Engineers can save owners money by using helical tiebacks for lateral support of retaining walls and foundations. Here a pair of retaining walls create a hillside terrace.
These retaining walls are held by helical tiebacks; the ends of the tiebacks protrude from the top faces of the red posts.
Avalon recommended the lowest portion of this wall be cast-in-place concrete to hold the lowest wood members of the wall above constant wet conditions.
Soils Engineer: Ashton Buckner of Haro, Kasunich & Associates, Inc.
Structural Design Engineer: Jody Collins of Ifland Engineers
Civil Engineer: Jon Ifland of Ifland Engineers
CASE STUDY #03 February 2025 (2 of 2)
The upper portion of the wall extends above the retained earth and functions as an impact wall to protect against debris flow from up the hill.
CASE STUDY #81 (1 of 2)
Avalon used helical tiebacks to laterally support a retaining wall of wide drilled piers on the edge of a sandy bluff.
Soils Engineer: Chris George, Haro-Kasunich & Associates.
CASE STUDY #81 (2 of 2)
Avalon installed 65-foot tiebacks into the bluff diagonally at approximately 25 degrees to support the retaining wall. Each of the 1.75 inch square-shaft helical tiebacks were tested to 73,000 lbs in tension.
Soils Engineer: Chris George, Haro-Kasunich & Associates.
Avalon builds retaining walls in difficult places, often inaccessible to large equipment.
Soils Engineer: Chris George, Haro-Kasunich & Associates.
CASE STUDY #05 (1 of 5)
The following five pictures concern the replacement of a collapsed retaining wall that had been supporting a creek-side home. The first photo shows the retaining wall which had fallen over.
CASE STUDY #05 (2 of 5)
With small equipment, Avalon installed vertical helical piers to support the new retaining wall, with helical tiebacks for lateral support.
CASE STUDY #05 (3 of 5)
Vertical and diagonal helix after preliminary concrete pour.
CASE STUDY #05 (4 of 5)
The tieback extensions are galvanized, epoxy coated, and taped for triple protection. Foam wrapping was installed to protect the tape from gravel backfill.
Structural Design Engineer: Robert Patterson, Patterson & Associates.
CASE STUDY #05 (5 of 5)
Completed wall with patio.
A retaining wall with helical tiebacks on a steep bluff.
Soils Engineer: Tharp & Associates
Design Engineer: Don Ifland, Ifland Engineers
CASE STUDY #13 (1 of 2)
Limited access is rarely a problem for Avalon. This site precluded the use of a tractor, and the steepness of the slope made the use of a portable drilling rig impractical. To make matters even worse, the soil was too weak to support a typical retaining wall.
CASE STUDY #13 (2 of 2)
The solution involved multiple steps. Avalon used vertical piers to support the weight of the wall and deck above, and pairs of helix tiebacks, one high and one low, to resist the lateral pressures of the hillside and house. In the photo below, the lower row of tiebacks are below grade.
Avalon installs retaining walls under existing houses.
Retaining walls can be used to expand a backyard.
The vertical steel beams are W beams, which are placed in deep holes, cleaned and primed to one foot below ground, and then concrete is poured in the holes.
Later, pressure treated lumber or reinforced concrete is placed between the W beams to create the wall.
Many owners opt for reinforced concrete between the W beams for a better-looking and longer-lasting wall.
In this photo, the owner stained the concrete between the W beams with concrete stain.
Avalon has fixed too many shabby retaining walls to consider putting our name to one that won't last.
We prime our W-beams before pouring concrete to protect them from rust at grade level.
To ensure the longevity of the retaining wall, we strongly recommend not using wood planks, but instead reinforced concrete or pressure-treated wood.
Avalon builds concrete walls with continuous horizontal rebar between the W-beames. This wall is ready for more formwork and then concrete to encase the rebar.
Such a wall is stronger than one built with wood planks or pre-fabricated concrete planks.
Concrete walls can be stained soon after pouring.
We recommend Smith's earth-friendly, water-based Moss Green, Olive Green, or Bark Brown for natural look.
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Avalon encourages engineers to explore designs with Expanded Polystyrene (EPS) for large backfills.
It is cheap, inert, non-toxic, stable, does not absorb water, and it is approximately 160 times lighter than compacted dirt.
Because it weighs so little, the pressure against the retaining wall is less, potentially saving the owner significantly on construction costs of the wall.
Here the tied-back retaining wall is ready for the installation of a sub-drain and the placement of EPS blocks and rock.
The rock will be placed in veins surround the tiebacks and between sections of EPS blocks. After the installation of the EPS blocks and rock, the tiebacks will be tightened.
In this photo, EPS blocks and rock veins are being installed. Earlier, special geo-fabric, rock, and a perforated pipe had been installed behind the base of the wall forming a sub-drain. Later, the filter fabric will be folded over the backfill, with soil placed on top.
Soils Engineering: Joe Rafferty, Redwood Geotechnical
Structural Design: Bob Patterson, Patterson & Associates.
A second wall with EPS block, with drain rock.
Soils Engineering Becky Dees, Dees & Associates
Structural Design: Bob Patterson, Patterson & Associates.
A third wall with EPS block. Gaps are filled with rock as water passages.
Soils Engineering: Becky Dees, Dees & Associates
Structural Design: Bob Patterson, Patterson & Associates.
Avalon built a series of impact walls to protect life and property against a potential log-slide. The wall is supported by 3.5" round shaft helical piers both vertical and diagonal, with W beams and C channel. (Photo taken before installation of 6x lagging between the vertical W beams.)
Soils engineer: Becky Dees, Dees & Associates.
Project engineer: Bob Patterson, Patterson & Associates.
Avalon Structural, Inc. 181 Ridgeview Drive Aptos, CA 95003 (831) 479-4389 (office) info@avalonstructural.com
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