One find at the 1938 and 1940-vintage subdivision was an extremely corroded piece of 1/2-inch iron pipe with a likewise extremely corroded piece of 3/8 in. rebar driven through it. The photo below shows two rebars at the left side of the frame, both flush with the ground and of recent origin, and on the right side of the frame the remains of the original 1940-vintage pipe 26 inches below grade.
The remains of the pipe were broken into three pieces which together made this thing:
The pipe was just so fragile that it broke into pieces as I dug around it as carefully as I could. I pulled the bottom 5-1/2 inch stub to examine and photograph it with the other pieces, to show that they all made the remains of a 1/2-inch pipe, and replaced it in the hole it had been extracted from.
Here is what the orientation of the monument looked like as found (the dashed lines represent the stub that I left in the ground for the time being):
The remnants of the pipe were leaning about 35° off plumb. The question is what the mechanism of rotation/movement was. The soil material that the pipe was set in is a plastic clay that evidently remains wet much of the year considering how severely the pipe was rusted. While there was fill placed on the lot above it, I'd think that the clay is native material at the site. We encountered it in digging in other places along the rear line of the subvision.
Kent a few years back a did an ROS like yours, where I retraced several 3/4" iron pipe originals from the same time period, in ground that was very sticky and known to cause problems for the homeowners throughout the area since I think it was as you describe - always moist, and not very strong on the hills of that area.
I had mistakenly at that time thought the pipes were not galvanized and said so on the map, but I believe that was my ignorance on what that type of soil can do to those monuments. Several which appeared to some to be leaning, were really badly corroded about 6 inches down and you had to dig down and get the vertical, bottom portion.
> Kent a few years back a did an ROS like yours, where I retraced several 3/4" iron pipe originals from the same time period, in ground that was very sticky and known to cause problems for the homeowners throughout the area since I think it was as you describe - always moist, and not very strong on the hills of that area.
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> I had mistakenly at that time thought the pipes were not galvanized and said so on the map, but I believe that was my ignorance on what that type of soil can do to those monuments. Several which appeared to some to be leaning, were really badly corroded about 6 inches down and you had to dig down and get the vertical, bottom portion.
Yes, that level of corrosion is quite unusual in the limestone soils of Central Texas. I think that the mechanism of rotation may be wet-and-dry cycles, although 35° off plumb in 70 years on a hillside seems surprisingly small.
The more I think about this one, the more I have to suspect that the mechanism of rotation off plumb was the force acting on the 3/8" rod inserted in the pipe that produced the bend in the rod. The clay may not really dry out much at all, even in the Summer. That would be consistent with the extreme corrosion. The damp clay is somewhat stiff, but plastic (deformable), so just some material that tumbled down the hill and ended up pushing on the rod could have rotated the pipe off plumb.
Under that mechanism, the base of the pipe would probably be a pretty good estimate of its original position.
Good job Kent.:good:
Thanks for sharing.