Log of the Bunker Ranch Observatory

Once we reached ground level, the fortunes of the BRO construction project seemed to turn, and things proceeded much more quickly. What follows here is the result of a 6-day marathon construction session in April/May of 2001.

The plastic was removed from the basement roof, and the footings for the rolloff roof rack were built on top of the basement roof, and the stairwell opening was extended upward to its final height. This last was an adventure; though it was late April, a cold storm had moved in, and it was snowing atop the nearby Chiricahua Mountains (about 10 miles to the west). The wind was blowing so hard that we were seeing flurries from the mountaintop storm. At one point, the builder scooped a trowel full of mortar to lay a block, and the wind blew the mortar off the trowel!

We coated the basement roof with waterproofing, and laid the plastic back down to provide additional water protection. Later, after the mortar had had time to cure, we also waterproofed the stairwell extension and the column footings.

The septic line, water line, and plumbing air vent lines were installed using the piping we'd thoughtfully put in the walls before filling them. We also ran the electric line from the power pole into the basement through a prepunched hole in the block wall.

The basement was then buried, and two holes were dug in the area where the basement access ramp used to be; forms were built in these holes for the two telescope pier footings. The footings were poured and prepared steel plates were embedded in the top; the telescope piers would bolt to these plates.

By now, the concrete trucks were getting used to finding this construction site. Each pier footer involved almost 5-1/2 tons (5,000 kg) of concrete, so it took two trucks. And the steel plates on each footer weighed 300 lb (135 kg) themselves.

That was a tough time. I drove 3 hours back to Tucson at the end of a construction day to pick up a U-Haul trailer. Then it was up early the next day to pick up the rebar cages for the pier footings and haul them down to the observatory. That night, after another day of construction, I drove back to Tucson to pick up the plates (which weren't yet ready the first day; my own fault for poor planning), then left at 3 a. m. to get to BRO at 6 to prepare for the 7 a. m. arrival of the concrete.

At the end of all that work, though, an observatory is still somewhat hard to visualize.

It is now one year since the basement hole was dug, but the long struggle to get the building put up is nearly ended.

After a short search, I found a structural engineer to do some calculations that would size the steel needed to hold up the basement roof. My own quick figuring showed that the concrete roof slab would weigh around 50,000 pounds (23,000 kg), and the weight of the overlying earth would be about 200,000 pounds (90,000 kg).

We'd poured the concrete slab for the basement floor with thick 4-foot-square pads at two positions in the center, and smaller pads at each end, to support 4 steel columns that would hold a center beam. So all of this weight had to be supported by the 4 walls and the center beam.

The roof was built essentially exactly like a small highway bridge, with support at both sides and down the middle, with steel bridge decking laid across the supports to hold the concrete. A 7-inch concrete slab would be poured over that, with rebar supports every 12 inches in both directions.

The center beam was sized to hold all of this weight with supports every 17 feet, though the beam is actually supported every 13 feet.

The structural engineer, unfortunately, lost my first set of drawings, and turned out to have a method of operation where he would never call you, but rather would wait until you called him for a status report. That's how I learned that nothing was happening. So I got him a second set of drawings, and I didn't get results for several weeks after that. The final tally was that it took 4 months to get the figures I needed.

It turned out that the beam would need to be a "12W50" I-beam, which means the web is 12 inches high and the beam weighs 50 pounds per foot (75 kg per meter). The basement required a beam length of 40'-4" (12.3 meters). The beam is about 10 inches (25 cm) wide and the steel is about a half-inch (1-1/4 cm) thick.

So I ordered the steel, had the support columns made, and found a trucking company to haul the I-beam and the 4 steel columns from Tucson to the BRO site. We then used a boom truck to drop the steel beam in place.

After that, we drilled holes in the top of the wall and epoxied some bolts into place. A steel plate was then fastened to the top of the wall using these bolts. The steel bridge decking was laid in and welded to the plate and to the center beam.

After lacing in the rebar, the roof slab was poured. In April of 2001, the basement was finally enclosed. We covered the fresh slab with plastic and waited three weeks for the concrete to cure slowly, for maximum strength.

With the basement walls up, the next step was to fill the walls with concrete. This sounded easy; rent a concrete pump and bring out a couple of loads of concrete, and pump away -- no muss and no fuss. Alas, it was not to be.

First, we punched holes in the walls and inserted short lengths of PVC to preserve openings for water, septic, air vents, and electricity to come in later.

