Construction is not my field, but I have built a lot of stuff to last, and I do know epoxies. Your points about sample collection and field test are spot on.
To me this situation looks like an afterthought. Either it’s a bandaid on another design issue, or somebody decided to dole out some extra steel and concrete contracts.
BTW, one of the biggest factors I’ve seen in epoxy joint durability is thermal cycling. Under a car’s hood these can be extreme and frequent, but in a tunnel are they considered a factor? Is accelerated life testing used in design qualification?
It is used in materials testing before a meterial, connection or item can be relied upon by the designer for use in his design. ASTM standards and other similar standards govern much of design and construction.
Most people don't understand that in commercial construction, unlike much of residential construction, the contractor or the tradesman does not design the element, select the materials or, in most cases, even select the connection method. Such items are handled by professional designers and the contractors just determine "means and methods" to execute what is shown on the documents.
When a lift falls, a trench collapses, a schaffold breaks, a concrete form or false-work breaks or a heat torch cacthes a roof renovation on fire, you can bet on "contractor error." But even if the tradesman or his boss, for cost or ignorance, selected the wrong epoxy, the basic design was stupid in my opinion, and the first cause in any intelligent forensic review.