SCIRT proposed that damaged gabion retaining walls could be refurbished by installing anchors through the existing baskets, secured into the ground behind them. This could provide a cost and time saving because baskets would not need to be removed or replaced and, therefore, significant volumes of excavation and backfill work could be avoided with resulting reduced construction time. In order to establish if this solution was feasible, two test anchors were installed by Rock Control in March 2014 to determine if the process was practical and was an efficient means to refurbish such walls.
The following observations were made:
- Drilling of the anchors was possible and while the mesh at the rear of the basket was awkward to penetrate, it could be done.
- During grouting there was no grout recovery and, therefore, uncertainty regarding the completeness of the grout penetration. This meant all anchors had to be load tested.
- Galvanising and sacrificial steel were the only corrosion-protection measures for self-drilling anchors.
- The testing regime needed consideration because measuring deflection while holding load might prove challenging and required designer testing requirement approval.
- It was suggested that loads for anchor tests be derived for individual or zones of anchors to ensure the load was not excessive. This would require specific load definition, rather than simply applying the largest load for the whole wall and testing all anchors.
- The gabion baskets were damaged by the plate used in testing. Therefore, using a textile layer or other protection under the plate might be advisable. Alternatively, the basket might need to be patch repaired.
- Anchors should be installed in the middle of baskets to allow sufficient space for the pressure plate to span.
In conclusion, both the installation and testing of the trial anchors through gabion baskets were successfully completed. For the future implementation, it was recommended the above lessons be adopted into the design and specification for installing anchors through existing gabion baskets.