If your hillside retaining wall is leaning, bulging or cracking, it may no longer be holding the soil the way it was designed to. On a slope, the soils report picks the fix, and the new wall has to be designed and permitted around what that report says.
I design and build on hillsides, and I prepare the plans and pull the permits myself. This is how I look at a wall that needs replacing.
Rimkus, a forensic engineering firm, sorts the signs by how fast to act.
Get it looked at now:
Treat the area near that wall as unsafe until an engineer has seen it.
Get a professional review soon:
Keep watching:
The same firm warns that what you see on the face often understates what is going on in the soil behind it.
On a hillside, the soil behind the wall and the rock under it set the rules. A licensed soils engineer and engineering geologist write that report. I don’t write it. I design around it.
LA County’s geotechnical manual lists what the report has to cover for a retaining wall:
The wall has to resist sliding and tipping over with a safety factor of at least 1.5 each way.
Taking out an old wall on a slope is its own risk. The same manual lists removal and replacement of retaining walls as one of the conditions that may need a temporary slope stability analysis. Before the old wall comes down, the engineers have to say how the slope stays put while there is no wall there.
The soils report and the space on your lot narrow this list down fast.
Cantilevered concrete wall. A reinforced concrete wall on a wide footing, shaped like an upside-down T. The weight of the soil sitting on the back of the footing keeps the wall from tipping. It needs room to dig behind the wall for that footing.
Soldier piles with lagging. Steel beams set in drilled holes and backfilled with concrete. The space between the beams is closed with lagging, usually timber or sprayed concrete. The Federal Highway Administration (FHWA) calls this the most common type of anchored wall in the US. The beams are drilled in, so it can work where there is no room to dig out a big footing.
Tiebacks. Ground anchors drilled back through the wall into stable soil or rock, then locked off to hold the wall in. They are often added to a soldier pile wall. FHWA notes ground anchors are also used to stabilize slopes and landslides. LA County wants every connection, tiebacks and lagging included, covered in the soils report.
Segmental block walls (Keystone is one brand). Stacked concrete blocks with layers of geogrid running back into compacted soil behind them. The blocks are the face. The reinforced soil does the holding. Federal standard details put the minimum geogrid length at 0.7 times the wall height, and never under 8 feet. On a steep lot there is often no room to dig that far back, and the cut itself can make the slope less stable. For a wall holding up a house or a steep slope, this type often does not fit. (More on what a steep lot changes, from access to foundations, in building on a steep slope.)
Water is behind most retaining wall failures. Rimkus calls drainage failure one of the most common causes of wall damage. Wet soil pushes harder, and trapped water adds its own pressure.
A wall needs a way to let that water out: gravel backfill, a perforated drain pipe, filter fabric, weep holes. Over time those clog with silt, debris and roots, and water builds up even when the yard looks dry.
LA County is strict here:
When I replace a wall, I draw the drain, the gravel and the outlet on the same plans as the wall.
In Calabasas, a retaining wall over 4 feet needs a soils report that backs up its design, and it gets its own permit. I go through the city’s hillside steps in hillside building permits in Calabasas and LA County.
In unincorporated LA County, the county’s building code manual says a wall up to 4 feet, measured from the bottom of the footing to the top of the wall, does not need a permit. That exemption does not apply if the wall holds up a surcharge. On a hillside, a slope, a driveway or a house above the wall can be that surcharge, so ask before you assume a short wall is exempt.
Inside the City of Los Angeles, the Department of Building and Safety has its own retaining wall bulletins. City, county or Calabasas, find out who has your lot first.
On a hillside wall, the design, the soils report and the build have to match. When one company designs it and another builds it, small changes in the field can drift away from what the engineers approved.
Vision In Design Inc is a design-build company. If you call me about a failing wall, I can’t give you an honest number until I know what the wall has to do, so I do a preliminary design first, and once you like the design, I give you the estimate. If you agree, we move forward. If not, we walk away, no contract, no obligation.
If you go ahead, I design the wall around the soils report, prepare the plans, and file and pull the permit. Then we build what was drawn and permitted.
More on hillside construction, and on structural and foundation repair if the wall problem has reached the house.
If you have a retaining wall on a slope that is leaning, cracking or leaking, call me at (818) 645-1129 for a free consultation. Have the address ready, a few photos of the wall, and any old soils report for the property.
Leaning, bulging or bowing are signs the wall may no longer be holding the soil as designed. Have an engineer look at it before deciding between a repair and a new wall.
In Calabasas, a wall over 4 feet needs one. In LA County, the plan checker decides if your job goes to geotechnical review. On a hillside, plan on it.
Sometimes. A segmental block wall needs a deep zone of reinforced soil behind it, at least 0.7 times the wall height under federal standard details. On a steep lot with a house above, there is often no room for it.
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