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Default Cinder Block Retaining Wall Question

Hello Everyone,

I am planning build two successive retaining walls 2' high (4' from
bottom of footer to top of the wall), and approximately 38' long.
The horizontal distance between the two walls will be approximately
three feet, with a step of 2' from the top of the bottom wall to the
top of the top wall, thus forming a small 3' planting terrace in
between. The total drop from top to bottom will be 4'.

I live in Southern California, so there is no frost line or threat of
freezing. The soil at 2' feet below grade is a composite of hard
clay/ virgin rotted sandstone. Both walls will be holding back a flat
grade. The newly formed terrace was previously a rounded/sloped mass
of unsupported earth, which was luckily only 4' high. The area above
the top wall runs flat to the back of the lot. Permitting is only
required for walls that are greater than 4' in height in my area.

My plan was to dig down to 2' below grade for each wall and pour a
concrete footer that is 8" in depth and 2' wide. I was planning on
using standard 8x8x16 cinder blocks for the wall itself. Based on
this, roughly two courses of cinder block would be below ground, while
another three would be above (yielding an exposed height of 2' for
each wall).

I am going to use rebar to tie the retaining wall to the footer, as
well as to provide lateral support through bond beam block running the
length of the wall. I will also fill and cap all blocks with solid
concrete. Both walls will be water proofed, be back filled with gravel
(covered with filter fabric to prevent clogging) and have a sloped
perforated drainage pipe leading water away from the wall.

The reason I have decided to build in this manner, rather than using a
pre-cast concrete dry stacking system, is that I plan, for aesthetic
reasons, to face the above ground sections of both walls with flagstone
veneer.

I have a few questions about this setup.

1. Do you think the placement of the top wall in proximity the bottom
wall would present any structural issues? If so, should I reduce the
size and depth of the footer in the top wall, thus reducing overall
weight?
2. Do I have to worry about moisture with regard to the underground
courses of cinderblock? If so, should I raise the footer?
3. Given that I am building a French drain, would I even need any weep
holes in the wall?

I am trying to build the most stable structure possible, but am worried
that I might be going into overkill mode. Any suggestions on my
questions above, or better way to build a similar type wall while still
allowing me to face with flagstone veneer would be very much
appreciated.

Naveen

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SJF
 
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wrote in message
ups.com...
Hello Everyone,

I am planning build two successive retaining walls 2' high (4' from
bottom of footer to top of the wall), and approximately 38' long.
The horizontal distance between the two walls will be approximately
three feet, with a step of 2' from the top of the bottom wall to the
top of the top wall, thus forming a small 3' planting terrace in
between. The total drop from top to bottom will be 4'.

I live in Southern California, so there is no frost line or threat of
freezing. The soil at 2' feet below grade is a composite of hard
clay/ virgin rotted sandstone. Both walls will be holding back a flat
grade. The newly formed terrace was previously a rounded/sloped mass
of unsupported earth, which was luckily only 4' high. The area above
the top wall runs flat to the back of the lot. Permitting is only
required for walls that are greater than 4' in height in my area.

My plan was to dig down to 2' below grade for each wall and pour a
concrete footer that is 8" in depth and 2' wide. I was planning on
using standard 8x8x16 cinder blocks for the wall itself. Based on
this, roughly two courses of cinder block would be below ground, while
another three would be above (yielding an exposed height of 2' for
each wall).

I am going to use rebar to tie the retaining wall to the footer, as
well as to provide lateral support through bond beam block running the
length of the wall. I will also fill and cap all blocks with solid
concrete. Both walls will be water proofed, be back filled with gravel
(covered with filter fabric to prevent clogging) and have a sloped
perforated drainage pipe leading water away from the wall.

The reason I have decided to build in this manner, rather than using a
pre-cast concrete dry stacking system, is that I plan, for aesthetic
reasons, to face the above ground sections of both walls with flagstone
veneer.

I have a few questions about this setup.

1. Do you think the placement of the top wall in proximity the bottom
wall would present any structural issues? If so, should I reduce the
size and depth of the footer in the top wall, thus reducing overall
weight?
2. Do I have to worry about moisture with regard to the underground
courses of cinderblock? If so, should I raise the footer?
3. Given that I am building a French drain, would I even need any weep
holes in the wall?

I am trying to build the most stable structure possible, but am worried
that I might be going into overkill mode. Any suggestions on my
questions above, or better way to build a similar type wall while still
allowing me to face with flagstone veneer would be very much
appreciated.

Naveen


You should be able to find a standard plan for such a wall. Years ago I got
one from our city building inspector. It showed details for a walls up to 4
feet high and up to 8 feet high.

Since your 3-foot setback from a 2-foot rise is within the one 1-1/2 to 1
angle of repose of ordinary soils, I would expect no special requirement for
either of the two low walls.

Not sure about the details of your french drain but if water can accumulate
behind the wall it must have an outlet -- usually weep holes. A pipe drain
could work if properly detailed as to slope and outfall point.

SJF










You mention clayey soils which may not permit drainage by normal
percolation. A french drain would seem to imply the use of weep holes.


  #3   Report Post  
Nehmo
 
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- naveenreddy_la -
I am planning build two successive retaining walls 2' high (4' from
bottom of footer to top of the wall), and approximately 38' long.
The horizontal distance between the two walls will be approximately
three feet, with a step of 2' from the top of the bottom wall to the
top of the top wall, thus forming a small 3' planting terrace in
between. The total drop from top to bottom will be 4'.


