September 17, 2013 Off

Retaining Wall – Built Right!

By in Retaining Walls

     At Blue Dot Landscaping, we build retaining walls the correct way. This article will show you the basics of building a retaining wall that will last. Note the first attempt by this homeowner’s original contractor did not work..     

 Poorly constructed retaining wall         Poorly constructed retaining wall          

    We take pride in our work with over 20 years of experience in the landscape construction business.  Every single one of our hardscape projects completed over the last 20 years is still there and is still working.  This includes stone walkways, driveways, patios with pavers, and much more… in addition to retaining walls.  What keeps us in business is the ability and the desire to complete every job the right way. Blue Dot Landscaping likes to see its clients pleased with their projects…. not just upon completion…. but for many years to come.

Excavation

After removing the cheap and poorly built concrete block wall, our task was to build a 70 feet long  retaining wall overcoming a difference of 5 feet between the two levels.  The upper level created a nice outdoor area for the homeowner overlooking a river.  The lower level abuts a river.  Yes, we said ‘river’ twice.  This river, as most do, sometimes rises and causes erosion problems.   We wanted to build as sturdy as possible the retaining wall in order to prevent any new failures.   We assured adequate foundation that would support the future structure. That was done by excavating a 4 ft wide by 2 ft deep trench, at the base of the retaining wall. That trench, filled with properly selected drainage material, forms the leveling pad, on which the wall lays. We made sure that the foundation soil was compacted until no movement was observable with a passing of the compactor plate tamper. All loose and soft materials that couldn’t be compacted were removed.

Excavation          Excavation

    To prevent mixing the soil with the drainage material we wrapped non-woven filter fabric over bottom and top. Geotextile filters retain soil particles while allowing seeping water to drain freely. We choose proper drainage aggregate – #57 stone – to fill the leveling pad. Used the flat plate tamper to assure that the leveling pad was densely compacted. We always use precision instruments as transit level to ascertain level.

Laying out that first course is the most crucial step of the process to insure accurate and acceptable result. We checked the blocks for level and alignment. We made sure that the blocks were in full contact with the base. The level was checked and re-checked.

first block of retaining wall

Laying the first layer of the block retaining wall

An important step was filling with drainage aggregate any openings in and between the segmental units. We back filled the first course with #57 stone : 36” wide and up to height of the segmental retaining wall unit.

backfilling the retaining wall

Backfilling the retaining wall

We used AnchorTM Diamond Pro Stone Cut retaining wall blocks; dimensions: 18” L x 12” W x 8” H; weight: 86 lbs; color: earth blend. The units had a lip on the bottom rear side to lock the blocks together and create a step effect.

 

   Building up, we placed and moved the segmental retaining wall units to the lips to establish proper setback. In the same manner as the first course we back filled the successive courses: used drainage aggregate to fill openings in and between units, placed drainage aggregate behind and up to height segments, compact.

         

    A major and important part of any retaining wall is geogrid.   We installed Stratagrid  SG200 – This type of geogrid reinforces the wall with its high molecular weight and high tenacity polyester yarn. The yarns are precision knitted into a dimensionally stable network of apertures providing tensile reinforcement capacity in both principle directions. A black UV stabilized saturation coating provides further chemical and mechanical benefits.  It provides a LTDS of 1919 lbs/ft.

geo grid

Installing Geogrid

First we made sure the drainage aggregate was level with the segmental blocks. The soil reinforcement needed to be install at a proper elevation and orientation. Then we cut geosynthetic reinforcement and installed with strength direction perpendicular to wall face. Placed segmental unit on top of the geogrid and established proper setback. We locked the geogrid between two blocks.We ensure that the reinforcement material was not seamed or overlapped.

    After cleaning off the last layer we installed segmental cap units as a finished touch. Covered the drainage aggregate with non-woven filter fabric, added topsoil, and finished the grade at the top of the retaining wall.

At the bottom, along the wall face we used non-woven filter fabric to wrapped aggregate stone 2 feet in diameter. After topsoil placement we had the wrapped stone and first two courses of the retaining wall below the ground.

 

To secure the top grade we used erosion control fabric, laid out sod and planted ground cover.

          

       The final product was an 8 ft tall (5 foot above ground and 3 feet below), 70 ft long  retaining wall that weights 252 000 lbs.  We really believe this will last a very long time… river or no river.

See our retaining wall page.

 

Update:  It happened – the most rainfall we’ve had in 100 years.  Look how high the river water rose…

tate25

3 Days later – YAY!

tate27
Written by Rich Regan - Blue Dot Landscaping - Visit Website

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