Surface support underground and in open pits: systems in which high-tensile steel mesh, rock bolts and shotcrete are designed together. The choice follows the rock mass class and the expected stress and deformation.
The problem
Underground and in open pits the main hazard is not the rock itself but the change in stress distribution after excavation. Stress concentrates around the new surface; if the mass is divided by discontinuities, blocks fall from the roof and the face; if the stress is high and the rock brittle, the surface breaks up and is ejected. What is at risk is the same in both cases: personnel, machinery, haulage routes and continuity of production. A roof fall is not only a safety incident; it means that panel is closed.
Early signs are read on the surface and by sound: new cracks in the roof and the face, bolt plates loading up and sinking in, map cracking in shotcrete, bulging of the mesh, a hollow sound in the roof, fresh shine on discontinuities. In an open pit, a hanging block, material collecting on the berm and a crack along the ramp edge belong to the same family. Recording these signs is the only honest data on whether the support system is adequate.
How we decide
The data we measure and compile: rock mass classification, orientation and spacing of discontinuity sets, size and shape of the opening, cover thickness and stress level, water conditions, expected deformation, rockburst potential, and in open pits bench height, face angle and blasting effects.
| Observation | Criterion | Decision |
|---|---|---|
| Blocky roof, low stress | Block falls occur, deformation limited | Surface support with bolts and mesh |
| High stress, brittle rock | Energy release and ejection risk | Energy-absorbing bolts, high-tensile mesh, dynamic detail |
| Heavily fractured, ravelling mass | The surface does not hold itself | Shotcrete together with mesh, ground support if needed |
| Large deformation expected | A rigid lining cracks | Ductile surface support, deformation allowance |
| Blocky open-pit bench face | Accumulation on the berm increasing | Anchored mesh, local bolting or berm widening |
| Ramps and infrastructure at risk | Material reaches the road | Ditch or flexible barrier: rockfall protection |
The critical distinction is between static and dynamic loading: under static loading the mesh is expected to carry the weight of the block; under dynamic loading it must absorb energy arriving in a short time without passing it on to the bolt head. The mesh, bolt and connection detail to be chosen are different in the two cases.
System family
| System | When suitable | Source |
|---|---|---|
| High-tensile surface support mesh | In drifts and tunnels, including dynamic loading | Geobrugg |
| Mesh installation handler | Unrolling the mesh by machine and pressing it to the roof without entering unsupported ground | Geobrugg |
| High-tensile anchored mesh | On open-pit bench faces | Geobrugg |
| Hexagonal double-twist wire mesh | Drapery under low load | Artusa manufacturing |
| Ring net panel | Local reinforcement and patching | Artusa manufacturing |
| Rock bolt, anchor, shotcrete | Load-bearing component | Artusa installation |
Unlike rockfall barriers, there is no harmonized assessment basis for underground surface support mesh; performance is shown by laboratory and field test reports. The specification should therefore state measurable performance instead of a product name: resistance to puncturing and to tension parallel to the surface, the test set-up, energy absorption. Shotcrete is defined by the EN 14487 and EN 14488 series, coatings by EN ISO 1461.
Installation
Underground, the sequence follows the principle of never entering unsupported ground. As the face advances, scaling and barring down come first, then the mesh is unrolled by machine and pressed against the roof, bolt holes are drilled through the mesh and the plate locks the mesh. Unrolling the mesh by machine shortens the time personnel spend under unsupported ground; that is the real gain.
In an open pit the sequence is the same as in slope work: scaling, setting out, drilling and grouting, laying the mesh, plates and pretensioning. Access to the bench face is by experienced specialists on rope access or with a basket platform; blasting and installation schedules are not allowed to overlap. Checkpoints: bolt hole length and angle, grout or resin record, plate seating and torque, mesh overlap and connection spacing, shotcrete thickness, damage check after blasting.
Acceptance and maintenance
Measured at handover: bolt pull-out test results, as-built bolt plan and spacing measurements, mesh overlap and clip spacing, shotcrete thickness and strength tests, coating class documents, and manufacturer test reports for mesh and bolts. Because corrosion rates can be high in mine conditions, the coating choice and the expected service life must be written in the acceptance file: choosing corrosion protection (Turkish), service life and warranty (Turkish).
Monitored in maintenance: bolt plates sinking in and loading up, tears and bulging in the mesh, cracks and debonding in shotcrete, corrosion, loosening after blasting. Where deformation continues, it is followed by point measurements or a monitoring device.
Frequently asked
- Mesh or shotcrete? On a blocky but sound roof, mesh and bolts may be enough; on a ravelling surface both are needed. The decision comes from the rock mass class and the expected deformation.
- What performance should the specification state? Not a product name, but measurable resistance values and the test method. Examples are in the specifications section (Turkish); the reasoning: writing a brand in the specification (Turkish).
- Ditch or barrier in an open pit? If the berm is wide enough a ditch is economical; if not, a flexible barrier comes in. Comparison: ditch or barrier (Turkish).
System and product pages (Turkish)
Field record
16 projects in this family in our records, 2014–2025: Türkiye, Ghana. Under confidentiality agreements, project and client names are not published.