Independent experts charged with reviewing the proposed $100 million fix to San Francisco’s famously sinking and tilting Millennium Tower endorsed the plan Tuesday, saying that they “see no reason to withhold approval of the building permit for the structural upgrade of the foundation.”

The four-person panel, hired by the city and headed up by Stanford engineering professor Gregory Deierlein, submitted its review of the “perimeter pile upgrade” plan to San Francisco officials.

The project calls for 52 piles to be drilled 250 feet down into bedrock to shore up the building, now leaning 17 inches to the north and west. The 2-foot-thick circular steel piles would be filled with steel reinforced concrete. Twenty-two would be sunk along Mission Street and 30 on Fremont Street.

Millennium Tower, a 58-story luxury tower just north of the new Transbay Transit Center, was named one of the top 10 residential towers in the world after it opened in 2009. Residents have included quarterback Joe Montana, baseball player Hunter Pence and the late venture capitalist Tom Perkins.

The Millennium Tower now sits on 950 reinforced concrete piles driven up to 90 feet deep into bay mud. The 52 new piles will extend into bedrock beneath the soils and will be structurally connected to the existing foundation by an extension of the building’s concrete mat.

The revelation in a 2016 Chronicle report that the luxurious skyscraper had settled 16 inches led to a flurry of lawsuits. Residents blamed the developer for not driving piles down to bedrock while the developer — Mission Street Development — claimed that “dewatering” during construction of the transit center had weakened the soil under the tower, causing the settling and tilting.

In all nine lawsuits have been filed, with no fewer than 146 lawyers involved. The parties have been in mediation for more than a year. Mission Street Development will coordinate the work, which is expected to be paid for largely through insurance settlements of the pending lawsuits.

While the San Francisco Department of Building Inspection has classified the pile solution as “voluntary,” rather than mandatory, adding the 52 bedrock-deep piles could stave off bigger problems in the future, the engineering panel concluded. Without the retrofit, the building could continue to tilt and “increase forces and deformations on the foundation, which may in the future, trigger mandatory repair provisions of the San Francisco existing building code.”

Howard Dickstein, president of the Millennium Tower Association, a homeowners’ group, called the panel’s report an “important milestone, which moves us closer to a retrofit of Millennium Tower.”

“We have high confidence in the design of this upgrade and we look forward to working with the city to complete the approval process and get the project under way,” he said.

Philip Aarons of Mission Street Development said his company’s “top priority has been to address and resolve the conditions that caused the building’s problems, no matter what the cause.”

“This plan addresses the impacts of nearby construction activities and soil conditions on the building, and is designed to protect it from similar impacts in the future,” he said.

In a memo to the Department of Building Inspection, the panel said “all our comments on the geo-technical and structural design have been adequately addressed by the design team, and there are no outstanding or unresolved issues.”

“In our professional opinion, once the foundation retrofit is constructed, the building is expected to have performance consistent with the stated design objectives,” the panel’s report said.

The panel met 11 times with the design team from engineering firm Simpson Gumpertz & Heger over 11 months.

J.K. Dineen is a San Francisco Chronicle staff writer. Email: jdineen@sfchronicle.com Twitter: @sfjkdineen