Preparing your Backyard for Retaining Wall Construction

Preparing your Site for Construction

Our backyard is very small and we needed to deal with several challenges in site preparation before starting construction.  We did not have easy access for equipment without involving my neighbor’s yard.  I talked to them and explained the magnitude of the project and they were happy to help out.  We decided to use the space between the two houses.  It was just big enough for a large skid steer to maneuver through but without this access it would have meant all hand labor. 

Allan Block has a great resource page for helping you ask the right question when getting started with your site preparation.  I used these helpful points to help me evaluate my site for property lines and utility locations and even how to discuss the project with my neighbors. 

Site Demolition

The entire slope where the walls were going was covered with overgrown brush, 4 large trees, old landscape timber edging and an old chain link fence.  Before any excavation could begin the site needed to be cleared.  Planning ahead for the demolition ultimately saved time and money.  I planned on removing the brush, the fence and the timbers myself, but not the trees.  So I contracted with a tree remover to take the trees down and haul the brush away.  I had all the brush piled in the front yard so the day the tree remover came it was ready to go.  What he and his crew did in 3 hours, I may still be working on.

The next things to go were all the stumps.  The machine this guy brought was a 4-wheel drive stump eating monster!  In less than three hours, 4 large stumps and about 75 small ones were chewed up into chips.  The end result was a clean canvas to start excavating.

Now that the hill was clear it was time to excavate.  The rented skid steer was delivered the next day and construction began.

Planning and Estimating your Segmental Retaining Wall

Our backyard wall was going to be a big project for a small backyard.  We needed to have a staging plan for all the material, but before that we needed to estimate the project and figure our budget.  The first step in building a retaining wall is to make a plan.  A good plan will lead to a good project.    To start, figure out how much grade change you are working with.  In our case we had around 7 ft.  We decided to cover this height with two terraced walls.  But how tall should each wall be?  We decided the lower wall should be about 3 ft tall for easy access for planting and gardening and the upper wall should cover the rest of the grade change and be as close to the property line as possible. 

Now that we knew the rough wall height and wall length (property line length) we used the incredibly easy AB Estimating Tool that we downloaded from allanblock.com.  When using this great tool, I had to remember to add a little to the wall height for the buried block.  You can also use this estimate to calculate the amount of wall rock and infill soil you will need.  Don’t forget to consider equipment rental such as a skid steer, plate compactor, diamond saw and maybe even a wet saw for cutting caps at the end.  It all adds up and if you plan ahead you will limit the surprises to your budget during the process.

How about staging the material?  I think a lot of do-it-yourselfers like me, forget that with a project of this magnitude you need to store/stage a lot of material.  Our project had 23 pallets of Allan Block, 3 truckloads of washed wall rock and 1 truck load of sand, drain piping and geogrid.  We also had to have a place to store the spoil, or the earth that we removed during the excavation of the hillside.  This was a huge pile that was there from day one until the end of the project when it was used as topsoil backfill.  Because we had a good plan for all the materials, the neighbors were surprised we had space to actually build the wall!  

Can I Use a Simple Gravity Wall?

The question often comes up whether a wall can be built by just stacking block using the installation recommendations found on the Allan Block website, or if geogrid reinforcement is necessary behind the wall.  Every time this question is asked, four equally important issues need to be addressed:  how tall is the retaining wall, what is going to be above the wall, what type of soil will be behind the wall, and what type of block is being used?

To help simplify this decision, take a look at the Maximum Gravity Wall Height Chart on the Allan Block website.  This handy chart can give you an idea of the maximum wall height for a variety of situations.  The AB Commercial Wall Manual also describes the fundamental principles of gravity walls and how to build them using Allan Block retaining wall blocks.

How tall is the retaining wall?

This is an important question to answer because the taller the segmental retaining wall (SRW), the more soil behind the wall is going to be trying to push the wall forward or tip it over.  This is called the wall’s external stability.  In order for a gravity wall to work, the weight of the block and crushed stone within the block must be greater than the forces pushing against the wall.

What is going to be above the wall?

It is intuitive that a landscape wall with a level planter bed of flowers above it would have less force pushing on the wall than if you were building a retaining wall to hold up your driveway, but what about a slope above the wall?  When your wall has a slope above it, there is more weight above the wall trying to push the wall over.  What another wall above, forming a terrace?  True, you might only have two 3-foot (0.9 m) walls, but that top wall of the terrace is going to be pushing on the bottom wall.  In summary, any time you have a surcharge (some type of additional weight) above the wall, your overall gravity wall height will be reduced.

 

What type of soil is behind the wall?

Clay soils are going to push against the wall more than granular sandy soils.  This is because a typical clay soil has a lower internal angle of friction than a sandy soil. Use the AB Commercial Wall Manual  to learn more about soils and their influence on the wall.

Which Allan Block retaining wall block is being used?

A wall made from AB Stones will tilt into the hill more than a wall made from AB Classic blocks.  This is because the AB Stones have a setback of roughly 12-degrees, while the AB Classic has a setback of about 6-degrees.  Therefore, under the same conditions, a gravity wall constructed from AB Stones will have greater stability than a wall built using the AB Classic.

Next time you are planning your landscape or retaining wall project, keep these four questions in mind.  Then, reference the Allan Block website to assist in designing a gravity retaining wall that you can enjoy for a lifetime.

