Anchored high-tensile mesh — how slope stabilization works and what EAD 230025 declares

Two documents, two jobs

EAD 230025-00-0106 was published by EOTA in June 2016 under the title "flexible facing systems for slope stabilization and rock protection". The document states that the product is not covered by a harmonized European standard, which is why the route is a European Technical Assessment (ETA).

How the system works

A mesh woven from high-tensile steel wire (tensile strength 1,770 N/mm² and above) is laid over the face and pressed to it by spike plates on soil nails or rock bolts. The nail rows are staggered by half a spacing, so the largest local mass that can break out between nails is limited to a width a and a length 2b. The mesh collects the driving forces and passes them through the plates into the nails; the nails carry the load into stable ground in tension and shear. The face is stabilized actively — the difference from a drape mesh, which only slows a block on its way to the toe.

Ordinary wire mesh of the same opening and wire diameter carries 45–50 kN/m in the longitudinal direction; high-tensile mesh reaches 150 kN/m. The difference is what allows the force to be transferred to the nails at an economical spacing. Open meshes allow full re-vegetation of the face, usually with an erosion-control mat under or integrated in the mesh — the hydroseeding step in our service list.

Dimensioning

Two failure modes are checked separately: surface-parallel sliding of the weathered layer along the slope, and local instability between the nails. Both are limit-equilibrium checks with partial factors on friction angle, cohesion and unit weight (Eurocode 7 concept); water and seismic load cases are treated as separate cases. Three tested resistances of the mesh enter the calculation:

Deep-seated failure mechanisms are checked with conventional stability analysis; the anchored mesh is a surface measure.

The five quantities the document declares

1. Mesh geometry — roll dimensions, mesh opening, number of openings, connection-clip dimensions.
2. Plate characteristics — dimensions and shape of the plate at the anchor head.
3. Mechanical resistances — four numbers together: longitudinal tensile strength z_k in kN/m, the relative elongation ε in that test in %, slope-parallel resistance Z_R and puncturing resistance D_R, and shear resistance in the nail direction P_R, in kN.
4. Connection strength — capacity at the joint of two rolls, z_c,k, in kN/m.
5. Durability — neutral salt-spray test on wire samples; hours until base-metal corrosion appears on less than 5 % of the surface. Hot-dip galvanized plates are specified separately.

Classes are not design values

The document gives two informative tables. The first groups meshes by puncturing and slope-parallel resistance:

The second groups by elongation: A — 6 % and below, B — 6 to 10 %, C — 10 to 14 %, D — above 14 %. Both tables are informative. The group is not an input to the calculation; the calculation needs the measured numbers. Writing "group 2 mesh" in a specification is the same shortcut as writing "MEL class 5" — it makes the offers incomparable.

Where the anchor layout comes from

The certificate gives the capacity of the mesh, not the anchor layout. Nail spacing, length and diameter come from a separate dimensioning calculation that uses the slope geometry, the ground parameters, the water condition and the seismic coefficient; the certified Z_R, D_R and P_R are its inputs. Without the ETA there is no calculation; without the calculation the ETA means nothing on its own. Both are requested together, and the nails are verified on site — see Anchor and rock bolt pull-out testing on site.

Eight clauses for the specification

1. The system shall be CE-marked with an ETA under EAD 230025-00-0106.
2. Longitudinal tensile strength at least [kN/m]; relative elongation in the same test at most [%].
3. Slope-parallel resistance Z_R at least [kN]; puncturing resistance D_R at least [kN]; shear resistance in the nail direction P_R at least [kN].
4. Connection strength at least [kN/m].
5. Durability: at least [hours] in the salt-spray test until base-metal corrosion reaches 5 % of the surface.
6. Plate type and size as declared for the system; mesh and plates of different manufacturers shall not be mixed.
7. Anchor layout from a project-specific dimensioning report using the certified resistances as inputs.
8. ETA, Declaration of Performance, dimensioning report and installation manual submitted with the offer.