Hi guys
I am building a 40′ retainer wall to level and reclaim some of the back yard , before it drops 75′ to the flood plain and river.
40′ long , that is , height grows from 15″ to 42″ across 40′ of the yard where the wall is going to be.
I bought some stone at a sale in the spring , and paid about $200 for $2,000 of stone. Gotta love a sale !
I have base stones that weigh 100 lbs. each to anchor the wall.
1) Base stones are rectangular , with no grooves to hold the wall stones that will sit on top. My trench is 12″ to 18″ deep and 24″ wide . I will fill the trench ( part clay and part topsoil)with 12″ of 1″ gravel and compact. The yard slopes at about a 45 degree angle , and I plan to back fill the space with 3/4″ gravel , then install a fire pit and patio on top.
The question is : do I need to be concerned about forces pushing the wall off it’s base ? I have cut a drain ( 4″ flexible O pipe ) from the bottom of the trench to the edge of the 75′ river bank.
2) As the wall tapers in height from 5 stones high to one , the 1 1/2″ setback means the top of the wall will be crooked , and the cap stones will not line up. How do I solve this problem??
Thanks for any help.
Stewie
Golf is like woodworking ” Always a new way to screw up the project” 🙂
Replies
I'm not clear- is this real stone, or modular concrete blocks? If you're using a wall system, generelly anything over 3' tall needs a geo-grid tieback built into the wall, going into the slope and anchored into undisturbed soil, not to mention geotextile fabric, drain pipe and crushed gravel behind the wall. Engineering is usually recommended too- you might get some guidance from the mfg's website.
If you start at the bottom lowest end, each succeeding course will step back till you get to the top, all your caps will line up.
For a 42" wall you might need to bury 1 or 2 courses to keep the bottom from kicking out
Congrats on your deal, but for me the major expense is in the prep- the unseen underneath part.Take your time with that.
That said, if you have real stone, thats another matter.
Steve
Hi Steve The material is mfg. concrete stone blocks from Simcoe Block . The tallest section ( 20' long) will be 5 courses @ 6" each , plus base stone 7 1/4" and 3" cap for total of 40 1/4". The ground slope of the last 5 feet will see 12" of the wall underground, so that is the first 2 courses.
The plan was 12" compacted gravel base , 24" wide. I could reduce the gravel base to 7" , and have the base row 5" below ground level? The river bank about 20' in front drops off 75' so tis an easy fix to install a 4" big O drain . How would I use geo-textile fabrick cloth? The second 1/2 of the wall will be 4 sections each about 5' long , going from 4 courses to one ( plus base and cap.) for a height of 34" tapering to 16". As far as the caps lining up , the light just went on! When there is no "first course" , the second is laid in line with the rest of the second course, NOT in line with the first course. DUHH ! :) Gravel backfill will be minimum 12" wide and deep under the base , and growing to 3 to 5' at the top. Thanks for your help Stewie
Stewie- I'd stick with your 12x24 gravel base, but I would still bury your base block. Obviously that means digging deeper to start your base.
You'll be glad you did.I use the geo-tex fabric as a separation membrane between your drainage stone and the face of the excavation. I usually make my drainage stone 18-24" from the back of the wall, run the fabric up the back, and anchor under the caps.This is all based on procedures I have come to rely on over the years. Check your mfg for their recommended construction details.Your milage may vary.
Objects in the mirror are closer than they appear.Steve
Steve Since I put the first 6" of gravel in this morning , I can shovel what I dug out , back against the front of the wall. Lots of clay , so it should harden in place. I have also considered driving in some rebar to hold the base and first row. The Geo-text cloth you mention is probably what I know as fabric cloth and use for keeping weeds down . I can see the benefit , and is an easy prevention to stick in place. Thanks, Stewie
Stewie- you shouldn't need the rebar- set the first course below grade nice and level and straight, lay the next, then start the backfil process, backfilling and packing and filling the cores as you go. Pack stone in front of the wall, to grade, and that thing shouldn't go anywhere. Drop in your drain pipe and away you go.Steve
Thanks, Steve. I'll email a pic. when done. Cheers, Stewie
I did a segmental block retaining wall several years ago to replace a failed wood wall. My wall is on a hillside that is about a 20% grade. I used keystone brand concrete blocks. They have a nice video that is very informative. They (and other makers) probably have useful information on their websites too. Keystone provided answers to my questions and an engineered design for my hillside. There is almost as much of my wall below the ground level as above. This was required to deal with the "kickout" issue.
