Designing and Planning a Retaining Wall

Our non-existent woodpile 

Do you all remember our poor non-existent woodpile?  I’m back to those contractors again that did our cement patio. Yes…the ones who screwed us!  Our original contract included a second cement pad that was supposed to be built for a woodpile that never came to fruition! Sigh… It was a beautiful idea; a woodpile 3 feet from the room that houses our woodturning stove. I could literally go out and gather wood without putting my shoes on. But THAT INVOLVED BUILDING A LARGE RETAINING WALL which was the highlight of their misquote!!  It’s not our fault that they would have lost money on us, get a better quote guy!  Once again, Thanks guys!   Our wood has been left out to rot without a place to store it.  No worries about us and how cold we might be all winter long! HA . Check out that contractor deceit HERE and what questions I will be asking next time so we don’t land in contractor mess land again. And on top of all that,  not even a month later, hiring a hot tub mover proved to be another fiasco.  I won’t even go there!  You will have to see that story for yourself right HERE.    

Well, we have decided we are going to do it ourselves!  We are sort of done with hired help for a while. YUP we are going to build a large retaining wall ourselves, and cement pad for our woodpile all by our lonesomes ….rasberries.!  We will figure it out!  It’s not rocket science.

Cheese n’ Rice, Get over it K. Rupp!  Move on!

The Retaining wall  PLAN AND DRAWINGS

Luckily though, what we took away from the patio workers was knowledge! The actual foreman and workers were great and because they felt bad for us, they were willing to give us any information we wanted. Ed watched every step while they were building our concrete patio.  He took notes on how everything was done.  We also jotted down the types of block they were using for the patio retaining wall so that we could match the stone and recreate what they did when we decided we would have to build our own wall and cement pad for the woodpile.  Planning out a retaining wall is tricky because half of it is buried.  Knowing what they did and seeing what makes up the wall is half the mystery. 

Ed started drawing, sketching and calculating what wall blocks and how much stone and aggregate he was actually going to need in order to build the retaining wall designed for a cement pad. 

THE DESIRED CONCRETE PAD

Just for you all, I recreated his drawings to make it easier to understand our upcoming project.  It will be a lot easier to come back to this post to reference what exactly is going on when you start seeing a whirlwind of digging and masonry pictures later on in the building process.  

This first drawing is an airplane view as if you were looking down.  It’s an 8×12 ft. simple concrete pad that we want to be able to stack our woodpile in one place.  We don’t need any fancy stamped concrete like our patio.  But we will be using the same wall blocks for the retaining wall so that it matches the other existing concrete patio.  The retaining wall will be going all around on all 3 sides.  Since the concrete will be adjacent to existing concrete, we don’t need the block on the 4th side.

THE RETAINING WALL CROSS SECTION

I recreated Ed’s drawings of the retaining wall cross section and what is involved with building a retaining wall.  This cross section is of the back 12ft. wall next to the fence that you saw in the first drawing.

Cross Section info:

• The base block should be completely buried.
• Adhesive goes in between each level of block.  Instead of adhesive, one can use pins however Ed is planning to use masonry adhesive.   
• Drain aggregate rock will fill in between the blocks and the trench and also on the slope in the area enclosed by the walls that come as high as the ground level.
• Cap stone on top of the wall block to finish it off.
• Cement will be poured on top of the compacted draining aggregate stone.

 This shows the slope that we will be working with.  To do this back 12 ft. wall we will dig a trench a little wider than the wall blocks.  Dirt will be tamped, flattened, and completely leveled.  We will dig down deep enough to allow for C&R(crush and run) and at least 1 full base block to be safe.  

How far should we dig down?

How far one digs down is totally dependent on the area you live and your local building requirements.  Do some research and figure out what is necessary for your soil composition.  There is some guidance offered on this website. https://allanblock.com  It talks about digging a minimum of 6 inches + an additional inch for each foot of wall height.  Please refer to your local stone supply business for information specific to your area.  

