Brigham City Bridge

Atlas Geofoam Solves Soil Stability Issue

The ever-changing complexities of the built environment are many, continually challenging the limits of civil engineering and the government agencies behind public infrastructure. At the Utah Department of Transportation, where the tag line is Keeping Utah Moving, the responsibility to plan, maintain, and operate the state highway system is relentless. New challenges often require innovative thinking and the UDOT relies heavily on a wide range of professional engineers, contractors, and consultants to think outside of the box in using new methods and materials to solve problems.

In Brigham City, which is just about an hour north of Salt Lake City, the issue was congestion at a highway interchange. Offering only a single lane of roadway in each direction over the bridge, the US 91 / I-15 interchange frequently backed up during rush hour to become a notable slow spot that frequently failed to keep people moving. Through congestion is not uncommon, site conditions significantly added to the situation’s complexity, compelling UDOT to look a little deeper for solutions than originally anticipated.

Atlas Geofoam enters the equation as a versatile, durable, structural solution used to resolve a vast array of civil engineering challenges. Made from closed-cell polystyrene, geofoam is well-known for its incredibly high compressive resistance, long-term stability, and the ability to be customized both in the manufacturing process and on-site as-needed to fit almost any circumstance.

The Challenge

When challenged to improve vehicular throughput at the two-lane interchange, UDOT’s initial thinking was to increase the roadway’s overall capacity by adding a sister bridge adjacent to the first. While this strategy would immediately double capacity, geotechnical investigations on soil and site conditions revealed such a solution would eventually cause more harm than good. Calculations on both soil settlement and global stability indicated that the weight of a traditional soil-built embankment for the second bridge would adversely impact the original bridge. Calculations also revealed that if soil were used to widen the embankment to accommodate the second structure, the primary settlement period could take six months or more. Furthermore, there was a possible 1 ½ to 2 inches of long-term settlement that could occur over a period of ten years or more, which was deemed excessive. Considering the potential for both long-range instability and the near-term inconvenience of having to wait for a minimum of six months after the soil was placed to build the rest of the embankment, UDOT had to look for other options. Alternatives to improving the embankment’s stability including using driven piles were investigated before engineers at Michael Baker International suggested molded polystyrene geofoam as a solution that could be implemented immediately.

Building anything involving an Interstate is difficult for a variety of reasons beginning with the intense need to keep the highway open and limited material laydown and staging space.

The Solution

Made from molded polystyrene, Atlas Geofoam is lightweight, durable, incredibly strong, and semi-indestructible under natural circumstances. Used as structural fill in areas where soil instability or other natural subsurface considerations like fault lines, water tables, or steep slopes come into play, geofoam provides a solid, environmentally inert structural platform. In the case of the Brigham City bridge, the embankments were built using two different grades of Atlas Geofoam, EPS 22 and EPS 29, to account for the immense loading they would bear in supporting the ever-increasing on- and off-ramp traffic.

Atlas Geofoam is a rigid, closed-cell plastic that is molded into standard-size blocks as large as 40 inch x 48 inch x 96 inch and custom-sized blocks as large as 40 inch x 72 inch x 288 inch. Though the cost of geofoam is generally more than soil, many contractors can realize savings best measured in time and convenience. Beyond the six months of soil conditioning time saved in Brigham City, builders can erect large structural components like embankments without specialized equipment. In this case, the embankments were built with manual labor, over just a few weeks.

Developing the exact configuration pattern of the blocks to minimizing material waste on a project of this magnitude benefits from careful oversight. Here the general contractor turned to geofoam design and testing expert, Marvin Cook, of Oracle Construction in Utah. Cook was able to help builders at Ralph L. Wadsworth Construction review the specification and configure the large blocks in layers to support the live loads while being mindful of budget and buildability.

Atlas Molded Products worked very closely with the contractor to orchestrate a steady stream of geofoam to the I-15/US 91 job site in a just-in-time delivery sequence. In using large volumes of geofoam for heavy civil infrastructure programs, it is important to be mindful not only of material delivery schedules but also material production schedules. Atlas Molded Products serves clients across North America from 16 manufacturing locations that combine to accommodate close-to-everywhere proximity. Despite their size, the large geofoam blocks are rather lightweight and have the potential to be blown by a strong wind, which is not a safe condition next to a highway. Atlas organized several separate truckloads of geofoam to the site each day to provide labor with what they needed without excess. Each delivery of pre-cut blocks was organized to help workers build right off the truck using two grades and several sizes of geofoam blocks.

Though Atlas pre-cut most of the blocks before delivery, the complex nature of the diverging diamond interchange on the west end of the project required some block customization, which was done using a hand-held hot wire cutter on site. Once the embankments were built, they were covered with a reinforced concrete slab and finally the roadway above.

Atlas Geofoam is a versatile, durable, and strong structural material that will not degrade in natural subsurface conditions. Atlas Molded Products is proud to partner beyond a purchase order and strives to help clients resolve logistical impediments to success. On the Brigham City Bridge, that meant storing the purchased materials at the local manufacturing facility until they were needed and then delivering them in pre-packaged bundles to help workers put them in place as they arrived on site. Atlas is dedicated to solving complex civil engineering and architectural building challenges across North America with a can-do attitude and a willingness to think outside of the box.

Brigham Bridge 3