Contractors who built the repair vault for tunnel machine Bertha have filed a lawsuit seeking millions in extra pay for extreme soil problems and other obstacles in the tricky 2014 job.

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The contractors who built tunnel-machine Bertha’s repair vault two years ago are suing for $11 million in extra pay, saying their unprecedented efforts in tough soil conditions cost much more than imagined.

Malcolm Drilling Company, which created the concrete-lined, 120-foot-deep access vault, filed the lawsuit this spring against Seattle Tunnel Partners (STP), prime contractors for the future Highway 99 tunnel.

The lawsuit adds a few details to a dramatic chapter in the tunnel saga, where crews fended off groundwater and sloppy soils to carve a vertical rescue path to reach the damaged tunnel machine.

The vault by itself qualifies as a megaproject, complete with engineering breakthroughs, and now some cost overruns.

The giant tunnel drill had been stalled deep underground next to Seattle’s central waterfront since overheating in December 2013. STP hired Malcolm to create the ring-shaped rescue vault — necessary to retrieve the 4-million-pound cutter drive at the machine’s front end and allow it to be lifted to the surface. A new bearing, protective seals, and some reinforcing steel were installed at street level.

Malcolm, based in San Francisco, asserts in the lawsuit, among other things, that soil conditions were worse than STP represented.

STP project manager Chris Dixon said this week that Malcolm knew about poor ground conditions because the firm previously built a wall of pillars next to the Alaskan Way Viaduct to protect the road from vibrations or sinkholes.

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The STP-Malcolm contract started at $932,477, to shoot concrete grout next to Bertha to form an underground wall that would resist groundwater. Dixon says the contract started low because STP thought about opening bigger parts of the ring project to bidding before choosing to stay with Malcolm.

Engineering was taking place at the same time, by Denver-based Brierley Associates, for a vault 120 feet deep with an inside diameter of 60 feet — at least twice the size of a vault to rescue tunnel-machine Excalibore in Sarnia, Ontario, two decades ago. By the time the vault was fully designed, STP and Malcolm agreed on a total of $18.9 million to cover the full costs.

Malcolm drilled down into the soil with hollow tools, filled those spaces with concrete, and positioned 70 of those pillars to form a ring. Dirt was scooped out from the circle, gradually descending. Work proceeded during two shifts a day.

Many obstacles slowed the job, according to the lawsuit in King County Superior Court:

• A layer of shells, left by 19th-century settlers, caused the state to halt work for a few days for archaeological study.

• Shallow utility lines near the vault needed to be moved.

• There were voids in the weak fill soil near the surface, adding safety hazards, Malcolm says. STP ordered rocks to be poured into the gaps, which Malcolm says made it more difficult to accurately set the columns.

• Groundwater flows and pressures were greater than expected, creating a need for extra pumping.

• The Alaskan Way Viaduct and some streets of Pioneer Square sank (more than an inch, according to state measurements), causing temporary delays and extra groundwater monitoring. The roadways reverted to normal, months later.

Finally, some of the new vault pillars were out of plumb, and groundwater seeped in. Excavation was suspended until grout could be added to fill the unexpected small gaps and add compressive strength to the ring.

Previously released records show that shaft walls had moved as much as .38 inch, and consultants worried the lower parts of the pillars would slide inward unless the ring was immediately stabilized. Brierley CEO Arthur McGinn and his team recommended Dec. 11, 2014, that digging be suspended at 74 of 120 feet down, until a structural review could be done.

“If we continue the current ‘repair as we go’ method of excavation, we significantly increase the risk of a catastrophic failure,” engineers said in a draft letter, updated days later to say that if left unchecked, the gaps “will have a significant impact” on strength and watertightness.

The problems were solved by January with Malcolm’s help, as time and costs accumulated. A month later, Bertha churned through the completed ring wall, into open air. Repairs were completed in late 2015 and the machine is now near Spring Street, on its way to South Lake Union.

In all, Malcolm says in the lawsuit its team did $9.8 million of extra work, and wasn’t fully paid for earlier STP jobs, bringing the claim to $11.1 million.

In the Seattle area, Malcolm has built the walls for Sound Transit underground stations, foundations for office and residential towers, and bridge supports for state highways.

John Kvinsland, Malcolm’s regional vice president in Kent, said he could not comment on litigation.

Dixon said talks are continuing, and he’s confident about reaching an out-of-court agreement.

The money Malcolm is seeking is not part of the $223 million in potential state overruns disclosed to lawmakers this week — a figure that covers only the state transportation department’s own rising costs to manage the tunnel project, now delayed until 2019, and build connecting roads.

Who might ultimately pay Malcolm?

That’s murky, because STP itself claims the state owes money for the vault and repair mission.

Legal fallout from Bertha’s rescue vault doesn’t end there.

Another court filing alleges that massive groundwater pumping violated the water rights of Enwave, the successor company to Seattle Steam, which supplies heat to downtown buildings. Enwave is suing both the state and STP, saying it lost the use of a deep well generating 250 gallons per minute, worth about $912,000 a year. STP’s Dixon said technical consultants are examining the circumstances.