by
dane » Tue Apr 30, 2024 9:27 pm
Unfortunately what they have approved is deeper than existing utilities - and that's not microtrenching, as generally understood by industry. The standard they passed is basically what we'd call a rockwheel process as done in the 1980's by cable companies, cutting typically a 2" to 4" wide slot, 22-26" inches deep. This only works if there are no existing utilities to cut into, because those are buried starting at 18" of depth. Cable companies used these slot cutting methods because they needed to place large 2" conduits, necessary for coaxial backbone and distribution cable.
Microtrenching instead is the placement of much smaller fiber-optic conduits and cables ABOVE existing utilities. Typically the depth is roughly 12" for the cut, though it can be as little as 8" and as much as 14". But critically, it CAN'T be 18+", because that is the depth at which other pre-existing utilities are buried. The 14" maximum, which is the deepest depth our equipment will cut, allows for a four-inch margin - but we prefer to cut to a max of 12" to allow more safety margin from existing utilities.
So, I'm not sure who has been pushing this standard in San Francisco, but we don't believe it's buildable or useful. You'd cut through lots of existing gas and communications lines in any regions with existing underground utilities. I've got a suspicion that it's being advanced by cell backhaul companies, who might actually use it as an alternative to aerial build-out in aerial served regions of the City, where there isn't a cable or telephone line at 18" of depth.
We remain hopeful for actual microtrenching standards in the future in San Francisco, and we will continue to advocate for that outcome.
And if you'd like to see underground deployment in your own town, and if you know City leadership well, ask them if they'll allow microtrenching or not - and if not, why not. Doing so is required by State law, which defines a microtrench as a minimum 12" depth. And the law also allows for shallower placement in some locations, upon mutual consent.
The state standard isn't perfect, but it is buildable and useful for fiber-optic deployment. The standard does allow for deeper placement - the state law allows for up to 26" depth, which could be useful in the limited cases where you're placing very large (typically 1.25") conduits or a large quantity of conduits into a large slot in a region without existing underground utilities.
Details on the state law can be found here:
https://alcl.assembly.ca.gov/sites/alcl ... lez%29.pdf
As to why many cities do not just permit the standard as defined in the law, we're baffled.
