Thrown-together retaining wall question
#1
06-19-17, 04:02 PM
Thrown-together retaining wall question
I want to put in a low retaining wall underneath a deck. The ground slopes down as the deck goes outward. More, the ground level drops off sharply as you go under the deck That is, the deck extends south of the house, and the ground to its west also slopes south, but the ground also slopes to the east right at the edge of the deck so the lowest point is under the deck and not to its west or south.
The drop is maybe 12-14" total, with most of the drop happening at the last 10 or so feet.
I recently added some soil to the ground west of the deck and I'd like to add some more. That means I really need a retaining wall of some sort. Not much of one, maybe 6" above the lowest point just inside the deck. It looks like this at that end:
I have a big load of concrete sections, from a demolished driveway from years back. They've just been sitting there:
Since looks don't really matter (the wall will be essentially out of sight), can I use these to make a retaining wall? Perhaps mortaring them together? The wall would be about 10, maybe 12, feet long.
The drop is maybe 12-14" total, with most of the drop happening at the last 10 or so feet.
I recently added some soil to the ground west of the deck and I'd like to add some more. That means I really need a retaining wall of some sort. Not much of one, maybe 6" above the lowest point just inside the deck. It looks like this at that end:
I have a big load of concrete sections, from a demolished driveway from years back. They've just been sitting there:
Since looks don't really matter (the wall will be essentially out of sight), can I use these to make a retaining wall? Perhaps mortaring them together? The wall would be about 10, maybe 12, feet long.
#2
06-19-17, 04:21 PM
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Is the retaining wall supposed to stop the dirt from moving? A true retaining wall starts underground. They aren't built by throwing some dirt & rocks under the deck not that it will hurt anything. It's just not a retaining wall. BTW, the deck doesn't appear to have the correct footings, posts or brackets.
#4
06-19-17, 06:44 PM
I was going to dig down to place the first level of the wall. That's why I asked about mortaring them together--I was going to bury the lower pieces. I thought I'd dig a pretty deep trench, place concrete pieces in it, then place more pieces on top to bring it up to at least 6" above the lowest ground level. The pieces are pretty heavy so I was thinking that mortar might make something pretty solid as well as filling in gaps, since they're also uneven.
The deck is on 18' pilings (about--it's been a long time) driven down to solid rock. They've been there since the late 80's and are not going anywhere, and have withstood multiple hurricanes and nor'easters, including a 6' storm surge from Hurricane Sandy that ripped off the decking but didn't budge the pilings.
The deck is attached to a house extension that's also on pilings. That room (the extension) extends about 20' from the house and foundation and there's a good slope under it the whole distance away. So there's a low point under the deck but it's about 25-30' away from the foundation.
The deck is on 18' pilings (about--it's been a long time) driven down to solid rock. They've been there since the late 80's and are not going anywhere, and have withstood multiple hurricanes and nor'easters, including a 6' storm surge from Hurricane Sandy that ripped off the decking but didn't budge the pilings.
The deck is attached to a house extension that's also on pilings. That room (the extension) extends about 20' from the house and foundation and there's a good slope under it the whole distance away. So there's a low point under the deck but it's about 25-30' away from the foundation.
Last edited by vanderdecker; 06-19-17 at 07:47 PM.
#5
06-20-17, 05:59 AM
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I don't know if there is a frost line there or not. If there is, it's best to dig to that depth. Then you can throw the rocks in there & pour concrete on top of it. The shims on top of the posts is the reason that I asked about footings.
#6
06-20-17, 11:32 AM
Thanks.
When the work was done all those years ago, there was some screwup between the architect, the contractor, and the subcontractor who did the piledriving regarding placement of a number of the pilings (out of several dozen). A few had to be shimmed, which apparently was considered an acceptable fix.
One issue I have here is that if I dig more than about 18" below mean ground level I hit water--the spot is ~100 feet from a large salt bay.
When the work was done all those years ago, there was some screwup between the architect, the contractor, and the subcontractor who did the piledriving regarding placement of a number of the pilings (out of several dozen). A few had to be shimmed, which apparently was considered an acceptable fix.
One issue I have here is that if I dig more than about 18" below mean ground level I hit water--the spot is ~100 feet from a large salt bay.
#7
06-20-17, 12:45 PM
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The deck is on 18' pilings (about--it's been a long time) driven down to solid rock.
One issue I have here is that if I dig more than about 18" below mean ground level I hit water
#8
06-22-17, 06:52 AM
No. It's standard construction near the water to build onto pilings driven down to rock. See here:
https://coxwood.com/news/pilings-bui...rm-foundation/
"...pilings, sometimes called timber piles, are the key to the foundations in areas where the water may come up onto the land. Pilings are driven down through the sandy soil to rest on solid ground or rock deep below the surface. From there they bear the load of your house. While concrete and steel are used for heavier buildings, most residential homes are built on wood pilings."
https://coxwood.com/news/pilings-bui...rm-foundation/
"...pilings, sometimes called timber piles, are the key to the foundations in areas where the water may come up onto the land. Pilings are driven down through the sandy soil to rest on solid ground or rock deep below the surface. From there they bear the load of your house. While concrete and steel are used for heavier buildings, most residential homes are built on wood pilings."
#9
06-22-17, 07:30 AM
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#10
06-22-17, 07:36 AM
Way down. Anytime you dig around me you hit water pretty quickly. We had to get a service in to do test borings to see how far down the pilings needed to go to reach rock. That's why the pilings are so long.
Last edited by vanderdecker; 06-22-17 at 09:08 AM.