- Nehmo -
Read This First.
Retaining Walls, Means and Methods
https://courseware.vt.edu/users/mike...r/P19part1.pdf

And consider a segmental block wall
http://www.versa-lok.com/contractor/cInstallationr.htm

--
|||||||||||||||| Nehmo Sergheyev ||||||||||||||||
  #4   Report Post  
DanG
 
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Default

It sounds good to me. You might consider turning back a "dead
man" made of block and bond beam at each end and one at mid point
to make the structure even stronger.

(top posted for your convenience)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Keep the whole world singing . . . .
DanG (remove the sevens)




wrote in message
ups.com...
Hello Everyone,

I am planning build two successive retaining walls 2' high (4'
from
bottom of footer to top of the wall), and approximately 38'
long.
The horizontal distance between the two walls will be
approximately
three feet, with a step of 2' from the top of the bottom wall to
the
top of the top wall, thus forming a small 3' planting terrace in
between. The total drop from top to bottom will be 4'.

I live in Southern California, so there is no frost line or
threat of
freezing. The soil at 2' feet below grade is a composite of
hard
clay/ virgin rotted sandstone. Both walls will be holding back
a flat
grade. The newly formed terrace was previously a rounded/sloped
mass
of unsupported earth, which was luckily only 4' high. The area
above
the top wall runs flat to the back of the lot. Permitting is
only
required for walls that are greater than 4' in height in my
area.

My plan was to dig down to 2' below grade for each wall and pour
a
concrete footer that is 8" in depth and 2' wide. I was planning
on
using standard 8x8x16 cinder blocks for the wall itself. Based
on
this, roughly two courses of cinder block would be below ground,
while
another three would be above (yielding an exposed height of 2'
for
each wall).

I am going to use rebar to tie the retaining wall to the footer,
as
well as to provide lateral support through bond beam block
running the
length of the wall. I will also fill and cap all blocks with
solid
concrete. Both walls will be water proofed, be back filled with
gravel
(covered with filter fabric to prevent clogging) and have a
sloped
perforated drainage pipe leading water away from the wall.

The reason I have decided to build in this manner, rather than
using a
pre-cast concrete dry stacking system, is that I plan, for
aesthetic
reasons, to face the above ground sections of both walls with
flagstone
veneer.

I have a few questions about this setup.

1. Do you think the placement of the top wall in proximity the
bottom
wall would present any structural issues? If so, should I
reduce the
size and depth of the footer in the top wall, thus reducing
overall
weight?
2. Do I have to worry about moisture with regard to the
underground
courses of cinderblock? If so, should I raise the footer?
3. Given that I am building a French drain, would I even need
any weep
holes in the wall?

I am trying to build the most stable structure possible, but am
worried
that I might be going into overkill mode. Any suggestions on my
questions above, or better way to build a similar type wall
while still
allowing me to face with flagstone veneer would be very much
appreciated.

Naveen



  #5   Report Post  
Tim Fischer
 
Posts: n/a
Default

Warning: nitpick ahead.

Cinder blocks haven't been made for years. Concrete blocks are what you're
referring to.

-Tim




  #6   Report Post  
 
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Thanks for all of the responses.

I thought cinder blocks were the cheaper blocks (the rough sandy
surface) pressed into mold forms, available at any big box hardware
retailers for about $1 a piece. Whereas concrete blocks were actual
concrete poured into a similar form and fully cured - this being
stronger and more expensive. I could be mistaken.

Here are are my thoughts to the various responses

1 .Segmental Block Wall - I thought about using something like this at
first when planning the project, but cannot find any that meet our
aesthetic needs. The house is essentially modern in design, and most of
the segmental block wall systems lend themselves to a farm
house/country appearance.

2. French Drain - I meant a pipe drain - it's the same thing by a
different name. I plan to use this as a means to move water away from
the back of the wall, along with backfilled gravel for percolation.
The question is whether adding equally spaced weep holes along the
bottom of the wall is redundant or still necessary. I suppose since I
plan to face the wall with flagtone using mortar, using maximum
drainage is the best thing.

3. Dead Man - I thought about this as well. I suppose it couldn't hurt,
and since I am planing to do the work myself it should not be too much
to ask for. I have seen deadmen discussed for timber retaining walls,
but am not quite sure how this would be accomplished using block.
Would I flip and build the bond beam blocks perpendicular to the wall,
and then mortar succesive blocks to form a line back into the earth?

One other issue I failed to mention is that my property is at the
bottom of a hillside. While the grade from the top wall is flat
running 40 feet back (20 into the adjacent property behind the line)
and then rises to a moderately steep hill, on which my neighbor's house
is built upon. During the 40 year flood in Los Angeles we had last
year I was told (I just bought this house) that the hillside became
saturated. This led to some degree of flooding in all basements and
garages along my side of the street. The one thing I am worried about
is the shifting and heaving (aside from the hillside actually coming
down) of clay under such wet conditions. Should I consider buidling
the footing with a key, to help prevent shifting?

In any case, my next door neighbor has two terraced block retaining
walls of similar design and greater height that look that they have
been standing for 30 odd years. There are no visible cracks or bulges,
and are retaining a moderately sloped hillside. If I use this as a
guide, I suppose if I design the wall preoperly, there should not be
any issues, given my lesser requirements.

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