Terra Engineering & Construction Co., Madison, Wis., is building a new $20-million utility system to support the growth of more than a dozen buildings on the west end of the University of Wisconsin - Madison campus.
Completely new, the system includes water mains, storm and sanitary sewers, cooling-water supply and return lines, high-pressure steam distribution for heating, electronic signal lines for controlling the buildings' mechanical systems, electrical distribution lines, and fiberoptic, coaxial and data exchange lines. It also includes some road work and paving.
Not only do the new utilities replace 20- to 40-year-old components that supported the few original buildings constructed on the west end of the campus; they also expand capabilities to permit better efficiency and support current and future expansion of the area.
Among the buildings served by the system are Children's Hospital, University Hospital, the University of Wisconsin School of Pharmacy, Nielsen Tennis Stadium, the Clinical Science building, the Wisconsin Alumni Research Foundation (WARF) building, and the Waisman Center — Research and Training Facility. The utility system is owned by the state of Wisconsin.
Construction started in May of this year. Completion is scheduled for late in 2008. Terra Engineering is self-performing about $12 million of the work, and is subbing the other $8 million.
The heating and cooling systems take water from nearby Lake Mendota. After sediment is removed, some of the water is distributed to a co-gen heating plant that generates high-pressure steam to heat the buildings. After heating the buildings, the condensed water from the steam is cooled, then returned to the lake at the same temperature as when it was taken.
Lake Mendota water is also used for the chiller system that cools the buildings. Cooling water is taken from the lake, sediment is filtered out and the water is pumped through the chiller system to cool the buildings. After being circulated, the cooling-system water is returned to the lake at its natural temperature.
The system is designed to prevent thermal or other pollution from harming the lake.
Building the new utility distribution system has presented Terra with numerous challenges.
The first is working around bustling crowds of students, workers and visitors that have to travel back and forth through the work site daily. Working in the heart of a high-traffic area that's home to two major hospitals, as well as thousands of students and visitors, Terra carefully has phased its work to be sure cars, buses, cyclists, and walkers can all still use the streets and sidewalks to go where they need to when they need to.
Doing so required putting in temporary roads, making sure major buildings always have at least one driveway open and working on separate segments simultaneously.
A second challenge has been keeping the work areas dry. The site is only a few hundred yards from Lake Mendota, so the water table is about 10 feet below the surface.
Since Terra is regularly working in trenches at depths of 15 feet to 20 feet, constant dewatering is required to keep the work areas dry. The pumps lift the water out of the work site and empty it into existing storm sewers.
Where sediment is prevalent, the water passes through a settling box that removes it before the water is discharged into the sewer.
All the steam vaults, electrical conduits, electrical vaults, and valves have to be made water-tight so their contents remain dry and work properly after the trench is closed.
To do that, Terra is using a concrete additive that makes the concrete more waterproof and creates a "self-healing" box. For added assurance, the electrical vaults are covered with a waterproof membrane.
The construction of each section starts with hydraulic excavators digging a trench 16 feet wide and 15 feet to 20 feet deep. At the bottom of the trench, Terra installs new concrete pipes for sanitary and storm sewers, as well as water mains.
Working in the trench requires use of a shoring box. On this project, Terra has used both a conventional type box with single-piece fixed sides, and ahs also used a rail system, in which the frame is installed in the ground and wall pieces are slid into the frame as the excavation goes deeper. Some trenches have also been lined with sheet piling instead of trench boxes.
After backfilling over the first layer of piping, Terra installs two 48-inch-diameter concrete water pipes that will carry the feed and discharge water for the cooling system. Each pipe section is connected to adjacent segments by flanges and a rubber gasket that will withstand pressures up to 200 psi without leaking. For extra assurance, each joint is finished with a hand-applied concrete collar inside and out.
When backfilling has covered the cooling-water pipes, the conduits and vaults for the electrical, fiberoptic, coaxial, telephone, and signal lines are constructed as the top layer.
Finally, when the trench and its contents have been enclosed, the at-grade work is completed, either with paving or landscaping, depending on the final use for the location. In some cases, peat excavated from the bottom of the trench is recycled as topsoil for the finishing.
Scott Zimmerman, P.E., is a vice president of Terra Engineering and a son of the company's founder. He is managing the University of Wisconsin-Madison West End Utilities project.
Says Zimmerman, "This project has presented an interesting challenge because we are working in a very public and crowded place that has to remain accessible and fully operational throughout the project. It's also challenging to work around existing utilities that must remain functional while we install their replacements."
He continues, "This project's logistical challenges, need for environmental sensitivity and special in-ground work conditions are a great fit for Terra. They let us bring together in one project all the things we've done very well for a long time."