GPS Use for Roadway Subgrade

Part 3 of “GPS is underutilized”

When spring rolls around, road construction gets into full swing. Road contractors were early adopters of technology and continue to drive the development of new applications and equipment. Among them are laser augmentation for vertical accuracy and the automation of paving and curb machines. In an effort to improve efficiency, the contractor needs to use technology wherever possible. This includes preparation of dirt grades and the application of subgrade materials.

 Standard Road Subgrades.

When working with a site, it is easy to “dial down” the surface in order to grade to the top of dirt, compacted subgrade, and rock. This vertical offset works well, even though it just lowers the entire site the set amount.

This drawing shows 3 layers that can be installed using a vertical offset. With a well-prepared subgrade, it is possible to pave using sonics and obtain good results in a basic parking lot.

For many road jobs, the subgrade is easily set with vertical offsets. A typical basic road design for urban rehabilitation work is one example. Here we see top of dirt and prepared native subgrade that can be done with vertical offsets.

The subgrade extends beyond the road/curb finish. To make this easier to model, just the finished surface can be built. The equipment operator can run the blade down the road section and use sonic and cross slope or a horizontal machine offset to pick up the additional 2 feet.

Extended Road Subgrades.

Where side slopes are built into a roadway, another layer of difficulty is added. The subgrade hinge represents the intersection of the side slope and the projection of the subgrade. It is shown in this drawing inside the red circle. Refer to the video for a better understanding. There are two ways to accomplish the production of the subgrade hinge, office calculations or field adjustment.