The goals of this $56-million project in the heart of San Rafael were to elevate and widen the northbound and southbound Highway 101 lanes for the addition of HOV (high occupancy vehicle) lanes and to construct a new southbound 101/eastbound Interstate 580 connector.

101/580 Interchange

One of the more innovative aspects of the project’s design was the use of both lightweight aggregates and EPS block (expanded polystyrene). The project is located immediately adjacent to the San Francisco Bay, so much of the native material underneath the site is what is referred to as “bay mud.” This material is very fluid and tends to not compact very well. Over time, the material displaces due to the weight of the structural section and live loads above, causing settlement on the surface. To counter these effects, the project was designed to incorporate the use of lightweight materials, which would reduce the amount of weight in the structural section, thereby causing less displacement of the native material below.

The project team says that through successful project partnering between the contractor and Caltrans, the project was completed three months early and within budget.

A particular challenge was the construction of retaining wall #3, a mural designed by Caltrans that was a distinguishing feature of the project. With its tight nooks and technical detail, special consideration had to be given to both the concrete mix design and construction technique. A team was immediately formed to maintain quality, which consulted with the concrete supplier to brainstorm for solutions. The supplier was able to design and propose a mix utilizing plastic admixture and smaller aggregate that would increase the fluidity of the concrete, thereby allowing the mix to reach all the tight areas.

Project Team

Owner: Caltrans, Sacramento
General Contractor: Ghilotti Bros. Inc., San Rafael
Engineer: Caltrans/URS, Sacramento
Major Subcontractors: RM Harris Co., Martinez; Linear Options, Menlo Park; Mike Brown Electric Co., Cotati; RE Serrano Inc., Martinez; Mid-State Barrier Inc., Livermore; WC Maloney Inc., Stockton