Geogrid is NOT landscaping fabric. It is heavy plastic designed to tie the blocks back into the dirt the blocks are retaining. Whether you need to build with geogrid depends on the usage. Cars or buildings above a retaining wall are more severe loadings than use as a playyard. Keystone was very helpful in providing useful engineering help. Manufacturers want you to use their products correctly and will usually help you do so. All you have to do is ask. It is critically important to provide proper drainage behind your retaining wall. Water and the wrong fill material will usually lead to early failure. There was an excellent article in either JLC or FH several years ago on retaining walls. Perhaps someone can provide a reference. I'm not near my library at the moment.
Thanks for the heads up. I'd say my grade is about 25 degrees behind the wall as level with the tpo is about 14' back. The plan is to backfill with 3/4" gravel and put a firepit/patio on top ( also a T box for my personal driving range :). Stone backfill should absorb a lot of push and provide excellent drainage.
If I shovel up against the front of the wall , the material dug out , I should get about 2' of the 40" wall buried. I have installed a 4" BIG O pipe at the bottom of the trench that runs out over the river bank and buried the pipe with 3/4" gravel. The first 20' will be 40" high , then the last 20' tapers to about 16" high, as the yard rises. This part will just have some kind of garden on top , so little foot traffic to "push". Stewie
Good point on the geo grid issue. My response was to the fabric usage behind the wall between the stone and the dirt. The geo-grid is important once the wall gets over 30-36" as a deadman to tie the wall into the hillside.Another issue- with a 42"wall, will there be provision for a railing/ fence?Steve
We have back filled the dug out clay to bury the base block (7 1/4") on the front side of the wall so wall height is down to 35". If we throw more of the excavated dirt vrs. the 2nd course , the height will be reduced to 29" , so no railing is in the plan. As the base stones ( 12" X 16" X 7 1/4" high ) had no grooves to hold the stone wall above them in place , we used construction glue to secure the first course to our base stone row. The 5 courses above the base are grooved to interlock and provide the regular 1/2 " set back on each course. Backfill will be 3/4" clear gravel , from minimum of 12" behind base row, to 10' behind the top course. Cheers, Stewie
"As the base stones ( 12" X 16" X 7 1/4" high ) had no grooves to hold the stone wall above them in place , we used construction glue to secure the first course to our base stone row"
I have a feeling they may have been the stones you were supposed to use on top, the cap stones.
I think 105 lb. cap stones would almost topple the wall. I have 20 3" thick cap stones 2 feet long X 16" wide to put on top when I get there. The 30 base stones were bought for about $30 and seemed like a good way to anchor the retaining wall. Stewie
You might be right, :), but why no grooves on top. Is that the norm?
Probably either column blocks or stair blocks.
They were probably meant for decorative garden blocks , or a one course retainer wall or to be overlapping steps ( @ 7 1/4") , or boat anchors. ? The price was right so I decided I could use them. Stewie
Keep the base at your original specs.
Bury the first 2 courses.
Dig 24" behind the wall.
12" of gravel, 12" of GOOD fill
Compact these in 8" rises, or for each course. Use a hand tamper or a plate compactor. I just built a 10'h x 24'l wall using a hand tamper. UUUUUGGGH!
I use a piece of plywood between the 2 materials to keep them separated...works REAL good.
4" perf. Drain behind first or second course run to daylight.
I always use chipped, not crushed, limestone for the base. compacts nicely, and still drains. Does not create a water "barrier".
Backfill wall so that water goes over the wall, not behind it.
If you have a huge slope (> 30 degrees) behind the wall, geogrid is recommended for walls over 4'. I use it on all walls anyway. One at first course, and then one layer every other course. Make sure the ground at the grid levels is well tamped and LEVEL. Stake grid well, and don't run the plate tamper directly on it.
Above all, take your time to do this right. Imagine what you'd have to go through to repair a wall that collapses because you wanted to go faster. Awful mess.
Have fun! If you've never built one of these, it's HARD WORK, but the end result is pure satisfaction.