On the appointed day, the pump arrived and the concrete trucks rolled in. The pump started pumping, and then died. The operator cleaned it out and tried again; another death. He then announced that he was unable to pump the concrete; it had been mixed incorrectly. But the concrete guys insisted that it had been mixed precisely as the pumping company had told them to do.

There was nothing for it but to send the concrete pump home (of course, he insisted on being paid anyway, and my builder concurred, though I was prepared to send him packing without payment). The builder and his 3 helpers then spent hours hurriedly unloading the concrete from the trucks into the walls with 5-gallon buckets. This was gracious on the part of the truck drivers; they would have had every right to leave, insisting that they couldn't take a chance on the concrete hardening inside their trucks.

Eventually, the job got done; it must have seemed like an unending nightmare.

After waiting a couple of weeks for the concrete to harden, the exterior of the basement walls was coated with a thick black waterproofing material, and the entire basement was wrapped in 6-mil plastic. The basement hole was then backfilled, and the walls were braced with lumber.

This turned out to be another major mistake; we should have poured the roof, to lock the tops of the walls into position, before backfilling. As it is now, the middle of the long walls tilts inward by about an inch, pushed by the weight of the earth -- the lumber bracing was no match for this pressure.

Notice the basement entry door at the bottom of the stairwell in the photo. I needed a door that could be embedded in a concrete-block wall, and I also wanted a door that would be fairly impenetrable. This led me to a company in Tucson that makes doors for prisons. The guy there said, "If you want a door that you can beat on with a sledgehammer for an hour, and not get anywhere, that's what we make." I was hooked.

This was one of the pleasant experiences of the project; the prison-door guys really took an interest in what I wanted, and designed something to meet all of my concerns. I suppose it intrigued them because it was something out of the ordinary for them -- in any case, they were very friendly and very helpful.

One interesting bit about this door is that the side frame has arms welded onto it that sit between the rows of block. These arms have vertically-aligned holes in them; the idea is to drop a rebar rod through those holes before filling the wall with concrete. This really makes the door a solid part of the wall.

Oh, and the door weighs upwards of 400 lb (180 kg)! Though I do wish that I had gotten the 4-foot (1.2 meter) door instead of the 3-foot (.9 meter) model.

After pouring the floor slab for the observatory basement, our new builder, who had just been brought on board at the behest of our first builder, had to take a 3-month hiatus to finish up some other projects. He would return in December to build the basement. This provided the setting for the second weather disaster.

The basement floor slab looked really nice when it was first completed. (Note the attractive model in the background.) Had we been able to immediately build the basement walls, we'd have been pretty well off. But it was not to be.

The month of October, normally a dry month, set a record for rainfall total that year. Owl Canyon, in the Peloncillo Mountains, had not one, but two 5-inch rainfalls. Seemingly, all of this water flowed through the construction site and down the ramp into the basement hole. By the time it all ended, there was about three feet of water over the top of the floor slab; the tie-in rebar for the basement walls was nearly completely underwater.

The water got pumped out in mid-November, revealing about 8 inches of good adobe clay mud covering the south end of the floor slab. This stuff proved nearly impossible to scoop away; it stuck to the shovel so well that you could turn the shovel upside-down and the clay would just hang there without falling off. Eventually, a small skid-steer loader was brought in to clear off the slab.

In early December, nearly 3,500 concrete blocks were delivered to the BRO site (we used 4"-high block instead of 8"-high block, partly for esthetics since the interior walls would not be finished out, and partly just to make it easier to handle the lighter-weight blocks). They were supposed to be dellivered to the floor slab, but a mixup meant that the ramp had not been repaired and was still washed out from all of the rain, so the block company was unable to go down the ramp.

So, for 2-1/2 days, while the builder was building the basement walls, we (and a neighbor with a pickup truck) stacked block from the pallets at ground level onto the pickup, backed the pickup down the ramp, and unloaded the pickup onto the basement floor slab. All told, it took 8 days to construct the basement walls.

But at least now we couldn't be hurt too much more by the rain.

After digging the hole for the basement, things stalled for a while. As it would ultimately turn out, our builder was having second thoughts about taking on the project. He did start to have the trenches dug for the footings for the basement walls, but nothing else happened. Thus were four months wasted.

And so it was that July arrived, with the attendant monsoon season, with no basement having been constructed in what had been up to then a nice dry hole. And it was not to be just anyJuly, but a July that would see a record for monthly rainfall.

