Slope stabilization that fits how your hillside was built.

Every hillside moves a little, all the time. How much comes down to how the slope was built and what it is made of. Man made slopes are supposed to have their fill soil compaction tested as it goes in, and fill that was not compacted properly leaves the slope unstable from the start. Clay makes it worse, because it expands and contracts with moisture and turns slippery when wet.

Plants and drainage are the other half of the story. Roots weave the soil together and cut down on runoff during heavy rain. Drainage is critical to how long a slope lasts, which is why well built slopes carry catch basins and V shaped ditches that break up the water before it can wash the slope out. When those protections fall short, the movement shows up as warning signs around the house, such as leaning trees, tilting fences and walls, gaps in the concrete, and leaning deck posts. The full set is on our hillside problem signs page.

Once a slope is moving, the goal is to slow it down and then stop it. We do that with three families of methods: piers, piles and walls. Each works a different way, and each costs a different amount.

Retaining wall systems hold back the slope and the sideways push it puts on the wall. Soldier piles are large drilled concrete piles set tightly in a line through the fill and into dense native soil. Soil nails are grouted bars drilled into the hillside and tied together behind a concrete or shotcrete wall. Each is covered in more detail on the hillside repair solutions page.

A retaining wall's job is to hold back the slope and the sideways load the slope puts on it. Walls can be built many ways. On a hillside we use piers, beams, helical piles and anchors together with the wall system, so the wall resists the sideways push and also gets support from below, which makes it less likely to settle downward.

When a slope already has a retaining wall, tiebacks can often be installed through the wall and anchored into the dense native soil behind the loose fill. That approach, the same one behind our retaining wall anchoring systems, costs far less than building a new wall. When a wall has been pushed too far to save, a new retaining wall with tiebacks is built to take the sideways soil load. A damaged wall with no moving slope behind it is retaining wall repair work rather than hillside work.

Soldier piles are the heavy option. The piles are drilled through the fill that forms the slope and down into the dense native soil beneath it, and then soil is compacted back behind them. The method needs special drilling rigs and is costly, so it is matched to slopes that call for it. The soldier pile method page walks through the steps.

Soil nails are similar to helical tieback anchors, except that each nail is a drilled hole filled with grout. A single threaded bar is drilled into the hillside, then grout goes in to encase the bar and lock it in place. Once the grout hardens, it adds skin friction, the grip between the grout and the soil around it, which helps hold the nail. The nails are tied into a rebar cage or mat, and a concrete or shotcrete wall is built to tie them together. The soil nailing process page covers how an install runs.

A moving slope can carry more than the yard with it. As the ground shifts, it pulls everything built on it downhill, including patios, decks and sometimes the house. When the home is moving as well, tiebacks can be installed on its foundation to anchor it into the native soil and keep it from moving sideways, and helical piers or push piers carry the parts of the house that have settled.

A row of hillside townhouses in Chino Hills shows the pattern. The structure had settled as much as 7 inches and was moving sideways toward the slope. Our crew installed 33 helical piers around the perimeter and lifted it 6 inches, with helical tieback anchors planned for the sideways movement. The Chino Hills townhouse project has the photos.

Every slope is built differently, so every stabilization plan is designed to fit the slope's current condition. Piers, piles and wall systems each have their own track record and their own cost, and the most expensive option is not always the better one. How far the slope has moved before anyone looks at it matters too. When movement is caught early, it may not have reached the house yet, which keeps the repair smaller.

It also matters which ground is moving. If the problem is the soil directly under the house rather than the slope, that is soil stabilization under a house. Slopes on commercial sites are covered by commercial slope remediation. For a home on a hillside, the first step is a free evaluation of the slope and the house together.