3.3 Base Selection

Many factors are considered beyond material testing and acceptance in accordance with the characteristics identified in Item 247. Selection factors often considered are:
  • availability and cost
  • surface thickness
  • subgrade stiffness and strength
  • lateral confinement
  • traffic volume and loading.
From these factors, a number of different selection matrices may be generated. The applicability of these factors may be weighed quite differently in each district.
An example of a decision matrix for the selection of base grades is contained in Table 3-8. Grades recommended in a chart similar to Table 3-8 should be chosen based on local experience and historical performance.
Table 3-8: Example Flexible Base Selection Chart
Shoulder Width
HMA Surface Thickness
Traffic (Design ESALs)1
Base Grades
< 3 ft.
Surface Treatment
< 500,000
4*
> 500,000
1-2
HMA < 3 in.
All traffic levels
1-2
HMA > 3 in.
< 500,000
4*
> 500,000
1-2 or 5
> 3 ft.
Surface Treatment
< 500,000
4*
> 500,000 and < 3,000,000
1-2 or 5
> 3,000,000
1-2
HMA < 3 in.
< 500,000
4*
> 500,000
1-2
HMA >3 in.
< 500,000
4*
> 500,000
1-2 or 5
1
Percentage of trucks in addition to design ESALS should be taken into consideration.
*Grade 1-2 requirements without minimum strengths.