Following a rock fall event at the sewage treatment works above one of the main tanks, CAN were called upon to provide emergency rockfall protection measures to alleviate concern over further rockfall damaging the infrastructure of the plant. The rock fall been stopped by an existing bund and catch fence, but this had filled the bund with debris and destroyed the existing catch fence. Some of the fallen rock had also caught on a ledge above a treatment tank and was sat precariously on the edge.
After inspection by CAN’s Engineer it was decided the rock face was stable enough to work safely below in the short term, and that the greater risk was creating a further rock fall while the fallen debris was dealt with. The decision was made to install a new catch fence below the loose rock on the ledge before making safe the material caught at height – this would act as protection to the treatment works while this was undertaken, and remain in place permanently to provide protection to the works in the long term.
Once the catch fence was in place CAN started work on the main rock face above, repairing the old rock fall netting and bolts that had been damaged during the rock fall. Once the netting was repaired the rock debris on the ledge was re-assessed and a plan was formed to make good. The ledge was a good width and the removal of this amount of rock from site would not have been very cost effective. Instead the rock was re distributed along the ledge using winches to move it into a safe position.
The largest boulders were broken up using expanding grout, and the end of one particular boulder that was overhanging the ledge was removed to change the centre of gravity so that it was in a stable in its position. Further areas to address were identified and in addition to repairing existing netting at height on the face, a further area of loose rock on the upper face was identified. An A-frame drill rig was used to install 20 rock bolts into the face here, which was then secured with 500m2 of TECCO G65/3 high tensile rockfall containment netting.
Duration: 18 weeks
Client: George Leslie Ltd.
Location: Dunoon, Scotland