This series of pictures shows us pouring what I call a sitting wall. What a job. The wall is formed around a 125 year old maple tree. The wall is a monolithic pour. That means the footing, wall and bench top are all poured at the same time. The key is the footing.
How do we get a footing around a tree this big?
In some ways we did and some ways we did it in a different way. The sitting wall that is 12 feet or so from the tree we could put in a typical footing. We dig it out 2 feet deep the length of the wall. Around the tree is a different tale. Where we could find openings in the roots we did a post footing. In other words we dug holes 2 feet deep between the roots. We were able to get 3 to 4 holes per 8 foot wall section. Believe me, it was hard to find a place to put a hole.
Are the post holes substantial enough to carry this wall?
The post holes by themselves filled with concrete is not enough to carry the wall. So what we have to do is install re-bar. Four 1/2″ re-bar per hole with re-bar running horizontally near the bottom of the wall and near the top of the wall . We also had a series of re-bar to reinforce the cantilevered concrete bench. The re-bar we install in the post holes is sticking in the hole near the bottom of the hole and extending up into the wall, but is bent at 90 degrees to catch the re-bar running horizontally both top and bottom in the wall.
Don’t the roots from the trees grow and heave or crack the wall?
Yes, in time they will. This is what we did. We encompassed 3 to 4 inches of sand over the roots between the post holes at the bottom of the wall. This enables the wall to float over the roots for many years. So the wall is in a way formed like a bridge. In other words we bridged the roots. The post holes full of concrete and re-bar will hold the wall in place both vertically and horizontally. Once complete I will show you the finished pictures.