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Metro Transit St. Louis Leak Remediation Design

Bi-State Development Agency

The Cross County MetroLink Extension Project, opened in 2006, was a 8 mile, 9 station extension to the existing alignment, expanding service towards the Clayton, Maplewood and Shrewsbury neighborhoods. Included in the alignment were 3 cut-and-cover tunnels (Tunnel #1, Tunnel #2, and Tunnel #3) and 2 below grade stations (Skinker Station and Big Bend Station). The tunnels and stations were constructed with castin-place base slabs and tunnel walls, and pre-cast concrete roof segments; concrete floor and wall segments were cast-in-place a bentonite-type waterproofing material was installed. Pre-cast arch tops were installed and waterproofed using a separate bentonite waterproofing membrane followed by 5 to 20 feet (1.5 to 6 meters) of granular backfill material. Tunnel #2, Tunnel #3, Skinker Station, and Big Bend Station began showing signs of water infiltration immediately following the completion of construction.

Inspection and Design Services for Tunnel Leak Remediation:

This water leakage has contributed to early concrete deterioration, as well as other serviceability issues. Gall Zeidler Consultants (GZ) initially performed a leakage assessment, analyzing possible causes of tunnel leakage into these structures. The Bi-State Development Agency (METRO) then tasked GZ with performing detailed leakage inspections of the structures affected by the leaks. These inspections determined both the location and severity of any water infiltration in the both tunnels and stations. Included in these inspections were digital tunnel scans.

Location:

St. Louis, Missouri

Date:

2010 – Present

Structure:

2 Cut and Cover LRT Tunnels, 2 Cut and Cover Stations

Length:

Approximately 1.10 miles (1.8 kilometers) total

Cross-section:

Height: 21.2 feet (6.5 meters), Width: 35 feet (10.7 meters)

Geology:

Fill, loess and glacial deposits; Cheltenham Syncline

Cost:

Rehabilitation cost: Approximately $30 million

Client:

Bi-State Development Agency

Owner:

Bi-State Development Agency