Construction of the $2 billion Southwest light rail line is nearly half done, but contractors continue to encounter difficulties — and added expense — building a tunnel in the Kenilworth corridor of Minneapolis.

A Metropolitan Council committee unanimously approved Wednesday a change order diverting $1.75 million from the project's contingency fund to pay for grouting between steel sheet pilings used in tunnel construction in the corridor.

"It's pretty remarkable what's being done in such a limited space," said Met Council Chairman Charlie Zelle, at the Southwest Executive Change Control Board meeting.

The amount approved is relatively small when considering the overall cost of  Southwest, the largest public works project in state history. A second change order, which has not been quantified, is "under negotiation," said project spokesman Trevor Roy.

All told, the council has executed 331 change orders totaling $133 million since construction of the Green Line extension began in 2018. That covers the project's entire route from Minneapolis to Eden Prairie, through St. Louis Park, Hopkins and Minnetonka.

Most of the change orders tapped the project's contingency fund — money set aside for unforeseen expenses. When the council applied for federal funding in August 2019, the contingency fund was about $204 million. As of mid-May, $83 million in contingency remained.

The Federal Transit Administration is paying $929 million of the project's cost, with local sources making up the rest.

The board's action underscores the complexity of building a light rail line along a nearly 2-mile wooded corridor that's close to homes and apartment buildings, shared with freight rail and once home to a popular bike and pedestrian path (which will be restored).

The decision to route the 14.5-mile line through the mostly affluent area of Minneapolis remains controversial and prompted litigation seeking to stop the project, an effort that ultimately failed.

The project's general contractor, Lunda/C.S. McCrossan Joint Venture, has been installing giant vertical sheets of steel using a press-in pile driver to stabilize soil and make room for tunnel construction. As the sheets were driven into the earth, some encountered boulders and other obstacles, causing them to shift and prompting the need for grouting.

Because parts of the excavation site have been flooded with groundwater, the contractor also has deployed special divers to monitor conditions.

"This work is pretty unique; it's so specialized," said construction director Brian Runzel, noting that another tunnel halfway complete under Hwy. 62 in Minnetonka hasn't been nearly as complicated.

It's no surprise the contingency fund is being tapped. The council said this winter it was delaying the line's planned 2023 opening, due in large part to construction difficulties in the Kenilworth corridor and the need to erect a mile-long wall closer to downtown Minneapolis separating light-rail and freight trains.

The project's overall cost and opening date are "still being analyzed," Roy said.

Janet Moore • 612-673-7752