designed
to provide additional shear stability for the wall raise. They comprise 32mm diameter reinforcing bars with a double corrosion protection made of an inner grouting, corrugated polyethylene sheathing extending across the concrete-to-rock interface, and an external grouting.
Sub-horizontal rock anchors connected the chute lining and wall raise to the rock face. They were installed in areas where the rock foundation level extended above the top of the existing chute wall and were constructed on a 1.5m horizontal and 1m vertical grid. Their location was determined on site to avoid interference with the vertical anchors. The anchor installation work was sub-contracted to an independent engineering company, which demonstrated the effectiveness of an A-frame drill rig and the skill of working at heights, as shown in Figure 5. As of November 2023, all anchors were successfully installed on site. Since then, the contractor has been connecting the monolith reinforcement
Above: Figure 3: Installation of Stage 2 temporary access during a 2023 spill event
Below: Figure 4: The cranes operating on the upgraded crane pads while working on the chute raise structure in June 2024
www.waterpowermagazine.com | August 2024 | 23
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