Alaska Street: Saving a 100-Year-Old Home, Heirloom Olive Trees — and $133,000

Back in 2005 when the City of Tacoma set out to widen Alaska Street, the goal seemed straightforward: accommodate a new middle school, a new fire station, and increased traffic demand.

The reality was anything but simple.

To meet AASHTO roadway standards, the city needed to cut into a hillside and construct a retaining wall. At the top of that hillside sat a 100-year-old home — and three heirloom Italian olive trees planted by the homeowner’s grandfather.

The homeowner made it clear: not one inch of his property would be disturbed.

That’s where the engineering challenge began.

The Situation

Tacoma needed additional roadway width for:

• Sidewalks

• Bike lanes

• A left-turn lane

To achieve that expansion, crews would need to excavate into a hillside directly below a private residence. Without a slope easement — and without the homeowner’s approval — traditional excavation and full geogrid-based wall solutions were not viable.

At worst, excavation would have come within two inches of the home’s foundation.

That wasn’t acceptable.

The Engineering Constraint

The City’s initial engineering study suggested a sheet pile wall design — but sheet walls come at a price.

According to the City’s Civil Engineer, Dan Seabrand, the sheet wall alternative was estimated at approximately $40 per square foot in material cost. It also would have required significant vertical embedment below grade to develop passive resistance, increasing excavation depth and construction risk.

The project needed:

• Minimal excavation

• Structural integrity

• Compliance with AASHTO standards

• Zero encroachment

• A visually acceptable solution for a residential neighborhood

That’s a narrow window.

The Hybrid Solution

Instead of choosing between a full MSE wall or a deep modular gravity system, the team redesigned the wall using GravityStone’s Vertical Hybrid System — a combination approach we discussed in a previous post.

The approach combined:

• A modular double-cell base (four courses high)

• A transition to single-cell units (three courses)

• A GravityStone Core (Fat Face) MSE section above, reinforced with geogrid once space allowed

This configuration delivered structural performance where needed — without requiring geogrid reinforcement across the entire wall and without deep vertical excavation.

The retaining walls ranged from 3 feet to 16 feet in height:

• 3–4 ft walls used Core units

• Taller walls incorporated the hybrid configuration

Most importantly, installation saved eight feet of excavation depth, allowing construction just six feet from the home’s foundation.

The hillside remained intact.The olive trees remained untouched.The home remained undisturbed.

The Financial Impact

In 2005 GravityStone’s material cost came in at approximately $20 per square foot. Compared to the $40 per square foot sheet wall alternative, Tacoma saved more than $80,000 in material costs alone. That's the equivalent of $133,000 today in 2026

But the savings didn’t stop there.

Because the system:

• Required less excavation

• Didn’t rely on heavy machinery

• Installed block-by-block efficiently

The project stayed on schedule and under budget.

As Seabrand put it, installing the hybrid system was “nothing short of an engineering miracle” given the tight right-of-way and zero encroachment constraint.

The Result No One Talks About Enough

A retaining wall isn’t just structural — it’s visual.

One of the overlooked strengths of the hybrid approach was that both structural strategies share the same face texture. From the street, no one could tell two systems were used.

The ultimate validation?

Two homeowners across the street later installed their own private retaining walls using GravityStone.

That’s not engineering approval.That’s neighborhood approval.

Why This Project Still Matters

Alaska Street wasn’t just a retaining wall.

It demonstrated that:

• Hybrid design can solve right-of-way limitations

• Deep excavation can be avoided with smart structural strategy

• Big block and cast-in-place are not the only options when sites get tight

• Structural solutions can respect existing property and legacy

• Cost savings don’t require compromising performance

This project set the stage for how GravityStone Hybrid walls would later be used in tight urban corridors, near structures, and in complex right-of-way conditions.

And not one olive tree was harmed.