Degradation is chemistry and it is slow. Mechanical damage is physics and it is episodic, site-specific, and much harder to generalise about.
Puncture, from the inside
A rock bag is filled with angular stone. Every sharp corner bears on the mesh from within, for the whole service life, and the load increases when the unit is lifted and again when it lands.
The method: static puncture, CBR, under ASTM and ISO procedures. A plunger is pushed through a restrained specimen and the resistance measured.
What it governs: tolerance of angular fill rock and irregular bed contact.
What controls it in practice:
- Fill selection. Stone that is durable and reasonably graded, without extreme angularity or slabby pieces that concentrate load on an edge
- Filling method. Dropping fill from height into a bag concentrates impact; controlled filling does not
- Bed contact. A unit landing on a sharp projection is point-loaded from outside as well as inside
The answer bank has a section on fill stone and product construction covering acceptable material.
Abrasion, from bedload
Sediment moving past the installation wears whatever it contacts.
The variable that dominates: how much material the channel actually transports. A sand-bed river in active transport is aggressive. A cobble-bed reach that moves material only in large events is not. Two sites with the same design velocity can be very different here.
Where it concentrates: at the bed, on the upstream face, and anywhere flow is locally accelerated.
What we can say: the mesh is evaluated for tensile, puncture, and tear, and the raschel construction limits how far a started tear runs. See raschel weave explained.
What we cannot say: an abrasion service life. There is no published abrasion figure and no site-transfer function from one to another.
Debris impact
Event-driven and occasionally severe.
Sources: woody debris in floods, ice floes at breakup, and on marine work vessel contact and dropped objects.
Why it matters beyond the damage: debris lodged against a structure changes the hydraulics. A raft against a pier is effectively a much wider pier and it increases the local scour the armor is there to resist. See bridge pier scour.
What limits the consequence: damage staying local. A unit with a hole is a unit with a hole, not an emptied unit and not a run travelling through the fabric.
Ice, where the evidence runs out
Ice does three things: it bonds to units and lifts them as levels rise, it shoves shoreward under wind and thermal expansion, and it abrades everything it moves against.
The honest position: we hold no citable ice-abrasion data.
That is a real gap and it is worth stating in a submittal rather than leaving to be discovered. In a severe ice environment it is the mechanism most likely to govern, and it is the one where our evidence is weakest.
What the answer bank does address is what changes at sites exposed to heavy ice or floating debris, and the practical design responses are covered in ice damage to bank protection: expect losses, design for incremental repair, extend the treatment above the ice band, and prefer a flatter slope where shove is a factor.
Vessel impact at a berth
A distinct case because it is routine rather than accidental.
Berth structures take contact from vessels and from fenders under load, and propeller wash abrades the bed and anything on it. The answer bank covers what happens under vessel impact at a berth.
The practical response is the same one that runs through all of this: individual units, incremental repair, and an inspection regime rather than a assumption of no losses. See scour at marine piles and dolphins.
What this means for a specification
Raise the abrasion regime. Bed material and transport rate are the inputs that matter, and they are site data you have.
Raise ice explicitly if it applies, and expect the honest answer to include a gap.
Raise debris if the catchment delivers it, because it affects both damage and hydraulics.
Expect a maintenance expectation, not a guarantee of none. A supplier claiming a mechanically hostile site produces no losses over decades is telling you something about their claims rather than their product.
Ask for the limitations page. When not to use rock bags exists to be quoted, including in a submittal that is testing us.
Where to go next
- What degrades the mesh fastest for the full ranking
- What failure actually looks like for inspection
- Ice damage to bank protection
- Which test standards apply
- Test data and standards
- The materials hub for the rest