If you have a sloped section of earth in your yard that needs support from a retaining wall, you can do much of the work yourself. An engineer can help you plan for any necessary rebar installation, then you can pump the concrete yourself or hire it out. Here are instruction to help you do much of this retaining wall project yourself.
Prepare to Build the Retaining Wall
Before you begin to dig a trench for the base of your retaining wall, you may first need to check with your local building department to see if you need a permit to build the wall. Depending upon the height of the wall and the amount of soil the wall is going to be holding back, you may need to have a permit with approval from a structural engineer on your plans to make sure your retaining wall is going to be sound. Your local building inspector will also tell you any specific rebar requirements for your retaining wall.
Excavate for Your Wall Footings
Next, find out the depth of your area's frost line by asking your local building inspector before you dig the footing trench. The frost line is the depth that moisture in your area's soil will freeze during the winter. For example, the frost line in Minnesota is a maximum depth of 60 inches, but in several southern states the frost line maximum is only 40 inches. You will need to dig the trench just below your area's frost line because freezing soil under your retaining wall's footings can cause damage to the foundation of the wall. This can lead to your wall moving within the soil and damage in the base of the concrete wall.
Now you can begin to dig a trench for your retaining wall to a depth below your area's frost line. The width of the trench will need to be as wide as your retaining wall, and the soil walls of the trench will create the forms for your footing.
Build the Forms
Measure and cut plywood forms to reach from the top of the trench to three and a half inches above where the top of your wall with end. Use a paint brush to apply motor oil over the inside surface of the plywood forms. This will prevent the concrete from sticking to the plywood forms after the concrete has cured. If your retaining wall requires rebar for strength, install the rebar at this point.
Screw in place two-by-fours as form supports every 24 inches on the outside of the forms to hold the forms in place. The form supports should reach all the way to the top of the forms. Attach plywood end pieces also coated in motor oil to cap off the ends of the forms.
Then, attach two-by-four spacers using wood screws every 24 inches along the top-inside of the forms. The spacers should be cut to the same measurement as your wall's width and will hold the forms in place. Pound wooden stakes into the ground on the outside of the form supports, next to each two-by-four. Connect the stakes to the form supports with wood screws.
Pump the Concrete
Pumping the concrete into your retaining wall forms will give you the ability to deliver the concrete into hard-to-reach areas. You can fill your forms with pumped concrete without building up the height of the forms in stages and without manually shoveling the concrete into your forms. You can do your own pumping with a concrete pump or hire a commercial concrete pumping truck to do the work. For more information about hiring a truck, contact a company like Masterlink Concrete Pumping.
If you do your own pumping, be sure to lubricate the pumping pipe with motor oil to prevent the concrete from getting stuck inside. Then, make sure your pump pipe is at least three times the diameter of the larges pieces of concrete gravel. When you mix the concrete for pumping, you don't want it too wet or too dry, but with a slump of between 50 and 150 mm.
When handling your own concrete pumping, you may use a vacuum-powered squeeze pump. This type of pump will pump out 20 cubic meters of concrete every hour through a three inch-wide pipe. A direct-acting pump is a larger capacity concrete pump, pumping out up to 130 cubic meters of concrete every hour through an eight-inch wide pipe. A direct-acting pump is usually used for larger concrete jobs.
Fill the forms with concrete, then let the concrete fully cure before removing the forms.