The Laws of Physics
Great moments in building history: Never underestimate them
Sheila had hired our company to do an extensive renovation of her 45-year-old home. The job entailed removing the existing roof and second story over the house and garage, and adding a large two-story addition behind the house and a second story over the existing first floor and attached garage.
When we excavated for the addition, we discovered that the house sat on a beefy 8-in. by 24-in. footing. But we were concerned about the ability of the garage to carry the load of the new second-story addition and the huge roof over it. So we decided to have the excavator dig down to allow us to check on the size and condition of the garage’s foundation and footing.
As it turned out, the garage’s concrete-block foundation did not sit on a nice big footing: It sat directly on sand.
After conferring with the city building inspector, we decided to underpin the foundation. We would do this by digging carefully under the block for about 3 ft., then skip 4 ft., then dig out another 3 ft. and so on. We would then pour concrete in the 3-ft. sections, let it cure, and come back and do the same in the 4-ft. sections we had skipped. This plan sounded good in theory—and in fact, we had successfully underpinned foundations on other projects. We plunged into the work.
Fortuitously, we removed the roof structure of the garage to lighten the load on the foundation before we started the underpinning. Two of us were assigned this job, and we could use the crew’s young laborer as we needed him. The laborer was new to our crew, and quite inexperienced. In fact, over the course of several projects, he’d made us laugh with his naive questions. Most of the time, we had no idea where he was or what he was doing.
My co-worker had a bad back, unsuitable for heavy slugging; consequently, he spent a fair amount of time supporting himself on his shovel, watching me work.
I had cleared out several sections by 10 a.m., and we decided to break for coffee. It was cool and shady in the excavation, so we sat down there for a few minutes. During a pause in the conversation, we heard a faint creaking sound, sort of like the noise wood makes as it comes under great tension and begins to crack. A few seconds later, the noise was much louder. We dropped our coffees and ran. I had barely cleared the back corner of the garage when there were several huge cracks, pops and bangs, and the garage that had been standing had fallen over hard against the side of the excavation, where only a few seconds earlier we had been drinking our coffee. One long shovel handle stuck
out between the ruins of the garage and
the excavation.
Nearly faint from fear, we sat down and considered what we had narrowly escaped. I guess it was too much to expect—that the sand would continue to support the garage, that the garage would be unaffected by all this activity. In hindsight, I think that digging under the concrete-block foundation wall in sections must have been the last straw. After all, there was still the weight of the garage walls, the weight of a 4-in. thick concrete slab, and no doubt the considerable weight of the fill under the concrete slab, all exerting significant pressure on the almost unsupported concrete-block foundation. There was no longer any fill around the outside of the foundation to help hold it all together. So given the laws of physics,
down the garage came.
After the garage fell down, a few minutes went by. Slowly, the cockeyed door at the back of the garage was forced open. The laborer, ashen faced, stuck his head out of the crooked opening. Apparently, incredibly, he was in the garage when it fell into the hole. The 4-in. thick concrete-slab floor had broken in half while he stood on it. As ever, his inexperience came through. With a trembling voice, he said, “Was this supposed to happen?”
An hour or so later, Sheila showed up, saw what happened and said she wished she had brought a bottle of whiskey. So did we. So did our boss. So did the laborer, who was out lying under a tree.
All turned out well, though. We finished the house a few months later—complete with a nice new garage.
—Tim Urch, Brantford, Ontario, Canada
Drawing by: Jackie Rogers
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