A 'Precarious Balancing Act' to Preserve a Stone Retaining Wall

A returning client asked about repairing a leaning retaining wall for a large planter in his driveway. The year before, I had repaired the porch on his late 1920s storybook-style bungalow home in Los Angeles. I suggested if he were to dig the soil out from behind the stone wall, we could add rebar, push it plump and pump in some concrete to bond it together.

Possessing a shovel and the gumption to use it, the homeowner started excavating behind the wall. A few days into the project, the middle section collapsed; he thought that the clay soil must have been holding it in place, but I suspected otherwise.

I investigated the collapsed section and found that it was an unreinforced wall with no rebar connecting the stone to its concrete footing and that the site’s expansive clay soil had managed to push the stone wall beyond the edge of its footing. Over the years, the clay soil would get saturated, push the wall a little, and then contract, with the remaining gap eventually filling in; the cycle had repeated itself to the point that the wall had nearly sheared off its footing, particularly in the area where it collapsed.

Complicating any repair efforts, the circa-1920s stone wall had been rebuilt in the 1970s using Portland cement mortar, which was stronger than the stone it held together (the stone broke when we tried to chip the mortar off). The original wall would have been built using lime mortar, which is relatively soft and would have been easy to break apart from the stone. As a result, we needed to reassemble the wall with large, salvaged pieces while I tried to get my hands on similar stone for infill.

I didn’t want to attempt to move the wall back onto the footing with a Bobcat and risk further collapse while repairing the wall, so my plan was to rebuild the collapsed portion, then bond the driveway wall in situ to a new, poured-concrete retaining wall, doing an end run around its precarious balancing act.

To read the rest of this story by contractor Gerret Wikoff for JLC, click here.