The article is long, but well worth the read. It gives a great explanation of what’s seen in the video, altho if the video had been available back in 1989, it may have altered a number of the details. I believe the author speculated that the final top filling would have been done by the CNR railway, while the video shows the narrow gauge dinkies going right on top, between the standard gauge tracks.

There is an Appendix A that is a contemporary description of the considerations used when filling large trestles. EG manually spreading the earth on the side slopes so that it’s beyond the natural angle of repose, filling evenly along the length of the structure so that undue lateral force isn’t exerted on individual bents, and armouring them so that they aren’t damaged if there’s rocks in the fill.

Interesting stuff, and thanks for posting this. Would be fun to model.

Cheers, but still not a modeller,
Ralph