Bridge Erected, Trail Connected

Posted: 12/28/2017

Anticipation, Coffee, and a 2 a.m. Hoist

In the wee hours of the morning on Saturday, September 9, before an audience of about 40 onlookers, and with adrenaline, anticipation, coffee, and donuts holding tiredness at bay, Civiltech Resident Engineer, Phil Hurst, P.E., coordinated the placement of a new 221-foot long bridge structure, the centerpiece and final link of the new Middlefork Savannah Trail Extension. The hearty crowd that had gathered at 2 a.m. to watch the bridge erection included staff from Civiltech, Lake County, and the Lake County Forest Preserve District, as well as curious neighbors.

Civiltech provided Phase I, Phase II, Structural Engineering, and Phase III Construction Engineering services on this exciting project. The Middlefork Savanna Trail system consists of almost 5 miles of aggregate trail that is used for hiking, biking, and cross-country skiing through a dedicated Illinois Nature Preserve. The improvement, for the Lake County Forest Preserve District, connects the Townline Community Park to the Middlefork Savanna Forest Preserve by a newly constructed 8-foot wide shared-use path along the west side of Academy Drive from IL Route 60 to Faculty Circle. The new connection provides the only pedestrian/bicycle bridge in Lake Forest that crosses the Metra railroad tracks.

The new path alignment into Middlefork Savanna follows a former driveway from IL Route 43, over the railroad tracks, and onto the historic site of the former J. Ogden Armour’s estate, currently Lake Forest Academy. The original bridge was demolished in 1954; however, parts of the original abutments still remain.

A Narrow Window of Opportunity

The planning, preparation, verification, and coordination necessary to complete the bridge installation was complex and multifaceted, creating tremendous anticipation and anxiousness in the build-up to lifting and placing the bridge. The most critical factor was coordination with Metra’s schedule which dictated the 3 hour window, between 2 a.m. and 5 a.m., in which the entire bridge installation needed to occur. Adding further complexity and coordination to that tight time frame, freight trains were still allowed to pass through with restrictions on how long they could be held-up. Once installation had begun, one freight train had to be held for a short amount of time.

Preparing the structure prior to lifting it into place also required precise coordination. The 12-foot wide, steel frame, timber planked bridge had arrived the Wednesday prior to the installation and was delivered to the site in five pieces needing to be assembled into a single structure. The assembly took two full days, the following Thursday and Friday, and was completed at 8 p.m., just hours before the scheduled installation. When it was finally time to hoist and set the bridge, two cranes were required and set up on either side of the railroad tracks.

The new structure was placed in the same location as the previous concrete bridge and was designed to sit within the existing abutments. The concrete abutments from the old bridge were retained to preserve the historic aesthetic and give reference to the old bridge. The existing abutments are now merely decorative, with the structural footings for the new bridge founded behind them. Verification of the dimensions and structural support of the new bridge with the existing abutments was another critical component in preparing for the installation.

Into the Light of Day

Once the bridge was set, contractors needed to set the anchor bolts, a process that took another two hours, bringing the project from the long night into the light of the next day. At that point, with the coffee and donuts depleted, the tremendous challenges met, and the careful preparation and coordination a success, Phil stated, “the tiredness finally set in.”