For example, In our area, we will dig down 16 inches for the main retaining wall:

• 10 inches of Crush and Run packed down and leveled
• 6 inches of BASE BLOCK 

How often do we compact the stone?

Every 2 inch layer of crush and run will get completely compacted and leveled before adding the next layer of crush and run.  This also is the same rule of thumb for the compacted aggregate at the top of the slope before the concrete gets poured.

What happens on the side of the retaining wall?

Because the retaining wall is on 3 sides, blocks turn a corner on both sides.  This leads us to the next drawing of what is going on underground on the sides of the retaining wall and concrete pad.

THE SIDES OF THE RETAINING WALL

• 1 type of corner block will be used to turn the corners on both sides.  In the picture it looks like there are 2 types of corner blocks but this isn’t the case.  It is a specialty corner block finished on 3 sides seen from 2 angles forming a corner.  In the picture you are seeing the finished long end stacked on top of a finished short end.  Stacking and alternating the block forms a corner with both outer sides being finished.  
• When turning the corner, the base block 1st layer needs to be completely buried on the sides of the retaining wall which will include 2 base blocks for our particular slope.  There is a step up according to the slope which will happen naturally working up the slope.  Crush and run will butt up against the blocks as you step up.  Look at the picture for a better understanding of what will be done. 
• Anything under the green line, will be hidden and underground.  When you have the first layer completely buried this is likely what will play out.  This is not exact, just simply a representation.  
• The blocks labeled C are just to give an idea that some of the blocks will have to be cut to fit in. 

NOTE: nothing pictured is to scale…these are just rough drawings to give you an idea.

NOTE: If planning a retaining wall without a cement pad at the top, one does have to consider more in terms of drainage.  Be sure to do more research on this aspect.  We did not have this issue because the top was concrete.

The MATH and CALCULATIONS- HOW MUCH stone and block will need to be delivered?

HAHA..Just skip this part if you want.  This part will be a help to anyone trying to figure out how much crush and run, stone gravel draining aggregate, and how many blocks to order for a project like ours. Seriously, I am going to geek out in this section and show you his math calculations to give you an idea how he came up with the amount of stone and blocks that needed to be delivered to our house for our upcoming project. The calculations are actually pretty simple math…no calculus here. 🙂 

HOW MUCH C&R(Crush & Run) DO WE NEED?

LxWxH is the formula used for volume of a rectangle.  To calculate we need to convert all measurements needed in the drawing from feet to inches. Here we only need to convert Length 12 ft. 

12 ft = 144 inches

The crush and run will only be used in the surrounding retaining wall not underneath the cement pad.  Here we will calculate 3 volumes of rectangles (because there are 3 sides to the retaining wall) and they will be added together.

C&R for long back wall: Height = depth of trench. 

NOTE: Here we only needed 10 inches deep of C&R but because it gets compacted so tight, he used the full 16 in depth to have enough C&R

L=12 ft. Length of long retaining wall | W=12 in. Width of trench | H=16 in. Depth of trench

LxWxH

12 ft.x12in.x16in.

12ft=144 inches 

144 in(length)x 12 in.(width) X 16 in.(height)= 27,648 cubic inches

C&R for both sides: multiply by 2 since there are 2 sides.  

NOTE: here even though we have a 6.5 stretch of wall on either side, we will only be calculating C&R for 2ft on each side where the base blocks will be underground.  We will add the C&R for the step ups in the next section.

L=2 ft. length of side wall  | W=12 in. Width of trench | H=16 in. Depth of trench

2(LxWxH)

2(2 ft. x 12in.x 16 in.)

2(24 in.x12 in x16 in.)= 9,216 cubic inches

C&R for step up on sides: multiply by 2 for both sides.

NOTE: In my drawing there are 5 step ups….but until we actually get in there we won’t exactly know how many step ups for sure.  We were just estimating.  We will dig out the same length as the max size block(1 ft.) with each step up which means L=12 in.  