It’s All About the Base for Walls with No Trouble

If you are thinking about building a retaining wall in your yard, remember: It’s all about the base.  This simple step often determines the success or failure of your project. 

Have you noticed retaining walls that sag in the middle or look like they are not level?  Such imperfections are noticeable to the eye, and unfortunately are not easy to fix once the wall is constructed.  Base preparation is the key to creating a professional, long lasting retaining wall.

Use these simple steps:

·               Remove all surface vegetation and organic materials such as black dirt under your base.

·               Start at the lowest point of your wall.

·               Dig a 24” x 6” deep trench.  Add an inch in depth for every foot of wall height.

·               Make sure the bottom of the trench is solid and has not been filled with loose soil.

·               Fill the trench with a well graded granular fill at least 6” deep. 

·               Use a plate or hand compactor to make to make sure the base is strong.  Compaction of this material is key to creating a solid foundation.

·               Use a 4 foot level to make adjustments by adding or removing granular fill where necessary.

When installing the first row of blocks, spend extra time and make sure they are level and true. 

So remember, if you focus on the base, you will be able to build a trouble-free wall that you can enjoy for a lifetime.

For more tips and instructions on building retaining walls, visit our website at allanblock.com

Allan Block Master Wall Builders - The Best of 2015

Allan Block Master Wall Builders - The Best of 201

Juan Urro - Land Tek

Master Wall Builder. The Best of the Best - The Cream of the Crop. Contractors that reach this level have both the knowledge and the skills to build top quality Allan Block walls. Set apart from other wall installers, the Master Wall Builder is more widely accepted and sought after by the engineering community to be specified on project plans.

These guys work hard and we appreciate them - Over 45 contractors earn the status this year.  Check out the list of Contractors that have reached this goal in 2015.

• Abel Popoca - CR Schmidt, Warrenville, IL
• Alejandro Ferrer - CR Schmidt, Warrenville, IL
• Alex Lommel - Arctic Terra, Anchorage, AK
• Andy Sketo - Landmark Stone, Cox's Creek, KY
• Anselmo Mendoza - Twinn Cedars Landscape. Tom's River, NJ
• Barry Bonell - Ladybug Landscaping, Kamloops, BC Canada
• Brian Tactikos - Panna LLC, Red Bank, NJ
• Brooks Sketo - Landmark Stone, Cox's Creek, KY
• Chris Burke - ICB, Albany, New Zealand
• Chris Pereira - Grade-A Construction, Kamloops, BC Canada
• Clint Pino - Cornerstone Retaining Walls, Evergreen, CO
• Cole Sampson - Sampson Construction Co., Roanoke, VA
• Darryl Creekmore - Slaton Bros, Centennial, CO
• Daryl Grassick - Canadian Lawn Care Langley, BC Canada
• David Paulus - Twinn Cedars Landscape. Tom's River, NJ
• Dennis Organ - CR Schmidt, Warrenville, IL
• Francisco Espinoza - Pedersen Company, St. Charles, IL
• Frank Nigro - Twinn Cedars Landscape. Tom's River, NJ
• Frank Nigro Jr. - Twinn Cedars Landscape. Tom's River, NJ
• Jim Dougherty - Slaton Bros, Centennial, CO
• John Graham - Alicon Ltd, Taukau, New Zealand
• John Lockett -- CR Schmidt, Warrenville, IL
• John McKnight - SBI, Louisville, KY
• Jon Calle - Pickering Valley Landscape, Elverson, PA
• Jose Alfuro - CR Schmidt, Warrenville, IL
• Jose Hernandez - CR Schmidt, Warrenville, IL
• Josh Boone - GreenState Landscaping. Lumberton, NC
• Josh Ulrich - Landmark Stone, Cox's Creek, KY
• Joshua Ross - Bzak Landscaping, Milford, OH
• Juan Munoz - CR Schmidt, Warrenville, IL
• Juan Reyes - Pedersen Company, St. Charles, IL
• Juan Urro - LandTek Construction LLC, Piscataway, NJ
• Kamal Preet Singh Chahal - Deerwood Landscaping Ltd., N. Vancouver, BC Canada
• Michael R. Nutto - Panna LLC, Oceanport, NJ
• Mike McKenzie - Slaton Bros, Centennial, CO
• Neri Campos - Slaton Bros, Centennial, CO
• Paco Espinoza - Pedersen Company, St. Charles, IL
• Pepe Resindez - SBI, Louisville, KY
• Peter McGlynn - Esposito Construction, Rahway, NJ
• Rene Gonzalez - Pedersen Company, St. Charles, IL
• Richard Wills - ICB, Albany, New Zealand
• Samuel Mendoza - Twinn Cedars Landscape. Tom's River, NJ
• Terry Gregory - Bzak Landscaping, Milford, OH
• Terry Moris -  - Landmark Stone, Cox's Creek, KY
• Tom White - Country Side Landscaping, Parker City, IN
• Tom Williams - T. Williams Inc, Wayne, NJ
• Troy Taylor - Greenstate Landscaping, Lumberton, NC

Thanks again for all your hard work building quality Allan Block retaining walls!  Want to see your name of this list? Learn how to become an Allan Block Master Wall Builder here.