Basic Concept
Stabilisations systems are used in areas where rockfall or an accumulation of failed material can not be permitted. This approach uses rock bolts on the face to secure unstable masses of rock in position. The high tensile steel mesh is used to support the rock between the bolt positions.
By strategically placing the rock bolts in low points or depressions on the rock face, the mesh can be secured around outcrops of unstable material. Once a plate has been installed, load can be applied to the plate through torque applied to the nuts on the rock bolt. This process commonly known as pre loading reduces any available strain in the mesh locally around the plate and pulls the netting closer to the rock face. This, in turn, stretches the mesh over the high points. Removing the strain from the rock netting further reduces the space into which any failed material can move. Any failed material remains on the face, acting as a protective layer to the rock surface, preventing further weathering or erosion.
Mesh with low strain characteristics is desirable when forming a stabilisation system. In some instances, the dimension from the high points to the low on the rock face may only be 50-100mm, therefore, tension will not be established in an overly flexible netting formed from mild steel.
The location of rock bolts can be designed as a regular pattern, but the designer should be open to slight changes of position once work begins on site. To maximise the potential for pre-loading the system, bolts should be placed in the lowest points on the rock face in order to make the most of the topography. Due important for the mesh to have uniform properties throughout.
The strength and length of the rock bolts used will depend on the size and density of the unstable mass as well as the geotechnical characteristics of the rock in the stable zone, providing the geotechnical bond for the anchorage. An increase in design load or the presence of a weak rock in which to secure the bolt may result in a requirement for longer or larger diameter bolts.
Rock bolts can be used without a mesh facing. However it is likely that the incorporation of a high tensile steel mesh facing will reduce the number of rock bolts required. Weathered or fragmented rock is difficult to secure with rock bolts alone.
Stabilisation systems offer the ability to retain a rock mass on a slope; therefore, the strength and longevity of the materials used become even more important. These systems are placed under higher loads, and the consequences of failure are often greater compared to drapery solutions.