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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.
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.