Rockfall Drapery Mesh Installation on Challenging Slopes
Installations of rockfall drapery systems are never easy; and never the same. Each project has a different set of challenges, with slope conditions and access to the slope as major factors. Hoff Geotechnik was recently appointed to install drapery mesh systems on a tricky slope along a railway line in KwaZulu-Natal Province in the Republic of South Africa. The biggest challenge was access to the top of the slope.
Three spots on the slope were washed away during the heavy rainfall. This caused debris to cover and damage the railway line at the toe of the slope. This also caused train operations to be suspended on this critical railway network.
The installation of the drapery mesh on the washed away slopes would mitigate the risk of rocks and debris falling onto the railway during the ensuing rainy season. Hoff Geotechnik first deployed an expert team of rockfall hazards mitigation engineers and technicians who studied the scope of work, drawings, and installation methods during an intensive training session. The scope of work in brief included establishing anchorage points for rope access, drilling and installation of steel anchor bars, installation of top and bottom steel cable, and connecting the mesh panels to the cables to cover the areas.
The challenge identified from the get-go was access to the slope, as one of the railway lines was functioning which meant that minimal access was possible from the bottom of the slope. The access from the top was also not easy going, as the areas were positioned on a steep slope with dense vegetation. The closest level area to start descending was more than 50 meters upwards on the slope.
The team of rockfall hazards mitigation technicians had to plan and strategize how to safely access and exit the three areas using rope access methods. They had to consider the degree of safety with which they could be able to use heavy tools and equipment while suspended; and the risk of loose materials or equipment falling onto people, and the railway line below. They also had to plan for working near moving trains and railway infrastructure.
In many rockfall installation projects, lifting equipment such as helicopters and cranes are used to transport and place materials, but in this case, all lifting, placing and lowering of heavy mesh rolls, cables, and anchors had to be achieved by a team of four rockfall hazards mitigation technicians and engineers.
After the pre-work planning, risk assessment, and access was completed; the team started with the installation of the simple drapery system. Drilling of the top anchor holes, 3 meters deep; and spaced 1,5 meters apart, started first. After drilling, the steel anchor bars were installed and grouted. The plan was to complete all drilling and anchor installation on the top of all three slopes, before mesh installation commenced. Once the anchors were completed the top cable was installed, and the mesh panels were connected and draped and over the slope areas. After the mesh panels were placed to adhere to the contour of the slope, it was connected using steel links. This all was achieved while the team was suspended on ropes.
The last objective was to install the bottom anchors, which again included drilling deep into the slope face, grouting, and connecting the mesh to the bottom cable. The installation of the simple drapery system was completed in a short timeframe, due to the urgency of the project. Hoff Geotechnik is proud that the project was completed with no safety incidents and according to all quality requirements.
Christian Mynhardt
BTech. Civil
