Major Wisconsin Project Succeeds Despite Constricted Conditions

November 2009 Vol. 64 No. 11
The first stage of the joint trench construction: iinstalling an electric conduit system under University Avenue in Madison, WI.
  • First configuration: MGE’s 12 inch steel gas main and the ATC 8 inch steel pipe were installed. The excavated trench cross section was 4 feet wide and 5 feet deep. This gave both steel pipes 2 feet of separation with a standard trench depth of 5 feet. During backfill, the lines were separated with plywood form work so MGE's gas main could be encased in compacted sand and ATC's cable pipe could be encased in a fluidized thermal backfill (FTB);
  • Second configuration: The concrete encased electrical duct package was added. The excavated trench cross section with all three utilities was 9 feet wide and 6 feet deep. The MGE electric duct was aligned in the middle of the joint trench and maintained 2 feet of separation with MGE gas and 3 feet of separation with ATC cable pipe. During backfill, the gas main was separated from the electric utilities and encased in sand. The electric duct and the cable pipe were encased in FTB to dissipate the heat generated by these utility packages; and
  • Third configuration: Electric duct and the cable pipe were installed. This excavated cross section was 6 feet wide and 6 feet deep. Once again, the two electric utilities had 3 feet of separation and were encased in FTB.

In many locations along the route, the three entities used every inch of trench width available.

The work zone was restricted to an area that was 24 feet wide. To maximize efficiency and safety, KS Energy Services staged its work and that of its subcontractor, InterCon Construction. Vehicles in the work zones were controlled using flag persons – directing out trucks with spoil and directing in trucks with sand, concrete and FTB. The steel pipelines were built alongside of the trenches, giving space for welders and pipe layers to work on their respective facilities.

Pedestrian crossings were of utmost importance. Temporary bridges were constructed over the trenches so that pedestrian and bicycle traffic would be unimpeded. In many cases, work was performed below these bridges as pedestrians crossed above. KS Energy often had some of its employees work as "ushers" to help pedestrians cross the busy work zone in areas where large machines and trucks were operating right next to the crosswalks. KS Energy met the goal of maintaining public safety in these areas.