- Company: SEMA Construction, Inc.
- Industry: Transportation
- Location: Denver, Colorado
- Expected Completion Date: August 1, 2012
- Project Website
In 2000, the commercial and residential redevelopment of the 4,700-acre former Stapleton Airport site was one of the nation’s largest urban mixed-use infill developments. This area is now a nationally acclaimed, new urban neighborhood with parks, schools, commercial and retail centers. The original redevelopment, however, lacked critical connections to Denver’s regional street infrastructure.
SEMA Construction, Inc. (SEMA) and Wilson & Company, Inc. (Wilson) were selected to partner with the City and County of Denver (CCD) on Denver’s first design-build transportation project. The goal of the Central Park Boulevard (CPB) project was to provide a direct connection between the Stapleton redevelopment on the south side of I-70 and The Shops at Northfield Stapleton, a 1.2 million square foot retail center, on the north side of I-70. To do this, the design-build team constructed a new interchange between Stapleton’s CPB and I-70.
This new interchange included the construction of a new, six-lane bridge over I-70 and two ramp bridges. Through a network of braided ramps, the new interchange connected CPB and two major interstate highways: I-70 and I-270. By creating an entirely new alignment and moving the direct connection between I-270 and I-70 by half of a mile, the new CPB interchange had a positive impact on both the infrastructure of the greater Denver area and the safety of the traveling public.
Based upon the scope and funding sources of this project, multiple stakeholders were involved including: CCD (owner), Colorado Department of Transportation (CDOT), Better Denver Bond Program, Stapleton Community, Federal Highway Administration (FHWA), Forest City-Stapleton and Park Creek Metro District. The design-build team effectively coordinated with all stakeholders throughout the life of the project and was responsible for all project elements including design, geotechnical, foundation, drainage, structure, retaining walls, roadway and pavement, traffic features, lighting and aesthetics work.
What impact does this project have on America?
The Central Park Boulevard & I-70 Interchange Design-Build project has a big impact on America, specifically anyone traveling in, out, and around Denver, Colorado. The CPB interchange serves as a highly visible gateway to Denver and the Rocky Mountains, and signifies the City’s commitment toward sustainability and enhancement. Because of its high traffic, multi-modal connectivity, this project also made a significantly positive impact on the traveling public.
The project team worked together to integrate the functional, structural, and safety needs of the entire complex with its visual integrity and aesthetic context. The team developed and incorporated many architectural and landscape features into the project which exceeded the contract requirements. CPB project design fulfilled its function and presented two unique contexts for its users: 1) a highway environment from the I-70 corridor, 2) a surface street network from Central Park Boulevard. In addition to vehicular traffic, the CPB Bridge had to accommodate pedestrian and bicycle connections through shared use paths on both sides.
This multimodal facility presented challenges in designing to the appropriate scale from multiple perspectives while maintaining a cohesive look. To meet this challenge, several elements were integrated to provide visual cues that were in harmony for each distinct user, while creating a consistent structural composition.
The bridge and its structure, abutment monuments, abutments and piers had to be at an appropriate scale for the I-70 traffic to understand its significance in connecting both halves of the community. The design shifted the abutment monuments forward to be closer to the abutment faces. This increased their visibility to the highway traveler and allowed ornamental trees to form a skirt framing the monuments; increasing the prominence of the bridge.
Rectangular center piers were designed to increase their appearance of size as well as to provide a visual mass appropriate to bear the weight of the bridge. Highway-facing retaining walls were consistent in scale, and presented a simple and clean appearance from the I-70 perspective.
The three-span bridges for the braided ramps complimented the scale of the CPB Bridge. Increasing the number of spans provided a more open space and created a bigger visual mass, with proportion consistent to the interchange as a whole. The team exceeded expectations by providing an aesthetic allowance of $200,000 for enhancements that exceeded commitments defined in the original plans. A few enhancements included custom pedestrian fencing, upgraded lighting, raised metal labeling, sustainable landscaping and a consistent sweeping arc design that accentuated the CPB Bridge.
