road widening excavation
Often times it will be required that a road be widened as the commercial and residential population in the area develops or the amounts of traffic begins to increase over time. Road widening can range anywhere from simply adding a paved shoulder or turn lane to full scale lane additions on a state highway. When a new road is being widened, significant excavation is often required through the existing earth to make way for aggregate bases and lifts of asphalt or concrete. A typical crew makeup for road widening excavation will be 2-3 operators, one laborer, and several trucks if hauling excess material offsite. Common equipment utilized for such excavation is a bulldozer, an excavator, a grader, and sometimes a loader.
First the road must be laid out with stakes showing both the horizontal restraints of the new widened edges and the vertical restraints of the new roads grade. Sometimes when a road is widened, the adjacent existing road will be milled and repaved or overlayed to match aesthetically and to eliminate the visible construction joint between the new widened section and the existing road. Also repaving the adjacent existing road makes it easier to achieve a fluent cross slope with the asphalt paver. A sawcut may be required on the existing road +/- 12” from from the edge of existing pavement running parallel with the road. This allows for a clean edge which also makes excavation easier.
A major consideration before widening excavation work on a new road is layout stakes. In terms of traffic maintenance when excavating for road widening, safety is a big consideration. Not only will the aggregate base installation often need to follow behind the excavation operation to keep drop-offs from occurring between new and existing pavement, but a temporary stone or asphalt wedge is often required to safely transition traffic and heavy equipment, should they intentionally or unintentionally enter the work zone. Wedging and bridging with temporary aggregate may also apply for drives that need to be maintained.
The layout information often required for road widening excavation will be the following:
Edge of road/shoulder stakes. Often lath and hub with a nail – 25-50’ apart – minimum of 4-10 feet past disturbed area (or directly on Right of Way line) to avoid being disturbed by construction. This depends on the preference of the contractor.
Horizontal info: centerline of proposed road, edge of shoulder (or edge of pavement if no paved shoulder), and centerline of swale (if one exists).
Vertical info (hub): Elevation of ege of pavement/shoulder, elevation of centerline of swale
If all of this info is requested, it may be too much to put on a lath stake, so it is often put on a note card in a waterproof enclosed unit.
For widening excavation of a road, the most important thing to consider in terms of productivity is having the right number of trucks available to receive the material directly from the excavator (preferably) in order to keep the equipment busy, reduce the number of times the material is handled, and to avoid waiting. With road widening work, it can be expected that productivity be slower than bulk excavation for a brand new road. The space is tighter and the quantity to be removed is often less than that of an entire new road being excavated. First, if organic material or topsoil exists on the surface it must be removed as it is considered unsuitable in terms of a pavement base. The highly organic material can decompose and deteriorate over time causing voids in the subgrade and can cause settling.
To begin excavation operations, the bulldozer will usually scrape and push the material into a scoopable pile for the excavator boom and bucket to pick up and place in the truck. Having the trucks adjacent to the excavator will speed up excavation time, but the logistics of the site often only allow for the truck to be behind the excavator requiring it to spin 180 degrees. Haul distance to dump site (if spoils are to be taken off site) is critical factor on both round trip time and number of trucks needed. Heavy traffic on haul road, access in and out of site, size of excavator bucket, and size of truck also play into the productivity of excavation as well.
The road is often cut 6-12” past the edge of road or curb, and will require backfill operations after installation of the road/curbs. A ‘grade checking’ task is often taken on by the laborer making him the set of eyes on the ground directing the excavator/dozer operators on how much earth to cut. Once the road is cut to the proper elevation, a roller (often vibratory) is used to compact the subgrade, so long as it’s of suitable condition and will not consolidate under compaction loads.
Sometimes a loaded dump truck is driven over the compacted subgrade (‘proof rolling’) and if minimal or no signs of rutting occur, the subgrade is deemed acceptable. For road widening work, the engineer typically desires to minimize the amount of time the widened road trench will be open for safety reasons involving pedestrians and more importantly moving vehicles. A maximum amount of time is usually allotted for the trench to sit open before it will need to be filled with material. This amount of time is often less than a working day as the site will typically need to be made safe before the end of each day.