Our dry stone entrance pillar we built recently near Baltimore Ontario got clipped yesterday. A large truck took the turn too close to the new gate entranceway and dislodged several of the stones. Ian, the driver was very upset and genuinely sorry. He told us he likes dry stonework a lot. He had needed to make a tight turn around the pillar and accidently caught the corner of the structure with the back of the truck. We were working on the north side of the entrance way and looked up too late to stop the damage from happening. Had it been a concrete gate it would have toppled over.
Ian figured the column would have to be rebuilt from about three and a half feet up at least. We were pleased to tell him that it wasn't necessary and that with any luck we could 'bump' the stones back into position. Which is what we did, with the aid of a sturdy scaffolding board. Ian was relieved to see he wouldn't have to to tell his boss about what had happened.
I remember a similar thing happening in Seattle at the N.W. Flower and Garden Show. We had built a dry stone arch there as a garden feature entrance to one of the displays. One evening just before the opening of the show a bobcat while backing up with a bucket of top soil
caught the side of the arch. It nearly knocked out one of the main voussoirs stones in the arch. The triangular stone stuck out precariously from the rest of the structure. We managed to carefully knock it back in with a 4 by 4. The arch looked fine again and people were able to safely walk under it during the entire show. If the arch had been a solid concrete or mortared structure, the whole thing would have fallen over when it was violently knocked by the bobcat.
It was the same thing with the truck incident yesterday. Dry laid structures 'yield' rather than crack and fall over when they are struck or shaken or subjected to heaving. Anyone researching the effects of seismic activity on manmade structures would do well to look into the merits of dry stone construction.
The walls and pillar don't look too worse for wear.