NOTE: The amount of c&R for the step ups will be compacted and butt up against 1 full block.  See pic.  Since the height of 1 full block is 6 inches, so will the depth of the compacted C&R.  This means H=6 in. + another 4 inches to compact.

L=12 in. length of step up  | W=12 in. Width of trench | H= 10in. Depth of the C&R butting up the depth of 1 block

2(5 step ups(LxWxH)

(2(5 step ups(12 in.x 12 in. x 10 in.))) =

2(5 step ups(1440 in.)

2(7200 in.)= 14,400 cubic in.

NOW ADD for TOTAL C&R:

27,648 in. + 9,216 in. + 14,400 in. = 51,264 cubic in.

This value is in cubic inches.

Now convert total to cubic yards:

In order to purchase, the stone store will need this measurement in cubic yards.  Use a conversion tool from cubic inches -> cubic yards. Here is a link to one: 

https://www.metric-conversions.org/volume/cubic-inches-to-cubic-yards.html

51,264 cubic in. =  1.098765 Cubic Yards

1.10 cubic YARDS.

HOW MUCH AGGREGRATE DO WE NEED?

If you look at the picture where the aggregate gets compacted on the slope, in order to figure out how much aggregate we will need, we need to find the volume of that triangular wedge.  (1/2xbase x height x depth) is the formula used for volume of a right triangular prism.  For our application and to simplify with my drawings, I depicted the image of this wedge that would be filled with aggregate on the slope.  He converted all measurements in the drawing from feet to inches.

6.5 ft = 78 inches

1.5 ft = 18 inches

10ft = 120 inches

AGGREGATE on the slope: Height = Height of the wedge of aggregate 

NOTE: Look at the formula and 3D wedge (as seen in textbooks).  When flipped, it looks like the wedge of volume that will be underneath the concrete pad.  We used the same variables flipped with the correct measurements for our application.                                                  

B=6.5 ft. wedge base  |   H=1.5 ft. Wedge height |    D=10ft. Wedge depth 

VOLUME= (AREA of BASE)xD

VOLUME = (1/2BxH)xD

1/2 x6.5 ft. x 1.5ft. x 10ft.

See above in converting  ft.-> inches 

1/2 x 78 in.(Base)x 18 in.(Height) X 120 in.(Depth)= 84,240 cubic in.

Now convert total to cubic yards:

In order to purchase the aggregate, the stone store will need your measurement in cubic yards.  Use a conversion tool from cubic inches -> cubic yards. Here is the link again: 

https://www.metric-conversions.org/volume/cubic-inches-to-cubic-yards.html 

84,240 cubic in. =  1.805556 Cubic Yards

1.81 cubic YARDS. 

We ordered 2 cubic yards of aggregate.

HOW MUCH WALL BLOCK DO WE NEED?

If you look at the picture of the retaining wall, in order to figure out how much wall block we will need, we needed to find the AREA of all 3 sides.  The back wall is a rectangle and to simplify things, for the 2 sides, we are finding the area of a 2 triangles. We will be adding all 3 of those areas to get the square footage of the amount of wall blocks.  The stone store will be asking for square footage but I will still show the values in square inches so we can find out specifically how many blocks will be needed.  Area of a rectangle is: Area=LxW.  Area for a triangle is Area= 1/2BxH. The measurements we will be using is converted to inches.

6.5 ft = 78 inches

2.5 ft = 30 inches

12ft = 144 inches

BLOCKS for long back wall:

L=12 ft. Length of long retaining wall | W=2.5 ft. Width of wall

Rectangle Area=LxW

12 ft.x2.5 ft.= 30 sq. Ft.

144 in(length)x 30in.(width)= 4,320 sq. inches

BLOCKS for 2 side walls:  multiply by 2 since there are 2 sides.

NOTE:  

B= 6.5 ft. Length of both side walls | H=2.5 ft. Height of wall

Triangle Area=1/2BxH

2sides(1/2BxH)

2(1/2 x 6.5ft. x 2.5 ft.)= 16.25 sq. ft. 

