Glossary & Related Links

Culvert: A culvert is a pipe or box structure that allows water to flow under a roadway or other obstruction in the landscape, such as railroad tracks. A culvert is used where surrounding areas are wet or intermittently wet or to allow the flow of a small stream or brook beneath the roadway. A culvert can also allow the passage of some wildlife.

Design Build: Design–build is a project delivery system led by a construction contractor, a design engineer and various subcontractors as necessary. Under design-build, VTrans retains the design and construction team together. More traditional project delivery is a two-step process where the project is designed, then bids are requested by construction contractors. The I-89 Culvert Replacement Project is using a design/build team led by J. A. MacDonald and Stantec.

Flowable fill: A mixture of sand, concrete and water, called flowable fill, is pumped into the old pipe culverts, which will remain in place and buried. This mixture is capable of filling all voids in irregular excavations and hard to reach places, is self-leveling, and hardens in a matter of a few hours without the need for compaction.

“Smart work zone” technology: Smart work zone technologies use computers, sensors and various communications methods, such as variable message signs, to alert motorists in real time about traffic conditions in highway construction work zones. When informed, motorists can take alternate routes if necessary, driver frustration can be reduced, and freeway congestion managed or eliminated. Smart work zones also enhance safety for both motorists and workers. Real-time information is especially helpful to motorists when there are traffic accidents, temporary closures, freezing conditions or any unexpected conditions on the freeway.

SEM tunneling: In SEM (Sequential Excavation Method) tunneling, excavation is done mostly by hand and small equipment. The surrounding soil is stabilized by driving pieces of tubing and rebar into the soil. Then excavation takes place in small segments of 4 feet or so, followed by application of a layer of “shotcrete” (a process in which compressed air forces mortar or concrete through a hose and nozzle onto a surface at a high velocity to stabilize that surface). Once the shotcrete is sprayed, the excavation continues further into the bank beneath the highway. Once the tunnel daylights on the other side, the precast concrete arch can be rolled into place.

Traffic diversion: A specially designated route for traffic to follow when the normal route cannot be used. In the South Burlington project, for example, the median was used to divert traffic while the mainline of the highway was excavated to install six box culverts.

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