Reincement Plastic Gravel Driveway Geogrid

In stabilization design, the geogrid and aggregate thickness required to stabilize the subgrade

and provide an adequate roadbed are evaluated. Recall that this application is primarily for

construction expedience. For design of permanent roads, this stabilization lift also provides

an improved roadbed (i.e., less subgrade disturbance, a gravel layer that will not be

contaminated due to intermixing with the subgrade, and a potential for subgrade

improvement of time). The base course thickness required to adequately carry the design

traffic loads for the design life of the pavement may be reduced due to the improved roadbed

condition, provided an assessment is made of the improvement.

As indicated in Table 1, geosynthetics used in this application perform multiple functions of

separation, filtration and reinforcement. Separation design requirements were discussed in

previous section. Because the subgrade soils are generally wet and saturated in this

application, filtration design principles are also applicable.

With respect to reinforcement requirements, there are two main approaches to stabilization

design. The first approach inherently includes the reinforcement function through improved

bearing capacity and there is no direct reinforcing contribution (or input) for the strength

characteristics of the geosynthetic. When this approach is used for geogrids, a geotextile or

graded granular soil separation layer is also required to address these functional

requirements. The second approach considers a possible reinforcing effect due to the

geosynthetic. It appears that the separation function is more important for roadway sections

with relatively small live loads where ruts, approximating 2 in to 4 in. (50 to 100 mm) are

anticipated. In these cases, a design which assumes no reinforcing effect is generally

conservative. On the other hand, for large live loads on thin roadways where deep ruts (> 4

in. {100 mm}) may occur, and for thicker roadways on softer subgrades, the reinforcing

function becomes increasingly more important if stability is to be maintained. It is for these

latter cases that reinforcing analyses have been developed and are appropriate.