2(1/2 x78in. x 30 in.)= 2340 sq. inches.

NOW ADD for TOTAL sq. Inches and sq. Footage

30 sq. ft. +16.25 sq. ft. = 46.25 square ft. OR

4,320 in. + 2,340 in. = 6,660 square in.  

Now Find out how many wall blocks to order if you need to be exact:

Each block: 10in. x 6 in. = 60 sq. in.

NOTE: knowing the size of 1 block means that now we can find how many blocks to order.

6660 sq. In./60 sq. in.= 111 wall blocks

NOTE: This is an estimate!!!!  Because we are doing simple math and we used the area of a straight right triangle(when it’s not exactly straight), always round up!  

NOTE: Most stone distributors move their wall block merchandise by the pallet which will contain so much per square feet.  Knowing how many blocks along with the square footage helps in many situations especially if you are buying off craigslist or through someone.  Always buy more..…round up!        

HOW MUCH CORNER BLOCK do we need?

Each block:  6 in. In height.

Our height of the wall = 2.5 ft. Or 30 inches.

30in./6in.= 5 corner blocks per side

2sides x(5corner blocks)= 10 corner blocks

HOW MUCH BASE BLOCK do we need?

Base block for long back wall: 

Each base block=16 in. length.

Our length of the retaining wall =12 ft. Or 144 inches

144in./16 in. = 9 full base blocks

Base block for 2 side walls: 

2sides(2 base blocks)= 4 base blocks

NOW ADD for TOTAL base blocks:

9+4= 13 base blocks.

NOTE: Turning the corner, we will use 2 base blocks on either side because one full row has to be completely buried.  Always round up…applications may be different and situational depending on the ground and slope.

HOW MUCH… WOW…

WOW….if you are still here hanging out in this math section and actually got to the end of it with me, you must be pretty serious about making your own retaining wall! I sort of want to applaud! HA.  No-one is going to care about this section, but you know that this is a possibility after reading all these crazy details.  I don’t want to just show pics that miss the details and leave you wondering how it was actually done. I want to give you the tools and templates that make you think ‘Yeah….I could do this!’    What seems like something unachievable for the average homeowner can be executed well when drawings and calculations simplify the process.  Use the math section as an example to help you plan out your retaining wall!  

What other Materials will we need for this project?

• Silt screen- This is to provide better drainage under the wall.
• Masonry adhesive- This is what glues the blocks together. 
• Masons line- This ensures wall is perfectly vertical. 
• Geogrid fabric- This ties the layers of aggregate and the wall together as one unit.
• Concrete expansion joint material- This provides padding between 2 concrete pads so expansion during the hotter weather won’t result in cracking.  
• Concrete reinforcing mesh- This adds strength to the concrete pad to minimize cracking of the pad.

Note: Be sure to check out our upcoming posts where these items will be used and seen in pictures when we are actually building the retaining wall.

The PROJECT BEGINS outside finally: 

OK, here we are folks!  We are off to a great start with some drawings and sketches. Not wasting any time, we are getting the whole family involved with this one!  After marking out the retaining wall with spray paint on the yard we are getting to work right away on digging the area up. 

So far so good as you can see!  And during this whole process, we got our special delivery right on the driveway.  Crush and Run, Aggregate, stone blocks etc. all ready to go.  Our woodpile is looking more and more like a reality! HA…..so excited!  

Let’s just hope these piles of stone don’t hang out forever here on the driveway for weeks knowing the type of weather we have been having.  You know how these projects go sometimes.  I will keep you updated on the progress.   Hmmm, what a fine looking trench we have there, we will have to see how this turns out.    TO BE CONTINUED…..  

K. Rupp

Stay tuned….the large retaining wall BUILD is in process and will be documented for all of you!  Make sure you catch my next ‘BUILD A RETAINING WALL’ post!

 

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