Mobility

Design-Build Creates New R.I. Links

Posted on August 17, 2012 by Rachel J. Burckhardt

Page 2 of 3

The design-build approach saved about 12 months of construction time, and the final cost is approximately equal to the engineer’s estimate prior to the preliminary designs and 25% below the engineer’s estimate at the preliminary (30%) design stage.
The design-build approach saved about 12 months of construction time, and the final cost is approximately equal to the engineer’s estimate prior to the preliminary designs and 25% below the engineer’s estimate at the preliminary (30%) design stage.


A Question of Alternatives

The successful result can in no small part be attributed to the design-build delivery approach, the first time this method of project delivery was used by RIDOT.

Experienced design-build teams have learned to think of design and construction as one continuous process. They are able to approach a project in a way that allows designers to understand how logistics, means and method contribute toward the best design approach. Contractors familiar with design-build understand that good design ideas enhance a project, and are not always “too costly.” For the owner, this holistic approach eliminates the risk of signing off on a design that is not constructible and reduces the likelihood of design errors and omissions.

In the case of the Wickford Junction station, collaboration within the team led to the development of no less than 20 so-called alternative technical concepts, or ATCs. All of them addressed cost savings, reduced accident risk and increased capacity for expansion. In several cases, the team even made suggestions that enhanced the project’s architectural design. Of the 13 ATCs submitted to RIDOT, 11 were accepted, saving more than $1 million in construction costs altogether. Some of the highlights include:

• Modifications in the preliminary design of a 1,300-foot-long retaining wall bordering on wetlands generated a significant reduction of both cost and risk. The original design had called for a soldier pile with precast lagging wall and a cantilevered safety walkway and railing. Instead, geotechnical engineers proposed a gravity precast retaining wall that did not require a large drill rig and crane but could be constructed with conventional earth moving equipment. Not only did this solution drive down equipment costs, it also increased the safety of the construction crew since construction equipment could be placed further from one of Amtrak’s high-speed tracks.
• The preliminary design for the passenger platform also called for pre-cast T-sections on mini-piles. The team, however, felt that a single-pour pier foundation with platform slabs precast on site would be a better solution, allowing the contractor to control the work on site (and eliminate the specialty contractor) while reducing the risk to Amtrak service, since construction equipment could be placed farther from the tracks. Revisiting the platform design from a design-build perspective also resulted in a simplified platform design made of flat slabs cast in beds on the site. Once cured to sufficient strength, the slabs could be lifted in place, eliminating the need for expensive and time consuming falsework.

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