| Contextual Infrastructure Planning and Design |
| Blending Complex Engineering Challenges and
Aesthetics into Community-Friendly Solutions |
| By Joan Witt, Tempe, Arizona 1-480-966-8295, witt@pbworld.com
|
| The design that our team
developed for a segment of Pima Freeway addressed complex engineering
challenges and community concerns, and it allowed construction to
be completed ahead of schedule. |
|
Figure 1: Shea Boulevard Single-Point Urban Interchange |
Figure 2: Pedestrian and Bike Path |
The Arizona Department of Transportation selected PB to design the
first segment of Pima Freeway to be built within the City of Scottsdale.
The residents feared the impacts from construction and they wanted
the freeway to serve as an attractive gateway to their City. The project
was under tight public scrutiny. Our design team had to address both
community concerns regarding aesthetics and noise as well as many
engineering challenges.
We were responsible for the fast-track design of:
- 2.4 km (1.5 miles) of depressed, access-controlled
freeway that consists of:
- Six general-purpose lanes
- Two auxiliary lanes
- One single-point urban interchange (SPUI) at Shea Boulevard-
a two-span, cast-in-place, post-tensioned concrete box girder
bridge (Figure 1)
- Three grade-separated structures and a pedestrian
and bike pathway (Figure 2)
- Onsite and offsite drainage systems
- Retaining and sound walls
- Signing, striping and lighting
- Traffic control plans.
The project constraints included high traffic volumes in the construction
corridor, numerous utility lines and limited right-of-way.
Creative Solutions
As described below, we combined "top down" construction
techniques with innovative design concepts to improve the technical
design and minimize traffic impacts, and we used architectural treatments
to enhance the aesthetics in the corridor and gain public acceptance.
Our team also worked in concert with the neighborhoods and nearby
businesses to incorporate community-friendly elements, such as pedestrian
and bike paths (Figure 2).
Top Down Construction.
By using the top down viaduct construction technique in our bridge
design for the Shea Boulevard SPUI, we minimized traffic delays and
risks to the public. The central part of the structure was constructed
first, with traffic detoured around the construction area. We designed
the high abutment required for this bridge so it could be constructed
at ground level without major excavation. After abutment and pier
construction, the superstructure was formed on the existing ground
and concrete was placed. After the superstructure post-tensioning
was complete, partial excavation under the bridge allowed access to
the drilled shafts for tie-back operations. Subsequently, traffic
was placed on the completed deck and the exterior ramp connectors
were constructed and attached to the new bridge.
Although the top down concept for building viaducts is not new, using
this technique was one of the keys to completing the project safely
and quickly, and with the least impact to traffic.
Figure 3: Innovative Culvert/Retaining Wall System |
Figure 4: Two Examples of Architectural
and Artistic Treatments (Decorative Handrails as well as Lizard
and Plant Designs Incorporated into the Bridge and Walls) |
Culvert/Retaining Wall System. Another challenge our design
team faced was accommodating all of the following elements within
a very restricted right-of-way:
- Travel lanes
- Retaining walls
- Shoulders
- Sound walls
- The utility corridor
- A pedestrian and bike path
- A 3-m by 4-m (10-foot by 12-foot ) box culvert.
To address this challenge, we developed a combination box culvert
and retaining wall system (Figure 3) that saved space while incorporating
the required engineering elements and aesthetic enhancements. The
retaining wall system resists all external forces and carries stormwater
while remaining within the restricted right-of-way. Our structural
team designed the wall system to include a box culvert above a retaining
wall as well as a 2-m (6-foot) extension to the exterior face of the
box culvert to act as an additional retaining wall. In some locations,
the total height of the wall system is 10 m (33 feet).
Detour.
The corridor's high traffic volumes and tight right-of-way required
creative solutions to construction challenges. To reduce construction
impacts to the surrounding neighborhoods and businesses and to shorten
the construction schedule, we developed a detour concept to move the
existing traffic out of the construction corridor. With no traffic
in the construction zone, one portion of the construction was completed
six months early.
Aesthetic Treatments. Our team worked with homeowners' associations
to incorporate their requests for privacy walls, landscaping, access,
lighting and pedestrian and bike paths. With the freeway being the
gateway to the Scottsdale, the city officials wanted the facility
to make a strong artistic statement. We worked closely with city staff
and their architectural treatment consultant to incorporate southwestern
design elements into the retaining wall system, other walls, bridge
piers and abutments (Figure 4), and to coordinate these treatments
with the neighborhoods. Our team also developed new concrete form
liner materials and worked with the City's artist to develop constructible
architectural treatments to enhance the freeway and the pedestrian
and bike paths.
Project
Exceeds Expectations
Working together with the Arizona Department of Transportation, the
City of Scottsdale and its architectural consultant, business owners,
and residents, we developed a vital transportation facility that was
based on sound engineering practices blended with aesthetics and community-friendly
elements. Our efforts exceeded ADOT's expectations by providing cost-effective
solutions that were completed within the construction cost estimate
and by facilitating the construction process, which resulted in the
project being completed 30 days early.
Our team also met the expectations of the City of Scottsdale by creating
a freeway with a unique appearance that serves as an attractive gateway
to Scottsdale. The Arizona Department of Transportation, the City
of Scottsdale, residents and businesses are all enjoying the benefits
of this truly successful project. In October 2000, this project won
an Outstanding Award for Engineering Excellence from the Arizona Consulting
Engineers Association. |
|
| Joan Witt, a Business Development Associate
with 15 years of experience in sales and marketing, is a marketing
coordinator with PB's southwest district. |
|
