Sounds like we need a volunteer time-nut with motion picture camera capability to document this event. --- Graham
On Thu, Sep 9, 2021 at 5:17 PM Lux, Jim <[email protected]> wrote: > On 9/8/21 6:54 PM, Tom Van Baak wrote: > > I am considering a below ground "clock room" away from the house. This > > will be for some low-drift quartz oscillators and also a couple of > > precision pendulum clocks. The goal is long-term, unattended, and very > > undisturbed operation. > > > > For scale, assume the room is 1 meter × 1 meter × 2 meters deep. So > > that's vastly smaller than digging a basement, but much larger than > > drilling a 8 inch round pipe. Digging down gives some natural > > isolation and temperature regulation. A couple tons of concrete gives > > high stability vertical walls for the pendulum clocks. > > > > If any of you have personal or professional experience with the design > > or construction of this sort of thing, especially experience with > > precast (utility) vaults or poured concrete, please let me know. > > > A few years back, we were looking at building a "test rubble pile" for > search and rescue applications (actually for testing equipment that > would be used for this). > > For the depths you're talking about (few meters) the easiest approach is > to get someone with a backhoe to dig a pit, then use the backhoe to > carry the precast vault, drop it in, and you're done. If you were going > more than "backhoe depth" you're looking at something like an auger, and > they can drill any diameter (up to about 4 feet) and any depth, as long > as they can get the truck into position (same as the backhoe). > > I went around looking at the precast concrete vendors - they're > available in any size you want. You can also just sink a drain pipe of > any size vertically, and fill the bottom with concrete. The vaults often > come with "knockouts" - places where you can bring conduit in by > knocking out the plug of concrete (it's cast with a thin ring, so you > hit it with a sledge) - the conduit (or duct, or sewer pipe) to vault > seal is done with a variety of goops. Some of the ones I've seen look > like tar (the same stuff used to fix roads, roofs, shower pans), others > use some sort of foam. > > The prices for this stuff are fairly standardized - your local utility > or roads department probably has a "standard bid list" for most of the > more common items that they use for doing estimates. Caltrans certainly > does (a 48" precast concrete manhole is about $1500). So that gives you > a ballpark when you start calling vendors. The big driver for most > people in a "residential" environment would be access. It's one thing > to have a double flatbed show up with a bunch of concrete pipe on it at > a business, totally another on a winding residential street. We had > stuff delivered on a flatbed truck with a small crane - but they could > just pull up to the site, sling the vault, and lower it to the ground, > and then the backhoe guy moved it. Going up a driveway, around the > corner, avoiding the fence, etc. would be different. Or, A *really big* > crane - I've seen that done - 80 or 100 foot boom in the street - they > pick the load up, lift it up and over the house and place it in the back > yard. > > https://precastconcretesales.com/manholes/ > > https://www.columbiaprecastproducts.com/products/precast-manholes/ > > https://www.gardenstateprecast.com/pdf/2019-price-list.pdf > > Google "precast concrete manhole" and select accordingly. > > > > You're looking at the "more than $1000 probably less than $10k" range, > all done in a day, plus a day of prep and a day of cleanup. > > Backhoes (in SoCal) are going for $300-500/day plus the operator > ($50-60/hr).. Or you can learn <grin> - it's hard to do precise work as > a rookie, but digging a hole is pretty easy to learn on your own. And I > just looked it up, the smaller skid-steer bobcat type could probably dig > a 2 meter deep hole, and you're less likely to do major damage like you > can with a full sized unit. > > Home Depot actually rents them.. 2-3 ton miniexcavator is $359/day , > $1005/week > > > https://www.compactpowerrents.com/rental-equipment/mini-excavator/25-3-ton-mini-excavator/ > You might find someone who's usually doing stuff like pools and spas, > and will dig your hole for you. In any case, probably not more than $1000 > > > One other source for design is "storm shelters" - FEMA has published > pre-engineered designs for a variety of inground shelters (often, > installed below a garage) > > > One final thing - even if it's waterproofed, it *will collect water* > either by condensation or seepage. You might need to make your clock > vault have some sort of dehumidifier and/or sump pump. > > > The other alternative is to "build a basement" - dig the hole by hand, > pour a slab, and either pour walls or stack blocks and pour into the > cavities. 1x1x2 meters is sort of doable.. figure standard 8x16" > blocks, so the "hole" is going to be 16+39=55" square - figure 5 ft. > That's big enough to stand in, but there is a significant cave-in > hazard, If you're down 2 meters, and the side collapses on you, you'll > probably die before they can dig you out. Or, your soil is sturdy > enough, you manage the risk. > I don't think you could dig 2 meters down with one of those small bobcat > backhoes or excavators, you'd have to dig a ramp, stack your blocks, > then backfill. > > > > In case this gets too off-topic for time-nuts, off-list email to me is > > fine ([email protected]). > > > > Thanks, > > /tvb > > _______________________________________________ > > time-nuts mailing list -- [email protected] -- To unsubscribe > > send an email to [email protected] > > To unsubscribe, go to and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- [email protected] -- To unsubscribe send > an email to [email protected] > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