What interesting obstacles or unusual circumstances did you overcome to complete the project?
The design-build team faced some considerable obstacles, including the owner’s significant expectations related to the aesthetic importance of the CPB project. The CPB project was a key element in realizing the Stapleton redevelopment vision of “a series of vibrant, mixed-use communities connected by an extensive system of open space and transportation improvements.” Additionally, the CPB interchange served as a highly visible gateway to Denver and the Rocky Mountains and signified the City’s commitment towards sustainability and enhancement. The design-build team’s response to this challenge was to integrate the functional, structural, and safety needs of the entire complex with high visual integrity and aesthetic context. To do this, the team proposed and directed a series of interactive design charrettes to collaboratively develop an appealing design, fully reflective of community interests. Throughout this process, the design-build team allowed their own proposed aesthetic features to be replaced if the charrette team recommended more preferred elements within a similar cost structure. To further ensure a high-end, impactful visual statement for the CPB project, the design-build team agreed to provide an art and aesthetic allowance of $200,000. This was used for enhancements that exceeded the commitments already defined in the original ‘Aesthetic Concept Plan’. A review of these enhancements included:
- • Upgraded street lighting elements that accented the bridge monuments, its abutment site walls and sweeping arc themes.
- • A custom pedestrian fence design that followed the sweeping arc design theme.
- • The use of natural stone on the bridge abutment monuments consistent with high quality treatments throughout the area.
- • Prominent, raised metal lettering on the curved site walls that strongly identified the bridge as “Central Park Boulevard”.
- • Significantly longer ramp overpass bridges were constructed to eliminate retaining walls and to provide a more open feel consistent with the overall theme of the interchange.
- • Sustainable landscaping was incorporated to add character and soften the architecture of the CPB interchange in the vicinity of the project.
What dangers and risks did you encounter, and describe any extraordinary methods used to keep workers safe?
A significant challenge the design-build team faced was managing this large-scope project in an area where two interstate systems came together (I-70 & I-270), while minimizing traffic hazards and ensuring public safety. Government estimates indicated that 228,000 drivers relied upon I-70 and 85,000 drivers relied upon I-270 on a daily basis. The history of this location revealed a high frequency and severity of accidents.
The design-build team responded to this challenge by developing and implementing a Construction Phasing Plan which enabled existing I-70 and I-270 traffic lanes to remain operational for the duration of the project, with the exception of limited night and weekend work. To accomplish this, construction of the ramp system was scheduled first so when it became necessary to build the new interchange bridge, the ramps were used to re-route I-70 traffic without the use of existing Stapleton streets for detours. Additionally, traffic was re-routed only at night when key activities were performed like erecting girders for the new bridge.
Exhaustive pre-planning by the design-build team and the implementation of an on-site safety team resulted in a safety program that exceeded industry standards.
The design-build team, including a Safety Manager and Safety Officer, developed a site-specific Safety Management Plan (SMP) prior to the onset of the CPB project. The SMP outlined job-specific safety regulations, addressed potential hazards and detailed the personal protection equipment required.
Although team members received in-depth safety training upon employment, the CPB Safety Manager conducted site specific safety training relative to each task of construction.
The team provided leadership and resources that enhanced employee awareness and participation to create a safe work environment. HSE&Q processes were integrated to ensure systematic recognition and reduction of risks to the team. Subcontractors were also required to achieve excellence in HSE&Q.
Daily safety briefings were held so each crew could review the daily project goals, potential safety hazards and safety strategies. These were mandatory for everyone; minutes were recorded and signed by each participant. ‘Weekly Tool Box Talks’ were held every Monday during the course of the CPB project. These weekly project safety discussions were led by the Superintendent and Project Manager. The topic that was reviewed in detail was related to the specific area of construction planned for that week to ensure jobsite safety. The entire team was required to attend and meeting minutes were recorded and signed by each participant. Additional focus on safety management was evident by the pulmonary function tests that were performed by a physician on any employee required to wear a respirator during construction.
