Building the Concrete Retaining Walls

These concrete walls need to be strong and heavy.

We need concrete retaining walls around the perimeter of the house as well as interior structural concrete walls.  These walls must support the weight of the house (point loads) as well as provide shear strength.  Importantly, these walls must contribute to the 1.5 million pounds of dead weight that we require to offset the hydrostatic pressure (so our house doesn’t float).

Where are we going with this?  Yes Scott, you are correct – more rebar.

Placing rebar in the north-west part of the perimeter retaining wall.

Placing rebar in the north-west part of the perimeter retaining wall.

We require two layers of reinforcing steel (rebar) on our perimeter retaining walls, an inside layer and an outside layer.  Each layer must go vertically and horizontally.  The outside layer is #5 rebar and the inside layer is #4 rebar (5/8 and 1/2 inch in diameter, respectively).  The interior structural concrete walls will utilize the same rebar pattern (one layer of #4 rebar 12 inches on center, vertically and horizontally).

The concrete walls will not be poured in place – they will be shotcrete (gunite).  To meet the building code requirements, we need a concrete test panel with the same rebar pattern as our most dense area in the retaining wall.  The concrete properties of the panel (e.g., strength and voids) must be tested by an independent inspector prior to proceeding.  We are planning to shotcrete our test panel on Wednesday (March 18).

Vertical rebar layers in place, 12 inches on center. Note the form on the top of the retaining wall, where the hollow core concrete panels will sit.

Outside vertical rebar in place, 12 inches on center. Note the form on the top of the retaining wall, where the hollow core concrete panels will sit.  The horizontal and inside layers are next.

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