The Peloncillo Mountains are about 3 miles to the east of the observatory; the mouth of Owl Canyon points directly at our property. One fine July afternoon, 5 inches of rain fell on the canyon. The construction site effectively funneled the resulting runoff sheet flooding directly down the ramp into the basement hole; by the end of the month, more than two feet of water stood in the hole. (Some of the local residents, who were by now beginning to recognize us when we came into the local cafe to eat, asked us if we'd brought scuba gear!)

You can imagine how we felt when our nicely excavated hole, with most of the trenching dug for the wall footings, wound up looking like this mess. Note, particularly, how badly washed-out the rampway is at the far end.

So everything stopped while we waited for the monsoon rains to end. During this hiatus, our builder notified us that he would no longer be working on the project, but he had found a substitute who would finish the job for us. I decided that I also had to take a much more active role in the project, and involved myself in the day-to-day details of the construction. As it turned out, this would have become an absolute necessity in any case.

Eventually, the monsoon rains went away, and the water was pumped out of the basement excavation. New trenches were dug for the basement wall footings, as we familiarized our new builder with the overall design, and, on September 20, 2000, the basement floor slab was poured.

The great observatory project was really moving along -- installation of utilities was proceeding nicely, and, in May of 2000, it was time to start work on the observatory itself. Once we'd dug the hole for the observatory basement, we could then locate the RV pad and run utilities to it with confidence that we weren't going to interfere with the building.

Little did I know that an entire year would pass before there was a basement in that hole.

The excavation was also the source of one of the more major mistakes in the construction. I wanted them to dig the ramp down to the bottom on the east side; however, the east side was a long wall and they wanted to enter from a short side instead. Since we already had plans for utilities and an RV pad north of the hole, they wanted to enter from the south.

I acceded to this request, but belatedly realized that that meant the ramp would be dug where the telescope pier footings would later be poured. Those footings really should have gone into undisturbed soil. Dealing with that problem later on would be a two-day job.

Oh, yeah -- basement. You're probably wondering what that has to do with an observatory ...

By design, BRO is located out in the desert far from any large cities; Tucson is about 105 miles away as the crow flies (and 175 miles by road from our house). This means that nipping out to the observatory for a quick evening observing session is quite impractical; nominally, a stint at the observatory would last a week or more. And that means that we'll need someplace to stay.

Now we do have an RV pad, and the travel trailer was parked out there during construction, but it just wasn't a suitable place to try to sleep during the daytime. It was pretty bright inside and the air conditioner was pretty loud.

So the decision was made to build a basement as part of the observatory:

• it would naturally stay reasonably cool when nobody was there (so you could keep the kitchen stocked with food safely)
• it would also be much easier to keep at a comfortable temperature during visits
• it would be quite dark, even during the day, for daytime sleeping
• it would provide an added measure of security

The basement was left uninsulated so the surrounding earth would keep the summertime temperatures down. In fact, while the basement was empty, the natural temperature inside was 54 degrees F (12 degrees C). This has worked out well; even with two computers running 24/7 in the basement (running the web site you're reading now!), the uncooled temperature has never exceeded 82 degrees F (28 degrees C).

One consequence of this is that it's a bit more difficult to keep the basement warm in the winter. However, once the basement walls have had time to absorb sufficient heat (this takes about two days), it's comfortable inside and the heat pump does not run excessively. The two computers that run 24/7 (and handle the web site you're reading now!) also help with heat during the winter; but, of course, they also contribute to that 82-degree summertime temperature.

At BRO, however, it's never easy. The basement could not be built directly underneath the building, as is normal, because large footers had to be poured for the telescope piers. These would have been rather inconvenient if located in the basement. Additionally, these footers had to be completely isolated from the building, so building vibrations would not transfer into the telescopes.

So the basement was built completely buried under two feet of earth, just to the north of the above-ground building. There's a 10-foot-wide stairwell that connects the basement with the upstairs.

Just to give some insight into how much attention to detail went into this:

The basement was quite deliberately built to the north of the observatory building. This placed the stairwell at the north end of the building, so the telescopes were located farther from the rolloff roof when it was in the rolled-off position for observing. This meant that more of the northern sky (including the North Star, Polaris) would be visible to the telescopes. And one small savings that we realized from this was that we could use the basement roof as the footer for the steel columns that form the rack the rolloff roof rolls onto; we didn't have to dig and pour 6 footers for them.