Safety audits were conducted on a regular basis by the Safety Manager and Safety Officer. Findings were presented to the Project Manager and corrections were required within a clearly outlined time frame.
How did you leverage new technologies to work faster and reduce waste?
SEMA demonstrated leadership in innovation and in leveraging new technologies throughout the duration of the CPB project. Highlighted below are some of the key areas where SEMA’s innovation in construction techniques and solutions to reduce waste were apparent.
– Geometric Design: SEMA initiated innovation in geometric design by identifying variable ramp design speeds that were more consistent with the AASHTO (American Association of State Highway and Transportation Officials) and CDOT design methodologies. This was done to better accommodate vehicle running speeds, advance ramp operations, and promote cost efficiencies. SEMA, furthermore, refined the geometric design to improve project operations and safety by implementing flatter horizontal ramp curvatures, reducing vertical and horizontal ramp grades and easing the skew of the north ramp intersection with Central Park Boulevard.
– Three-Span Bridges at the Braided Ramp Overpasses: SEMA’s distinctive bridge design opened up the grade-separated ramp crossings and eliminated the ‘tunnel effect’ to improve driver sight distances, awareness and safety.
– Drainage and Water Quality: By the use of approved ATC S-10 ‘ecology embankment’, SEMA incorporated an innovative water quality feature that more efficiently handled stormwater. This feature treated water immediately after it ran off the pavement; minimizing the need for more costly and inefficient water quality storage and treatment facilities.
– Bridge Deck Durability: The use of higher quality concrete (Class H) on all bridge decks significantly reduced the risk of salt penetration and surface deterioration of the decks.
– Environmental Sustainability: In response to CCD’s commitment to a sustainable environment, SEMA incorporated many innovative construction techniques and materials that were in-line with the owner’s approved ‘Greenprint Denver’strategies. Some examples of this included:
• The use of NIOSH compliant pavers which reduced paving emissions.
• The incorporation of Intelligent Transportation System (ITS) facilities that improved sustainability.
• A focus on the re-use of materials on-site which eliminated 150,000 cubic yards of imported material and reduced the energy and emissions required by truck hauling.
• The re-use of existing light standards and the rehabilitation and re-use of sign structures into the project. Sign structures that could not be used were returned to CDOT for use in other state projects.
• An incorporation of LEED (Leadership in Energy and Environmental Design) certified activities that included water conservation and stormwater quality.
SEMA contracted with subcontractors who could support sustainable aspects of the CPB project. One key example of this was the use of alternative cement binders consisting of fly ash and limestone. This material reuses waste materials and has a more positive impact on the environment because it requires less energy and virgin raw material to manufacture. Not only does this material have a smaller carbon footprint, but it also provides much greater strength and longevity than portland cement alone.
Additionally, SEMA used existing site soils to create the ramps and terrain, eliminating the need to import 2000 truckloads of material. More than 90% of the project materials were manufactured or extracted within 100 miles of the project site, avoiding the emissions of long-range shipping. Exterior light pollution was minimized through the use of lower-level lighting rather than high-mast lighting. Ongoing water efficiency was achieved by irrigation that used less than 10 gallons per square foot, per season. Further environmental sensitivity was reinforced in the surrounding landscaping concepts which included low maintenance buffalo grasses that require less water and energy to maintain.
SEMA was responsive to the owner’s desire for a quality project that minimized future maintenance costs. While the owner’s original concept included hot bituminous pavement, the project team minimized maintenance expenses and improved surface durability by proposing concrete pavement for the interchange ramps, resulting in an estimated life-cycle cost savings of two-million dollars.
Furthermore, the design-build team proposed that retaining walls, except for the bridge abutment walls which were necessary for aesthetic considerations, be eliminated from the owner’s original design in order to reduce construction costs and future maintenance.