[time-nuts] Re: in-ground clock room

[Graham / KE9H]

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 <jim at luxfamily.com> 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 (tvb at leapsecond.com).
> >
> > Thanks,
> > /tvb
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