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Tue March 17, 2015 - Midwest Edition
Open park space within urban environments is vital to the development and general well-being of the surrounding communities. As the population in these areas continues to grow and become more dense, the need for dedicated park space also becomes more imperative.
The transformation of underutilized industrial areas into parks and community gardens is one example of how modern city designers and planners are overcoming this challenge. Another solution includes the installation of green-roof systems on different kinds of structures located in even denser areas where a conventional park is simply not an option. Both of these are innovative approaches to solving the growing problem of deficient open park space within dense urban areas.
Chicago-based Western Waterproofing Company, a member company of Western Construction Group, recently completed a mammoth project to restore and waterproof a 750,000-sq. ft. (69,677 sq m) concrete parking garage (equivalent to 12 football fields) located underneath the newly designated, 20-acre Maggie Daley Park in downtown Chicago. Western served as the general contractor on the garage project.
Formerly known as North Grant Park/Daley Bicentennial Plaza, Maggie Daley Park is part of a larger network of adjacent parks including Millennium Park to the west and Grant Park to the south. It is bordered on the east by Lake Michigan and Lake Shore Drive. This entire park system was built on top of underground garages. Together these interconnected garages comprise the largest parking facility in the country. The vicinity of land that these parks occupy was previously an underutilized rail yard.
Named after Chicago’s beloved former first lady, Maggie Daley, who died of breast cancer in 2011, the iconic Maggie Daley Park was designed to breathe life back into the downtown area. A portion of the park, including a 40-ft. (12 m) tall rock climbing wall, play garden and ice-skating ribbon that can accommodate 700 skaters at one time, was opened to the public in December 2014. Additional work on the park is scheduled to be completed in spring 2015.
The $60 million project was divided into three phases — removal of the existing park by James McHugh Construction Company; waterproofing and repairs to the concrete parking structure by Western Construction Group and re-installation of the park and construction of its new features by Walsh Construction.
The concrete parking structure, originally waterproofed in the 1970s, had become compromised from years of wear and tear and ground water infiltration. Essentially a giant green roof, ensuring proper waterproofing of the large parking structure was key to maintaining the park’s overall integrity and sustainability.
Should any leaks or drainage issues occur to the garage in the future, the new park and its amenities would have to be pulled up and the entire parking structure re-waterproofed — a timely, costly and disruptive measure that the waterproofing team did not want the city or its residents to have to endure. There was no room for error on the project.
The scope of the parking garage project included structural repairs to the existing concrete roof slab, full removal and re-installation of a new waterproofing system and major drainage improvements. The project was full of challenges along the way related to logistics, coordination with other contractors, a tight schedule, public relations, location of the project, and the sheer size of the job site. In order to help with jobsite logistics, security and contractor coordination, high definition cameras were installed high above the park to record the site 24/7. These cameras were used on a daily basis by the management team to coordinate daily activities, work locations, material staging locations, as well as jobsite safety and security.
The project began with Desman Associates, a Chicago-based engineering firm, to brainstorm solutions to resolve the parking garage’s major drainage issues. While the parking garage sloped naturally from north to south, pooling water had become a problem in specific areas of the park, due to the lack of drains throughout the massive garage roof. This problem was solved by the installation of numerous new drains and a composite drainage mat system.
After the existing park (North Grant Park/Daley Bicentennial Plaza) was completely demolished and removed from the site, work began on preparing the 750,000-sq.-ft. (69,677 sq m) surface for application of the new waterproofing system. The entire surface of the concrete roof was power washed and then shot-blasted to achieve the proper surface profile required by the waterproofing manufacturer. Next, installation of the waterproofing system began.
The waterproofing system, manufactured by American Hydrotech, consisted of seven layers, which all serve an important function in the overall operation of the system. The initial step of applying the system consisted of spraying the concrete deck with primer. The first layer of the system consisted of melting rubberized asphalt bricks to a liquid state by heating the 40 lb. (18 kg) bricks to 400 degrees in a kettle. The rubberized asphalt would then be poured out onto the concrete, while it was still hot and in its liquid state. Workers then spread the rubberized asphalt out to evenly coat the area. In total, this project required more than 1.3 million lbs. (589,670 kg) of rubberized asphalt applied by multiple crews consisting of 40 workers per day. In order to fast-track production, all crews worked from opposite corners of the deck, then slowly worked their way to the middle.
Constant measurements were taken during the process to confirm that the material was not being spread too heavy or too thin along the deck. After the first layer of rubberized asphalt was spread out, workers rolled reinforcing felt fabric onto the layer of melted rubber, while still in its liquid state. Another layer of melted rubber would then be poured and spread out over the area. The next step required workers to roll out sheets of heavy-duty, rubberized asphalt protection board, which was specially made to prevent tree roots from puncturing the waterproofing.
