Was Epoxy Used Appropriate for Loads

If production was rushed there are many things that could go wrong with the epoxy. It would be interesting to find out which crews installed which parts, using which lot numbers of epoxy precursors, along with when the epoxy resins were processed. Perhaps more care was taken with the processes in the big tunnels than the less important ones-- or perhaps different teams of workers followed directions better than others and worked on different tunnels. Perhaps the care measuring the epoxy hardener and resin were not so exacting, or the materials were tainted with moisture or the handling techniques for the resin and hardener could have allowed for some premature interaction within a storage vessel curing. Tricks to speed up or slow down the polymer reactions could also have sacrificed the integrity of the resulting material. Dissimilar coefficient of expansion (metal bolt versus epoxy) could have applied extra forces that took advantage of the material’s nature to creep. Now we come to the expected operating temperature range… Under ground and under water, the major tunnels might have more stable temperature ranges than an entrance ramp that faces the sun in July – note that the picture posted in the DN article shows sunlight streaming in the entrance. I am suggesting that due to being well above the Glass Transition Temperature of the epoxy, there was more creep (and it happened faster) than was expected. This is could be reminiscent of the Space Shuttle O-ring disaster. On another note I wonder why a lighter fire-proof material was not used instead of concrete. These slabs I thought were basically making a return duct for vehicle exhaust gasses.