The final layers of the system included a drainage mat, filter fabric and approximately 400,000 cu. ft. (11,326 cu m) of gravel overburden. In order to help speed up the project, Western worked directly with the manufacturer to have special, extra large rolls of drainage mat made for the project. Standard rolls of drainage mat are 4 by 75 ft. (1.2 by 22.9 m) but American Hydrotech manufactured job-specific rolls that were 7 by 150 ft. (2 by 45.7 m). This helped to keep the project on schedule. Installing the layer of gravel overburden was completed by Walsh, although, a large amount of coordination was required between Walsh and Western to accomplish the task.
Now that the entire deck was covered by the waterproofing system, no trucks were able to drive on the system without causing damage. This fact made the task of installing the gravel overburden a huge challenge. Using the overhead cameras, a phasing plan was designed to accomplish the task.
The plan was to allow a few temporary access roads on top of the waterproofing, which would then be leak-tested and repaired before overburden was installed on the access roads. A large conveyor truck with an extra-long reach was used to shoot the gravel over the waterproofing system, without needing to drive over the system. Extra gravel was piled along the sides of the temporary access pathways with the intent that it would be pushed over the pathways by hand, prior to repairs of the temporary pathways. This is one of many examples of how Western used innovative thinking to solve problems, overcome obstacles, and deliver the project on time with the highest quality.
At the same time that waterproofing work was being completed on the topside of the garage roof, structural repairs were being performed on the underside of the roof slab. Coordination between crews on the topside and underside of the slab was a daily challenge for the management team. Use of cell phones was not an option due to very limited reception inside the garage. In order to overcome this obstacle, Western’s management team was headquartered inside the garage for the duration of the work. This allowed constant oversight of the work being performed.
Another obstacle Western encountered during this work was poor ventilation. This problem was solved by using high-powered vacuum fans to circulate air throughout the work locations. Since a large portion of the garage was closed during this work, every day represented a loss of possible revenue to the owner. Therefore, there was no room for extensions in the schedule. 24/7 monitoring of the garages was also required during this work due to high volumes of pedestrian traffic in the area.
The work inside the garage consisted of 3,000 sq. ft. (278.7 sq m) of overhead concrete replacement, and the detachment of two pedestrian access tunnels from the garage. Due to the excessive loads placed on the roof slab by the park above, the concrete slab was poured with additional reinforcing steel. This made removal of delaminated concrete more difficult. All 3,000 sq. ft. (278.7 sq m) of the concrete was removed using hand-held jack-hammers. After removal, all exposed rebar was sandblasted and coated. When prep work was complete, concrete was re-applied using a dry-mix, shotcrete method.
Due to the messy nature of this method, Western took additional precautions to cover the floor, which prevented staining of the asphalt surface. As a nationwide corporation, Western Waterproofing used its resources to complete this work on a tight schedule by joint venturing with the St Louis branch that had more experience with this application. At the completion of this work, more than 1,000 cu. ft. (28.3 cu m) of concrete had been removed and replaced, requiring more than 130,000 lbs. (58,967 kg) of cement.
Simultaneous to the work being completed to both the topside and underside of the slab, Western also was busy on the south end of the garage performing structural repairs that would disconnect two underground pedestrian access tunnels from the garage. The design team had noticed that these two tunnels were moving at a different rate than the garage, therefore creating large cracks which were proving to be tripping hazards for pedestrians. The design team intended on solving this problem by separating the structures from each other and installing an expansion joint to fill the void and prevent leaking. This task required Western to essentially re-build a large portion of the tunnel.
When the owner learned that Western was capable of performing much more than waterproofing and concrete restoration, Western was invited to perform additional repairs at another pedestrian access point on the north side of the garage. This access point was the busiest and most commonly used entrance and exit for the garage, which in itself created large challenges for completion of the work. The scope of work included full removal and replacement of about 300 sq. ft. (27.9 sq m) of a 14 in. (36 cm) thick supported slab. This slab served as a stair landing for the exterior pedestrian entrance. The owner required pedestrian access below the area of work at all times. In order to achieve this, Western had a large shoring system erected that allowed removal of the concrete to occur and also allow pedestrian traffic directly below.
To ensure that there were no breaches in the waterproofing system after it had been installed, International Leak Detection (ILD) was hired to use its sophisticated Electric Field Vector Mapping (EFVM) technology to locate even the smallest leak in the roofing membrane.
EFVM works by applying water to the membrane surface, then delivering a low-voltage, pulsating charge between the nonconductive membrane and the conductive structural deck. A breach will cause an electrical connection to occur. ILD inspectors then circle, number and document the leak for repairs to be made.
The garage restoration work took a total of 33,554 hours to complete, with about 45 workers on the job per day. Western used its own resources to self-perform over 95 percent of the entire scope of work.